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1
Fonseca, Ariadne Do Carmo. "Fragmento tectónico cabo frio: aspectos de campo, petrografía e geoquímica." Anuário do Instituto de Geociências 17 (December 1, 1994): 109–31. http://dx.doi.org/10.11137/1994_0_109-131.
Повний текст джерелаАнотація:
The main lithological units which occur in the "Cabo Frio Tectonic Fragment" are orthogneisses and paragneisses. The orthogneisses have granitic-granodioritic-tonalitic compositions, with amphibolitic enclaves and intercalations and are cutted by granitic aplites. The paragneisses are metapelites, with intercalations of amphibolite, quartzites and calc-silicate rocks, metamorphosed in upper amphibolite facies, in intermediate pressure conditions. Geochemically, the orthogneisses correspond to a metaluminous high-K calc-alkalic series, with monzogabbro, quartz-monzodiorite and monzonite compositions. Otherwise, the petrography indicates a low-K calc-alkalic series, suggesting a pre-collisional granitoids series related to oceanic crust subduction. A divergence between the compositions obtained by the petrography and geochemistry can be the result of problems in the analyses of alkalies. The amphibolites, associated to the orthogneisses, also present calc-alkalic metaluminous character, with basaltic and andesitic compositions, suggestive of orogenic emplacement. The paragneisses show compositions varying between lithoarenite and arkoses, with peraluminous character, probably deposited in a continental are or ative continental margin environment.
2
BOGDANOVA, Alyona Romanovna, Nadezhda Vladimirovna VAKHRUSHEVA, and Pavel Borisovich SHIRYAEV. "Main and rare earth elements of amphibolites of the Ray-Iz massif (Polar Urals)." NEWS of the Ural State Mining University, no. 4 (December 20, 2020): 19–27. http://dx.doi.org/10.21440/2307-2091-2020-4-19-27.
Повний текст джерелаАнотація:
Relevance. The Ray-Iz massif contains the Tsentralnoye chromium ore deposit and is unique in terms of variety of metamorphic rock associations. It has been studied since 1932. However, some aspects of geology and petrology in the literature are not fully covered. One of these areas is a vein series of rocks localized in ultramafic rocks. The spatial confinement of amphibolites to the Central zone of metamorphism, which is consistent with the zone of distribution of deposits and ore occurrences of chromites, determines the need for a detailed study. Purpose of work. Study of mineralogical and petrographic characteristics, as well as the geochemistry of lanthanides of amphibolites of the Ray-Iz massif (Polar Urals). Results. The study of the nature of REE distribution in rock-forming minerals made it possible to determine that the variation in the amount of REE (33–75 g/t) within one rock is associated with the quantitative content of the main minerals-concentrators. The main mineral concentrator lanthanides in garnet amphibolites is garnet, while amphibole is in garnet-free pyroxene-bearing amphibolites. Based on the results of the chemical composition of amphibole and coexisting plagioclases and amphibolite garnets, the temperature was calculated using amphiboleplagioclase by T. Holland, J. Blundy, as well as the garnet amphibolite by L. L. Perchuk geothermometers and pressure based on amphibole geobarometer by M. W. Schmidt. Conclusion. The nature of the distribution of lanthanides in the main rock-forming minerals, amphibole and garnet, has been revealed. Comparison of parameters and compositional features of amphiboles made it possible to conclude that there is a direct relationship between temperature, pressure, the sum of REE and TiO2 , as well as (La/Yb)n , in the mineral.
3
Ahmid-Said, Y., and B. E. Leake. "The composition and origin of the Kef Lakhal amphibolites and associated amphibolite and olivine-rich enclaves, Edough, Annaba, NE Algeria." Mineralogical Magazine 56, no. 385 (December 1992): 459–68. http://dx.doi.org/10.1180/minmag.1992.056.385.02.
Повний текст джерелаАнотація:
AbstractThe Kef Lakhal amphibolitcs and associated amphibolitc and olivine-rich enclaves are dcscribcd and their major and trace element chemistry indicates that both amphibolites were evolved medium to high alumina tholeiitic basalts with talc-alkaline affinities probably formed within plate settings. The olivine-rich enclaves are disrupted periodotites of the type lherzolite-harzburgite and probably represent mantle residua after melting.
4
Moazzen, Mohssen, Zohreh Salimi, Yann Rolland, Michael Bröcker, and Robab Hajialioghli. "Protolith nature and P–T evolution of Variscan metamorphic rocks from the Allahyarlu complex, NW Iran." Geological Magazine 157, no. 11 (March 18, 2020): 1853–76. http://dx.doi.org/10.1017/s0016756820000102.
Повний текст джерелаАнотація:
AbstractMetamorphic rocks associated with ophiolitic rocks occur on the eroded surface of a NW–SE-trending anticline in the Allahyarlu area, NW Iran, between the Caucasus and Zagros orogenic belts. Metapelitic rocks consist mainly of quartz, muscovite chlorite, altered biotite and garnet. S1 is the pervasive schistosity, wrapping garnet, which is folded by the second schistosity (S2). The amphibolite records only one phase of deformation as the main lineation. The rocks experienced metamorphism up to the amphibolite facies, then overprinted by greenschist facies condition. Thermobarometry indicates an average pressure of c. 5 kbar and an average temperature of c. 600 °C for the amphibolite facies metamorphism, corresponding to a ∼33 °C km−1 geothermal gradient in response to a thick magmatic arc setting. Greenschist facies metamorphism shows re-equilibration of the rocks during exhumation. Amphibolites whole rock geochemistry shows trace elements patterns similar to both island arc and back-arc basin basalts, suggesting that the protolith-forming magma of the amphibolites was enriched at shallow to medium depth of a subduction system. Negative Nb anomaly and slight enrichment in light rare earth elements (LREE) and large-ion lithophile elements (LILE) of the amphibolites indicate arc-related magmatism for their protolith and a back-arc sialic setting for their formation. 40Ar–39Ar dating on muscovite separated from two gneiss samples, and hornblende separated from three amphibolite samples, documents a Variscan (326–334 Ma) age. The magmatic and metamorphic rock association of the Allahyarlu area suggests the existence of an active continental margin arc during the Variscan orogeny, without clear evidence for a continental collision.
5
Bogoch, R., and M. Shirav. "Carbonate nodules of probable stromatolitic origin in amphibolite from the Neoproterozoic terrain of southern Israel." Mineralogical Magazine 68, no. 4 (August 2004): 579–89. http://dx.doi.org/10.1180/0026461046840213.
Повний текст джерелаАнотація:
AbstractSeveral small bodies of massive to banded amphibolite occur within plagioclase-quartz-biotite hornblende gneiss at or close to its boundary with a quartz diorite pluton in the Neoproterozoic terrain of southern Israel. Entrapped within the amphibolite are nodules consisting mainly of calcite+talc, and rare banded marble. Remnant laminae and certain geochemical features such as the negative Ce anomaly and depleted δ13C of the nodules sugggest that they initially formed as stromatolites. The local geological setting of the amphibolites together with the presence of the enclosed meta-carbonates favoured an origin as sediments, although some of the geochemical data point to a basaltic precursor and some of the carbonates have a puzzlingly high (>1000 ppm) Ni content. The origin of the amphibolites is thus enigmatic.
6
Moyen, Jean-François, and Gordon R. Watt. "Pre-Nagssugtoqidian crustal evolution in West Greenland: geology, geochemistry and deformation of supracrustal and granitic rocks north-east of Kangaatsiaq." Geological Survey of Denmark and Greenland (GEUS) Bulletin 11 (December 5, 2006): 33–52. http://dx.doi.org/10.34194/geusb.v11.4915.
Повний текст джерелаАнотація:
The area north-east of Kangaatsiaq features polyphase grey orthogneisses, supracrustal rocks and Kangaatsiaq granite exposed within a WSW–ENE-trending synform. The supracrustal rocks are comprised of garnet-bearing metapelites, layered amphibolites and layered, likewise grey biotite paragneisses. Their association and geochemical compositions are consistent with a metamorphosed volcano-sedimentary basin (containing both tholeiitic and calc-alkali lavas) and is similar to other Archaean greenstone belts. The Kangaatsiaq granite forms a 15 × 3 km flat, subconcordant body of deformed, pink, porphyritic granite occupying the core of the supracrustal synform, and is demonstrably intrusive into the amphibolites. The granite displays a pronounced linear fabric (L or L > S). The post-granite deformation developed under lower amphibolite facies conditions (400 ± 50°C), and is characterised by a regular, NE–SW-trending subhorizontal lineation and an associated irregular foliation, whose poles define a great circle; together they are indicative of highly constrictional strain. The existence of a pre-granite event is attested by early isoclinal folds and a foliation within the amphibolites that is not present in the granite, and by the fact that the granite cuts earlier structures in the supracrustal rocks. This early event, preserved only in quartz-free lithologies, resulted in high-temperature fabrics being developed under upper amphibolite to granulite facies conditions.
7
Soret, Mathieu, Philippe Agard, Benoît Ildefonse, Benoît Dubacq, Cécile Prigent, and Claudio Rosenberg. "Deformation mechanisms in mafic amphibolites and granulites: record from the Semail metamorphic sole during subduction infancy." Solid Earth 10, no. 5 (October 23, 2019): 1733–55. http://dx.doi.org/10.5194/se-10-1733-2019.
Повний текст джерелаАнотація:
Abstract. This study sheds light on the deformation mechanisms of subducted mafic rocks metamorphosed at amphibolite and granulite facies conditions and on their importance for strain accommodation and localization at the top of the slab during subduction infancy. These rocks, namely metamorphic soles, are oceanic slivers stripped from the downgoing slab and accreted below the upper plate mantle wedge during the first million years of intraoceanic subduction, when the subduction interface is still warm. Their formation and intense deformation (i.e., shear strain ≥5) attest to a systematic and transient coupling between the plates over a restricted time span of ∼1 Myr and specific rheological conditions. Combining microstructural analyses with mineral chemistry constrains grain-scale deformation mechanisms and the rheology of amphibole and amphibolites along the plate interface during early subduction dynamics, as well as the interplay between brittle and ductile deformation, water activity, mineral change, grain size reduction and phase mixing. Results indicate that increasing pressure and temperature conditions and slab dehydration (from amphibolite to granulite facies) lead to the nucleation of mechanically strong phases (garnet, clinopyroxene and amphibole) and rock hardening. Peak conditions (850 ∘C and 1 GPa) coincide with a pervasive stage of brittle deformation which enables strain localization in the top of the mafic slab, and therefore possibly the unit detachment from the slab. In contrast, during early exhumation and cooling (from ∼850 down to ∼700 ∘C and 0.7 GPa), the garnet–clinopyroxene-bearing amphibolite experiences extensive retrogression (and fluid ingression) and significant strain weakening essentially accommodated in the dissolution–precipitation creep regime including heterogeneous nucleation of fine-grained materials and the activation of grain boundary sliding processes. This deformation mechanism is closely assisted with continuous fluid-driven fracturing throughout the exhumed amphibolite, which contributes to fluid channelization within the amphibolites. These mechanical transitions, coeval with detachment and early exhumation of the high-temperature (HT) metamorphic soles, therefore controlled the viscosity contrast and mechanical coupling across the plate interface during subduction infancy, between the top of the slab and the overlying peridotites. Our findings may thus apply to other geodynamic environments where similar temperatures, lithologies, fluid circulation and mechanical coupling between mafic rocks and peridotites prevail, such as in mature warm subduction zones (e.g., Nankai, Cascadia), in lower continental crust shear zones and oceanic detachments.
8
Dolníček, Zdeněk, and Jana Ulmanová. "Chemické složení granátů v amfibolitech z lomu Libodřice u Kolína (kutnohorské krystalinikum, Česká republika)." Bulletin Mineralogie Petrologie 30, no. 2 (2022): 205–13. http://dx.doi.org/10.46861/bmp.30.205.
Повний текст джерелаАнотація:
Three types of garnet-bearing lithologies sampled in the quarry Libodřice near Kolín (Kutná Hora Crystalline Complex, Czech Republic) were studied by means of BSE imaging and electron microprobe analyses. The first type is represented by common garnetic amphibolites, in which garnet forms isolated millimetre-sized porphyroblasts containing numerous inclusions of minerals of the host amphibolite matrix (plagioclase, epidote, amphibole, sulphides). The composition of weakly zoned garnet is Alm55-56Grs30-37Sps1-5Prp5-12Adr0-3. Second type is garnetite, composed of garnet+quartz or garnet+epidote, in both cases with minor amphibole, which forms rare centimetre-thick bands in amphibolites. The garnetite garnet is distinctly zoned, with cores enriched in spessartine component (Alm42-51Grs29-38Sps11-16 Prp2-8Adr0-3Ti-Grs0-1F-Kat0-1) and margins depleted in Sps and enriched in pyrope component (Alm49-54Grs28-35Sps4-10 Prp7-11Adr0-1F-Kat0-1). The origin of the pronounced enrichment in Mn is interpreted in terms of specific chemical composition of protolith of this garnetite, which was likely represented by a chemogenic precipitate rich in Si, Al, Fe, Mn and in places possibly also Ca. The last found garnetiferous lithology is represented by zoned reaction skarn rimming small xenoliths of calcitic marbles enclosed in amphibolites. The garnet-rich zone of the skarn is dominated by chemically homogeneous grossularite with composition Grs73-76Adr16-21Alm2-5Ti-Grs1-2Sps1F-Kat1Gol0-1.
9
Shiraishi, Kazuyuki, Takanobu Oba, Morihisa Suzuki, and Ken’ichi Ishikawa. "Subsilicic magnesian potassium-hastingsite from the Prince Olav Coast, East Antarctica." Mineralogical Magazine 58, no. 393 (December 1994): 621–27. http://dx.doi.org/10.1180/minmag.1994.058.393.11.
Повний текст джерелаАнотація:
AbstractTwo subsilicic magnesian potassium-hastingsites (4.55 and 4.34 wt.% K2O) and one magnesian potassium-hastingsite occur in calc-silicate pods in well-layered gneisses from the transitional amphibolite- and granulite-facies terrain of a Cambrian metamorphic complex, East Antarctica. Subsilicic magnesian potassium-hastingsite is the most K-rich Ca-amphibole yet reported:
10
Belic, Maximilian, Christoph A. Hauzenberger, and Yunpeng Dong. "Multistage Metamorphic Evolution of Retrograded Eclogites from the Songshugou Complex, Qinling Orogenic Belt, China." Journal of Petrology 60, no. 11 (November 1, 2019): 2201–26. http://dx.doi.org/10.1093/petrology/egaa007.
Повний текст джерелаАнотація:
Abstract The Qinling Orogenic Belt is one of the major collisional orogens in eastern Asia and marks the boundary between the North China Craton and South China Craton. The Songshugou complex is the largest basic to ultrabasic body to be found in the North Qinling Belt, and was emplaced as a lens-shaped body at the southern margin of the Qinling Group. A detailed petrological investigation of garnet amphibolite, augen amphibolite and well-foliated amphibolite together with garnet zoning patterns of major and trace elements, inclusions in garnet, and thermodynamic modelling indicate a multistage metamorphic history. Garnets clearly show characteristics of discontinuous growth, as they display optically light-colored snowball-textured cores surrounded by a darker mantle with few inclusions as well as chemically a sudden increase in grossular and decrease in almandine components. A partly resorbed rim is not recognized optically but mineral inclusions and a discontinuous chemical composition of garnet are proof of this third garnet growth stage. Rare earth element distribution patterns of garnet also show clear evidence for discontinuous growth and allow us to identify the reactions responsible for garnet growth. Garnet core compositions as well as amphibole inclusions allow us to constrain a P–T window where this rock equilibrated in a first stage. Calculated pseudosections and the application of the garnet–amphibole thermometer indicate an upper amphibolite- to lower granulite-facies metamorphic episode at 630–740 °C and 0·7–0·9 GPa. The presence of relict omphacite as well as a discontinuously grown garnet mantle with rutile inclusions clearly places the peak metamorphic stage in the eclogite facies. Garnet (XGrs, XAlm, XPrp) and omphacite isopleths (XMg, XNa) constrain this event at 1·7–2·1 GPa and 570–650 °C. Consistent temperatures of 500–650 °C were also determined by clinopyroxene–garnet geothermobarometry for this event. Growth of an outermost rim as well as different stages of garnet breakdown to plagioclase + amphibole coronae and the nearly complete replacement of former omphacite by a variety of symplectites point to an intricate retrograde P–T path. In more strongly retrograded samples plagioclase + amphibole ± quartz pseudomorphs entirely replace former garnet grains. Certain coronae around garnets and symplectites also contain prehnite and pumpellyite, which formed during a late retrograde stage or during a different event at very low P–T conditions (250–350 °C). Based on the detailed petrological study, we favour a multistage metamorphic history of the Songshugou metabasic rocks. The age of the eclogite-facies metamorphic event must be related to the deep subduction of the Songshugou complex during the early Paleozoic, although the age of garnet core growth remains enigmatic. The development of garnet cores indicates an upper amphibolite-facies regional metamorphic overprint succeeded by an eclogite-facies event around 500 Ma and subsequent retrogression seen in replacement of garnet and formation of symplectite. The latest imprint evidenced by prehnite and pumpellyite may be the result of fluid infiltration during the fading orogenic phase or represents a low-temperature overprint by a later process, probably related to the uplift of the North Qinling terrane at around 420 Ma.
11
Rollinson, H. R. "Early basic magmatism in the evolution of Archaean high-grade gneiss terrains: an example from the Lewisian of NW Scotland." Mineralogical Magazine 51, no. 361 (September 1987): 345–55. http://dx.doi.org/10.1180/minmag.1987.051.361.02.
Повний текст джерелаАнотація:
AbstractAmphibolite blocks from an Archaean (2.9 Ga) trondhjemite-agmatite complex in the Lewisian at Gruinard Bay have a varied trace element and REE content. Whilst some of the variability is attributable to element mobility during high-grade metamorphism and subsequent trondhjemite magmatism, it is for the main part considered to be a primary feature of the amphibolites. The observed trace element and REE chemistry is best explained in terms of source region heterogeneity and suggests a melting regime comparable with that beneath certain types of mid-ocean ridge. There are geochemical similarities between the amphibolites and the Lewisian layered gabbro-ultramafic complexes, and the two may represent the derivative liquid and associated cumulates respectively from a common parent magma. Thus there is a parallel between the processes which generated some Archaean amphibolites and layered gabbro complexes and those operating beneath modern ocean ridges. Hornblendite and amphibolite pods enclosed within tonalitic gneiss, also found as blocks in the agmatite complex, are geochemically distinct from the main group of amphibolites and are probably of calc-alkaline parentage.
12
Oke, SA. "Petrography, Geochemistry and Petrogenesis of Maru Amphibolite, Northwestern Nigeria." Nigerian Journal of Technological Research 10, no. 1 (April 14, 2015): 44. http://dx.doi.org/10.4314/njtr.v10i1.8.
Повний текст джерела
13
Coish, Raymond, Jonathan Kim, Nathan Morris, and David Johnson. "Late stage rifting of the Laurentian continent: evidence from the geochemistry of greenstone and amphibolite in the central Vermont Appalachians1This article is one of a series of papers published in CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology." Canadian Journal of Earth Sciences 49, no. 1 (January 2012): 43–58. http://dx.doi.org/10.1139/e11-013.
Повний текст джерелаАнотація:
Metamorphosed mafic rocks from west-central Vermont crop out in tectonic slices of the Stowe Formation within the Rowe–Hawley Belt of New England. The rocks include greenstone and amphibolite, which are interpreted to have been basaltic flows and gabbroic intrusions, respectively. Even though the rocks have been metamorphosed to greenschist or amphibolite facies, their igneous origins can be deciphered through careful use of geochemistry. Three geochemical types have been identified. Type 1 and 2 samples have geochemical characteristics similar to those found in mid-ocean ridge basalts (MORB), except that they have slightly elevated light rare-earth element (LREE) concentrations and are higher in Nb/Y ratios. Their Nb/Y ratios are similar to basalts found in Iceland and parts of the Afar region of the East African Rift. Types 1 and 2 are similar to metabasalts of the Caldwell and Maquereau formations in southern Quebec. The less-common type 3 samples have highly enriched LREE and are high in Nb/Y and Zr/Y ratios, similar to some alkali basalts from Afar and Iceland. Detailed analysis of the geochemistry suggests that greenstones and amphibolite from the Stowe Formation formed as basaltic eruptions during very late stages in rifting of the Rodinian continent that eventually led to formation of the Iapetus Ocean. This interpretation is consistent with tectonic models of the Vermont and Quebec Appalachians.
14
Frost, M. T., G. Tsambourakis, and J. Davis. "Holmquistite-bearing amphibolite from Greenbushes, Western Australia." Mineralogical Magazine 51, no. 362 (October 1987): 585–91. http://dx.doi.org/10.1180/minmag.1987.051.362.13.
Повний текст джерелаАнотація:
AbstractHolmquistite idioblasts occur in a hornblende-titanite-quartz-plagioclase amphibolite, in contact with a lithium (spodumene) pegmatite at Greenbushes, Western Australia. Unit cell parameters, chemical data and the results of a mineralogical investigation of holmquistite and associated minerals in the amphibolite are given.
15
Hollis, Julie A., Marie Keiding, Bo Møller Stensgaard, Jeroen A. M. Van Gool, and Adam A. Garde. "Evolution of Neoarchaean supracrustal belts at the northern margin of the North Atlantic Craton, West Greenland." Geological Survey of Denmark and Greenland (GEUS) Bulletin 11 (December 5, 2006): 9–32. http://dx.doi.org/10.34194/geusb.v11.4914.
Повний текст джерелаАнотація:
The Archaean North Atlantic Craton of West Greenland collided at c. 1.9 Ga with a lesser-known Archaean craton to the north, to form the Nagssugtoqidian orogen. The Palaeoproterozoic metamorphic grade and strain intensity decrease northward through the orogen, allowing investigation of the reworked Archaean components in its northern part. Two Archaean supracrustal belts in this region – the Ikamiut and Kangilinaaq belts – are investigated here using field mapping, aeromagnetic data, zircon geochronology, and geochemistry. Both belts comprise quartzo-feldspathic and pelitic metasedimentary rocks, amphibolite, and minor calc-silicate rocks, anorthosite and ultramafic rocks. PbPb and U-Pb dating of detrital zircons and host orthogneisses suggest deposition at c. 2800 Ma (Kangilinaaq belt) and after 2740 Ma (Ikamiut belt); both belts have zircons with Neoarchaean metamorphic rims. Metasedimentary rocks and orthogneisses at Ikamiut share similar steep REE signatures with strong LREE enrichment, consistent with local derivation of the sediment and deposition directly onto or proximal to the regional orthogneiss precursors. Zircon age data from Kangilinaaq indicate both local and distal sources for the sediment there. Geochemical data for Kangilinaaq amphibolites indicate bimodal, mixed felsic–mafic source rocks with island-arc basaltic affinities, consistent with a shelf or arc setting. Both belts experienced a similar tectono-metamorphic history involving Neoarchaean amphibolite facies peak metamorphism at c. 2740–2700 Ma, possibly due to continued emplacement of tonalitic and granodioritic magmas. Nagssugtoqidian lower amphibolite facies metamorphism at c. 1850 Ma was associated with development of the large-scale F2 folds and shear zones that control the present outcrop pattern. The observed differences in the sources of the Kangilinaaq and Ikamiut belts and their shared post-Archaean history suggest they were formed in different Neoarchaean environments proximal to and on a continental plate, and were amalgamated in a convergent margin setting shortly after their deposition.
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Espeche, María José J., Raúl Lira, and Nicolás A. Viñas. "Aportes a la metalogénesis del basamento proterozoico superior-cámbrico de las Sierras Pampeanas Orientales: mineralogía, termometría e isótopos de azufre del skarn Malagueño (Cu- Fe±Zn), Sierra Chica, Córdoba, Argentina." Andean Geology 47, no. 1 (January 31, 2020): 14. http://dx.doi.org/10.5027/andgeov47n1-3112.
Повний текст джерелаАнотація:
On-going mining operations in a marble quarry (Cantera Centro) from Malagueño, Sierra Chica de Córdoba, Argentina, have unearthed veins, veinlets and lenses of sulfides (pyrrhotite>pyrite≅
chalcopyrite>>sphalerite). These veins and lenses are up to 0.3 m thick and 2-3 m long, although intermittently can extend about a hundred meters. They are associated with skarns. The metasedimentary host sequence, largely composed of gneisses, amphibolites and marbles, was intruded by amphibolic metagabbro and metadiorite dykes, metatonalite plutons and alkali-feldspar metagranites; the whole complex was metamorphosed into medium to high amphibolite facies and strongly deformed as a result of the a regional event M2-D2/D3 that affected the Neoproterozoic-Cambrian basement during the Pampean orogeny. Except for gneisses, all the other metamorphic lithologies register evidence of differential alteration into skarn, although the process was preferentially developed on marbles, amphibolites and metagranite, and to a lesser exten on mafic and mesosilicic dykes. The metasomatic rocks are characterized by a garnet>>pyroxene skarn (Grs27-48Adr22-34Alm15-27Sps9-21), formed after the replacement of the metagranite; a pyroxene-rich skarn (Hd42-63Di32-50Jo3-5) developed after para-amphibolite, and a garnet (Adr54-71Grs22-40Alm4-7Sps1-2) (±wollastonite) skarn that replaced a calcic marble. The dykes show poor metasomatic replacement and lack sulfides of metasomatichydrothermal origin. Retrograde mineral associations include hastingsite, ferroactinolite, epidote, clinozoisite, sericite, plagioclase (An18), chamosite and calcite. The sulfide mineralization is paragenetically associated with late-stage, infilling skarn-hydrothermal minerals that were sequentially deposited as: calcite→clinochlore→quartz→pyrite→pyrrhotite→chalcopyrite+sphalerite; these phases occur as veins and veinlets within the garnetpyroxene skarn, and as massive pyrrhotite lenses in the piroxene-rich skarn. Microthermometric data from fluid inclusions in sulfide related calcite, together with the geothermometric data from the Fe/Mg ratios in clinochlore and the phase equilibria data from intergrown high and low T ºC pyrrhotite phases, all constrain the infilling gangue phases and sulfide crystallization temperature within the ~360 °C to 250 °C range; the gradual termal decrease is in agreement with the temporal depositional sequence of the infilling phases. Fluid inclusion petrographic data and salinity estimations suggest that sulfide precipitation was triggered by boiling, from a fluid of moderate to high salinity (~14.5 to 33.5 wt% eq. NaCl). Evidence that the fluid evolved under dominantly reducing conditions are the high Fe+2/(Fe+2+Fe+3) ratios and molar proportions of subcalcic garnet (Alm+Sps) in garnet-pyroxene skarn, the presence of fluid inclusion sulfide daughter crystals in calcite, the high H2S/SO42- ratios in the sulfide-bearing fluid and the presence of pyrrhotite among the sulfide phases. Disseminated primary chalcopyrite and pyrite in metagabbro-diorite dykes (Cu ~300 ppm) and the high contents of Cu in amphibolite (~900 ppm) suggest that these protolithic lithologies were the probable sources of metals (Cu>>Zn±Ag). Values of δ34SΣfluid between ~-4 to +1.4‰ obtained from the fractionations factors of pyrite, pyrrhotite and chalcopyrite within the thermal range 350-150 ºC, indicate a magmatic source for sulfur, likely provided by leaching or desulfidation of primary sulfides of the metagabbro-diorite dykes. Metals and sulfur supplied by these dykes and amphibolite would have been redistributed in the skarn after the circulation of the metasomatic-hydrothermal fluids. Skarn bodies would have formed by infiltration of deep metasomatic fluids and fluid-rock interaction which affected lithologies of the Upper Proterozoic-Cambrian metamorphic basement. Fluids could have derived from hidden Cambrian intrusives, or from the surrounding regional migmatization, channeled along lithological contacts and faults/fractures. Field setting, textural and mineralogical evidence of sulfide mineralization in the skarn assemblage of Cantera Centro, suggest a Cambrian age associated to the post-deformational stage of the Pampean Orogeny.
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Dusel-Bacon, Cynthia, and Kari M. Cooper. "Trace-element geochemistry of metabasaltic rocks from the Yukon-Tanana Upland and implications for the origin of tectonic assemblages in east-central Alaska." Canadian Journal of Earth Sciences 36, no. 10 (October 1, 1999): 1671–95. http://dx.doi.org/10.1139/e99-077.
Повний текст джерелаАнотація:
We present major- and trace- element geochemical data for 27 amphibolites and six greenstones from three structural packages in the Yukon-Tanana Upland of east-central Alaska: the Lake George assemblage (LG) of Devono-Mississippian augen gneiss, quartz-mica schist, quartzite, and amphibolite; the Taylor Mountain assemblage (TM) of mafic schist and gneiss, marble, quartzite, and metachert; and the Seventymile terrane of greenstone, serpentinized peridotite, and Mississippian to Late Triassic metasedimentary rocks. Most LG amphibolites have relatively high Nb, TiO2, Zr, and light rare earth element contents, indicative of an alkalic to tholeiitic, within-plate basalt origin. The within-plate affinities of the LG amphibolites suggest that their basaltic parent magmas developed in an extensional setting and support a correlation of these metamorphosed continental-margin rocks with less metamorphosed counterparts across the Tintina fault in the Selwyn Basin of the Canadian Cordillera. TM amphibolites have a tholeiitic or calc-alkalic composition, low normalized abundances of Nb and Ta relative to Th and La, and Ti/V values of <20, all indicative of a volcanic-arc origin. Limited results from Seventymile greenstones indicate a tholeiitic or calc-alkalic composition and intermediate to high Ti/V values (27-48), consistent with either a within-plate or an ocean-floor basalt origin. Y-La-Nb proportions in both TM and Seventymile metabasalts indicate the proximity of the arc and marginal basin to continental crust. The arc geochemistry of TM amphibolites is consistent with a model in which the TM assemblage includes arc rocks generated above a west-dipping subduction zone outboard of the North American continental margin in mid-Paleozoic through Triassic time. The ocean-floor or within-plate basalt geochemistry of the Seventymile greenstones supports the correlation of the Seventymile terrane with the Slide Mountain terrane in Canada and the hypothesis that these oceanic rocks originated in a basin between the continental margin and an arc to the west.
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Grapes, Rodney, Kurt Bucher, and Paul W. O. Hoskin. "Monazite-epidote reaction in amphibolite grade blackwall rocks." European Journal of Mineralogy 17, no. 4 (July 25, 2005): 553–66. http://dx.doi.org/10.1127/0935-1221/2005/0017-0553.
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Ilnicki, S. "Variscan progradeP-Tevolution and contact metamorphism in metabasites from the Sowia Dolina, Karkonosze-Izera massif, SW Poland." Mineralogical Magazine 75, no. 1 (February 2011): 185–212. http://dx.doi.org/10.1180/minmag.2011.075.1.185.
Повний текст джерелаАнотація:
AbstractSeveral bodies of moderately foliated and porphyroblastic metabasites crop out on the SE side of the metamorphic cover of the Karkonosze granite within metapelites of the Sowia Dolina area (West Sudetes, Saxothuringian zone). Depending on the microstructural setting of the Ca-amphiboles in the rocks, different mineral-chemical trends have been determined for Si,XMg, AlVI,A[Na+K] which serve as semi-quantitative indicators of temperature and pressure changes. Porphyroblasts and prisms oblique to the main foliation in schistose metabasites show zoning from Mg-hornblende and actinolite to tschermakite, and then to Mg-hornblende (or actinolite). Matrix amphiboles and those in pressure shadows around some porphyroblasts have tschermakitic cores and actinolitic rims. Rarely, Ca-amphibole is accompanied in schists by late- to post-tectonic cummingtonite. Thermobarometric calculations involving empirically calibrated amphibole equilibria enable a reconstruction ofP-Tpaths for individual rocks and the unravelling of the metamorphic evolution of the metabasites. Peak metamorphic temperatures of 615–640°C and pressures of 7.3–8.2 kbar were preceded by a variably preserved earlier stage (T = 370–550°C, P = 2.8–6.2 kbar). The final metamorphic episode took place at 450–550°C and 2.5–4.8 kbar and is recorded particularly in rocks close to the Karkonosze pluton. The metabasites shed new light on the history of metamorphism in the Sowia Dolina area. The first two stages ofMP-MTmetamorphism, coeval with Variscan deformation events (continental collision, burial and subsequent exhumation), took place under epidote-amphibolite then amphibolite facies conditions. The last stage partly concurred with the final stages of Variscan deformation and overlapped the onset of thermal activity associated with the Karkonosze granite. This metamorphic event is documented by metabasites (occasionally cummingtonite-bearing) outcropping close to the granite. Finally, a prehnitebearing assemblage reflects retrograde re-equilibration under greenschist/sub-greenschist facies conditions (T<300–350°C,P<2.5–3 kbar), which might also be partly due to hydrothermal activity around the pluton.
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Knudsen, Christian, Jeroen A. M. Van Gool, Claus Østergaard, Julie A. Hollis, Matilde Rink-Jørgensen, Mac Persson, and Kristoffer Szilas. "Gold-hosting supracrustal rocks on Storø, southern West Greenland: lithologies and geological environment." Geological Survey of Denmark and Greenland (GEUS) Bulletin 13 (October 12, 2007): 41–44. http://dx.doi.org/10.34194/geusb.v13.4972.
Повний текст джерелаАнотація:
A gold prospect on central Storø in the Nuuk region of southern West Greenland is hosted by a sequence of intensely deformed, amphibolite facies supracrustal rocks of late Mesoto Neoarchaean age. The prospect is at present being explored by the Greenlandic mining company NunaMinerals A/S. Amphibolites likely to be derived from basaltic volcanic rocks dominate, and ultrabasic to intermediate rocks are also interpreted to be derived from volcanic rocks. The sequence also contains metasedimentary rocks including quartzites and cordierite-, sillimanite-, garnet- and biotite-bearing aluminous gneisses. The metasediments contain detrital zircon from different sources indicating a maximum age of the mineralisation of c. 2.8 Ga. The original deposition of the various rock types is believed to have taken place in a back-arc setting. Gold is mainly hosted in garnet- and biotite-rich zones in amphibolites often associated with quartz veins. Gold has been found within garnets indicating that the mineralisation is pre-metamorphic, which points to a minimum age of the mineralisation of c. 2.6 Ga. The geochemistry of the goldbearing zones indicates that the initial gold mineralisation is tied to fluid-induced sericitisation of a basic volcanic protolith. The hosting rocks and the mineralisation are affected by several generations of folding.
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Obioha, Young Ezenwa. "Geochemistry evolution of Schists of northwest Obudu area southeastern Nigeria." Global Journal of Geological Sciences 19, no. 1 (July 13, 2021): 29–39. http://dx.doi.org/10.4314/gjgs.v19i1.3.
Повний текст джерелаАнотація:
Geochemistry of schists of Obudu area was carried out using ICP-MS and ICP-ES techniques in order to determine the geochemical evolution of the area. 40 samples were analyzed for their major, trace and REE composition. Field mapping revealed that gneisses, amphibolites and schists comprising migmatitic schists (MS), quartz-mica schists (QMS), garnet-mica schists (GMS), and hornblende biotite schists (HBS), intruded by granites, granodiorites, quartzofeldspathic rocks and dolerites occur in the area. Structural studies revealed that the schists trend approximately NE–SW (5 – 30o ) indicating the Pan-African event. Modal analysis revealed that the schists have average concentration of quartz (15vol.%), plagioclase (An45-19 vol.%), biotite (15vol.%), garnet (9.0vol.%) and muscovite (6vol.%), the remaining consists of accessory minerals. Geochemistry showed that all the schists have molecular Al2O3 > CaO+K2O+Na2O, indicating they are peraluminous metasedimentary pelites. Trace and REE element results show that all the analyzed schist samples are depleted in Hg, Ag, Be, Bi, and Sb below < 1.0ppm, but relatively enriched in Ba, Sr and Zr with average concentration of 996, 675.73, 243.13 ppm respective. The HREE are depleted with ΣHREE < 10.2, but the LREE are relatively enriched with ΣLREE > 289.54. The ΣLREE/ΣHREE ratio ranges from 9.17 to 33.4, with a large positive delta V at Eu. These findings indicate that the schists of Northwest Obudu area are highly fractionated and had attained at least the uppermost amphibolite metamorphic grade. The schists had contributed to the development of the Pan-African continent.
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Dasgupta, Somnath, P. K. Bhattacharya, G. Chattopadhyay, H. Banerjee, N. Majumdar, M. Fukuoka, and Supriya Roy. "Petrology of Mg-Mn amphibole-bearing assemblages in manganese silicate rocks of the Sausar Group, India." Mineralogical Magazine 52, no. 364 (March 1988): 105–11. http://dx.doi.org/10.1180/minmag.1988.052.364.09.
Повний текст джерелаАнотація:
AbstractMg-Mn amphibole (tirodite), with or without pyroxmangite in the total absence of pyroxenes and high-calcic pyroxenoids, occurs in the Mn silicate rocks of the Sausar Group, India. The rocks were metamorphosed to amphibolite facies condition (T ∼ 650°C, P ∼ 6 kbar). Tirodite-pyroxmangite pairs developed in both carbonate-free and rhodochrosite-bearing assemblages. Also tirodite coexists with either kutnahorite or manganoan calcite in the absence of pyroxmangite. Mineral reactions inferred from modal abundances and compositions of the phases indicate stabilization of the amphibole alone from a bivalent cation-bearing residual unbuffered XCO2 system with XMn < 0.3. On the other hand, tirodite-pyroxmangite pairs appeared in unbuffered low to intermediate XCO2 assemblages with XMn > 0.35. Pyroxenes and high-calcic pyroxenoids did not appear in the present situation, though they occur elsewhere in rocks with broadly similar contents of immobile components. Closely associated assemblages of diverse mineralogy suggest that the XMn and XCO2, rather than the physical conditions of metamorphism, are the decisive factors in promoting the observed phase assemblages.
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Zeck, H. P., C. Ottesen, and J. Toft. "Volume effect of a gabbro-amphibolite transition." Chemical Geology 67, no. 1-2 (January 1988): 141–53. http://dx.doi.org/10.1016/0009-2541(88)90011-3.
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Sokolov, S. D., S. A. Silantyev, A. V. Moiseev, M. I. Tuchkova, and V. E. Verzhbitsky. "Amphibolites of the metamorphic basement of Wrangel island: age, nature of the protolite and conditions of metamorphism." Геохимия 64, no. 12 (December 20, 2019): 1222–46. http://dx.doi.org/10.31857/s0016-752564121222-1246.
Повний текст джерелаАнотація:
New data on petrography, geochemistry and geochronology of metamorphic rocks sampled from Neoproterozoic basement of Wrangel Island are presented. Oceanic affinity for mafic rocks underwent greenschist to amphibolite facies conditions (350600C) has been established by geochemical data. Protolith of this rock belongs to products of the evolution of magmatic melts parental for MORB. Protoliths age is 61713 and 69812 Ma was determined by U-Pb isotope dating of Zircons from these rocks (SHRIMP II and La-ICP MS). There are two main stage of metamorphism could be established: Neoproterozoi Early Paleozoi (amphibolite and greenschist facies conditions) and Middle Cretaceous (greenschist facies condition only), Last stage of metamorphism related to Chukcha deformation events accompanied by formation of folded nappes structure and consequent extension. An comparison of studied rocks with samples dredged at Chukcha Borderland evidenced for certain similarity existing between these rock assemblages judging by their petrography and chemistry.
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Gieré, R., T. Jeffries, R. Garcia-Sanchez, and C. T. Williams. "Light element distribution in an amphibolite-facies metapelite." Geochimica et Cosmochimica Acta 70, no. 18 (August 2006): A202. http://dx.doi.org/10.1016/j.gca.2006.06.407.
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Qiu, H. N., and J. R. Wijbrans. "When did amphibolite-facies overprinting occur in Dabieshan?" Geochimica et Cosmochimica Acta 70, no. 18 (August 2006): A512. http://dx.doi.org/10.1016/j.gca.2006.06.941.
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Ružička, Peter, Pavol Myšľan, and Tomáš Mikuš. "Minerálne zloženie kryštalických vápencov z lokality Dobšiná - Kruhová (Slovenská republika)." Bulletin Mineralogie Petrologie 29, no. 2 (2021): 285–96. http://dx.doi.org/10.46861/bmp.29.285.
Повний текст джерелаАнотація:
Crystalline limestones containing fragments of amphibolites from the locality Dobšiná - Kruhová are part of the Klátov complex (Northern Gemericum, Western Carpathians). The colour of studied rocks is light grey with massive texture and granoblastic structure. Inhomogeneous mottled to breccia-like character of a crystalline limestones is caused by the presence of amphiboles in the studied rocks. The identified mineral association of crystalline limestones consists of calcite, amphiboles (pargasite, magnesio-hornblende, actinolite), clinopyroxenes (diopside), albite and titanite. Chemical zonation of amphiboles from the crystalline limestones and fragments of amphibolites have been studied in BSE imaging. Light grey BSE zone is represented by pargasite (with more Fe2+ up to 1.37 apfu and less Mg up to 2.26 apfu) and dark grey BSE zone is represented by magnesio-hornblend and actinolite (less Fe2+ 0.68 apfu in magnesio-hornblende; 0.62 apfu in actinolite and more Mg up to 3.30 apfu in magnesio-hornblende and up to 4.03 apfu in actinolite). Diopside has slightly higher content of Al (up to 0.13 apfu) and low content of Fe2+ (up to 0.17 apfu) with XMg ratio in the range 0.83 - 0.96. Chemical composition of albites is Ab91.12-98.21An1.52-5.12 with ortoclase component in the range 0.22 - 4.49 mol. %. Titanites from the amphibolite fragments and crystalline limestones have identical chemical composition (Ca up do 1.00 apfu, Si up to 0.97 apfu). Lower content of Ti (0.88 - 0.95 apfu) and higher content of F (up to 0.27 wt. %) and H2O (up to 0.38 wt. %) is present. In titanites not very significant (Al, Fe3+) + (OH, F) ↔ Ti + O substitution was also identified. We assume that pargasite and magnesio-hornblende are products of prograde etape of metamorphosis unlike actinolite which is product of retrograde etape of metamorphosis. Diopside was generated by dehydration and decomposition processes of magnesio-hornblende and pargasite in a high-temperature prograde regime of metamorphosis in the conditions of upper amphibolite facies. Calcite is chemically pure, presence of dolomite has not been confirmed.
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Schulz, Bernhard, Claude Triboulet, and Claude Audren. "Microstructures and mineral chemistry in amphibolites from the western Tauern Window (Eastern Alps), and P-T deformation paths of the Alpine greenschist-amphibolite facies metamorphism." Mineralogical Magazine 59, no. 397 (December 1995): 641–59. http://dx.doi.org/10.1180/minmag.1995.059.397.08.
Повний текст джерелаАнотація:
AbstractAmphibolites in the Mesozoic part of the parautochthonous Lower Schieferhülle (LSH), the allochthonous Upper Schieferhülle (USH) and the overlying Austroalpine basement (AA) in and around the western Tauern Window (Eastern Alps) suffered a progressive Alpine deformation. Lineations and foliations L1-S1, L2-S2 defined by preferentially oriented (Na-Ca) amphiboles as well as F3 folds and further foliations Smyl and S4 in the metabasites are structures of successive deformational stages with a constant W-E main extension axis of strain. The (Na-Ca) amphiboles in assemblages with epidote, chlorite, albite/oligoclase and quartz are zoned with similar continuous zonation trends from early actinolite in the cores to magnesio-hornblende and tschermakitic hornblende, and from magnesio-hornblende to late actinolite in the rims in the three lithostratigraphic units. Geothermobarometry involving tremolite-edenite and (pargasite-hastingsite)-tremolite end-member equilibria in amphiboles allowed us to reconstruct prograde-retrograde P-T paths for the Alpine greenschist-amphibolite facies event. The paths passed P/Tmax at 6–7 kbar/600°C. Similar shapes of the paths in AA, USH and Mesozoic LSH indicate a common metamorphic history and a stacking of these units prior to or during the pre-Pmax evolution. Moderate P-T ratios are characteristic for the temperature-dominated compression paths and indicate continental collisional rather than subduction zone metamorphism. The middle to late Alpine greenschist-amphibolite facies event appears as an independent metamorphism along a complete P-T loop which may have followed an earlier and poorly documented high-pressure/low-temperature event.
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Valverde-Vaquero, Pablo, Greg R. Dunning, and Cees R. van Staal. "The Margaree orthogneiss: an Ordovician, peri-Gondwanan, mafic-felsic igneous complex in southwestern Newfoundland." Canadian Journal of Earth Sciences 37, no. 12 (December 1, 2000): 1691–710. http://dx.doi.org/10.1139/e00-053.
Повний текст джерелаАнотація:
The igneous protoliths of the Margaree orthogneiss intruded the peri-Gondwanan rocks of the Port-aux-Basques Complex, in the southwestern corner of the Hermitage Flexure, prior to regional deformation and metamorphism. Field relationships and UPb geochronology indicate that the Margaree orthogneiss represents a 20 km long, mafic-felsic intrusive complex formed by amphibolite, dioritic orthogneiss, 474+14-4 Ma hornblende-bearing tonalitic orthogneiss with mafic enclaves, 472 ± 2.5 Ma and 465 ± 3 Ma biotite-bearing granitic orthogneiss, and minor ultramafic rocks. Most amphibolite have the chemistry of volcanic-arc tholeiite and are interpreted to be coeval with the intrusion of tonalitic and granitic magma with volcanic-arc geochemical signatures. Locally, mafic magmatism continued after the intrusion of the 465 Ma granite. The Margaree orthogneiss and its country rock were overprinted by upper amphibolite-facies metamorphism and deformation associated with the final closure of the Iapetus Ocean. A late-synkinematic granite dates the late stages of the high-temperature regional deformation at 417+7-4 Ma, while metamorphic titanite (411 ± 2 Ma) is interpreted to date extensive recrystallization under amphibolite-facies conditions as Early Devonian. The Margaree orthogneiss is broadly coeval with the plutons that postdate the Early Ordovician Penobscottian arc passive margin imbrication in central and southern Newfoundland. It also coincides with the extensive late Arenig early Llanvirn back-arc rifting event along the entire peri-Gondwanan margin of the northern Appalachians. The external position of the Port-aux-Basques Complex with respect to the back-arc elements in the Hermitage Flexure, coupled with the rock types and geochemistry of the orthogneiss, suggest formation of the Margaree orthogneiss in an arc and (or) back-arc transitional setting.
30
Suwa, Kanenori, Masaki Enami, and Tatsuro Horiuchi. "Chlorine-rich potassium hastingsite from West Ongul Island, Lützow–Holm Bay, East Antarctica." Mineralogical Magazine 51, no. 363 (December 1987): 709–14. http://dx.doi.org/10.1180/minmag.1987.051.363.11.
Повний текст джерелаАнотація:
AbstractChlorine-rich potassium hastingsite occurs in a calcareous pegmatite, a replacement zone and an amphibolite lens within hornblende gneiss on West Ongul Island, Lützow-Holm Bay, East Antarctica. The amphibolite lens and hornblende gneiss were metamorphosed to the kyanite-sillimanite grade of the granulite facies during Proterozoic metamorphism. Chemical analysis (3.27 wt.% Cl), unit cell parameters and optical properties of the Cl-rich potassium hastingsite are given. Cl-rich (> 3 wt.%) calcic amphiboles reported from various rock types are mostly more than 0.9 in (Na+ K) content, more than 0.4 in K/(Na + K) ratio, more than 0.75 in Fe2+/(Fe2++ Mg + Mn) ratio and more than 1.9 in AlIVcontent (total iron as FeO and O = 23). The unit cell volume of Cl-rich hastingsite is distinctly larger than that of Cl-poor hastingsite.
31
Berger, A., M. Herwegh, and E. Gnos. "Deformation of monazite in an amphibolite-facies shear zone." Geochimica et Cosmochimica Acta 70, no. 18 (August 2006): A47. http://dx.doi.org/10.1016/j.gca.2006.06.203.
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Borsi, L., R. Petrini, F. Talarico, and R. Palmeri. "Geochemistry and Sr-Nd isotopes of amphibolite dykes of northern Victoria Land, Antarctica." Lithos 35, no. 3-4 (June 1995): 245–59. http://dx.doi.org/10.1016/0024-4937(95)99070-d.
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Goulart, Luís Emanoel Alexandre, and Mauricio Antonio Carneiro. "Evolution of arc magmatism in the Carmópolis de Minas Layered Suite, Minas Gerais, Brazil: Sm-Nd and Rb-Sr isotope geochemistry." Rem: Revista Escola de Minas 66, no. 4 (December 2013): 447–54. http://dx.doi.org/10.1590/s0370-44672013000400007.
Повний текст джерелаАнотація:
The Carmópolis de Minas Layered Suite (CMLS) is a Neoarchean Unit metamorphosed at amphibolite- to granulite-facies conditions, comprised of metaultramafic rocks, amphibolites and metarhyolites. The CMLS is marked by two distinct phases of tholeiitic and calc-alkaline magmatism. Previous geochemical data and regional constraints suggest that the CMLS is possibly a metamorphosed arc-tholeiitic suite of the type boninite-basalt-andesite-rhyolite, interpreted in this study as a dismembered remnant of the juvenile oceanic arc. The rocks of tholeiitic affinity record a signature of depleted to enriched mantle with positive to weakly negative εNd(t) and predominantly positive εSr(t) values, indicating some degree of crustal assimilation. The rocks of calc-alkaline affinity present a signature of juvenile crust with εNd(t) close to the CHUR and weakly positive εSr(t) values. The Sm-Nd isochron age of 2736 ± 300 Ma obtained with εNd(i) = +0.4, suggests the edification of an intra-oceanic arc during the late phases of the Rio das Velhas Tectonothermal Event. The arc evolution involved tholeiitic magmatism in the early stages in association with calc-alkaline magmatism, of probably anatectic character, in the tardy-orogenic stages.
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Chamberlain, V. E., R. St J. Lambert, and J. G. Holland. "Geochemistry and geochronology of the gneisses east of the Southern Rocky Mountain Trench, near Valemount, British Columbia." Canadian Journal of Earth Sciences 22, no. 7 (July 1, 1985): 980–91. http://dx.doi.org/10.1139/e85-103.
Повний текст джерелаАнотація:
Petrographic, geochemical, and geochronological data are presented on the gneisses of the Bulldog Creek block, the Mount Blackman block, and the Hugh Allan Creek block, which lie to the east of the Southern Rocky Mountain Trench (SRMT) south of Valemount, British Columbia.Petrographical and geochemical data, especially immobile-trace-element ratios (Nb: Y, Ti: Zr), and CaO versus Y and AFM plots are used to deduce the probable origins and protoliths of the gneisses. The Mount Blackman block consists of a psammitic paragneiss, probably derived from an immature arkosic sedimentary protolith, intruded by sills of tholeiitic basalt, now amphibolites. The Bulldog Creek block consists of felsic orthogneisses of calc-alkaline affinity, which are structurally concordant with mafic orthogneisses of possible tholeiitic basalt parentage. The Hugh Allan Creek block consists of a felsic orthogneiss with a probable alkaline granite protolith.Rb–Sr, and some U–Pb analyses show that each block has experienced a separate geological history. The Mount Blackman block psammitic paragneisses are the only analysed gneisses east of SRMT with a probable Archean Rb–Sr model crustal residence age. U–Pb analyses on zircons from these gneisses give a 1950 Ma minimum source rock age, and Rb–Sr whole-rock analyses suggest a 1860 ± 50 Ma age for amphibolite-facies metamorphism of both paragneisses and amphibolites. The Bulldog Creek block gneisses have a metamorphic age of at least 640 Ma, but their Rb–Sr systematics have been extensively disturbed, possibly during Mesozoic retrogressive metamorphism. The Hugh Allan Creek block gneisses have a Rb–Sr model crustal residence age of ~900 Ma and a metamorphic age of 805 ± 11 Ma. It is not possible to correlate any of these lithologies or events across the SRMT with the Malton block, and it is concluded that the SRMT is the site of a major fault or faults at this latitude.
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Baker, A. J. "Eclogitic amphibolites from the Grampian Moines." Mineralogical Magazine 50, no. 356 (June 1986): 217–21. http://dx.doi.org/10.1180/minmag.1986.050.356.04.
Повний текст джерелаАнотація:
AbstractAmphibolites from the Grampian Moines of Scotland contain clinopyroxene-plagioclase symplectites and plagioclase-hornblende coronas around garnet. The clinopyroxene-plagioclase symplectites are interpreted as former omphacites. It is inferred that an eclogitic garne-tomphacite-quartz assemblage once existed, but has since undergone partial reaction to an amphibolite facies hornblende-plagioclase assemblage. An early high-pressure metamorphic event occurred in parts of the Moine.
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Ahmad Aminuddin, Muhammad Irman Khalif Bin, Nugroho Imam Setiawan, I. Wayan Warmada, Kamar Shah Ariffin, and Kotaro Yonezu. "PETROGRAPHY AND GEOCHEMISTRY OF METASEDIMENTARY ROCKS FROM THE TAKU SCHIST IN KELANTAN, NORTH-EAST PENINSULAR MALAYSIA." Journal of Applied Geology 5, no. 2 (January 18, 2021): 124. http://dx.doi.org/10.22146/jag.61183.
Повний текст джерелаАнотація:
The Taku Schist, which is located in the north-east Peninsular Malaysia, is characterized by its North-South oriented elongated body. It forms part of the Indonesian orogenic build-up that was generated via the convergence of the Sibumasu continental unit and Sukhothai Arc. Subsequent petrography analyses of the metasedimentary rocks sourced from the Taku Schist revealed that their formation was attributable to the metamorphism of greenschist into amphibolite facies, which could be observed near the Triassic and Cretaceous intrusions of the Kemahang Granite. The evolutionary process of the rocks could be linked with the interactions occurring between contact and regional metamorphisms. The resulting chemical classification upon their assessment disclosed that the metasedimentary rocks of Taku Schist were made up of greywacke and shale, grouped into the quartzose sedimentary provenance, and belonged to the Continental Island Arc (CIA). This information is required for the tectonic setting discrimination purpose. It is a reflection of the episodic contractions underwent by the Taku Schist, wherein they would lead to the Sibumasu sedimentary cover along with both an accretionary wedge and the genetically-correlated Bentong-Raub melange to different greenschist. Otherwise associated with amphibolite facies, the conditions and depths of the facies were determined according to their position in relation to the upper plate of the Sukhothai Arc.
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Goodman, S. "Survival of zincian staurolite to upper amphibolite facies metamorphic grade." Mineralogical Magazine 57, no. 389 (December 1993): 736–39. http://dx.doi.org/10.1180/minmag.1993.057.389.19.
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LaFontaine, Daniel, Audrey Bouvier, and Mary Louise Hill. "Garnet Geochemistry and Lu-Hf Geochronology of a Gold-Bearing Sillimanite-Garnet-Biotite Gneiss at the Borden Lake Belt." Geosciences 12, no. 5 (May 23, 2022): 218. http://dx.doi.org/10.3390/geosciences12050218.
Повний текст джерелаАнотація:
The Kapuskasing Structural Zone transects the Wawa and Abitibi greenstone belts in the Superior province of the Canadian Shield. At the southern margin of the Kapuskasing Structural Zone (KSZ), the Borden Gold deposit hosts low-grade-gold mineralization within upper amphibolite- to granulite-facies sillimanite-garnet-biotite gneisses. Here, we present the geochemistry and Lu-Hf geochronological studies of a gold-hosting garnet-bearing gneiss to constrain the formation history of the deposit and regional geological history. The garnet is almandine-rich, and contains inclusions of quartz, biotite, pyrite, and zircon. The absence of chemical zoning in garnet is likely due to intracrystalline diffusion at peak metamorphic temperatures. The 176Lu-176Hf internal isochron of two garnet fractions and three corresponding whole-rock splits from a gneissic unit yield a precise internal isochron age at 2629.0 ± 4.3 Ma (MSWD = 0.66), with an initial 176Hf/177Hf = 0.281210 ± 0.000010 corresponding to an εHfi = +4.1. This signature suggests a mafic source, which was derived from a long-term depleted reservoir, for this metasediment. The Lu-Hf age is consistent with the youngest age population of zircons from the paragneisses, which were previously dated in the area. Our results thus provide upper constraints on the timing of retrograde upper-amphibolite metamorphism and gold mineralization at Borden.
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Wang, Ende, Changik Han, Jianming Xia, and Sunggi Yun. "Geochemistry and Tectonic Significance of Chlorite Amphibolite in Nanfen BIF, Benxi Area, Northeastern China." Journal of Geoscience and Environment Protection 03, no. 05 (2015): 54–61. http://dx.doi.org/10.4236/gep.2015.35007.
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Cherneva, Zlatka, Elena Stancheva, Lilan-Anna Daieva, and Emilia Voynova. "Geochemistry of orthogneisses from the northern part of the Central Rhodope, Bulgaria." Geologica Balcanica 37, no. 1-2 (June 30, 2008): 61–72. http://dx.doi.org/10.52321/geolbalc.37.1-2.61.
Повний текст джерелаАнотація:
The late Jurassic igneous protoliths of the two-mica and leptitoid gneisses in the Central Rhodope Asenitsa unit correspond to a range of metaluminous granodiorite to wide-spread peraluminous leucogranite compositions. Despite the amphibolite facies metamorphic overprint, the major and trace elements distribution of the igneous protoliths are preserved to a significant extent. Systematic geochemical variations display magma fractionation trends The most indicative of the latter are increasing Rb/Sr ratios from 0.1 to 22, decreasing Eu/Eu* values from 0.8 to 0.1, and decreasing Zr/Hf ratios from 40 to 11 towards the most felsic orthogneisses. The whole orthogneiss suite is distinguished by high LILE/HFSE ratios that support crustal dominated and evolved magma source.
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MORISHITA, Tomoaki, Shoji ARAI, Akihiro TAMURA, and Yoshito ISHIDA. "Petrology of a peculiar amphibolite boulder rich in deep vivid green-colored amphibole porphyroblast from Hidaka Town, Hokkaido, Japan." Japanese Magazine of Mineralogical and Petrological Sciences 37, no. 1 (2008): 1–14. http://dx.doi.org/10.2465/gkk.37.1.
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Espeche, María José, and Raúl Lira. "Ecandrewsite (ZnTiO3) in Amphibolites, Sierras de Córdoba, Argentina: Mineral Chemistry and Comparison with Different Worldwide Paragenetic Occurrences." Canadian Mineralogist 60, no. 4 (July 1, 2022): 677–86. http://dx.doi.org/10.3749/canmin.2100055.
Повний текст джерелаАнотація:
ABSTRACT Ecandrewsite (ZnTiO3) and other ilmenite-group minerals have been found in amphibolites of the Sierras de Córdoba basement, Argentina, in an area where zinc is a relatively widespread element in the associated metasedimentary and metaigneous sequences. Ilmenite group minerals occur as anhedral to subhedral, tens to a hundred micrometer-sized relic inclusions in titanite. Electron microprobe analyses reveal compositions along a discontinuous solid-solution trend ranging from manganoan ferroan ecandrewsite toward ilmenite s.s., passing through intermediate members such as ferroan manganoan ecandrewsite, zincian manganoan ilmenite, and manganoan ilmenite. Considering that thermodynamic constraints do exist for the solubility of ZnTiO3 in ilmenite under mid- to high-grade regional metamorphic conditions, we believe that ecandrewsite and Zn-rich ilmenite compositions were attained by metasomatic fluid–mineral reactions during retrograde regional metamorphism, i.e., after the centripetal replacement of protolithic Zn-bearing ilmenite group species by titanite. The original composition of the ilmenite group species might have been Zn-poor ilmenite; however, the attainment of ecandrewsite compositions possibly needed an external supply of zinc provided by the fluid. The variations of the zinc contents were controlled by the substitution of Fe by Zn + Mn in the absence of any type of regular zonation. This is the first worldwide report of ecandrewsite in amphibolites, which has so far been described in quartz-rich metasediments, quartz-gahnite exhalites, kyanitic schists, nepheline syenites, metamorphosed volcanic hosted massive sulfide (VHMS) mineralizations, and albitites. The presence of ecandrewsite in amphibolite, as has been proved for zincian ilmenite and gahnite in other metasedimentary sequences elsewhere in the world, could become another pathfinder or indicator mineral for Zn-enriched portions of the crust.
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Schulz, Bernhard. "Mineral chemistry, geothermobarometry and pre-Alpine high-pressure metamorphism of eclogitic amphibolites and mica schists from the Schobergruppe, Austroalpine basement, Eastern Alps." Mineralogical Magazine 57, no. 387 (June 1993): 189–202. http://dx.doi.org/10.1180/minmag.1993.057.387.01.
Повний текст джерелаАнотація:
AbstractAlternating eclogitic amphibolites, mica schists and orthogneisses in the Schobergruppe to the south of the Tauern Window suffered a post-Upper-Ordovician progressive deformation D1-D2which produced parallel planar-linear structures in all the rocks. Zoned garnets, preferentially oriented zoned clinopyroxenes (Jd 35-42%) and albite (An 7-9%) give evidence of high-pressure metamorphism (550-650°C 14-16 kbar) of the metabasites. Ca-amphiboles crystallized during subsequent decompression. In a kyanite-staurolite-garnet mica schist 300 metres below the metabasites, garnetbearing assemblages grew synchronous with the development of foliations S1and S2. Garnets are zoned with increasing XMgand decreasing-increasing-rcdecreasing Xcafrom cores to rims. Albitic plagioclase (An 1-3%) and micas are enclosed in garnet cores and rims, are in contact with garnet, and occur with garnet in microlithons. When these minerals are used for geothermobarometry, a prograde P-T evolution (460 to 680°C with coeval pressure variations which reach high-pressure conditions can be estimated. This suggests that garnet-plagioclase geobarometry with albitic plagioclase works in the relevant P-T field. Similar garnet zonation trends and a similarly shaped P-T path from mica schists of an adjacent region with late-Variscan cooling ages, points to an eady-Variscan age of the syn-D1-D2high-pressure and subsequent amphibolite-facies metamorphism.
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Minitti, Michelle E., Malcolm J. Rutherford, Bruce E. Taylor, M. Darby Dyar, and Peter H. Schultz. "Assessment of shock effects on amphibole water contents and hydrogen isotope compositions: 1. Amphibolite experiments." Earth and Planetary Science Letters 266, no. 1-2 (February 2008): 46–60. http://dx.doi.org/10.1016/j.epsl.2007.10.047.
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Liu, Xiaochun, Shuwen Dong, Huaimin Xue, and Jianxiong Zhou. "Significance of allanite-(Ce) in granitic gneisses from the ultrahigh-pressure metamorphic terrane, Dabie Shan, central China." Mineralogical Magazine 63, no. 4 (August 1999): 579–86. http://dx.doi.org/10.1180/minmag.1999.063.4.10.
Повний текст джерелаАнотація:
AbstractA recent study of granitic gneisses in the ultrahigh-pressure (UHP) metamorphic terrane from Dabie Shan, central China reveals that allanite-(Ce) is a widespread REE-bearing accessory phase. The microprobe analyses show that allanites-(Ce) have nearly uniform chemical compositions, with total REE contents ranging from 23 to 28 wt.% and a La/Ce ratio of 0.57–0.73. All allanites-(Ce) are replaced or rimmed by epidotes and commonly form a relatively REE-poor rim near the interfaces. The textural relations and mineral chemistry suggest that allanite-(Ce) crystallized prior to metamorphism and therefore was of igneous origin, whereas the surrounding epidote was the product of metamorphism. Granitic gneiss, composed chiefly of sodic plagioclase, microcline and quartz with minor amounts of Mn-rich garnet, biotite, low Si phengitic mica, epidote, chlorite and sometimes amphibole, was formed at 495°C and ∼5 kbar, corresponding to the retrograde metamorphism of UHP rocks. Accordingly, it is believed that granitic gneisses have not experienced UHP metamorphism. This implies that a large scale tectonic juxtaposition developed before the epidote-amphibolite facies retrograde metamorphism of UHP rocks during the late continental collision in Dabie Shan.
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Assadi, Aziza O., Nomo N. Emmanuel, and Yamgouot N. Fadimatou. "Petrogenesis and Tectonic Setting of the Gold-Bearing Magmatic Rocks of the North-Western Melfi Massif, Central Chad." European Journal of Environment and Earth Sciences 3, no. 4 (July 13, 2022): 23–31. http://dx.doi.org/10.24018/ejgeo.2022.3.4.304.
Повний текст джерелаАнотація:
This paper presents petrographic and geochemical data on magmatic rocks of the north-western Melfi massif (part of the Gera Massif at the center of Chad) in the Adamawa-Yadé domain. The study area consists of syenite and granite, all crosscut by minor dykes and quartz veins. Syenite and granite show porphyritic texture and are dominated by K-feldspar and plagioclase phenocrysts, biotite, a variable proportion of quartz, and often few amphiboles. These rocks are characterized by low Mg#, Ni and Co, high K2O, Na2O, LREE/HREE ratio, I-type geochemistry as well as positive Eu anomaly, suggesting an origin from partial melting of crustal rocks (here garnet-amphibolite) and metasomatized mantle-derived component with the input of sediments. The compositional evolution from syenites to granite raises the fractional crystallization process in their petrogenesis and involves the fractionation of amphibole, biotite, plagioclase, apatite, magnetite, and ilmenite. Studied samples are affected by the post-magmatic hydrothermal alteration with an assemblage made of epidote, biotite, sericite, and opaques minerals. In addition, they are characterized by considerable gold concentration (Au = 0.6-3.8 ppm) suggesting that the north-western part of the Melfi massif in the center of Chad is a preferential site of gold mineralization. The K-rich calc-alkaline to shoshonitic geochemistry and the pronounced Nb, Ta, and Ti negative anomalies of these rocks, combined with their high Nb/Ta (7.55-32.10), La/Nb (1.80-11.73), and La/Ta (21.53-376.60) ratios but low Rb (57.60-138.30 ppm) indicate that they are subduction-related or arc-related magmas belonging to the Great Central Gondwana Arc (GCGA) formed further to east-directed subduction direction.
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Soda, Yusuke, Taku Matsuda, Sachio Kobayashi, Motoo Ito, Yumiko Harigane, and Takamoto Okudaira. "Reversely zoned plagioclase in lower crustal meta-anorthosites: An indicator of multistage fracturing and metamorphism in the lower crust." American Mineralogist 105, no. 7 (July 1, 2020): 1002–13. http://dx.doi.org/10.2138/am-2020-7284.
Повний текст джерелаАнотація:
Abstract This paper describes the formation mechanism of reversely zoned plagioclase, which has been observed frequently in lower crustal shear zones and is indicative of multistage fracturing and meta-morphism in the lower crust, by studying the microstructural and chemical characteristics of plagioclase in sparsely fractured anorthosites and anorthositic mylonites from the Eidsfjord shear zone, Langøya, northern Norway. Based on the field relationship between sparsely fractured anorthosite and anorthositic mylonite, the fracturing of anorthosite occurred before the formation of mylonite. In sparsely fractured anorthosites, transgranular fractures are observed; hydration-reaction products, including Na-rich plagioclase, occur within cracks and fractures, suggesting that hydration reactions occurred during or after fracturing. The hydration reactions in sparsely fractured anorthosites are estimated to have occurred at higher-pressure (P) amphibolite-facies conditions (~0.9–1.0 GPa and ~550–700 °C). In anorthositic mylonites, which are considered to have initiated by fracturing and subsequent hydration metamorphism at lower-P amphibolite-facies conditions (~0.7 GPa and ~600 °C), recrystallized plagioclase grains often show compositional zoning with an Na-rich core and a Ca-rich rim. Because the compositions of metamorphic plagioclase grains in the sparsely fractured anorthosites and those of the Na-rich cores of the reversely zoned plagioclase in anorthositic mylonites are similar to each other, the Na-rich cores of the matrix plagioclase in the anorthositic mylonites have recrystallized under higher-P amphibolite-facies conditions and then been overgrown or replaced by the Ca-rich rims under lower-P conditions. Consequently, the reversely zoned plagioclase observed frequently in lower crustal shear zones is an indicator of multistage brittle fracturing and subsequent hydration metamorphism during exhumation, providing information relevant to understanding the deep rupture process caused by repeated seismicity alternating with aseismic creep below the seismogenic zone.
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Swiffa Fajong, Isaac, Marvine Nzepang Tankwa, Donald Hermann Fossi, Sylvestre Ganno, Cyriel Moudioh, Landry Soh Tamehe, Cheo Emmanuel Suh, and Jean Paul Nzenti. "Lithostratigraphy, Origin, and Geodynamic Setting of Iron Formations and Host Rocks of the Anyouzok Region, Congo Craton, Southwestern Cameroon." Minerals 12, no. 10 (September 23, 2022): 1198. http://dx.doi.org/10.3390/min12101198.
Повний текст джерелаАнотація:
In Cameroon, most of the iron formation occurrences reported are found within the Nyong and Ntem Complexes. The Anyouzok iron deposit is located in the Nyong Complex greenstone belts, which represent the NW margin of this Congo craton. The main lithological units comprise the iron formations (IFs) unit, consisting of banded IFs (BIFs) and sheared BIFs (SBIFs), and the associated metavolcanic rocks unit consisting of mafic granulite, garnet amphibolite, and biotite gneiss. Within the Anyouzok area, BIFs are rare, while SBIFs are ubiquitous. This study reports the petrography, mineralogy, and whole rock geochemistry of IFs and interbedded metavolcanic rocks of the Anyouzok iron deposit. The abundance of cavities, higher Fe contents (49.60–55.20 wt%), and strong Eu anomalies (Eu/Eu* = 2.14–3.17) within the SBIFs compared to the BIFs suggest that SBIFs were upgraded through post-depositional hydrothermal alteration activities. REE signatures indicate the contribution of both seawater and hydrothermal fluids during BIFs precipitation. Mafic granulite and garnet amphibolite protoliths were derived from the partial melting of a metasomatized spinel lherzolite depleted mantle source. The overall compositional variations of the Anyouzok IFs and interbedded metavolcanic rocks endorse an Algoma-type formation deposited in the back-arc basin under suboxic to anoxic conditions.
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Holm, P. E., T. E. Smith, B. D. Grant, and C. H. Huang. "The geochemistry of the Turriff metavolcanics, Grenville Province, southeastern Ontario." Canadian Journal of Earth Sciences 22, no. 3 (March 1, 1985): 435–41. http://dx.doi.org/10.1139/e85-042.
Повний текст джерелаАнотація:
Fifty-seven samples of the Turriff metavolcanic sequence from the Hastings region of the Grenville Province have been chemically analyzed. Ten major-element oxides and ten trace-element values for each sample were determined by standard X-ray fluorescence techniques. The sampled sections consist predominantly of mafic flows, subordinate intermediate flows, and minor felsic flows and pyroclastics. The sequence has been regionally metamorphosed to lower amphibolite facies. The geochemical data indicate that the metavolcanics represent a tholeiitic mafic–silicic bimodal sequence. Immobile-element discriminant diagrams indicate that the Turriff metabasalts are most similar to recent oceanic ridge basalts, whereas the metabasalts from other published studies of Grenville metavolcanics have an island-arc tholeiite affinity. However, because of the many chemical similarities between continental and oceanic ridge tholeiites, the bimodal nature of the sequence, and the field relationships, it is most likely that the eruption of the Turriff metavolcanics was associated with the rifting of continental crust, perhaps leading to the development of a marginal sea.
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Hervé, Francisco, Jorge Lobato, Ignacio Ugalde, and Robert J. Pankhurst. "The geology of Cape Dubouzet, northern Antarctic Peninsula: continental basement to the Trinity Peninsula Group?" Antarctic Science 8, no. 4 (December 1996): 407–14. http://dx.doi.org/10.1017/s0954102096000582.
Повний текст джерелаАнотація:
Cape Dubouzet is mainly composed of a volcanic-subvolcanic complex of extrusive rhyolitic breccias, a banded rhyolite and a semi-annular body of dacite porphyry rich in xenoliths of metamorphic rocks. Major and REE geochemistry indicate that the volcanic rocks are calc-alkaline and that they are genetically related by fractional crystallization of a plagioclase-bearing assemblage from a common magma. Rb-Sr data suggest that the rhyolitic complex is of Middle-to-Late Jurassic age, and that it is intruded by Late Cretaceous stocks of banded diorite and gabbro. All these rocks are partially covered by moraines whose clasts are of local provenance. Xenoliths in the dacite porphyry suggest that the northern tip of the Antarctic Peninsula is underlain by a metamorphic complex composed of amphibolites, meta-tonalites and pelitic gneiss containing garnet, sillimanite, cordierite, hercynite, and andalucite. Such rocks are not known in the Scotia metamorphic complex, nor in the Trinity Peninsula Group and its low grade metamorphic derivatives, which also occur as rare xenoliths in the dacite. Previous dating of xenoliths collected from the moraines suggested a late Carboniferous age for this amphibolite-grade metamorphism. Both the Jurassic-Cenozoic magmatic arc of the Antarctic Peninsula and the accretionary complex rocks of the Trinity Peninsula Group were thus developed, at least in part, over pre-existing continental crust.