Dissertations / Theses on the topic 'Ultramafic rock'

This study deals with reverse faults within intensely carbonated metalherzolites, with related gold mineralisations, from the Voltri Massif, and in particular within the Lavagnina Lakes area, in the Gorzente Valley. This area is located in northwest Italy among the municipalities of Casaleggio Boiro, Lerma, Mornese, and Bosio (Alessandria, Italy; GPS coordinates WGS84, 44.600685° N, 8.784286° E). The Voltri Massif is a metaophiolitic complex, which occurs within the Eastern edges of the Ligurian Alps. It is made up of of metaophiolitic rocks associated with metasediments and slices of subcontinental lithospheric mantle. These rocks underwent a complex Alpine tectono-metamorphic evolution, with blueschist- to eclogite- facies peak metamorphism with variable retrogressive overprints. For this study the analysed structures are the upper crustal deformational events (UDC), from late- to post-orogenic linked to the collisional events. These deformational events are linked to different structural regimes, and developed during the late-Alpine to early-Appenine events. The Lavagnina Lakes area is mainly characterised by outcrops of serpentinites, lherzolites, metabasites, metagabbros, lenses of metasediments, and listvenites (in decreasing order of volumetric extension). From a structural point of view, this area is characterised by brittle to brittle-ductile systems of shear zones, with associated carbonates and chalcedony-quartz veins associated with local gold mineralisations. Hydrothermal, carbon-rich fluids permeated the rocks and sustained these deformation stages producing widespread and intense carbonate-rich alteration zones, exclusive meso- and microstructures within carbonates fault zones, called fault pearls, chalcedony shear veins along fault surfaces, widespread quartzchalcedony and carbonates veining, and leading to local gold mineralisation. The geological survey allowed identifying four main structures (Chapter 5) that I studied in detail. In particular I studied the Bisciarelle Creek thrust fault for the occurrence of meso- and microstructures never reported in literature, called fault pearls. Their compositional and textural characteristics, described in chapter 5.3.4, make the fault core of the Bisciarelle fault a peculiar geological object. 2 The data shown in chapter 7 provide constraints on the chemical properties of the fluid that generate the intense carbonation along the Bisciarelle fault. Through the mass transfer profiles was possible to identify and quantify those elements transferred from the fluid to the rock and vice versa. The morphometric image analysis results (Described in chapter 5.3.5) show that the fault pearls have circular shape irrespective to the direction of observation (parallel and orthogonal to the slickenlines), with values that indicate a nearly perfect circular shape. These values are in line with the roundness values, hence the fault pearls in three-dimensions can be considered as nearly perfect spheres or as very spherical textures. Single-spot SEM-EDS (Chapter 8) analyses show that ferroan dolomite makes the pearl bands (CaO: 29.13±2.33 wt%; MgO: 19.03±4.86 wt%; FeO: 1.77±0.87 wt%) and that minor compositional variations across large and thin bands exist, and that silica makes most of the chalcedony veins (SiO2: 97.97±3.23 wt%). Elemental imaging by LA-ICPTOFMS (Chapter 8) provides a detailed account of the distribution of chemical elements within pearls, matrix, and chalcedony shear veins. Mineral paragenesis and elemental imaging by LA-ICP-TOFMS confirm the hypothesis of hydrothermal derivation of the fault rock. This is best evaluated by comparing the concentration ranges of the key trace elements As, Sb, In, Ga, Ag, Zn, and Cu of fault pearls levels and chalcedony with those of the same elements in the average upper crust. Such comparison clearly shows that the peak concentrations of these elements are 5 (Cu, Zn) to 50 (Sb, In) times higher than those of the upper crust, demonstrating that the Bisciarelle fault fluid was capable to transport and deposit a suite of ore elements. These evidences are fundamental to discuss the possible origin of the fluids that developed the carbonation and the fluid-rock interactions along the Bisciarelle thrust fault and along the main fault of the Lavagnina Lakes area. On the basis of all the constraints described, the fault pearl features are compatible with a genesis from a process called “transient” boiling in microfluidics. This process occurs within cavities when a liquid is instantaneously overheated and a vapour phase nucleates and expands up to explosive boiling, and so generates a myriad of vapour bubbles. Such process, which occurred during mixed mode fracturing in the fault, implies that pearls might reflect the liquid-vapour 3 fractionation of chemical elements in a boiling hydrothermal fluid during seismic failure. The close association of fault pearls with seismic-related structures such as submicron carbonates coating of slip surfaces, quartz microtexture related to silica gel deposition, syn-kinematic filamentous phase, injection veins with similar characteristics and overpressure with respect to seismic pseudotachylites along slip zone supports the hypothesis that fault pearls developed during shear events at seismic rates, and hence are considerable as paleo-seismic events indicators. Moreover I discuss the tectonic evolution of the Lavagnina Lakes area linked to the syn-kynematic fluid rock interaction, the origin of the fluids and the gold mineralisations of the area. The occurrence of syn-tectonic fluid flow and consequent fluid-rock interaction (e.g. carbonation) along the two systems of Reverse Shear Zones (RSZ1-RSZ2), is testified by: metasomatic alteration (ALT-1, ALT-2, and ALT-3), at least three main systems of veins (V1, V2, and V3), and hydraulic and cockade breccias. The evidence that the carbonation took place along these structures, in particular along the RSZs systems, and within their damage zones, highlights how these structures acted as important fluid pathways and played a major control in the distribution of the ore deposits. Finally, I stress out further consideration about the comparison between the gold mineralisations of the area with the gold mineralisations of the whole Voltri Massif.

From the abstract: In the layered sequence of the Bushveld Complex a number of distinct, but possibly genetically related groups of transgressive, postcumulus, ultramafic and mafic rock are recognised. The main part of this thesis investigates a suite of postcumulus rocks for which the name iron-rich ultramafic pegmatite is proposed. The majority of iron-rich ultramafic pegmatite bodies examined are from the upper critical zone of the layered sequence at Rustenburg Platinum Mines Amandelbult Section, in the northern sector of the western Bushveld Complex. Field relationships imply that the iron-rich ultramafic pegmatites should be considered as an integral feature of the layered sequence, even though they transgress the cumulates. Consequently, this thesis also includes a study of the cumulate sequence at Amandelbult. A second group of postcumulus, ultramafic rocks which is investigated comprises latiniferous ultramafic pipes; the Driekop pipe has been selected as a case­ study. This thesis is presented in four sections, namely, an introduction and verview, and studies on the Driekop pipe, the cumulate sequence at mandelbult and the iron-rich ultramafic pegmatite suite. A new classification scheme of discordant bodies of postcumulus, ultramafic rock in he Bushveld Complex is proposed (see also Viljoen & Scoon, in press). In he scheme presented here, two main varieties of postcumulus, ultramafic rock re recognised, namely, non-platiniferous magnesian dunites and iron-rich ltramafic pegmatites.

Les Iles Salomon forment une double chaîne d'îles située au nord-est de l'Australie entre la Papousie Nouvelle Guinée et les Iles Vanuatu (Océan Pacifique), résultant de la récente collision (<10 Ma) du plus grand plateau océanique au monde - Ontong Java (OJP) avec l'arc volcanique des Iles Salomon, issu de la subduction de la plaque Pacifique sous la plaque indo-australienne (depuis 43 Ma). Résultant de cette collision, des écailles de roches ultramafiques (péridotites et pyroxénites) et mafiques (basaltes et gabbros) ont été obductées et affleurent au nord-est des Iles Salomon. L'objectif de cette thèse est d'étudier ces roches en utilisant une approche pluri-disciplinaire (pétrologie, minéralogie et géochimie) afin de déterminer leur origine et leur formation. Les harzburgites de Choiseul et les pyroxénites de Santa Isabel et San Jorge ne sont pas liées à OJP mais résultent d'un mécanisme complexe du métasomatisme du manteau d'arc par des fluides issus de la plaque subductée. Ces fluides, riches en éléments lithophiles (Cs, Ba, Rb, Sr et Pb) sont des magmas hydratés résultant de la fusion des sédiments subductés. Les roches mafiques (incluant les basaltes et les gabbros) représentent un complexe ohiolitique complet de bassin d'arc. En conclusion, la formation et l'exhumation de ces roches ultramafiques et mafiques des Iles Salomon sont étroitement liées à la collision OJP-arc
The Solomon Islands are a double chain of islands in the Pacific Ocean (Noth-east of Australia) resulting from the recent collision (<10 Ma) of the world's largest oceanic plateau Ontong Java (OJP) with the Solomon arc. In response of this collision, thin fault slices of peridotites, pyroxenites, gabbros and basalts are now exposed on the islands of Santa Isabel, san Jorge and Choiseul (Northeastern Solomons). Although some pillow basalts are OJP-related, the origins of the most of the mafic and ultramafic rocks remain uncertain. The Choiseul peridotites are interpreted to have two stage origins: 1-residual harzburgites formed beneath an ocean ridge; 2) infiltration of a reactive metasomatic agent released from the slab. Similar but more complex metasomatic process results in the formation of the pyroxenites from San Jorge and Santa Isabel. This metasomatic agent released from the slab is likely to represent an hydrous granitic melt derived from the subducted sediments. The mafic rocks (including the basalts and gabbros) are interpreted as portions of an arc-backarc crust. As a result, the formation and the exhumation of the ultramafic and mafic rocks from the Solomon Islands are directly related to the OJP-arc collision

The ultramafic cumulate rocks of the Raglan horizon in the Proterozoic Cape Smith fold belt of northern Quebec have a common parental liquid in equilibrium with olivine of Fo89 composition. Cumulate olivines have experienced a trapped liquid shift to lower forsterite composition proportionally to the fraction of trapped liquid in the cumulate. Anomalously low nickel contents in analyses of both olivine and whole-rock chemistries are observed only in cumulates with the most modal olivine and which are proximal to known Ni-Cu-(PGE) deposits. The calculated compositions of the trapped liquid fraction indicate that most of the Raglan cumulates formed from Fe-rich high-MgO basalts, which are restricted to the base of the Chukotat volcanic stratigraphy. We propose that a lower degree of adiabatic partial melting of a mantle source accounts for the Fe-rich nature of these parental liquids and may provide an explanation for the presence of numerous Ni-Cu-(PGE) deposits in the sills of the Raglan horizon.

Inversion of potential field geophysical data to generate physical property models is becoming increasingly common in the exploration industry. This study aimed to develop relationships between physical properties and mineralogy in ultramafic rock-hosted mineral deposits, based on an analysis of the crater facies-dominated Anuri kimberlite (Canada) and the intrusive magmatic sulfide deposit at Kabanga (Tanzania). Physical property distributions for rock types and minerals that contribute to density and magnetic susceptibility were characterized in both deposits. Magnetic susceptibility is directly related to magnetite abundance, which is an igneous phase and is produced by serpentinization of ultramafic rocks of both deposits. Magnetite in kimberlite also occurs in crustal xenoliths, which dilute the diamond content. Consequently, susceptibility in the Anuri kimberlite is inversely related to diamond grade. In the Kabanga magmatic sulfide deposit, susceptibility is unrelated to ore content, but does indicate the degree of serpentinization. Density is a function of dense minerals concentrated with ore during primary sorting and settling processes in both deposits. As such, density is directly correlated with ore in both volcaniclastic kimberlite breccia of the Anuri kimberlite and ultramafic rocks at Kabanga. However, serpentinization decreases the density of ultramafic rocks significantly, masking any density anomalies associated with sulfide minerals. Modeling demonstrates that a pervasively serpentinized rock with up to 50% sulfide minerals can have a density equal to that of a barren ultramafic rock. A combination of susceptibility and density can be used to identify high-grade rocks in both deposits. In the Anuri kimberlite, rocks with high diamond contents have susceptibilities less than 10 x 10⁻³ SI and densities of 2.42 - 2.51 g/cm³. In magmatic sulfide deposits, susceptibility and density can be used to accurately calculate ore mineral abundances. Relationships developed between physical properties and mineralogy for these deposits can not only be applied to other crater facies-dominated kimberlites and both intrusive and extrusive magmatic sulfide deposits, but also to other ultramafic rock-hosted mineral deposits with comparable geologic processes. Consequently, both magnetic and gravity surveys can be interpreted in combination to give a powerful remote tool in predicting grade.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

Este trabalho tem como objetivo investigar os processos controladores da mobilidade e concentração de níquel (Ni) em rochas ultramáficas serpentinizadas no Escudo Sul-Riograndense (ESrg), Rio Grande do Sul (RS), Brasil. A composição primária das rochas ultramáficas hospedeiras de Ni constitui um parâmetro relevante, mas os processos secundários são os controladores mais importantes dessas mineralizações, principalmente a serpentinização, pressupondo-se que o Ni possa migrar da olivina ou metamórfica para os minerais do grupo das serpentinas. Para a caracterização mineralógica e textural das rochas ultramáficas serpentinizadas da porção oeste do ESrg, foram aplicadas técnicas de petrografia e Microscopia Eletrônica de Varredura. Para a análise química dos elementos em rocha total foi realizada fluorescência de Raios-X, ICP e ICP-MS. Estas técnicas permitiram classificar quimicamente as rochas e relacionar a variação da intensidade dos eventos metassomáticos, metamórficos e hidrotermais que modificaram a mineralogia dos protólitos. No entanto, foram necessárias estudos de detalhe dos minerais individuais, notadamente olivinas e serpentinas com o uso da microssonda eletrônica para determinar as concentrações de Ni e suas variações nos diferentes corpos ultramáficos investigados. Dessa forma, foi possível quantificar e identificar os minerais concentradores de Ni e a relação dos eventos com a mobilidade e concentração dos elementos. Os resultados de microssonda indicam que as olivinas dos peridotitos do Maciço Pedras Pretas possuem baixos teores de níquel que variam de 0,13% a 0,21% e a média é 0,17%, enquanto que as olivinas dos harzburgitos da Sequência Cerro Mantiqueiras possuem teores mais elevados na média de 0,31%. As olivinas do Pedras Pretas possuem composição homogênea enquanto que aquelas do Cerro Mantiqueiras mostram variações composicionais importantes com conteúdo de Fo 92-98 e teores de níquel entre 0,3% e 0,4%. Tais variações no Cerro Mantiqueiras podem estar relacionadas a diferenças na composição do protólito ou a outro fator desconhecido que necessita futuras investigações. As olivinas e serpentinas no Cambaizinho e Serrinha mostram valores de níquel entre 0,19% a 0,3%, comparáveis ao Cerro Mantiqueiras, porém bem mais elevados que o Pedras Pretas. Este estudo mostra que os corpos ultramáficos do Cambaizinho- Serrinha e Cerro Mantiqueiras possuem potencial para desenvolver depósitos de Ni não sulfetado devido as concentrações relativamente elevadas de Ni nas olivinas. Entretanto, tais depósitos não se desenvolveram devido a dois fatores principais: o primeiro está ligado à superposição de eventos de metamorfismo e deformação recorrentes no tempo e no espaço que propiciaram a mobilização do Ni; o segundo fator é atribuído a ausência de agentes supergênicos favoráveis para a formação de depósitos lateríticos como os observados na região norte do Brasil.
This paper investigates the processes controlling the mobility and concentration of nickel (Ni) in serpentinized ultramafic rocks in the Sul- Riograndense Shield (ESrg), Rio Grande do Sul (RS), Brazil. The primary composition of the ultramafic Ni host is a relevant parameter, but the secondary processes are the almost important controllers of these mineralizations, mainly serpentinization, assuming that Ni may migrate from igneous or metamorphic olivine minerals to the group of serpentine this phase. For the mineralogical and textural characterization of the serpentinized ultramafic rocks of the western portion of ESrg, were applied techniques of petrographic and scanning electron microscopy. For chemical analysis of elements in rock whole was performed X-ray fluorescence, ICP and ICP-MS. Although these techniques allow chemically classification of rocks and relate the variation of intensity in which metasomatics, metamorphic and hydrothermal events, changed the that mineralogy of the rock, however analysis of individual mineral detail, notably olivine and serpentine minerals using the electron microprobe detail, were necessary to determine the concentrations of Ni and variations in different ultramafic bodies investigated. Thus, it was possible to quantify and identify the Ni concentrators minerals and the relationship of events with the mobility and concentration of the elements. The microprobe results indicate that the olivine of peridotite Pedras Pretas have low contents of NiO ranging from 0.13% to 0.21% and averaged 0.17%, while the olivine harzburgites Cerro Mantiqueiras have higher levels of NiO averaging 0.31%. The olivine of Pedras Pretas have a homogeneous composition as those of Cerro Mantiqueiras show important compositional variations with a content of forsterite the Fo 92-98 and NiO contents of between 0.20% and 0.40%. Such variations in Cerro Mantiqueiras may be related to differences in the composition of the protolith or another unknown factor that needs further investigation. The olivine and serpentine in Cambaizinho and Serrinha, show NiO values between 0.19 % to 0.3 %, values comparable to the Cerro Mantiqueiras, but higher than the Pedras Pretas. This study shows that the Cambaizinho, Serrinha and Cerro Mantiqueiras have the potential to develop non- sulphide Ni deposits, due high Ni concentrations in olivine. However, these deposits are not developed due two main factors: the first is linked to the superposition of events the metamorphism and deformation applicants in time and space, that enabled the Ni mobilization; the second factor is attributed to lack preservation of profiles suitable for the Ni concentration, due to uplift and erosion lateritic subsequent.

This Ph.D. Thesis is intended as a multidisciplinary research work on the Zermatt-Saas (Western Alps) serpentinites and associated carbonated rocks. The main goal of this thesis is to decipher the carbonation processes involving serpentinites and the concomitant element mobilization, while also attempting at defining the serpentinites’ subduction-to emplacement- evolution. To address these aims, field work activities, spanning from acquisition of macro-structural data to sampling of representative lithologies, and detailed petrography were carried out on a sequence of serpentinites, carbonated serpentinites and listvenites from the Mount Avic Massif (Zermatt-Saas Zone, Aosta Valley, Western Alps) and neighbouring area of Vercoche. On the selected data set a wide range of geochemical analyses were carried out not only to define the bulk rock compositions but also to trace, by means of EMPA, LA-ICP-MS, µ-Raman applied to microstructurally selected sites, variations and chemical gradients of elements relevant for this study (i.e., redox sensitive elements such as C and S, but also major and trace elements). In order to decipher the subduction-to emplacement evolution of serpentinites, detailed petrology and geochemical investigations were applied to unravel the signature of fluid-rock interaction during subduction. Moreover, by integrating structural, petrological and geochemical results with thermodynamic modelling, the P-T-(t)-d paths representative of the evolution of serpentinites were obtained. Serpentinites from the Mount Avic massif retain structural and geochemical fingerprints of a long-lived evolution. Mantle (and oceanic) relics can be easily distinguished from the prograde metamorphic recrystallized phases: clinopyroxene, olivine and Cr-cores within magnetite preserve their mantle texture and, in part, their original composition. These features suggest that the serpentinites derived from mantle peridotites, mainly represented by harzburgite, that were exhumed and exposed at the Mesozoic Tethyan Ocean floor prior to alpine subduction. In this context, mantle peridotites likely interacted with seawater that enhanced the pervasive serpentinization and caused the progressive replacement of olivine and pyroxene by serpentine-lizardite with “mesh” and “bastite” textures, respectively. Bulk rock trace and REE patterns obtained on serpentinites as well as in situ concentrations of trace and rare Earth elements on serpentinite forming minerals suggest that the Mount Avic serpentinite still largely retains its oceanic geochemical signature despite intense Alpine subduction metamorphism. At the onset of the Tethyan ocean closure due to convergence between the Paleo-Europe and Paleo-Adria continental plates, the serpentinites underwent prograde metamorphism during Alpine subduction. Different mineral assemblages marking superposed fabrics are variably retained within the serpentinites. In foliated serpentinites, despite the pervasive overprinting provided by S2 foliation, relics of pre-D2 structures are preserved. In particular, Ti-chondrodite, clinopyroxene, olivine, antigorite and magnetite-bearing assemblage, marking pre-to early D1 metamorphic stage, attest for peak UHP conditions attained at Pmin = 2.8-2.85 GPa for T = 600-645°C. The crystallization of Ti-clinohumite along Ti-Chondrodite rims during D1 deformation stage, suggest that serpentinites, after reaching the peak metamorphic conditions, experienced a quasi-isothermal decompression from pre-to early D1 conditions, still within typical Alpine subduction geothermal gradient of 6.5-8.0°C/km. Detailed LA-ICP-MS analyses carried out on clinopyroxene, humite, olivine and serpentine minerals showed that Zr, Ti, Hf and Sr elements were mobilized during the transition from the mantle to the subduction environment. The lizardite-antigorite transition phase was accompanied by Sr, Cl and alkalis release in an open system which likely occurred in early oceanic stage and was complete at T>390°C. Differently, the partitioning of Ti, Hf, Zr between clinopyroxenes and Ti-clinohumite supports the idea that mantle clinopyroxene breakdown and successive high-pressure clinopyroxene and Ti-clinohumite crystallization took place in a closed space environment. During the retrograde path, the serpentinites re-equilibrated at Pmin = 2.4-1.7 GPa and T = 510-610°C; at these conditions, D2 deformation stage caused the crystallization of Ti-clinohumite and Ti-chondrodite in textural equilibrium along S2 foliation planes together with olivine, clinopyroxene, antigorite and magnetite. Locally, veins and shear zones marked by clinopyroxene, olivine and Ti-clinohumite postdating S2 foliation, attest that during syn-to-post-D2 exhumation hot geothermal gradients (20°C/km), indicative of greenschist facies re-equilibration, were reached. These new results provide unprecedented insights on the geochemistry, petrology and P-T peak conditions at which the Mount Avic serpentinites (Zermatt-Saas Zone) re-equilibrated during the alpine subduction and exhumation and allow for a comparison with the UHP serpentinite slices belonging to the Cignana Lake and Valtournanche (Créton) units of the Zermatt-Saas Zone north of the Aosta-Ranzola fault. Serpentinites of the Mount Avic massif underwent carbonation likely during their retrograde evolution, which caused the formation of carbonate-bearing lithologies comprising carbonated serpentinites and listvenites. These metasomatized rocks represent valuable records of CO2 sequestration enhanced by fluid-rock interaction mainly focused along serpentinite shear zones. Fluid-rock interaction, responsible for the genesis and evolution of carbonated serpentinites and listvenites, is attested not only by macro-scale, but also by micro-scale structural features. Petrographic observations suggest that the Mount Avic serpentinites, after having experienced D2 and post-D2 stages at high-pressure and greenschist facies conditions, respectively, likely reached lower T and P conditions while being progressively infiltrated by CO2-rich fluids. Ti-clinohumite relics within partially carbonated serpentinite, presently pseudomorphically replaced by olivine and ilmenite and the presence of Ti-clinohumite not yet replaced by olivine and ilmenite, but still in equilibrium with olivine and clinopyroxene, constrain the P-T conditions attained by serpentinites prior to carbonation and supports the hypothesis that the initiation of carbonation of serpentinites took place just before, or even simultaneously with, Ti-Chu breakdown, likely during the early retrograde greenschist facies re-equilibration of serpentinites. Based on thermodynamic modelling, the equilibrium P-T conditions for listvenitization are constrained at 0.3GPa and 300°C and the minimum amount of CO2, required for the infiltrating fluid to produce the listvenite mineral assemblage is XCO2 (min) = 0.02. Upon fluxing of CO2-bearing fluids, carbonated serpentinites are progressively transformed into listvenites as evidenced by the crystallization of quartz as a product of talc breakdown, making-up matrices together with aggregates of magnesite and fuchsite fibres, attesting for the presence of K in the infiltrating fluid. The presence of Cr-spinel, magnetite and mesh texture relics in listvenites is regarded as a clear petrogenetic relationship with serpentinites. Electrolytic fluid infiltration modelling suggests that the Mount Avic listvenites attained low T and very high fluid/rock (F/R) ratios: prolonged fluid infiltration at low temperatures causes the solubility of quartz to increases to the point that part of the SiO2 present in the listvenite matrix is dissolved in the fluid and then precipitated in veins which diffusively characterize listvenites. Furthermore, with progressive fluid infiltration, MgO/SiO2 ratio increases up to a point (at F/R between 6 and 7 and ca. 38-42% CO2), where the infiltrating fluid removes CO2 from the system. The dissolution of carbonate and concurrent silicification of the altered rock, once all the talc has reacted with CO2,aq to form magnesite and quartz, is thermodynamically predicted at T ≤ 200°C under prolonged fluid influx. The petrographic investigation on sulfides allowed to depict a chemical gradient: from serpentinites to listvenites the sulfide abundance decreases in accordance with the decrease in S (wt%) abundance observed by measured bulk rock values as well as predicted by thermodynamic models. In serpentinites the sulfur-poor heazlewoodite and pentlandite are associated with awaruite Ni-Fe alloy, in accordance with the observations that Fe-Ni alloys tend to be preferentially found in peridotites that have been only partially serpentinized. Passing to carbonated serpentinites the sulfide abundances progressively decreases and their composition changes. In particular, in carbonated serpentinites, neither Ni-Fe alloys nor pentlandite are identified while sulfur-poor heazlewoodite forms aggregates with sulfur-rich Co-bearing NiS. Finally, the transition from carbonated serpentinites to listvenites is marked by the limited presence of small-grained pentlandite and haezlewoodite, and absence of alloys while magnetite is progressively replaced by hematite displaying martite texture. The pseudomorphic martitic replacement of magnetite by hematite due to magnetite oxidation, observed exclusively within listvenites, and not in carbonated serpentinites where sulfides are still present, suggests that once the sulfides are completely dissolved, the fluid continues to evolve towards high oxygen fugacity (fO2) conditions. Prior to fluid infiltration, serpentinites attained very low fO2 and fS2 as constrained by the presence of Ni-Fe alloys (i.e., awaruite) and sulfur-poor assemblage (heazlewoodite and pentlandite) in magnetite-bearing antigorite-serpentinites. Within the successive steps of fluid infiltration, the redox conditions of the system changed: the passage from serpentinites to carbonated serpentinites is marked by more oxidising conditions, by a marked increase in Fe3+/Fetotal ratios and by the stability of heazlewoodite with sulfur-rich Co-bearing NiS (millerite). The transition from carbonated serpentinites to listvenites is marked by the consumption of sulfides and the concomitant constant increase in fO2. It is likely that sulfides in the Mount Avic carbonated serpentinites and listvenites were dissolved by sulfate-dominant fluids in oxidising rocks. Listvenites are predicted to be stable at high-fO2, above the MH (magnetite-hematite) buffer where hematite is expected to be stable, consistently with petrographic observations of pseudomorphic replacement of magnetite by martite-textured hematite. Interestingly, nickel shows high mobility during the carbonation process, passing from being retained in sulfides and alloys in serpentinites (awaruite, pentlandite and heazlewoodite) to form rare millerite in carbonated serpentinite and listvenites and to be concentrated in trevoritic cores within spinels in listvenites. The comparison between serpentinites and listvenites by means of trace elements allows to evaluate that the compatible elements (V, Sc, Zn, Cr, Ni and Cu) were redistributed between the two rock types suggesting a mainly closed-system behaviour during listvenitization and internal cycling of such components from the host minerals in the serpentinite. Differently, higher incompatible (K, Rb, Sr, Ba Nb) and fluid mobile elements concentrations in listvenites suggest that these elements were sourced externally from the serpentinites. Moreover, Co zoning within sulfides in carbonated serpentinites may reflect the interaction of the host rock with saline fluids, whose provenance could be attributed to dehydration reactions affecting serpentinites or to fluids released upon metasediments devolatilization. Based on stable carbon and oxygen isotope compositions of magnesite, it is proposed that the CO2-rich fluids promoting serpentinite carbonation derived from devolatilization of metasedimentary rocks in the subduction zone while metaperidotites were already facing early exhumation conditions during their early retrograde evolution. During syn-to-post D2 early retrograde path serpentinites experienced strain conditions favourable for the formation of shear zones; such structures served as preferred pathways for CO2-rich fluid circulation and enhanced the carbonation of serpentinites and the formation of listvenites. Only in Oligocene times, when the post-emplacement tectonics was active, the rheological contrast between serpentinites and listvenites worked as weakness surface that facilitated the nucleation of the normal fault along which listvenites and carbonated serpentinite crop out. The combination of field, macro and micro-structural, petrological and geochemical data with thermodynamic modelling, provide new and unprecedented insights 1) on the P-T-(t)-d history of the serpentinites from the Mount Avic: this represents the first attempt at defining a P-T stability field for the Zermatt-Saas serpentinites south of the Aosta-Ranzola fault in the Western Alps; 2) on the interaction of CO2-bearing fluids with serpentinites to form carbonated serpentinites and listvenites and how this process controls element mobilization, variations of redox sensitive elements and carbonation.

The Caraiba copper-rich hypersthenite-norite complex in the Early Proterozoic Curaca terrane of northern Bahia, Brazil, is not a tholeiitic layered sill as has been previously suggested. It is re-interpreted as a series of multiple dyke-like intrusions, possibly derived through partial melting of an incompatible element enriched harzburgitic to orthopyroxenitic lithospheric mantle source region. It contains peridotitic and gabbroic xenoliths. Copper-rich gabbroic xenoliths may represent volcanic rocks taken to upper mantle depths by a process of subduction. The chemistry of some of the regional mafic rocks and of three granitoid generations suggest for the Curaca terrane a tectonic evolution similar to Phanerozoic continent-continent collision belts, which was possibly initiated at an Andean-type margin. A Middle Proterozoic mafic dyke swarm that post-dates the main period of crustal growth is interpreted as having originated from a heterogeneous garnet-bearing source in the asthenospheric mantle, and is likely to be related to a mantle plume or hotspot during the development of the coeval Espinhaco aulacogen. The parental magma of these dykes is thought to have resided in small zoned magma chambers. Comparison with other mafic dykes from the Brazilian shield suggests derivation of the Early Proterozoic dykes from more depleted, more refractory, lithospheric mantle sources than those of the younger dykes, which are believed to have had a significant asthenospheric contribution in their petrogenesis. The chemistry of these dykes reflects the evolution of the sub-continental mantle with time.

Ecological and ecophysiological investigations carried out at the ultramafic outcrop near Meikle Kilrannoch, Angus, Scotland are reported. The outcrop is botanically famous for its rare plant species, particularly the endemic Cerastium fontanum ssp. scoticum and the nationally rare Lychnis alnina. The studies were made on the main outcrop (called MK1) which is dome shaped, and on a much smaller low-lying area (called MK1.5) about 300 m from it. The overall aim of the studies was to investigate the relationship between the soil physico-chemical environment and species distribution on the open areas of the ultramafic site and to experimentally test for causality; and to offer an explanation for the open character of the vegetation on the skeletal soils. Variograms which were constructed for soil properties and vegetation data to investigate soil micro-spatial variation and vegetation pattern showed differing levels of spatial dependence, always indicating high intrinsic variability. The cause of this high variability was probably cryoturbation for the soil and morphological characters for plants. The gradient analyses (Principal Components Analysis and its canonical form, Redundancy Analysis) used to study soil - vegetation correlations suggested that A ostis vinealis, Cerastium fontanum ssp. scoticum and Lychnis alpina were most abundant in areas up-slope with lower concentrations of soil magnesium; Cochlearia pyrenaica ssp. alpina and Festuca rubra were associated with bigger stone sizes, and the latter occurred in wetter areas with higher of ions. A comparative solution culture experiment based on the local soil chemistry was used to study the growth responses to magnesium and nickel of Cerastium fontanum ss. scoticum, Cochlearia pyrenaica ssp. al ina and Festuca rubra. The results for Festuca and Cerastium were in agreement with the findings of the gradient analysis: Festuca was indifferent to both magnesium and nickel and Cerastium was susceptible to high magnesium; the reduction of dry weight by nickel in the Cochlearia conflicted with its suggested association with high soil nickel in the gradient analysis. The impacts on the photosynthetic systems of three Cochlearia species of different concentrations of iron and nickel were identifiable only in the non-ultramafic C. pyrenaica where the addition of nickel decreased photosynthesis but the effect could be ameliorated by the addition of high concentrations of iron. The open character of the skeletal soil at the MK1 site was discussed in terms of 'carrying capacity'. Vegetation development was suggested to be controlled at least partly by large stones covering the soil surface. Further factors such as space fragmentation, possible plant-to-plant interactions, and low density of flowering individuals and restricted seed dispersal were also considered. To test if major nutrients were limiting plant growth, major nutrients (NPK) were applied to the MK1.5 skeletal soil. The significantly higher X's and recruitment and change in life history traits (larger rosette sizes, earlier maturing and higher seed production) in the fertilised populations of C. pyrenaica ssp. alpina resulted in a significantly higher plant cover in the fertilised quadrats. The better growth of plants in the fertilised quadrats was reflected in their lower total non-structural carbohydrate (TNC) concentrations in May and their higher TNC in August. The present series of investigations found that magnesium and nickel toxicity had an effect on the intra-site distribution of the ultramafic species and also confirmed earlier reports on the importance of magnesium and nickel toxicity in ultsamafic exclusion. Large stones and low soil phosphorus concentration are proposed as limiting factors for the development of closed vegetation on the skeletal soil areas of the sites.

The Bay of Islands Ophiolitic Complex (BOIC) is one of most well preserved and well-exposed ophiolites in the world. The BOIC consist of four massifs; these are the Table Mountain (TBL), North Arm Mountain (NAM), Blow-Me-Down Mountain (BMD) and Lewis Hills massifs. Proposed geological environments of the BOIC in Newfoundland are diverse; ranging from oceanic spreading ridge to supra-subduction setting. The BOIC has a complete ophiolite sequence as defined at the Penrose Conference (Anonymous, 1972) including ultramafic mantle rocks, ultramafic to gabbroic cumulate rocks, sheeted dikes, pillowed basaltic rocks and capping sedimentary rocks in structurally ascending order. We studied harzburgite and overlying massive dunite in the BOIC. Harzburgite is generally medium-grained, and contains olivine, orthopyroxene, Cr-spinel, clinopyroxene and rare sulfide minerals. Harzburgite is massive to strongly deformed, with local development of mylonitic shear zones. A foliation and lineation are defined by elongated and fragmented grains of orthopyroxene and Cr-spinel. Dikes, sills, veins, and irregularly-shaped bodies of dunite and pyroxenite are present throughout the harzburgite unit. Dunite is the predominant lithology of the Blow-Me-Down Mountain. It is typically fine- to medium-grained, massive, and contains minor Cr-spinel and rare sulfide minerals. Dunite contains olivine, Cr-spinel and minor pyroxenes in some samples. Olivine crystals are commonly partly replaced by serpentine along fractures and in outer rims. Bulk rock and mineral composition data suggest that harzburgites are mild to highly refractory mantle residues after partial melting. In contrast all dunite samples show a cumulate geochemical signature from a mafic melt that originated from highly refractory mantle peridotites. Our study suggest that the harzburgite in the BOIC originally formed as oceanic lithosphere at a slow spreading ridge, possibly in the vicinity of active arc systems, whereas the parental melt for dunites formed in subduction setting. The second part of this study measured trace element compositions for olivine, Cr-spinel and bulk rock of dunite. The measured bulk rock compositions are compared to those of calculated based on mineral chemistry and their abundance. This comparison suggests that the trapped melt fraction was negligible during the crystallization of the dunites. The calculated melt compositions for the dunites confirm that the melt formed in subduction setting.

That there are a number of distinct ophiolitic belts separating some of the major tectonic zones of Greece and the eastern Mediterranean is generally well known. These have previously been interpreted as the remnants of back-arc basins, Mesozoic rifts, and supra-subduction zone type ophiolites. However mafic and ultramafic rocks present in the region of the Serbo-Macedonian Massif, northern Greece, do not appear to fit this model, and have generally been neglected in tectonic interpretations. The aim of this study is to determine how these bodies arrived at their current position, what is their true nature, and how do the answers to these questions help in the interpretation of the way that this section of continental crust was assembled. A multidisciplinary approach was taken to this problem. Structural and tectonic measurements and observations led to the conclusion that the main mafic and ultramafic bodies were accreted into the continental crust via a process of subduction accretion. Further to this, the continental crustal material between the main complexes is composed of tectonic melange material and not microcontinental fragments derived from the northern margin of Gondwana. A geochemical investigation of the Vavdos and Volvi Complexes demonstrates that the origin of these generally depleted lithologies was from a plume source, Volvi being thought to be a seamount, and the Vavdos Complex and associated along strike units, thought to be the disrupted remnants of an oceanic plateau. These conclusions have required the re-interpretation of current tectonic models for the region, and a new model is presented at the end of the thesis.

The aim of this study is to define mineralogical and geochemical characteristics of phlogopite-pargasite enriched ultramafic-mafic cumulate rocks from Kuranç
ali (Kirsehir) and their implications for petrology and regional geological setting. The Kuranç
ali rocks, found within an allochthonous sliver, are representative for the isolated members of the Central Anatolian Ophiolites, derived from closure of Izmir-Ankara-Erzincan branch of Alpine Neotethys. The rocks overthrust the Metamorphic Ophiolitic Mé
lange (the uppermost part of the Central Anatolian Metamorphics) and cut by felsic dykes of the Late Cretaceous Central Anatolian Granitoids. The Kuranç
ali rocks are unusually enriched in phlogopite and pargasite with varying crystal sizes. They are also composed of diopsidic augite, plagioclase, rutile, ilmenite, sphene, apatite and pyrite. The rocks are divided into six types
clinopyroxenite, clinopyroxenite-with-hydrous minerals-plagioclase, phlogopitite, hornblendite, layered gabbro and diorite. Evaluation of detailed EMP data from constituent minerals of different rock types showed that phlogopite with high Fe2+-Fe3+-Al[6]-Ti, diopsidic-augite with high Ca-Al(t)-Ti, Si-undersaturated pargasite with high Al[4]-K-Na-Ti-contents and intercumulus plagioclase with a wide range of composition (an%=40.61-98.58) display unusual compositions. Substitution mechanisms and elemental variations of the minerals suggest crystallization from hydrous metasomatized mantle, high water pressure and oxygen fugacities during formation of the Kuranç
ali rocks. Major oxide, trace and rare earth element abundances of the rock units were used to evaluate petrological characteristics. Chemical and tectonic discrimination diagrams, and parallel multi-element and REE patterns with highly enriched in LILE and LREE relative to HREE and HFSE show strong calc-alkaline affinity with slight alkaline features. Troughs at Nb-Ta and Ti characterize the rocks but these elements are slightly enriched than N-MORB. The rocks show high LREE/HREE ratios. Both unusual mineralogical and geochemical features of the rocks show that the rocks were generated in an arc environment. Moreover, they require a mantle wedge source strongly influenced by metasomatic components (fluid/melt) derived from subducting slab and/or OIB-like alkaline melt. Comparison of the rocks with tectonically well-defined rocks displays that they are generated in an intra-oceanic arc environment, but owe a comparison with fore-arc back-arc Central Anatolian Ophiolites within supra-subduction zone environment revealed that Kuranç
ali rocks are different and generated in an arc basement.

The Townlands iron-rich ultramafic pegmatite is a relatively large pipelike body situated in the western corner of Rustenburg Section, Rustenburg Platinum Mines. It is characterised by a strong negative magnetic signature and transgresses the noritic layered sequence of the upper critical zone of the Bushveld Complex. The layered rocks are downwarped in the vicinity of the pipe and are in sharp contact with the pegmatitic material. The pegmatite varies in composition between dunite and wehrlite, with the marginal zones being more wehrlitic in composition. Olivine (Fo₃₀ - Fo₅₂) and clinopyroxene (Wo₄₅En₃₀Fs₂₅ - Wo₄₅En₃₇Fs₁₈) are the dominant constituents and accessory phases include ilmenite, Ti -magnetite, apatite, amphiboles, chlorite-group minerals, biotite, ilvaite and a host of unusual ore minerals. The Fe-Ti oxides exhibit exsolution textures typically found in slowly cooled igneous rocks and temperatures of formati on are consi dered to be in excess of 800°C. The UG2 chromitite leader layers intersected by borehole TLP.l are enriched in Fe and Ti and exhibit compositions intermediate between chromite and Ti-magnetite. The ore mineral assemblage includes a primary sulphide assemblage consisting of troilite, chalcopyrite, cubanite and pentlandite, and an array of unusual phases formed by late-stage secondary processes. The unusual sulphides mooihoekite and haycockite, that occur in certain parts of the pegmatite, are considered to have formed by partial replacement of the primary assemblage and a possible paragenetic sequence is discussed. Mineral compositions and whole rock geochemical data are consistent with an origin for the pegmatite by crystallization from a fractionated melt. It is suggested that intercumulus fluids, trapped during the crystallization of the noritic layered sequence, accumulated in an area of structural weakness, in response to an increasing overburden pressure and/or tectonic activity. Evidence is also presented that indicates that the Townlands pegmatite may consist of at least two separate, but adjoining pegmatite bodies.
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Studies have been completed into the spectral response of alkaline and other ultramafic rocks from arid and semi-arid regions. To date these rocks have not been investigated spectrally in a systematic fashion using the latest field and airborne imaging spectrometers. The objective was to determine how spectral geological techniques could be used to locate these rock types when they are exposed, weathered and reduced to residual soil. The data used in this study were spectra obtained from field spectrometers (PIMA and GER IRIS MkIV) and airborne scanners (GEOSCAN MkII, GER IS and HyMap). These data were gathered at four sites within Australia. The data processing software packages used for the analyses were commercially available image processing systems (is S'600and ENVI) and a modified version of PIMAVIEW for processing spectra. Spectra were measured, in the field and the laboratory, of alkaline and other ultramafic rocks to determine if they had diagnostic spectral absorption features. These studies demonstrated that there are diagnostic spectral absorption features common to alkaline and other ultramafic rocks including dunite, peridotite and serpentinite. The diagnostic spectrum in the SWIR2 region (2000nm to 2500nm) has absorption features located near 2300nm and 2380nm and results from Mg-OH bearing minerals including serpentine, talc and phlogopite. The VNIR spectra of these rocks also have distinct absorption features, but since these are caused by minerals that are common to a variety of rocks and soils, they have not been considered in this study. When weathered under arid and semi-arid conditions, ultramafic rocks break down into smectite clays, primarily saponite. Saponite has a similar spectral signature to the primary Mg-OH bearing minerals. Further weathering and removal of magnesium results in saponite altering to kaolinite and then to opaline silica. These minerals may occur in residual soils derived from ultramafic rocks. Spectral investigation of mixtures of saponite and other minerals showed that there are linear changes the absorption features of spectra, depth, wavelength and shape, as the proportion of saponite to other minerals varies. The ability to identify ultramafic rocks from the distribution of their diagnostic spectra was confirmed by analysing data obtained from surface samples and airborne scanners. The coincidence of results obtained from field studies and airborne scanner data signifies that data acquired remotely are as useful as spectra obtained in the field, for mapping the extent of ultramafic rocks. Present and past imaging systems have been investigated to determine the specifications required to suit this application. These investigations included sampling the spectra of ultramafic and background rocks with the band pass characteristics of various instruments. The signal-to-noise ratio that is required of scanner data to ensure it is useable was also studied. These studies indicated a specification for data of at least eight and preferably, thirty two channels in the SWIR2 (between 2000nm and 2500nm) obtained with a signalto-noise ratio in excess of 200: 1, ideally 400: 1 at 2200nm. Scanners producing data with these specifications can be used to locate ultramafic rocks from their spectral signature, whether exposed or covered by residual soils in a variety of geological environments. The success of applying these techniques will however depend on the spectral contrast between ultramafic rocks and their backgrounds. Rocks that produce Mg-OH bearing minerals or have near 2300nm absorption can result in areas being mistakenly identified as containing alkaline and other ultramafic rocks. However, in this study it was demonstrated that carbonate soils and rocks that have a near 2300nm absorption feature can be spectrally distinguished from alkaline ultramafic derived saponite using HyMap scanner data. In South Australia dolomite appears to have altered to saponite at surface but kimberlites in the area can still be detected by processing HyMap scanner data with spectral as opposed to conventional image processing techniques.

Serpentinization is a complex set of hydration reactions, where olivine and pyroxene are replaced by serpentine, magnetite, brucite, talc and carbonate minerals. Serpentinization reactions alter chemical, mechanical, magnetic, seismic, and hydraulic properties of the crust. To understand the complicated nature of serpentinization and the linkages between physical and chemical changes during the reactions, I performed flow-through laboratory experiments on cylindrically cored samples of ultramafic rocks. Each core had a well-mated through-going tensile fracture, to investigate evolution of fracture permeability during serpentinization. The samples were tested in a triaxial loading machine at an effective pressure of 30 MPa, and temperature of 260°C, simulating a depth of 2 km under hydrostatic conditions. Fracture permeability decreased by one to two orders of magnitude during the 200 to 340 hour experiments. Electron microprobe and SEM data indicated the formation of needle-shaped crystals of serpentine composition along the walls of the fracture, and chemical analyses of sampled pore fluids were consistent with dissolution of ferro-magnesian minerals. The rate of transformation of olivine to serpentine in a tensile fracture is calculated using the data on evolution of fracture permeability assuming the fracture permeability could be represented by parallel plates. Assuming the dissolution and precipitation reactions occur simultaneously; the rate of transformation at the beginning of the experiments was ~ 10-8-10-9 (mol/m2s) and decreased monotonically by about an order of magnitude towards the end of the experiment. Results show that dissolution and precipitation is the main mechanism contributing to the reduction in fracture aperture. The experimental results suggest that the fracture network in long-lived hydrothermal circulation systems may be sealed rapidly as a result of mineral precipitation, and generation of new permeability resulting from a combination of tectonic and crystallization-induced stresses may be required to maintain fluid circulation. Another set of flow through experiments were performed on intact samples of ultramafic rocks at room temperature and effective pressures of 10, 20 and 30 MPa to estimate the pressure dependency of intact permeability. Porosity and density measurements were also performed with the purpose of characterizing these properties of ultramafic rocks. The pressure dependency of the coefficient of matrix permeability of the ultramafic rock samples fell in the range of 0.05-0.14 MPa-1. Using porosity and permeability measurements, the ratio of interconnected porosity to total porosity was estimated to be small and the permeability of the samples was dominantly controlled by microcracks. Using the density and porosity measurements, the degree of alteration of samples was estimated. Samples with high density and pressure dependent permeability had a smaller degree of alteration than those with lower density and pressure dependency.
Ph. D.

This study presents mineralogical, geochemical and Sr, Nd, Hf, Pb, O isotopic results for intrusive rocks and ultramafic-mafic xenoliths that represent different levels of the thickened Kerguelen Archipelago crust. These results show that intrusive rocks have origins similar to those of the Kerguelen flood basalts. They have undergone fractional crystallisation surimposed on a general magmatic evolution from tholeiitic-transitional to alkaline affinities. Mafic and ultramafic xenoliths are cumulates from deep and shallow levels. They mostly crystallised from early tholeiitic-transitional series, some were then infiltrated by highly alkaline magmas. Some mafic cumulates have geochemical characteristics consistend with crystallisation from mildly alkaline basalts. Oxygen isotopes show that some intrusive rocks have undergone low-temperature re-equilibration but clinopyroxene oxygen isotopes retain a mantle origin signature for both the intrusive rocks and mafic cumulates. The magamatic evolution from tholeiitic-transitional to alkaline affinities might be explained by a decrease in the degree of melting coupled with decreasing magma supply through. Three different source origins are recquired to explain radiogenic isotopic compositions : (1) mixing between a SEIR-like component and the Kerguelen Plume component, (2) the activity of the Kerguelen Plume alone and (3) the third component could be attributed to either the presence of a « continental component » in the source or to small-scale heterogeneities within the Kerguelen plume itself or by occurrence of old subcontinental lithospheric mantle fragments that can interact with ascending magmas
Cette étude présente des données minéralogiques, géochimiques et isotopiques de roches intrusives et de xénolithes mafiques / ultramafiques représentant différents niveaux de la croûte épaissie de l'Archipel de Kerguelen. Ces données montrent que les roches intrusives ont une origine similaire à celle des basaltes de l'Archipel. Elles ont subi des processus de cristallisation fractionnée surimposés à une évolution magmatique (affinité tholéiitique-transitionnnelle à alacaline). Les xénolithes mafiques / ultramafiques sont des cumulats de niveaux profonds et superficiels. Ils ont principalement cristallisés à partir de magmas tholéiitique-transitionnels mais certains ont pu cristalliser à partir de magmas alcalins. Certains cumulats tholéiitique-transitionnels ont subi une infiltration secondaire fortement alcaline. Les isotopes de l'oxygène montrent que certaines roches intrusives ont subi des re-équilibrations à basses températures cependant les cpx des roches intrusives et cumulats ont gardé une signature mantellique. L'évolution depuis un magmatisme tholéiitique-transitionnel à un magmatisme alcalin peut s'expliquer par une diminution du degré de fusion partielle couplée à une diminution de composition en isotopes radiogéniques : (1) un mélange entre une composante type SEIR et une composante Plume de Kerguelen, (2) une composante Plume de Kerguelen seule et (3) une composante qui pourrait être attribuée à la présence d'une composante continentale, à des hétérogénéités dans le plume ou enfin à la présence d'anciens fragments de manteau subcontinental lithosphérique

High concentrations of potentially toxic elements (PTEs) in surface and near-surface environment may be attributed to both anthropogenic sources, including industrial and agricultural activity, and geogenic source, mainly due to natural weathering of rocks. Considering the geogenic sources, ultramafic rocks (e.g., dunite, peridotite, pyroxenite, and serpentinites) are among the most critical from the environmental point of view; in fact, they are characterized by high contents of Cr, Ni, Co, and other PTEs which can have potential harmful impact on ecosystems and human health if released into soils and waters during weathering and pedogenic processes. As a matter of the fact, weathering of ultramafic rock produces ultramafic soil containing high concentration of PTEs, including Cr, Ni, and Co compared to soils derived from non-ultramafic bedrock. Although ultramafic rocks and relative soils cover approximately 1% of the Earth’s surface, they are distributed worldwide and are commonly associated with ophiolite complexes; for this reason, they play an important role in environmental management. The main objective of this PhD thesis was to determinate the mineralogy and the chemistry of PTEs of ultramafic soil profiles from the Voltri Massif and to evaluate how lithological, textural, and structural properties of the ultramafic bedrock with various degree of serpentinization and deformation may affect the PTEs re-distribution and the fate in the soils during pedogenesis, as well as to assess their environmental implications in the ecosystem. The multidisciplinary and multiscale approach, used in this PhD thesis, has allowed to highlight a series of considerations that led to the following conclusions: • In the studied rocks, Cr, Ni, and, subordinately, Co are invariably the PTEs with the highest concentrations; in addition, V, Cu, and Zn are generally found in high concentrations. The main factors controlling the PTEs distribution within the studied ultramafic rocks appeared to be the serpentinization degree and the deformation style and intensity. The main source of the PTEs are spinel-group minerals. Moreover, PTEs-bearing phases are also represented by the other rock-forming minerals (such as serpentines, olivines, pyroxenes, and chlorites) and some accessory phases (e.g., ilmenite and other oxides, sulfides). • The studied ultramafic soil profiles vary in thickness from 35 to 80 cm and are characterized by weakly developed A and C horizons and a very thin O horizon (up to 5-10 cm). In general, in the soils the mineralogy of the skeleton (sandy and silty fractions) is closely related to bedrock mineralogy as expected for primitive A-C soils (in order of abundance: antigorite, chlorite, spinel-group minerals, pyroxenes, authigenic phases, quartz, olivine, and tremolite). The clay fraction is mainly composed by amorphous or low-crystalline Fe-oxyhydroxides, serpentines, smectite and illite/smectite mixed-layer clay, and clinochlore. Cr and Ni values have very variable concentrations over a wide range. Cr and Ni decrease according to serpentinization degree of bedrock. Co, Zn, and Cu do not show a clear correlation with bedrock serpentinization. V increase with the serpentinization of the bedrock. The PTEs concentrations in the studied ultramafic soil profiles are linked both to the primary minerals, inherited by bedrocks (e.g., serpentines, spinel-group minerals, pyroxenes, chlorites), and to their stable authigenic products (Fe-oxyhydroxides and clay minerals). The PTEs leached from the primary minerals is mainly scavenge by goethite, and subordinate by clay. • The results evidence that Cr, Ni, and, Co systematically exceed (up to one order of magnitude) the residential and industrial threshold values (CSC) according to Italian law (D.M. 471/1999; D.Lgs 152/2006) both in rocks and soils. However, combining all my results, I have demonstrated that the critical PTEs concentrations in the studied profiles have a geogenic origin and are linked both to the primary minerals, inherited by bedrocks, and to their stable authigenic products. Considering the high stability of authigenic products in supergenic environment, it is evident that this mineral species are effective and often permanent traps for the most important PTEs of ultramafic soils and bedrocks, thus reducing its bioavailability. A study of this kind that combine the bulk chemistry of outcropping rocks and the relative soil profiles with their geological, structural, mineralogical, and crystallochemical data, can be also a useful tool in environmental concerns to determine the PTEs distribution, to evaluate their potential mobility and bioavailability as well as to discriminate the natural geochemical background from possible source of contamination.

The South Manasan ultramafic intrusion (ca. 1880 Ma) located in the Early Proterozoic Thompson Nickel Belt (TNB) contains Ni and platinum group element (PGE) mineralization hosted by disseminated sulfide. Whole-rock Ni values range from 0.3 to 1.7 wt. % and total precious metals (TPMs) range from 0 to 1.3 ppm Pt + Pd + Au and equate to tenor values (i.e., metal in 100% sulfide) of 11-39 wt. % Ni and 8-27 ppm TPMs. The South Manasan intrusion is a steeply dipping sill-like body with a boudinaged outline having a strike length of approximately 1200 m, average width of 125 m and a minimum depth extent of 1000 m. The intrusion is composed of approximately 25% fresh dunite, 50% serpentine altered dunite and 25% tectonized and carbonate altered dunite. The most intense alteration is found near the intrusion’s margin where it is in contact with metasedimentary rocks of the Pipe Formation, part of the surrounding Ospwagan Group. In fresh dunite the sulfide assemblage characterized by an intercumulate texture is dominated by pentlandite with accessory pyrite; the latter having a symplectic-like texture. The pentlandite-pyrite assemblage in the serpentinized dunite, although still characterized overall by an intercumlate-texture, has well developed platy intergrowths with chlorite and serpentine. In the most intensely modified unit (the carbonate altered dunite) the sulfide assemblage consists primarily of pyrrhotite and pentlandite. Whole-rock geochemical data (n=360), modal mineralogy and mineral chemistry obtained on representative drill core throughout the South Manasan intrusion have been used to establish a type section in order to evaluate the relative roles of primary magmatic versus secondary (i.e., serpentinization, carbonate alteration and deformation) processes. These data indicate that the primary silicate-sulfide assemblage was systematically modified during : serpentinization, carbonate alteration and deformation of the South Manasan intrusion such that a sequence of primary versus secondary events can be established. Intrusion of the original komatiitic magma and formation of the South Manasan intrusion took place at a shallow level into consolidated Ospwagan Group sediments with subsequent contamination of this melt with crustal S. This triggered sulfide saturation and generation of an immiscible sulfide melt. Calculated Ni and TPM tenor values constrain the R factor to between 500 and 2500. The early crystallization of olivine inhibited the sulfide melt from settling to the bottom of the magma column and as a consequence, the sulfides now have a primary interstitial magmatic texture. The current sulfide association dominated by pentlandite>>pyrite>chalcopyrite has a mineral paragenesis that is consistent with subsolidus re-equilibration of a primary pentlanditepyrrhotite- chalcopyrite assemblage. The subsequent processes of serpentinization, deformation and carbonate alteration resulted in modifying the primary sulfide assemblages and their textures (i.e., to platy habits), but did not greatly alter the bulk composition, in particular metal contents, except for addition of volatiles (H2O, CO2). It is concluded therefore that the enrichment of the sulfide assemblage at South Manasan in Ni and PGEs is a consequence of a primary magmatic process involving high R factor and that the effects of later overprinting processes (alteration, deformation) are not responsible for the presently observed high-tenor sulfide association.

The type of feedstock and host rock utilised in ex situ and in situ Carbon Capture and Storage by Mineralisation (CCSM) is an important aspect of these technologies, and detailed appraisal of candidate mineral/rock performance in the presence of CO2 may greatly improve CCSM efficiency. Here, a detailed mineralogical and geochemical investigation of serpentine minerals and ultramafic rocks under laboratory-controlled experiments simulating ex situ and in situ process conditions is presented. Feedstock serpentine minerals were analysed comprehensively, prior to experimental processing. The identification of antigorite was unequivocal using a combination of X-ray diffraction, Fourier Transform Infrared Spectroscopy and/or Thermo-gravimetric Analysis. However, the analysis of chrysotile and lizardite proved to be more challenging, especially when the two polymorphs were finely inter-grown. This study highlighted the structural, textural and chemical complexity of serpentines and showed that great care must be taken when analysing this mineral group for CCSM. Investigation of the acid leaching of serpentine minerals under conditions of 70°C and 1.4M NH4HSO4 provided fundamental insights into the rate and extraction efficiency (EE) of Mg2+ and associated controlling factors, under conditions relevant for ex situ CCSM. It is demonstrated that EE is a function of mineral reactivity and depend on a complex interplay between crystal structure and chemistry. Generally, poorly crystalline and highly disordered phases with low levels of Al3+ were found to be suitable feedstock materials for acid digestion pre-treatment. Chrysotile, lizardite 2H1 and poorly crystalline serpentines showed up to 85% Mg2+ EE after 3 h of acid leaching, and hence are recommended as best feedstock materials for CCSM, whilst antigorite and Al3+-rich serpentines proved to be largely unsuitable, showing low levels of EE of ~ 20%. Examination of dunite, harzburgite and serpentinite under conditions relevant for in situ CCSM, i.e. 70°C and 100 bar CO2 pressure, provided insights into rock reactivity as a function of composition and texture, and the progression of in situ mineral carbonation. The rate of net Mg release and thus the extent of subsequent carbonation were greatest for serpentinite, providing ca. 3% carbonation after six months. However, mineral reactivity within serpentinite was preferential, i.e. significantly enhanced within secondary vein serpentine, being thus, the main source of Mg2+ for magnesite precipitation. Reaction-induced transformation and hence mineral carbonation of dunite and harzburgite were less pronounced over the same time-scale. The reaction of serpentinite with wet supercritical CO2, as opposed to CO2-saturated brine, significantly affected rock integrity, with the exposure of more surface area and promotion of fluid-rock interaction. In particular, it is shown that ferric iron oxidation and the precipitation of goethite impacts upon surface mineral dissolution at exposed surfaces, thereby hindering subsequent carbonation. Overall, this study highlighted the importance of host rock choice for in situ CCSM and the need for detailed petrographical and geochemical investigation of any proposed CCSM repository prior to technological process modelling.

The Central Asia Orogenic Belt is one of the largest accretionary orogenic belts in the world. In this belt, many sulfide‐bearing mafic‐ultramafic intrusions occur along faults, including the Kalatongke complex in southeast Chinese Altay and the Huangshandong intrusion in east Tianshan. The Kalatongke complex is a composite body including ~308Ma dioritic intrusion and 287Ma sulfide‐bearing mafic intrusion. The dioritic intrusion consists of biotite‐hornblende gabbro, diorite and quartz diorite. This intrusion was formed from a mixture of an evolved mantle‐derived magma and a crust‐derived adakitic magma combined with fractional crystallization of clinopyroxene, amphibole and plagioclase. The mafic intrusion is dominantly made up of norite in which sulfide ores, including disseminated, massive Ni‐Cu and massive Cu‐rich ores, are hosted. This intrusion was formed from two different pulses of basaltic magmas that had different magma evolution histories. The early magma pulse reached sulfide‐saturation due to minor crustal contamination and a small amount of sulfide (<0.03%) was removed before the emplacement. The evolved magmas then entered a shallow magma chamber and assimilated crustal materials to attain sulfide‐saturation again. Sulfide liquids segregated from the magma to form massive Ni‐Cu and massive Cu‐rich ores through further fractionation and residual silicate melts formed norites. A second pulse of magma underwent removal of <0.02% sulfides with stronger crustal contamination, and re‐attained S‐saturation during the emplacement and became a phenocryst‐laden magma. This magma then intruded the earlier formed massive sulfide ores and norites, forming the disseminated sulfide ores. The Permian Huangshandong mafic‐ultramafic intrusion hosts the largest magmatic sulfide deposit in east Tianshan. It consists of a layered unit of lherzolite, gabbro and diorite and a massive unit of olivine gabbronorite and gabbronorite. Both units formed from siliceous high magnesium basaltic (SHMB) magmas derived from a hydrous, depleted mantle source. The two units of the Huangshandong intrusion formed from magmas that have undergone different processes through the evolution of the magma plumbing system. The early magma pulse gained sulfur‐saturation before the emplacement and small amounts of sulfide (<0.03%) were removed to result in a PGE‐depleted, high‐Mg magma. This magma achieved sulfide‐saturation again in a staging magma chamber through crustal contamination and fractional crystallization of olivine and Cr‐spinel (an AFC process) to form the layered unit. A second magma pulse underwent fractionation of more olivine +/‐ Cr‐spinel but less sulfide (<0.003%) removal before the emplacement and became evolved, PEG‐undepleted and low‐Mg before the injection into the magma chamber. Mixing of the two magmas triggered sulfide‐saturation to form sulfide ores with variable PGE, Ni and Cu compositions. The study suggests that SHMB‐like magmatism, produced by melting of depleted and hydrous mantle source, may be an important feature of orogenic belts. Mafic‐ultramafic intrusions formed from SHMB‐like magmas may host economic sulfide deposits, particularly sulfide Ni‐Cu sulfide deposits.
published_or_final_version
Earth Sciences
Doctoral
Doctor of Philosophy

Since its formation at 4.5 Ga, the Earth underwent a complex evolution that progressively differentiated its original composition into the reservoirs that we presently know. Our knowledge on the composition and differentiation mechanisms active in the Early and Ancient Earth are still fragmentary for the paucity of suitable preserved rock records. The poor knowledge on the Archean mantle composition arises a series of problems spanning from the effective chondritic composition of the Earth to how volatile elements (hydrogen, oxygen, chlorine and fluorine) were added to the Earth. For the unavailability of mantle sectors preserving the Archean geochemical signature, valuable information on the Archean mantle composition can be exclusively extracted from Archean mantle-derived igneous rocks. In the Archean greenstone belts, different products of mantle melting are found as lavas and sills spanning in composition from tholeiites through Fe-picrites to komatiites. All these rocks are generally affected by extensive alteration which prevent the bulk rocks to be fully informative on the primary mantle melt composition and particularly on its volatile element contents. However, in some of these rocks primary igneous mineral phases such as amphibole are preserved that may be useful to constrain the primary melt composition including its volatile budgets. In this thesis amphibole-bearing ultramafic rocks of late Archean and Early Proterozoic age (Stone et al., 2003; Fiorentini et al., 2004; Fiorentini et al., 2008) were selected. For comparison amphibole-bearing ultramafic rocks from different tectonic settings of the Phanerozoic were also considered. The Archean and Early Proterozoic rocks share many petrographic and textural similarities with hornblendites and amphibole-bearing pyroxenites from Phanerozoic orogenic settings. In all studied rocks the crystallisation of amphibole follows that of the early crystallising minerals: olivine + spinel ± orthopyroxene + clinopyroxene. The chemical composition of Archean and Early Proterozoic amphiboles is more similar to that of amphibole from alkaline lavas than that of amphibole in orogenic settings. The geobarometric calculations on Archean and Early Proterozoic rocks yield large uncertainty on the pressure of crystallisation with values between 0 and >3 Kbar, which are not conclusive about the deep or shallow origin of amphibole. In the Archean and Early Proterozoic rocks amphibole is in clear disequilibrium with the early crystallizing clinopyroxene. Modelling of melt differentiation suggests that amphibole crystallized from a melt percolating the cumulate pile. Such melt evolved by crystallization of olivine and pyroxene and subsequently modified its composition in response to olivine assimilation. A major problem in the studied Archean and Early Proterozoic rocks is about the origin of the H2O necessary to stabilize amphibole. The H2O concentrations in the Archean and early Proterozoic amphiboles are comparable to those of either subduction-related or amphibole megacrysts from alkaline lavas, thus suggesting that melts in equilibrium with amphiboles possessed almost the same water contents irrespective of age. According to the composition of amphibole in fluid-mobile elements (e.g., F, Cl, B and Sr) a contribution of seawater-derived fluid in the Archean and Early Proterozoic rocks is unlikely. The range of δD values of the Archean and Paleoproterozoic amphiboles is between -99.5 ‰ and -129.8 ‰, that is slightly lower than the mantle range but still consistent with a magmatic origin for water. The hypothesis of a crustal contribution in the origin of the amphiboles (and in turn a crustal origin of water) contrasts with the oxygen isotope signature of amphibole showing δ18O values lighter than those of the mantle. Because the involvement of recycled crustal materials, able to provide the required seawater-like geochemical anomalies, is unlikely for the genesis of the studied amphiboles, the light δ18O signature is interpreted as a primary feature of the mantle source. In order to monitor possible changes marked by amphibole in the secular evolution of the Earth’s mantle, the trace element composition of the melt in equilibrium with amphibole from Archean and Early Proterozoic rocks was calculated and compared with that of melts produced nowadays at the different geodynamic settings. Equilibrium melts show increasing Nb/Y ratios from komatiites through tholeiites to Fe-picrites that are in agreement with the increased alkalinity of the parental melt as inferred from the literature. All calculated melts share an incompatible trace element pattern paralleling that of present-day OIB. The comparison of the water content in primary melts calculated from Archean-early Proterozoic amphiboles and present-day primary mantle melts reveals that the mantle source of the Archean komatiites had a much higher water content than that characterizing present day OIB. The highly variable water contents in Fe-picrites however suggest a large heterogeneity in the composition of the mantle source. The comparison between the Archean-early Proterozoic amphiboles and those from the Phanerozoic has also revealed heterogeneities in the Nb/Ta ratios of the mantle through the Earth’s history. Some of the calculated melts (since early Proterozoic) show an enriched Nb/Ta signature that is independent from space (geological setting) and time and that was interpreted as a primary feature of the different mantle sources. The observed heterogeneous Nb/Ta signature of the Earth’s mantle was interpreted as related to the addition of extra-terrestrial material after the mantle-core equilibration prior to 4.4 Ga and to an incomplete equilibration of these domains during the Earth’s evolution. In conclusion, the data of this thesis suggest that the Earth’s mantle is much more heterogeneous than commonly assumed. The occurrence in the Archean and Early Proterozoic of mantle domains enriched in volatile elements but unrelated to subduction processes has been documented. An extra-terrestrial signature for some mantle domains was also reported and I do not exclude that the light oxygen isotope signature of the Archean and Early Proterozoic rocks is also a reminiscence of extra-terrestrial inputs possibly related to the meteoritic Late Veneer.

Le fonctionnement et la structure hydrogéologiques des aquifères de socle des granites et des gneiss sont aujourd'hui relativement bien compris. En revanche, dans cet ensemble, les aquifères dans les péridotites sont très peu étudiés et mal compris. Dans ce contexte, les massifs obductés de Nouvelle-Calédonie présentent un laboratoire naturel exceptionnel pour améliorer la connaissance de cet hydrosystème original en contexte tropical. Ainsi l'objectif du présent travail de thèse est d'approfondir la connaissance de la structure et du fonctionnement hydrogéologiques de ces massifs. L'analyse porte d’abord sur le manteau d'altération constitué de la cuirasse, des latérites, des saprolites grossières et du saprock. Plus de 60 essais hydrauliques sont menés sur les massifs de péridotites et les résultats sont compilés aux données existantes. La conductivité hydraulique moyenne des latérites est évaluée à 1.10-7 m/s et celle des saprolites grossières et du saprock à 8.10-7 m/s. L'hétérogénéité de cet horizon altéré est marquée par une gamme de variation de la conductivité hydraulique sur six ordres de grandeur et l'analyse piézométrique met en évidence des connexions hydrauliques avec le substratum fracturé profond. Le substratum est ensuite considéré. L'étude de la fracturation est réalisée à partir de mesures structurales sur affleurement et de la description de près de 1000 m de carottes de forages. L'analyse de la fracturation met en évidence l'importance du réseau serpentineux par sa densité d’une part, et par son lien avec l'altération supergène d'autre part. De plus, il est vérifié que la conductivité hydraulique du substratum diminue avec la profondeur. Cette variation est liée à la diminution de la densité de fractures altérées. Ainsi, à l'issue de ces analyses, la structure des massifs de péridotites est définie. Un réseau primaire de fractures d’espacement décimétrique lié au réseau serpentineux préstructure les péridotites. Sur ce réseau se surimpose un réseau de fractures dont l'espacement est décamétrique et caractérisé par une altération supergène. Les fractures altérées présentent localement de fortes conductivités hydrauliques, de l'ordre de 10-5 m/s. En profondeur l'espacement des fractures est hectométrique et les fractures sont majoritairement fermées, scellées par les minéraux néoformés ou par l'effet de la pression lithostatique. Les réseaux de fractures déca et hectométriques, visibles également sur l'effet d’échelle de la conductivité hydraulique, sont majoritairement verticaux, développés par instabilité de dissolution lors des processus d’altération. Cependant, des structures à faible pendage existent également et permettent la percolation du réseau. Enfin, à partir de ces nouveaux résultats et de l’intégration de l'ensemble des données acquises sur les différents massifs, un modèle de structure et de fonctionnement hydrogéologiques est proposé à l'échelle du massif. Ce modèle comprend l'horizon des latérites qui constitue un aquitard homogène sous lequel se développe l'aquifère dont l'épaisseur est de l'ordre de cinquante mètres. Le substratum est discrétisé en trois couches dont la conductivité hydraulique décroît de 2.10-7 à 2.10-8 m/s entre 50 m et 250 m environ sous le mur de l'aquifère. Les modèles numériques construits permettent de valider le modèle conceptuel unitaire et montrent que l'état de saturation des massifs est contraint par leur géomorphologie. Au terme de ce travail, plusieurs aspects doivent encore être approfondis. Le rôle hydrogéologique de la cuirasse doit être précisé et considéré dans le modèle hydrogéologique. Enfin, compte tenu du développement possible de structures très perméables, voire pseudo-karstiques, la connaissance de la distribution des structures drainantes doit être améliorée. Les résultats appliqués de ce travail de recherche sont exposés dans un rapport final et un guide méthodologique livrés dans le cadre du projet CNRT « HYPERK »
Water resources of hard-rock (gneisses or granites) aquifers have significantly been studied in the past two decades. The hydrogeological behavior and structure of these aquifers are thus relatively well understood. On the other hand, aquifers in mantle-type basements, such as peridotites, are poorly studied and understood, mainly because they are not common and of limited extent. In this context, New Caledonia is a great laboratory offering unique opportunity to improve the knowledge of these original types of hydrosystems in tropical climate. Thus, the objective of this thesis is to improve the knowledge of these aquifer systems within weathered peridotites. Firstly, the study focuses on the characterization of the weathered layers of the peridotites composed of, from top to bottom, iron oxides/ferricrete, laterite, coarse saprolite and saprock (ie. top of the bedrock, with up to 20 % of weathered material). More than 60 hydraulic tests are performed and results were compiled with existing data. Mean hydraulic conductivity (K) of laterites is estimated around 1.10-7 m/s while mean value in coarse saprolites and saprock is around 8.10-7 m/s. Heterogeneity of this altered layer is high; K varies between six orders of magnitude and hydraulic head data analysis reveals a hydraulic connection with the deep fractured bedrock. Secondly, the fresh rock part of peridotites is studied. Fracture network analysis is derived from outcrop structural measurements and from the description of about 1000 m of cumulated borehole cores. This work highlights the importance of serpentine network, because of its high density and its critical impact on weathering. Moreover, the observations reveal that hydraulic conductivity decreases with depth within the substratum, due to the vertical decrease of weathered fractures density. These new results allow defining a structural framework of the massifs. It is characterized by a primary decimetrical fracture network closely related to the serpentine network. This network is overprinted by a secondary weathering network which reveals decametric spacing (ca. 30 m) and in places K values of 10-5 m/s. At depth, spacing is hectometrical and fractures are sealed by lithostatic pressure and/or subsequent mineral precipitations. These deca- and hectometric fracture networks, which are also visible on the scale effect of hydraulic conductivity, are primarily vertical and are the result of dissolution instabilities occurring during weathering processes. However, low- angle fractures do occur and allow the percolation of the network. Finally, on the basis of these new results and the integration of all existing data from different massifs a new hydrogeological conceptual model is proposed at the scale of a massif. The model includes a homogeneous lateritic aquitard and a coarse saprolite and saprock aquifer which is about 50 m thick. The bedrock is subdivided into three layers whose hydraulic conductivity decreases from 2.10-7 m/s to 2.10-8 m/s, respectively 50 and 250 m below the aquifer base. Numerical modelling validates this unitary conceptual model and reveals that the saturation of the massifs depends on their morphology. At last, several aspects require further research. The role of the ferricrete layer must be specified and considered in the hydrological model. Moreover, distribution of the fracture network remains to be fully addressed and should be studied with care given the potential development of highly permeable structures that could conform to pseudo-karstic drains. The applied results of this work are available in a “Technical guide” and a “Technical report” of the “HYPERK” CNRT Project

A Nappe Lima Duarte, localizada na porção oriental do sistema orogênico Tocantins Meridional, sudoeste do estado de Minas Gerais, é constituída por rochas supracrustais de alto grau (gnaisses e micaxistos com e sillimanita e quartzitos) com lascas de ortognaisses arqueanos tonalíticos - granodioríticos (antigos terrenos TTG) tectônicamente intercaladas. É nesta Nappe de Lima Duarte que ocorrem os dois corpos metaultramáficos tema deste estudo. O corpo ultra máfico de Lima Duarte, bandado - estratificado, sem foliação evidente, encontra-se encaixado em uma zona de cisalhamento entre hornblendabiotita gnaisses e migmatitos, e sillimanita - muscovita - biotita - quartzo xistos/gnaisses. Trata-se de um corpo lenticular alongado em direção NW - SE, com 700 metros de comprimento e aproximadamente 300 metros de largura. Já o corpo ultramáfico de Olaria aflora como um conjunto de blocos anguloso de alguns metros de tamanho, e ocorre como corpo lenticular pequeno encravado em hornblenda - biotita ortognaisses. Em ambos corpos o grau de intemperismo impossibilita estabelecer as relações de contato com as rochas encaixantes. O corpo de Lima Duarte apresenta bandamento composicional como relíquia ígnea, indicando que se trata do fragmento de um corpo bandado - estratificado desmembrado. Seus litotipos, que ocorrem alternados em bandas centimétricas, são constituídos por proporções variáveis de olivina, ortopiroxênio, magnésio-hornblenda, espinélio / magnetita, Mg-clorita e serpentina e, considerando a Mg-hornblenda como substituta do clinopiroxênio ígneo, representam metadunitos, metaharzburgitos, meta-olivina- ortopiroxenitos e metalherzolitos, serpentinizados com intensidade variável. O corpo de Olaria apresenta texturas grano-nematoblásticas poligonizadas a lobadas, e é constituído de ortopiroxênio e hornblenda - espinélio + Mg-clorita + olivina, com serpentinização apenas incipiente em olivina. Os minerais do corpo de Lima Duarte são mais magnesianos (Mg/Mg+Fe2+mais altos, hornblenda e ortopiroxênio sem pleocroísmo), enquanto os de Olaria são mais ricos em ferro (Mg/Mg+Fe2+mais baixo, ortopiroxênio e hornblenda pleocróicos), sugerindo protólitos mais magnesianos para Lima Duarte. As texturas e paragêneses metamórficas (ortopiroxênio - olivina - Mg-hornblenda - Mg-Al-espinélio, + Mg-clorita) sugerem condições de limiar fácies anfibolito-fácies granulito. A evolução metamórfica é modelada com base nas variações composicionais que ocorrem no anfibólio cálcico e na Mg-clorita. A quebra final da Mg-clorita, definida pela reação: Mg-Clorita forsterita + enstatita + espinélio + H20, representa as condições de pico alcançadas, com reconstituição parcial retrometamórfica da clorita. . Estimativas termobarométricas com o programa Thermocalc para a paragênese olivina - ortopiroxênio - espinélio - hornblenda forneceram temperaturas de 810ºC para o corpo de Lima Duarte e 840ºC para o de Olaria, compatíveis com as estimativas citadas na literatura para as rochas encaixantes e com as condições de quebra da Mg-clorita. No corpo de Lima Duarte, a intensa serpentinização ocorreu inicialmente através e substituições por domínios composicionais, resultando em texturas pseudomórficas de olivina (mesh) e ortopiroxênio (bastita), tornando-se mais pervasiva a seguir, com serpentinização da hornblenda e clorita, implicando mobilidade de Ca e Al no sistema.
The ultramafic rocks of this study occur in the Lima Duarte nappe, which is constituted of high-grade metassedimentary rocks such as sillimanite schists and gneisses as well as quartzites, with intercalated tectonic slices of tonalitic-granodioritic gneisses and migmatites from the archean TTG basement. This nappe belongs to the eastern part of the southern Tocantins Orogenic system, in southwestern Minas Gerais State, Brazil. The ultramafic rocks make up two bodies in the Lima Duarte nappe. The Lima Duarte body is stratified, without foliation, included in a shear zone between sillimanite-garnet schists and gneisses and hornblende-biotite gneisses and migmatites as a lenticular body approximately 700 m long and 300 m thick. The Olaria body outcrops as a few meter-size boulders, possibly as a lenticular body intercalated in hornblende-biotite orthogneisses. Neither body exhibits its contacts with the country rocks due to the intense weathering. The Lima Duarte body exhibits layering inherited from stratified igneous rocks, and thus represents a fragment of a dismembered stratified igneous complex. It´s rock types, constituted by varying proportions of olivine, orthopyroxene, magnesian hornblende, green spinel, magnetite, Mg-chlorite and serpentine, occur alternated in centimetric bands and, if hornblende is taken as correspondent to clinopyroxene, can be identified as metadunites, meta-olivine orthopyroxenites, metaharzburgites and metalherzolites, all serpentinized in various degrees. The Olaria body exhibits grano-nematoblastic, polygonized to lobate textures, and is constituted by orthopyroxene - hornblende - green spinel + olivine + Mg-chlorite, with incipient serpentinization in olivine grains. The Lima Duarte rocks are more magnesian (higher Mg/Mg+Fe2+ in minerals, non-pleochroic orthopyroxene and hornblende) than the ones from Olaria (lower Mg/Mg+Fe2+ in minerals, pleochroic hornblende and orthopyroxene). The metamorphic textures and parageneses (olivine - orthopyroxene - hornblende - Mg-Al-spinel + Mg-chlorite) suggest metamorphic conditions transitional from amphibolites to granulite facies, with late low-grade serpentinization in the Lima Duarte body. The metamorphic evolution is modeled through continuous compositional changes in calcic amphibole and Mg-chlorite. The final breakdown of chlorite, through the reaction: Mg-chlorite olivine + orthopyroxene + spinel + H2O represents peak conditions, with later partial retrometamorphic reconstitution of chlorite. Thermobarometric estimates for the paragenesis orthopyroxene - hornblende - olivine - spinel with the help of Thermocalc yielded 810oC for Lima Duarte rocks and 840oC for Olaria rocks, in good agreement with previous results for the high-grade country rocks from literature and for the chlorite breakdown conditions. In the Lima Duarte body, the intensive serpentinization started with compositional domain substitutions, mainly in olivine and orthopyroxene, resulting in pseudomorphic textures (mesh and bastite, respectively). In later stages, calcic amphibole as well as chlorite suffered serpentinization, thus indicating Ca and Al mobility in the system.

Ces travaux de thèse apportent de nouvelles contraintes sur la concentration et le comportement de l’H dans le manteau lithosphérique et reposent sur l’étude pétro-géochimique de trois séries de xénolites de péridotites à spinelle, associant les concentrations en élément majeurs et en traces y compris l’H dans les minéraux dits anhydres (les NAMs, ici, olivine, pyroxènes) et hydratés (amphibole). Les effets de la remontée des xénolites dans du magma hôte sur les concentrations en H des NAMs ont pu être étudiés sur une série de xénolites de péridotite du champ volcanique d’Eifel (Allemagne). Une variation intra cristalline de concentration en H peut être identifiée dans l’olivine et non dans les pyroxènes coexistant. Ces profils de concentration en H peuvent être utilisés pour estimer des vitesses de remontées des magmas. Dans le cas des volcans étudiés, ces vitesses sont estimées entre 3.5 et 12 m.s-1. Ces résultats suggèrent que les pyroxènes sont de meilleurs proxy que l’olivine pour quantifier la concentration mantellique de l’H. Les xénolites de Ray Pic (Massif Central, France) ont permis de discuter dans un contexte de point chaud, l’effet de la fusion partielle et du métasomatisme à grande échelle sur les concentrations en H des NAMs. Les concentrations en H des minéraux ne suggèrent pas de lien avec le métasomatisme subit, qu’il soit modal, cryptique, à rapport liquide/roche élevé ou faible. Cependant, en comparant les concentrations en H avec un marqueur de la fusion partielle (Yb du cpx), l’H semble avoir un comportement similaire à une MREE (e.g., Sm ; D(cpx/liquide)~0.29). Enfin, des xénolites composites associant une péridotite accolée à un agent métasomatique ont permis de cibler l’influence du métasomatisme de petite échelle (pluri-centimétrique). L’interaction magma roche identifiée sur une harzburgite en contact avec du basalte montre dans les cas des olivines, des variations chimiques couplé entre éléments majeurs en fonction de leur proximité au filon et les concentrations en H. Plus l’olivine se rééquilibre avec le liquide moins elle contient d’H. Parallèlement dans cette étude, trois échantillons présentent une lherzolite en contact avec une pyroxénite avec 14% d’amphibole, une clinopyroxénite avec 40 % d’amphibole et une amphibolite (98% d’amphibole). Cette contiguïté avec un filon métasomatique permet l’étude du comportement de l’H en contexte de percolation en bordure de filon. Chaque échantillon présente des concentrations en H homogènes pour chacune des phases minérales. Cependant plus les filons contiennent d’amphibole moins il y a d’H dans les NAMs. D’autre part, une nouvelle fois, la corrélation positive entre les concentrations en H des NAMs et le Sm(cpx) en tant que marqueur de métasomatisme suggère que l’H se comporte comme une MREE.En conclusion, les minéraux des spl-harzburgites contiennent en moyenne un peu plus d’H que ceux des spl-lherzolites. Les concentrations en H des olivines sont sensibles à la dévolatilisation lors de la remontée dans le système magmatique et le rééquilibrage avec le magma. Au contraire, les concentrations en H des pyroxènes, spécialement l’opx, sont très homogènes suggérant des concentrations mantelliques. Le comportement de l’H lors de la fusion partielle et du métasomatisme reste complexe ; nos données suggèrent que l’H suit les MREE tel que le Sm
This thesis provides new constrains on H concentrations and H behaviour in the lithospheric mantle and is based on a petro-geochemical study on 3 spinel-peridotite xenoliths series with major and traces elements analyses, including H in nominally anhydrous minerals (NAMs, olivine and pyroxenes) as well as hydrous minerals (amphibole).Ascent effects through a magmatic system on H concentration of NAMs are studied for a xenoliths series from the Eifel volcanic field (Germany). Intracrystalline variation in H concentration are observe in olivine but not in the coexisting pyroxenes. Such H concentration profiles are used to calculate the rate of magma ascent. For the studied volcanoes, the calculated rate of magma ascent is between 3.5 and 12 m.s-1. Such H concentration variations imply a devolatilisation affecting only olivine, whereas the pyroxenes are homogeneous and then can be used as a better proxy for mantle H concentrations.Ray Pic xenoliths (French Massif Central) belongs to a mantle plume setting, implying the possibility to assess the effect of partial melting and large scale metasomatism on H concentration of NAMs. The H concentrations determined do not suggest a strong link with the suffered metasomatism whether modal, cryptic, at low or high melt rock ratio. However, using H concentrations and a marker of the partial melting (Yb in cpx), H seems to behave as a MREE (e.g., Sm, D(cpx/melt) ~ 0.29).Finally, the composite xenoliths with a peridotite adjacent to a metasomatic agent allow to target the influence of small scale metasomatism (pluri-centimetric). A magma-rock interaction between a harzburgite and a basaltic patch shows that, for olivines, chemical variations in major element as a function of olivine proximity to the vein, is coupled to H concentrations of NAMs. More the olivines are close to equilibrium with the basalt, more the H concentrations are low. Alongside in this study, three samples consist of a lherzolite adjacent a pyroxenite (14% amphibole), to a clinopyroxenite (40% amphibole) and to an amphibolite (98% amphibole) respectively. This special relationship with a metasomatic vein allows to study the behaviour of H during wall rock percolation. Each sample display homogeneous H concentration within each NAMs. However, H concentration is inversely correlated to modal content in amphiboles in the peridotite. Furthermore, a positive correlation between H in NAMs and Sm(cpx) here as a marker of metasomatism suggests, again, that H behaves as a MREE.To conclude, minerals from harzburgite contain in average a bit more H than the one in lherzolite. The H concentration in olivine are sensitive to degassing during magma ascent toward the surface and reequilibrium with magma. On the contrary, H concentration in pyroxenes, especially opx, are very homogeneous suggesting mantle concentration. The behaviour of H during partial melting and metasomatism is complex. However, our data suggest that H broadly follows MREE

The ulttamafic and related lithologies of the Swat valley ophiolite lie along the Main Mantle Thrust (MMT) between the Kohistan island arc and Indo-Pakistan plate. The textural and mineralogical characteristics of the ultramafic rocks seem to be the result of a complex interplay of a number of processes including partial melting, serpentinization, metamorphism, carbonation and late-stage hydrothermal alteration. The modal mineralogy of the least modified varieties (non-carbonated serpentinized) of the ultramafic rocks indicate that the majority of them them are harzburgites. The chemical composition of the primaiy phases (chrome spinel and pyroxenes) and major, minor as well as trace element contents of the non-carbonated ultramafic rocks suggest that the major bulk of the rocks originated as the upper mantle residue left after an intermediate degree of partial melting. Pervasive serpentinization of the rocks, evident from the almost common occurrence of serpentine and orthopyroxene bastites, was followed by a low to medium grade regional metamorphism converting the original low temperature serpentine (lizardite) to antigorite, forming olivine and, rarely, diopside. The trace amounts of Ni-rich opaque phases in the rocks largely formed by the modification of primary sulphides during serpentinization. Locally, alteration by a CO2-bearing fluid resulted in the carbonation of the formerly serpentinized ultramafic rocks forming quartz- and/ or talc-carbonate lithologies. The oxygen and carbon isotope composition (delta18Ocalculated = +13.6 1.2 � SMOW; delta13Ccalculated= -1.8 0.7 � PDB) indicates that the fluids responsible for carbonation were probably derived from the subduction-related metamorphism of the carbonate-bearing sedimentary rocks of the Indo-Pakistan plate. Late-stage hydrothermal activity by Be, B and K-bearing fluids, apparently related to quartz veins and stockworks, has affected the ultramafic rocks mainly the carbonated types because of their highly fissile and permeable nature. This process has produced emerald, Cr-tourmaline and fuchsite. The chromium in these phases was extracted from the host ultramafic rocks. The oxygen isotope composition of parental waters (delta18Ocalculated = +14 1.7 � SMOW), calculated from the measured values of emerald, quartz, tourmaline and fuchsite, is high in the delta18O component. This high delta18Ocalculated well as the range of 5D of channel waters from emerald (-42 6.6� vs SMOW) and that of fluid calculated (-47 7.1 � vs SMOW) are consistent with both metamorphic and magmatic origin. However, the close similarity between the measured 5D values of the hydroxyl waters in fuchsite (-74 to -61� vs SMOW) and tourmaline (-84 and -69 %o vs SMOW) with pegmatitic muscovite and tourmaline suggests that the mineralization was probably caused by modified (18O-enriched) hydrothermal solutions derived from an S-type granitic magma.

The fractionation of stable isotopes at high temperatures offers a unique insight into the sources and processes operative during planetary accretion. Through analysis of meteorites and samples that are representative of planetary reservoirs, a coherent picture is built of the isotopic variation present in solar system materials. However, this objective is complicated by the selection of samples appropriate to characterise the isotopic composition of the entire Earth. In minimising the uncertainty in this assumption, ultramafic (olivine-rich) rocks are used, as these are most representative of the Earth's mantle, which constitutes ~ 70% (by mass) of the Earth. Peridotites from the Balmuccia massif and a global selection of komatiites, with care taken to select only the least chemically-modified examples, were collected and characterised. Because it is known that stable isotopes fractionate during magmatic processes, the best estimate of the composition in equilibrium with the primitive mantle is computed by considering the petrogenetic processes that lead to the formation of these rocks. Through the course of this exercise, a new model is posited to explain chemical depletion in peridotites, which arises, not only from melt extraction, but from pressure-solution re-distribution of pyroxenes, two complementary processes. It is proposed that, since the chemical trends observed in peridotites are of global significance, this process is ubiquitous, occurring in-situ in zones of adiabatic decompression mantle melting. Komatiites, as high degree partial melts of the mantle, require high mantle temperatures that can only have been achieved early in Earth history. It is demonstrated that the origin of the two distinct komatiite types, Aluminium-Depleted and Aluminium Undepleted, reflects not only the pressure, but the degree of melting. Over time, their mantle sources incorporate progressive amounts of depleted, upper mantle material, effectively tracking crustal growth. Furthermore, because the magnitude of stable isotope fractionation is proportional to 1/T2, these high temperature samples allow an assessment of mantle composition through time and space. Due to the small variations in isotope composition at these high temperatures, optimised analytical procedures for the measurement of Cu, Fe, Zn and V isotopes are detailed, and document improved precision with respect to previously published methods. Using this technique, new values for the Fe and Zn isotope compositions of the Bulk Silicate Earth are derived. Supplementary analyses of the isotopic composition of Mars, together with already-published analyses of chondritic meteorites (the supposed building-blocks of Earth) and the Moon, shows that the Earth-Moon system has a fractionated isotopic composition. With this information, a new interpretation of the timescales and composition of Earth's accretion is suggested. Briefly, the volatile element budget of the Earth was set early in its accretion, by material more volatile-depleted than any of the known chondrite groups. Accretion then became progressively more oxidising, culminating in the Moon-forming impact, which delivered % of the Earth's complement of iron, and, importantly, in an oxidised form, as observed in the contemporary mantle. These interpretations are underpinned by experimental measurements of expected iron isotope fractionation factors between common igneous phases - silicates, oxides and metal. These determined partition coefficients are also applied to a series of igneous problems, including the generation of basalt, crystallisation of the lunar magma ocean, and the formation of granites.

In questa tesi si applica un’indagine multidisciplinare guidata dall’analisi strutturale per studiare l’evoluzione tettono-metamorfica di rocce ultrafemiche appartenenti a unità ofiolitiche affiorati nella parte occidentale delle Alpi o intrappolate nel basamento prealpino durante la collisione varisica. L’analisi si focalizza sulla Zona Zermatt-Saas (ZSZ) in alta Valtournanche (AO), al contatto di questa zona e la parte esterna del bordo meridionale della Zona Sesia Lanzo nella Valli del Tesso e del Tessuolo (TO) e nel Massiccio dell’Argentera, in alta Valle Gesso (CN). Le prime due aree si trovano nella Zona Piemontese che include unità derivanti da litosfera oceanica ristrutturate durante la convergenza alpina. L’ultima zona è situata nei Massicci Cristallini Esterni delle Alpi che includono in prevalenza rocce di origine continentale con scarsi relitti di rocce di probabile origine oceanica, ristrutturate e pervasivamente riequilibrate durante il ciclo Varisico. L’analisi meso- e micro-strutturale è stata integrata dall’analisi minero-chimica, dalle stime termo-barometriche e dalla modellazione petrologica delle associazioni di minerali metamorfici all’equilibrio, dalla datazione radiometrica dei fabric e dall’analisi geochimica di micro-domini selezionati. Le serpentinite di Créton in Valtournanche sono state interpretate come una scaglia di litosfera originariamente adiacente alla dorsale medio oceanica della Tetide Alpina, metasomatizzata e percolata da Fe- e Mg-gabbri, che ha raggiunto condizioni di ultra alta pressione (UHP) durante la convergenza Alpina, come registrato dalle associazioni a Ti-chondrodite e Ti-clinohumite, precedentemente allo sviluppo della foliazione di alta pressione, dominante a scala regionale, e datata a 60-70 Ma. Il paragone delle condizioni metamorfiche registrate con un modello numerico di subduzione Alpina ha convalidato l’evoluzione ricostruita e ha permesso di restaurarne la posizione nel sistema di subduzione in funzione dell’evoluzione termo-barica dedotta per queste rocce. La serpentinite di Gias Vej in Valle del Tesso ha registrato un’evoluzione strutturale comune alle rocce ofiolitiche e continentali ad essa adiacenti e ha raggiunto un picco metamorfico eclogitico, come testimoniato dalle paragenesi di alta pressione a Ti-clinohumite, durante la subduzione Alpina. Presso il Lago Brocan dell’alta valle Gesso in Argentera, boudins di serpentinite e diopsidite, associati a boudins di anfibolite e marmi, si trovano avvolti e allineati dalla foliazione migmatitica regionale di età tardo-Varisica. Essi verosimilmente rappresentano, analogamente alle rocce Alpine studiate, i relitti della sutura dell’oceano Reico, riequilibrati in condizioni di alta temperatura-bassa pressione e trasposti durante la collisione Varisica ed il successivo collasso tardo orogenico. In conclusione, i risultati ottenuti mostrano come l’utilizzo integrato di tecniche laboratoriali e modellistiche, basate su un solido lavoro di terreno, possano descrivere e individuare unità tettono-metamorfiche nei domini di affinità oceanica in catene montuose risultanti da uno o più cicli di Wilson e dare un contributo alla ricostruzione delle loro evoluzione geodinamica, anche quando scaglie di crosta oceanica sono frammentate e disperse nella cicatrice profonda di un’antica sutura continentale.
The tectono-metamorphic evolution of serpentinites and associated rocks has been investigated in the Alpine ophiolitic Piemontese Zone (PZ) – in the Zermatt-Saas Zone (ZSZ) and near the Sesia-Lanzo Zone (SLZ) rim – and in the Variscan migmatites of the Argentera External Crystalline Massif (ECM). Materials selected for laboratory work contain sequences of meso- and microstructural imprints containing parts of the tectonic evolution of both mono- and poly-orogenic environments (in our case the Piemontese Zone in the Penninic of the Western Alps and the Argentera EMC – Provençal domain of the Alpine collisional front at the Alpine belt termination within the Western Mediterranean). In the Zermatt-Saas Zone serpentinite of Valtournanche, meso- and microstructural analyses have been coupled with petrological investigation, geochemistry, and radiometric dating. In Valtournanche, Créton serpentinite has been interpreted as a slice of mid-ocean ridge lithosphere, affected by gabbroic percolation and hydrothermalism, deeply involved in the Alpine subduction complex, reaching UHP conditions (2.9-3.3 GPa and 600-630 °C) prior to be exhumed at HP conditions 60-70 Ma and incorporated in a mix of slices of oceanic material of heterogeneous origin and metamorphic evolution. Gias Vej serpentinite registered Eclogite facies conditions and was coupled with slices of continental material at the southern border of the Sesia Lanzo Zone before the record of Pmax conditions. At Lake Brocan in Valle Gesso, remnants of serpentinised spinel lherzolite and diopsidite are suggested to represent a most probable vestigial suture zone of the Rheic Ocean in the External Crystalline Massif of Argentera; this relict survived repeated transpositions and dismembering during migmatisation of the deep Variscan crust related to Variscan continental collision. The obtained results indicate that investigation of ultramafic rocks by a structure-driven multidisciplinary approach, can unravel the most complete memory of the divergent and convergent tectonic evolution of old oceans. Similar investigation strategies of laboratory procedures, based on solid structural fieldwork, may more diffusely support circumscription of tectonic units in ocean-derived sequences and contribute to redefine their translational tectonic trajectories during mountain-building processes.

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Os estágios do período pós-cosilisional do Ciclo Brasialiano/Panafricano na região de Cocalinho, porção leste do estado de Mato Grosso, divisa com o estado de Goiás, é marcado por corpos graníticos intrusivos associados a rochas máficas e ultramáficas. O Plutão Itacaiu é um corpo extenso e alongado segundo um trend regional, na direção NE/SW. É caracterizado por um magmatismo expressivo de natureza alcalina e composição que varia de monzo a álcali-feldspato-granitos. Este extenso corpo é definido por três fácies petrográficas denominadas de Fácies Biotita-Granito, Fácies RiebeckitaBiotita-Granito e Fácies Biotita-Granito Porfirítico. Os granitóides imprimem evidências de processos deformacionais decorrentes de duas fases de deformação, representada principalmente pelo desenvolvimento da foliação penetrativa marcada pela orientação preferencial dos minerais placóides, com direção NE e mergulho para SE, variando de baixo a alto ângulo, e foliação milonítica decorrente do cisalhamento de característica transcorrente. A composição química permitiu classificar essas rochas como granitos do tipo-A, gerados em ambiente de arco magmático e intra-placa pós-colisional. Dados geocronológicos U/Pb extraídas de cristais de zircão indicaram idade de cristalização variando de 806.6±4.0 a 582.9±6.3 Ma, consistentes com aquelas registradas para o Arco Magmático de Goiás. Idades modelo TDM= 0.97 a 1.08 Ga, mostram valores positivo εNd(T) = +4.39, +4.31,+3.69. Os valores positivos de εNd sugerem um empobrecimento do magma que deu origem aos granitóides em ETR leves. O valor negativo de εNd indica origem a partir de fusão parcial de crosta continental Paleoproterozóica. As rochas máficas-ultramáficas ocorrem alinhadas aproximadamente a leste-oeste, com variáveis níveis de alteração. Definem um magmatismo toleítico a cálcio-alcalino, metaluminoso, de caráter intermediário a ultrabásico. Os estudos isotópicos sugerem caráter juvenil do magma parental, devido aos valores positivos de εNd(T). As idades modelo variam de TDM = 0,71 a 1,44Ga e estão relacionadas a outras unidades de rochas juvenis do Arco Magmático de Goiás
Post-collisional stages of the Brasiliano/Pan-African Cycle in the region of Cocalinho on eastern Mato Grosso, bordering the State of Goiás, are represented by granitic intrusive bodies associated with mafic and ultramafic rocks. The Itacaiu Pluto is an NE-SWelongated body conform to the regional trend. It is characterized by a expressive magmatism of alkaline nature and composition ranging from monzo the alkali-feldspargranites. This extensive body is defined by three petrographic facies termed biotitegranite Facies, riebeckite-biotite-granite Facies and biotite-granite porphyry Facies. The granitoids show evidence of deformational processes resulting two-phase of deformation, represented mainly by development of penetrative foliation marked by the preferred orientation of minerals placoid, with direction NE and dip to SE, ranging from low to high angle, and mylonitic foliation resultant by strike-slip shear. The chemical composition allowed to classify the rocks as granite type-A, generated in magmatic arc environment and intra-plate post-collisional. Geochronological data U / Pb extracted in zircon crystals indicated crystallization age ranging from 806.6 ± 4.0 to 582.9 ± 6.3 Ma, consistent with those recorded for the Goiás Magmatic Arc. model ages TDM= 0.97 to 1.8 Ga, show positive values of εNd(T) = +4.39, +4.31,+3.69. Positive values of εNd suggest impoverishment of the magma that gave rise to the granitoids in LREE. The negative value of εNd indicates origin from partial melting of continental crust Paleoproterozoic. The rocks mafic-ultramafic occur aligned approximately east-west, with varying degrees of alteration. Define a tholeiitic to calcium-alkaline magmatism, metaluminous, of character intermediate to ultrabasic. The Isotopic studies suggest juvenile character of the parental, magma due to positive values εNd(T). The model ages ranging from TDM = 0.71 to 1,44 Ga and are related to other units of juvenile rocks of the Goiás Magmatic Arc.

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Este trabalho apresenta os resultados de estudos geológicos e petrográficos realizados na região do Distrito de Noroagro – município de Comodoro no Estado de Mato Grosso com enfoque na geoquímica e geocronologia Sm e Nd de diques e “plugs máficos”, intrudidos nas rochas do Granito Rio Piolho e do Complexo Rio Galera. Os diques estudados situam-se no sudoeste do Cráton Amazônico na província Rondoniana San – Ignacio, especificamente nos domínios da Faixa Alto Guaporé. Petrograficamente, as rochas apresentam como aspectos macroscópicos feições estruturais características de rochas maciças de granulação fina a media variando de máficas a ultramáficas e cor cinza- esverdeada a preta. Apresentam texturas inequigranulares e composição gabroica ou peridotítica, constituídas, essencialmente, por minerais máficas (piroxênios e anfibólios) e plagioclásio por vezes alterados por processos de saussuritização. Opticamente, são rochas holocristalinas, textura ofítica a cumulática (peridotitos) onde os piroxênios representam à fase cumulus e os plagioclásios a fase inter-cumulus. Dados geoquímicos enfatizam que o magmatismo é do tipo toleítico, de natureza subalcalina, estando a totalidade das rochas no campo dos Basaltos de Fundo Oceânico – OFB (Ocean Floor Basalts), sendo que duas amostras apresentam assinatura de arco de ilhas. Datações de Sm- Nd indicaram idades de 1,24 , 1,27 e 1,57 (Ga) e apresentam ɛ Nd (t)a entre +6,27e + 6,50 para os gabros +5,80 para metapiroxênito. Os valores positivos de ɛ Nd (t)a juntamente com a razão 87Sr/86Sr de 0,704 para litotipo metagabro confirma que as rochas máficas –ultramáficas da região da Fazendas Maringá e Imaculada são derivadas de manto empobrecido
This works presents the results of Geological studies and petrographics realized in the Noroagro District, Comodoro municipality of Mato Grosso State focused on Geochemistry and Sm/Nd geochronology of dykes and maphic plugs emplaced in Rio Piolho Granite and Rio Galera Complex. The studied dykes is located in southwest of Amazonian Craton, Rondonian-San Ignácio Province, specifically in the Alto Guaporé Belt. Petrographically the rocks exhibit macroscopic strutural feature characteristics of massiveslightelly oriented rocks, fine to médium grain ranging of mafic to utramafic composition and greenhish – gray to black color. They presets inequigranular textures and gabbroic or peridotite composition, consisting essentially of mafic minerals (pyroxene and amphibole) and sometimes altered plagioclase and its partial saussuritization process. Optically Show holocrystalline granular rocks, with cumulate and ophitic texture ( peridotites) where pyroxene representes the cumulus crystal phase and the plagioclase inter-cumulus phase. Geochemical data emphasize that the magmatism is tholeiitic with sub-alkaline nature, being all of the rocks in the field of Ocean Floor Basalts (OFB) and two samples representes signatures island arc. Geochoronological Sm-Nd data indicated ages of 1,24 ,1,27 and 1,57 (Ga) and Show ɛ Nd (t)a between + 6,27 and +6,50 for gabbro and +5,80 for pyroxenite. The positive ɛ Nd (t)a values together with razão 87Sr/86Sr ratio of 0,704 for metagabbro suggests for the mafic- ultramafic rocks of region of Maringa and Imaculada Farm are derived of depleted mantle.

La susceptibilité des roches faiblement magnétiques a une origine complexe : aux grains ferromagnétiques se rajoutent des contributions dla-, para-, et antlferromagnétiques. Celles-ci ont été mises en évidence grâce à de nouvelles techniques de mesures magnétiques en champ fort et température variable. Les propriétés liées aux phyllosilicates et carbonates ferromagnétiques, à la pyrrhotite et à la goethite ont été particulièrement étudiées. La susceptibilité magnétique ainsi analysée permet de suivre l'évolution pétrologique des roches, en particulier en fonction du métamorphisme et de l'altération. L'anisotropie de susceptibilité magnétique doit être interprétée en fonction de la nature et de l'orientation préférentielle des grains magnétiques. En prenant en compte les mécanismes de la déformation on a accès ainsi à certaines données structurales difficilement appréhendées par les méthodes classiques du fait de la sensibilité et la rapidité des mesures magnétiques ; il s'agit en particulier des linéatlons d'étirement en zones peu déformées. Les éléments d'une modélisation quantitative de la relation entre déformation et anisotropie magnétique sont discutés. Les études de cas ont porté sur des roches sédimentaires non métamorphiques à mésozonales, principalement alpines, sur différents granites et sur des péridotites.

Une nouvelle approche petrologique pour definir l'evolution des roches ultramafiques des massifs ophiolitiques est etablie, par l'etude petrochimique d'une serie harzburgitique de cherzolitique situe a terre neuve et par l'etude structurale et petrologique des peridotites et websterites du complexe du cap ortegal (espagne). Ce travail sert de support pour definir la methodologie permettant de suivre l'evolution des parametres chimiques lors d'une fusion partielle

Les terrains ultramafiques de Nouvelle-Calédonie, riches en Ni, Co, Mn et Cr sont exploités par des mines à ciel ouvert, ce qui génère l'émission de poussières riches en métaux. L'objectif de ce travail est de développer des approches pour estimer le risque environnemental lié aux poussières émises par les mines à ciel ouvert et les usines de traitement du minerai de nickel. L'estimation de la fraction biodisponible des métaux contenus dans deux fractions granulométriques de poussières, celle inférieure à 100 ~m mobilisable par le vent (F<1 OO~m.) et celle susceptible de pénétrer le système respiratoire (PM1 0), a été réalisée par extractions cinétiques à I'EDTA. L'obtention des PM10 a nécessité la mise au point d'une technique de tri par transport des particules dans un tube horizontal grâce à un flux d'azote. Les extractions cinétiques ont permis de discrimtner trois fractions de métaux: rapidement extraite, lentement extraite et non biodisponibles. Les concentrations en métaux potentiellement biodisponibles sont toujours très élevées et la fraction lentement extraite est toujours la plus concentrée. Pour F<1 00 ~m. les constantes cinétiques de la fraction lentement extraite sont plus faibles pour les poussières de sols miniers que celles de sols forestiers. Les poussières issues de sols miniers seraient alors un réservoir en éléments métalliques biodisponibles à plus long terme. La bioindication lichénique avec traitement en données compositionnelles des concentrations en métaux permet de définir un indice de dispersion des poussières. Cette méthodologie pourrait appuyer les réseaux de surveillance de la qualité de l'air en Nouvelle-Calédonie
Bioavailability estimation of nickel, cobalt and manganese in dust from ultramafic soils likely to be mobilized by wind and~eve lopment of a bioindication tool using lichen for dust emitted by mining activities in New Caledonia New Caledonian altered ultramafic soils, particularly rich in Ni, Co, Mn and Cr, are extracted by opencast mines which generale dust rich in metals. The objective of th is work is to develop approaches for environmental risk assessment of dust emitted by opencast mines and nickel ore metallurgical plants. The assessmentof metals' bioavailable fraction from two dust granulometrie size fractions, one less than 100 IJm which is mobilizable by wind (F<1001Jm,) and another one able to penetrate the respiratory system (PM 1 0), has been determined by kinetic extraction with EDT A. The development of a new separation deviee based on particle transport subjected to a nitrogen flux in a horizontal tube has been necessary for PM1 0 segregation. Kinetic extractions le ad to the distinction of th ree metal pools: rapidly labile, less rapidly labile and non-bioavailable. Trace metal potentially bioavailable concentrations were always high and the less rapidly labile pool is always the most concentrated pool. Concerning F<1 001Jm, the less rapidly kinetic constant of the less rapidly labile pool is weaker for mining soils than forest soils. F<1001Jm fractions from mining soils representa more durable reserve in trace metal than the same fraction from forest soils. Bioindication using lichens with compositional data analysis of their metal concentration allow defining an indicator of emission dispersion. This methodology could support air quality monitoring networks in New Caledonia

Les données isotopiques et en éléments en traces sur roches et minéraux de la région de Mako au Sénégal, mettent en évidence l'existence au sein de la croûte birimienne de roches magmatiques diversement différenciées (de cumulats ultramafiques à rhyolite) provenant de trois sources magmatiques parfaitement identifiées : une source déprimée plus juvénile à l'origine de la lignée tholéiitique 1 ; une source faiblement enrichie à l'origine de la lignée tholéiitique 2 et une source très enrichie dont est issue la lignée calco-alcaline. On peut ainsi proposer pour le groupe de Mako l'évolution géodynamique suivante : i) ouverture d'un océan entrainant la mise en place des roches de la lignée tholéiitique 1 au niveau d'une dorsale océanique, ces dernières ayant des caractéristiques proches des MORB ; ii) subduction intra-océanique induisant un magmatisme conduisant à la formation d'un arc insulaire immature qui se caractérise par un magmatisme tholéiitique dont les roches de la lignée tholéiitique 2 seraient les témoins ; iii) maturation de l'arc insulaire et mise en place des roches de la lignée calco-alcaline liée à l'enfoncement de la plaque plongeante et à l'épaississement de la partie crustale de l'arc
The isotopic and trace element data on rocks and minerals in the Birimian Mako region of Senegal reveal the existence of variously differentiated magmatic rocks (from ultramafic to rhyolite cumulates) from three perfectly identified magmatic sources: a more juvenile depleted source at the origin of the tholeiitic series 1; a weakly enriched source at the origin of the tholeiitic series 2 and a highly enriched source from which the calc-alkaline series originates. We can thus propose for the Mako group the following geodynamic evolution: i) opening of an ocean resulting in the emplacement of the rocks of the tholeiitic series 1 in the setting of an oceanic ridge, the rocks having characteristics close to the MORB ; ii) intra-oceanic subduction inducing magmatism leading to the formation of an immature insular arc which is characterized by a tholeiitic magmatism represented by the tholeiitic series 2; iii) Maturation of the insular arc and emplacement of rocks of the calc-alkaline series related to the subduction of the plate and thickening of the crustal portion of the arc

L'etude cartographique en depit d'un tectonique complexe, a permis d'observer de bas en haut: sequence mantelique (harzburgites a enclaves dunitiques); sequence cumulative (dunite principale, plastiquement deformee, wchrlites, pyroxenites, gabbros et plangiogranites)

Deux nouvelles calibrations de methodes thermobarometriques a partir de donnees experimentales. La premiere basee sur la solubilite de diopside entre clinopyroxene et orthopyroxene. Elle prend en compte l'effet d'elements mineurs tels que na et fe. Ce thermobarometre, combine avec le thermometre base sur la solubilite de l'enstatite dans les deux pyroxenes fournit un bon outil pour tester l'etat d'equilibre des peridotites a spinelle. La deuxieme calibration est basee sur la solubilite du chrome dans la spinelle et le grenat coexistants

Des ensembles d'alterations sont distingues, et les processus majeurs de formations des horizons type isalterite a kaolinite, gibbsite, hematite et goethite sont decrits. Les mineralisations en or associees a ces formations sont de differents types. Une methode de prospection de l'or dans les materiaux lateritiques en milieu equatorial humide est proposee

L'etude petrographique des facies permet de scinder le vourinos en trois unites lithologiques. L'analyse des donnees structurales, texturales et petrologiques conduit a interpreter le vourinos en terme de diapirisme. Par ailleurs, la determination de la composition chimique des differentes phases minerales et des conditions thermobarometriques revelent que les peridotites ont subi une rehomogeneisation a basse temperature et sous l'effet de le percolation de phase fluide. On considere que le cortege ophiolitique du vourinos resulte d'une refusion locale d'un manteau oceanique deja appauvri, vraisemblablement a l'aplomb d'une zone de subduction