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1
Colgan, Elizabeth Anne. "Petrogenesis of the Eshowe melilitites." Master's thesis, University of Cape Town, 1992. http://hdl.handle.net/11427/17331.
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Includes bibliography.The Eshowe melilitites intruded marginal cratonic crust at approximately 80my. Their intrusion followed after a long period of extensive rift tectonism associated with the breakup of Gondwanaland. The intrusives represent the final phase of alkaline and basaltic magmatism that commenced at about 200my. This magmatism was probably related to mantle processes responsible for the continental fragmentation and was controlled by a fluctuating mantle thermal regime. The Eshowe melilitites intrude an area of attenuated crust in an essentially rift valley setting. Petrological, and chemical evidence suggest that the Emtilombo melilitite does not represent crystallisation of a primary magma. The magma was generated in the asthenosphere but reacted with incompatible element and probably CO₂ and H₂O enriched lithosphere and perhaps crustal sources on its way to the surface. The Emtilombo melilitite contains microxenoliths of mantle derived spinel peridotite and of a suite of dunitic rocks that are believed to be high pressure cumulates of earlier alkaline magmas. These latter trapped melts would have introduced metasomatising agents into the lithosphere. The dunitic melts are believed to represent earlier intrusions related to the Eshowe alkaline volcanism. The chemistry of the olivine phenocrysts and microphenocrysts and complex zonation patterns on olivine xenocrysts (macrocryst and some complex phenocrysts) suggest the Emtilombo magma formed by mixing of several batches of melt. The 'parental magmas' to the Eshowe occurrences are therefore considered to consist of a mixture of asthenospheric and lithospheric components and a variety of different melts. The 'parental magma' to the Emtilombo dyke was an incompatible element enriched ultramafic melt that contained microxenoliths of spinel lherzolite and the dunitic suite of rocks. Changing oxygen fugacities are believed to be controlled by a loss of volatiles at relatively shallow depths in the mantle or lower crust. These changes are reflected by the spinel chemical trends and perovskite crystallisation. The change occurred after complex zonation patterns had developed on the olivines. The microphenocryst olivines are believed to be the only population of grains that crystallised from the Emtilombo 'parental magma'. Mode of emplacement of the melilitites is probably influenced by the nature and volume of magma in the intrusion, its volatile content, and to some extent the nature of the country rock. The Eshowe melilitites show a wide variety of intrusive modes and also demonstrate how late stage processes, possibly during or post consolidation, influence the geochemistry of the rock type.
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Wang, Yan. "Petrogenesis of permian flood basalts and mafic-ultramafic intrusions in the Jinping (SW China) and Song Da (Northern Vietnam) districts." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B37758743.
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Ozdemir, Yavuz. "Volcanostratigraphy And Petrogenesis Of Suphan Stratovolcano." Phd thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613051/index.pdf.
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This study is concerned with volcanostratigraphic and petrologic evolution of the Süphan, which is a 4050 m high Quaternary stratovolcano in eastern Anatolia. The eruptive products of Sü
phan Stratovolcano, including transitional mildly alkaline to calc-alkaline rocks, are lavas, domes and pyroclastics ranging in composition from basalts to rhyolites. Ar-Ar age data from different levels of the volcanostratigrafic succession yield a range of 0.76-0.06 Ma. Textural features, wide temperature ranges obtained for intermediate members, and the linear trends of whole-rock geochemistry are strongly suggestive of magma mixing in the evolution of Sü
phan volcanics. Presence of crystal clots in many lavas suggests that cogenetic plutonic rocks were also involved in the mixing process. Comparison of whole-rock, melt inclusion and glass chemistry data of Sü
phan to data from experimental studies reported in literature indicate that the melt inclusions describe true liquid lines of descent from a common hydrous parent at pressures of ~500 MPa. EC-AFC modeling of trace element and isotopic compositions reveals 2-8% crustal contamination in the differentiated lavas. REE modeling indicates that primitive rocks of Sü
phan volcanics were products of mixing of melts from spinel and garnet lherzolite sources, with contributions of 60% and 40%, respectively, in the mixture. A two-stage petrogenetic model is proposed for Suphan stratovolcano. Mantle- derived melts stall and undergo chemical differentiation in a deep hot zone in lower to mid-crust
variably evolved melts ascending from this zone are arrested and mixed at a shallow level where they construct a sub-volcanic magma reservoir beneath Suphan.
4
Student, James John. "Silicate Melt Inclusions in Igneous Petrogenesis." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/28719.
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Silicate melt inclusions are ubiquitous in quartz phenocrysts, yet there are few studies of such inclusions from porphyry copper systems. A melt inclusion forms when magma is trapped in a growing phenocryst. If a phenocryst is able to preserve the original parent magma, then accurate information can be obtained for ancient volcanic systems. In recent igneous systems, melt inclusions are commonly preserved as optically clear homogeneous glass representative of magma stored at depth before eruption. Melt inclusions are difficult to recognize in quartz phenocrysts from porphyry copper system because they are crystalline and hidden by exsolved magmatic volatiles. The inclusions range in size from less than 5 to over 150 μm. In order to evaluate the magmatic contribution to economic mineralization, we conducted three separate studies to determine whether or not crystallized melt inclusions preserve representative samples of magma.
The first study modeled the phase relationships that occur during equilibrium crystallization and melting of haplogranite magma trapped in quartz. Results from the model are similar to observations made during the heating of crystallized melt inclusions from porphyry copper systems. It is necessary to re-melt the crystal and volatile phases before chemical analysis. Micro-explosions caused by heating resulted in the loss of important chemical components. Our second study evaluated several microthermometric heating procedures using synthetic melt inclusions trapped at conditions similar to those inferred for porphyry copper systems. A synthetic hydrous melt was saturated with saline hydrothermal solutions allowing both melt and aqueous fluids to be trapped in quartz. Based on microthermometric measurements from these coeval melt and aqueous fluid inclusions we were able to predict the known trapping temperature and pressure of formation. This technique can be applied to natural samples to constrain trapping pressures and temperatures. It was found that slower heating rates could be used to avoid overheating and that heating under a confining pressure greatly minimizes the decrepitation of inclusions.
The third study examined the copper concentrations in melt inclusions from the Red Mountain, Arizona porphyry copper system. Older andesite magma contains pyroxene with melt inclusions of higher copper concentrations compared to melt inclusions in quartz from quartz latite. The higher water concentrations in crystallized melt inclusions in the quartz, and abundant aqueous fluid inclusions indicates that the exsolution of water from the magma occurred prior to the trapping of melt inclusions in quartz. The lower water concentrations and the absence of aqueous fluid inclusions indicates that the andesite never reached the stage of water exsolution. The results obtained here are consistent with models that suggest that copper is extracted from the melt by saline magmatic fluids, producing a metal-charged hydrothermal solution and leaving behind a metal-depleted melt and serves to identify the potential contribution of melt inclusion studies to constrain the origin of ore metals in porphyry copper deposits.Ph. D.
5
Jurinski, Joseph B. "Petrogenesis of the Moosehorn igneous complex, Maine." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-04072010-020130/.
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Brown, Elizabeth Ann. "Rhyolite Petrogenesis at Tower Mountain Caldera, OR." PDXScholar, 2017. https://pdxscholar.library.pdx.edu/open_access_etds/3997.
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Tower Mountain Caldera is the main feature of an Oligocene volcanic field located in the Umatilla National Forest, eastern Oregon. It is perfectly suited to investigate models of rhyolite petrogenesis as all of the important rock components for evaluating generation models are present in a single location and thus are presumably related; basalts, intermediate igneous rocks (which consist of older plutons and younger volcanic rocks, which are ~coeval with rhyolites), metamorphic basement rocks of significant grade, and rhyolites of varying composition. The formation of the caldera produced the Dale Tuff, which comprises the intra-caldera and outflow facies. 40Ar/39Ar dating places the age of the tuff at 32.66 ± 0.36 Ma. Post-caldera rhyolites erupted along apparent ring fractures and elsewhere. Radiometric U-Pb dating of zircons from three of these rhyolites yielded ages of 32.167 ± 0.020 Ma (#CH07a), 31.798 ± 0.012 Ma (#TM5), and 31.426 ± 0.016 Ma (#CH08a). All rhyolites at Tower Mountain range from low to high silica varieties. Some of the post-caldera rhyolites are chemically similar to the Dale Tuff, such as sample CH07a, and have compositions typical of rhyolites of calc-alkaline volcanic centers (I-type rhyolites), while others are similar to A-type rhyolites (CH08a and TM5). The ages indicate that the calc-alkaline rhyolites were followed by the A-type rhyolites. The petrogenetic relationships between the various rocks types were evaluated. Partial melt modeling based on experimental melts produced from crustal material indicates that batch partial melting of metamorphosed high silica crustal material modified by the addition of more primitive mafic material by assimilation/contamination is the most likely source for the Tower Mountain rhyolites.
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Wallace, Graeme M. B. "Petrogenesis of the McGerrigle plutonic complex, Gaspe, Quebec." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63877.
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Shaw, Andrew. "The petrogenesis of Hercynian granites, French massif central." Thesis, Birkbeck (University of London), 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397092.
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Becker, Mona Louise. "Petrogenesis of the Springfield Granodiorite, southeast Pennsylvania Piedmont." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-05092009-040419/.
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Wood, Patricia Ann. "Petrogenesis of the Spruce Pine pegmatites, North Carolina." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-08222008-063320/.
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Paterson, Bruce Andrew. "Accessory mineral growth histories : implications for granitoid petrogenesis." Thesis, University of St Andrews, 1990. http://hdl.handle.net/10023/11059.
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Accessory minerals in granitoids are major repositories of several geochemically-important trace elements and isotopes and in order to quantify the influence that they have over granitoid petrogenesis it is necessary to characterize fully their behaviour. In particular it is necessary to understand accessory mineral/melt partitioning of trace elements and within grain elemental diffusivities, the latter is of relevance when assessing the state of isotopic equilibration between a refractory accessory phase and a contacting melt. In this study the backscattered electron (BSE) imaging technique, coupled with quantitative electron microprobe analysis indicate that granitoid zircons and titanites (mainly taken from Caledonian intrusive complexes) are commonly compositionally zoned. The zoning textures observed in these minerals, namely crystal face-parallel zoning, non-planar compositional zoning (included here are subhedral and anhedral core structures) and compositional sector zoning, indicate that the kinetic factors of crystal growth, i.e. within magma elemental diffusion rates, crystal growth rates, interface kinetics and dissolution kinetics, are largely responsible for the patterns of compositional zoning that have been observed. This fording is in marked contrast to other studies which have assumed that kinetics are not important in crystallizing plutonic granitoid magmas. Accessory mineral growth histories have been studied in a few well constrained samples from the Caledonian-age Strontian Complex of NW Scotland. The zircons from the central intrusion of this composite pluton have abundant inherited cores. The cores contain a variety of zoning structures and have a wide range of composition, which are taken to indicate that the cores had a wide variety of ultimate sources. Titanites from both the outer and inner intrusions have compositional sector zoning and the range of composition shown by the titanites is largely due to this fact. In this pluton magma composition appears to have little influence on titanite chemistry. The REE abundances in both parts to the intrusion are largely controlled by the accessory phases and each of these phases have very different rock-normalised REE distribution patterns. These abundance patterns are dependent on the relative partition coefficients that each phase has for the REE, the accessory mineral assemblage present and the crystallization order of that assemblage. The zircons from the central acid member of the Strontian Complex, which are known to have substantial U-Pb inheritance were extracted and analysed for their Sm-Nd isotopic composition. The results apparently indicate that refractory zircons can also preserve their Sm-Nd isotopic composition, a phenomenon not previously reported. That is diffusion of Sm and Nd (and presumably the other REE) within refractory zircon at elevated temperatures appears to be sufficiently slow that complete isotopic equilibration between a zircon and a contacting melt may not always occur. Such disequilibrium potentially enables granitoid magma provenance to be studied with much greater resolution than hitherto possible.
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Mensing, Teresa Marie. "Geology and petrogenesis of the Kirkpatrick Basalt, Pain Mesa and Solo Nunatak, Northern Victoria Land, Antarctica /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu14873326364761.
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Badger, Robert L. "Geochemistry and petrogenesis of the Catoctin Volcanic Province, central Appalachians." Diss., This resource online, 1989. http://scholar.lib.vt.edu/theses/available/etd-03042009-041139/.
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Therriault, Ann Marie. "Petrogenesis of the Sudbury Igneous Complex: The shocking story." Thesis, University of Ottawa (Canada), 2001. http://hdl.handle.net/10393/6378.
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The Sudbury Structure, Ontario, is the remnant of a 1.85 Ga old impact crater, 200--250 km in diameter. Erosion and tectonism have affected the Sudbury Structure and resulted in considerable brittle and ductile deformation, and the removal of the surface expression of the crater structure and all exterior deposits typical of many terrestrial impact structures. However, substantial amounts of the interior deposits, including the craterfill products, have been preserved within the Sudbury Basin. Although most workers acknowledge an impact origin for the Sudbury Structure, the origin of the Sudbury Igneous Complex (SIC), located inside the Sudbury Structure, remains controversial. The objectives of this study are to elucidate the division of the SIC into lithologically separate phases and to understand their relation to impact and endogenic igneous processes by using physical, chemical and computer methods, and to model the genesis of the SIC. The SIC is a 2.5--3.0 km thick, ∼60 x 27 km elliptical igneous-rock body, consisting of four major lithologies (top to base): granophyre, quartz gabbro, norite, and the so-called contact sublayer. All these lithologies are continuous across the complex, except for the contact sublayer. Modal compositions reveal that the current nomenclature is improper. According to the IUGS classification, "quartz gabbro" samples should be classified as quartz monzogabbros and "norite" samples as quartz gabbros or quartz monzogabbros. In view of these observations, an updated terminology is proposed (top to base): upper unit, transition zone, middle unit, lower unit, and contact sublayer. Gradational mineralogical and geochemical variations between the SIC lithological units are evidence of a single melt system for the SIC. The occurrence of primary hydrous minerals, deuteric alteration, and abundant micrographic and granophyric intergrowths demonstrate that this melt was rich in H 2O. The intergrowths and other far-from-equilibrium textures are likely due to rapid crystallization as a result of a large undercooling caused by the exsolution of a volatile phase. The SIC differs from other known terrestrial impact melt sheets only by its great thickness and its chemical layering. It is concluded that the SIC is a differentiated impact melt sheet, the only one identified on Earth to date.
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Roopnarain, Sherissa. "Petrogenesis of Carbonatites in the Alnö Complex, Central Sweden." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-215436.
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The Alnö Complex is a Late Precambrian alkaline and carbonatite intrusion (c. 30km2) into Early Proterozoic country rock that extends from the north east, to the north western shoulder of Alnö Island. Carbonatites are rare among volcanic provinces, with Oldoinyo Lengai of northern Tanzania being the only active carbonatite volcano in the world today. The high carbonate mineral volumes and rare earth element (REE) concentrations of carbonatites, in combination with the intrusive-extrusive nature of their suites contribute to the rarity of these rocks. Carbonatites, through their peculiar petrological and geochemical compositions, provide vital insights to the composition and condition of the Earth’s mantle. The genesis of the Alnö carbonatites and their relation to other lithological units at the complex is however, only partially understood. This stems from the epistemological division of carbonatites as having either a ‘magmatic’ or ‘reactive’ origin. This study focuses on sampled carbonatites from the Alnö Complex, employing an oxygen and carbon isotope approach on their native calcite, complemented with petrological and mineralogical methods in order to constrain petrogenesis. As a reference, oxygen and carbon isotope data of calcite from an earlier Alnö investigation as well as from an array of data from comparative alkaline complexes elsewhere are also discussed. The combined data and the derived findings support a scenario that is consistent with the ‘magmatic’ model wherein carbonatites have a primary mantle-derived origin, and prospectively stem from a parent magma akin to that of Oldoinyo Lengai, but have experienced a degree of silicate and sedimentary assimilation. The extraction of the Alnö carbonatites for their rare earth metals is a looming possibility due to the current volatility in the rare earth market. The risks and opportunities involved in this kind of natural resource extraction provide a context wherein sustainable development paradigms can be applied. The capacity of the Alnö environment to withstand the impact of development in the mining sector is discussed through a perspective of establishing a quarry, and quarry-related methods for rare earth extraction.
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Aboazoum, Ali Saleh Ali. "Petrogenesis of Palaeocene granites, Island of Skye, N.W. Scotland." Thesis, University of Glasgow, 1995. http://theses.gla.ac.uk/6432/.
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This thesis documents an investigation of selected intrusions of the Palaeocene granites on the Isle of Skye, and includes: petrography, mineral chemistry (include REE concentrations) fluid inclusions, whole rock major-, trace- and rare-earth-elements, together with stable oxygen and hydrogen and Sr-Nd isotope geochemistry on whole rocks and mineral separates. The data presented indicate that the granites are geochemically related and have been severely affected by 'associated' hydrothermal fluid(s), especially the Loch Ainort Granite. The hydrothermal fluids most likely represent the limited mixing between magmatic and meteoric waters in Beinn an Dubhaich Granite. In contrast, the other granites are likely to have been affected by meteoric water alone, with water-rock interaction having occurred below 500°C.The coarsening of granophyric texture outwards from alkali feldspar phenocrysts, the low concentration of Fe3+ in pyroxenes, together with the slight variations in Fe2+: Mg ratio of biotites, suggest a slow cooling history for the granites. The (two feldspar) Beinn an Dubhaich and Glamaig granites have small negative Eu anomalies compared with the (single feldspar) Loch Ainort and Marsco granites, suggesting the important role of plagioclase fractionation during granite evolution. The most important reservoirs for the REE in the Skye granites are amphibole, pyroxene and apatite. The inflection present in the plot of MnO against SiO2, the non-linear and divergent relationships between K2O, Rb, Sr and ?Nb against SiO2, and the presence of an anomalous group of granites which are characterised by low Zr, Y and Nb, but with high SiO2 contents, mitigates against simple mixing as the dominant process responsible for the compositional diversity of the granites.
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Parkinson, Ian J. "Geochemistry and petrogenesis of forearc peridotites, ODP Leg 125." Thesis, Durham University, 1993. http://etheses.dur.ac.uk/5637/.
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ODP Leg 125 recovered peridotites from Conical Seamount in the Mariana forearc and Torishima Forearc Seamount in the Izu-Bonin forearc. The peridotites recovered comprise about 95% harzburgites and about 5% dunites, which are variably serpentinised (mostly 60-100%). The Leg 125 peridotites represent some of the first extant peridotites recovered from a forearc selling. A detailed petrographic, mineral and bulk-rock chemical study of the peridotites has been undertaken in order to elucidate information about melting and fluid processes in the forearc mantle wedge. The harzburgites are highly refractory in terms of their mineralogy and geochemistry. They have low modal clinopyroxene, highly magnesian olivine (Mg# = 91.1-93.6) and orthopyroxene (Mg# = 91.6-93.2) and chrome-rich spinels (Cr# = 60-80) and very low incompatible element contents (Ti <80 ppm). Furthermore they are more refractory than the most depleted abyssal peridotite, which suggests that the harzburgites can be interpreted as residues to extensive partial melting (>20%). The Ti concentrations in the clinopyroxene indicate that the harzburgites are residues to -25% fractional melting. However, petrographic and other geochemical information show that the Leg 125 harzburgites have had a complicated melting and enrichment history. Many samples have olivine fabrics which are interpreted as having formed beneath a spreading ridge. Orthopyroxenes have lobate grain boundaries often associated with fresh olivine neoblasts. This texture is interpreted as showing the incongruent melting of orthopyroxene, a process which happens at low pressures (-3 kb) and high water pressures. These two types of textures indicate that the peridotites have had a two stage melting history. Moreover, the V concentrations in the clinopyroxenes can be explained by -15% partial melting at low oxygen fugacities (FMQ-1), followed by 5- 10% melting at high oxygen fugacities (FMQ+1). Oxygen thermobarometry calculations are in accordance with the peridotites last equilibrating under oxygen fugacities of greater than FMQ+1.The bulk-rocks have chondrite-normalised REE patterns showing extreme U-shapes with [La/Sm](_N) ratios in the range 5.03-250.0 and [Sm/Yb](_N) ratios in the range 0.05 to 0.25; several samples have possible small positive Eu anomalies. On extended chondrite-normalised plots the bulk-rocks also show enrichments in Sr and Zr relative to their neighbouring REEs and are enriched in LREE, Rb, Cs, Ba, Sm, and Eu relative to abyssal peridotites. Covariation diagrams based on clinopyroxene data show that Sr, Ce, Nd, Sm, Eu and Zr are enriched in the clinopyroxenes and that the enrichment took place during or after melting. The enrichment component is most likely a melt derived from the underlying subduction zone. A multistage melting and enrichment model is proposed for the peridotites where they first melt 10-15% beneath a spreading ridge. The resulting depleted spinel Iherzolite is enriched and then melted again 10- 15% above the subduction zone to produce the spatially associated boninites. A final enrichment event takes place during and after this melting event to produce the characteristic trace element enrichments in the Leg 125 peridotites.
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Smith, T. P. L. "Petrogenesis of a composite Hercynian pluton, Santa Eulalia, Portugal." Thesis, University of Reading, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233641.
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Humphreys, Madeleine Clare Sperryn. "Andesite petrogenesis and magmatic processes at Shiveluch Volcano, Kamchatka." Thesis, University of Bristol, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425118.
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Hickmott, Donald Degarmo. "Trace element zoning in garnets--implications for metamorphic petrogenesis." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14743.
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Pattison, David R. M. "Petrogenesis of pelitic rocks in the Ballachulish thermal aureole." Thesis, University of Edinburgh, 1985. http://hdl.handle.net/1842/15601.
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Ilbeyli, Nurdane. "Petrogenesis of collision-related plutonic rocks, central Anatolia(Turkey)." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4889/.
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Central Anatolia exhibits good examples of calc-alkaline and alkaline magmatism of similar age in a collision-related tectonic setting (continent-island arc collision). In the Central Anatolia region, post-collisional plutonic rocks (around 79.5 to 66.6 Ma) intrude Palaeozoic-Mesozoic metamorphic rocks overthrust by Upper Cretaceous ophiolitic units to make up the Central Anatolian Massif. In the Massif, three different intrusive rock types are recognised based on their geochemical characteristics: (i) calc-alkaline (Behrekdag, Cefalikdag, Celebi-BCC); (ii) transitional (Baranadag-B); and (ii) alkaline (Hamit-H). The BCC and B plutonic rocks are metaluminous, I-Type ranging from monzodiorite to granite. The H plutonic rocks are metaluminous to peralkaline, predominandy A-Type ranging from nepheline monzosyenite to quartz syenite. Two types of igneous enclave have been recognised in the BCC plutonic rocks; (i) fine-grained (Type-I); and (ii) medium-grained to porphyritic with feldspar megacrysts (Type-II). Field, petrographic and geochemical evidence suggest that the Type-I enclaves originated from injection of mafic magma into more silicic magma. Field, petrographic and mineralogical evidence together with major and trace element geochemistry suggest that the Type-II enclaves formed as cumulates of early-crystallised minerals (e.g. clinopyroxene, plagioclase, amphibole and biotite) from the granitoid magmas. All intrusive rocks show enrichment in LILE and LREE relative to HFSE and have high (^87)Sr/(^86)Sr and low (^143)Nd/(^144)Nd ratios. These characteristics indicate an enriched mantle source region(s) carrying a subduction component inherited from pre-collision subduction events. Rb, Nb, Y versus SiO(_2) diagrams and the tectonic discrimination diagram of Rb and the (Y+Nb) suggest that the BCC, B and H plutonic rocks have been affected by crustal assimilation combined with fractional crystallisation processes. Coexistence of calc-alkaline and alkaline magmatism in the Central Anatolian Massif has been attributed to mantle source heterogeneity before collision. Either thermal perturbation of the metasomatised lithosphere by delamination of the thermal boundary layer (TBL) or removal of a subducted plate (slab breakoff) are the likely mechanisms for the initiation of the post-collisional magmatism in the Massif.
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Severs, Matthew Jeremiah. "Applications of Melt Inclusions to Problems in Igneous Petrogenesis." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/28310.
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Understanding the different igneous processes that magmas undergo is important for a variety of reasons including potential hazards associated with volcanoes in populated regions, magmatic hydrothermal ore deposition, and tectonic processes. One method of obtaining geochemical data that can help constrain petrogenetic processes is through the study of melt and fluid inclusions. The research presented here examines melt inclusions through experimental, analytical and field studies to better understand igneous petrogenesis.
One potential problem associated with melt inclusions is water-loss during laboratory heating. A Raman spectroscopic technique was developed to determine water contents of silicate glasses, and this technique was applied to monitor water loss from natural melt inclusions that were heated for varying lengths of time. The results suggest that water loss is insignificant when heated for less than 12 hours but significant water loss can occur with longer duration heating.
The distribution of trace elements between silicate melts and phenocrysts growing from that melt can constrain igneous processes such as fractional crystallization, assimilation, and partial melting. Partition coefficients were determined for syngenetic clinopyroxene, orthopyroxene, and plagioclase in equilibrium with a dacitic melt using the Melt Inclusion-Mineral (MIM) technique. Melt inclusion chemistry is the same regardless of mineral host phase, suggesting that the melt inclusions have not been subjected to re-equilibration processes or boundary layer development. Partition coefficients from this study are similar but typically lower than published values.
Three closely-spaced monogenetic eruptive units from the active Campi Flegrei volcanic system (Italy) with similar eruptive styles were examined to better understand the evolution of the magmatic system. Results suggest fractional crystallization as the dominant process taking place over time but that magma mixing was significant for one of the eruptions. Trace element geochemical data suggest a mixed magma source of within-plate and volcanic arc components, and still retain a T-MORB signature from the subducting slab.Ph. D.
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Allen, Charlotte M. "Petrogenesis of the reversely zoned Turtle pluton, Southeastern California." Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54480.
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Few plutons with a reversed geometry of a felsic rim and mafic core have been described in the geologic literature. The Turtle pluton of S.E. California is an intrusion composed of a granitic rim and granodioritic core and common microgranitoid enclaves. Field observations, mineral textures, and chemistries, major and trace element geochemistry, and isotopic variability support a petrogenetic model of in situ, concomitant, magma mixing, and fractional crystallization of rhyolitic magma progressively mixed with an increasing volume of andesitic magma, all without chemical contribution from entrained basaltic enclaves. Hornblende geobarometry indicates the Turtle pluton crystallized at about 3.5 kb. A crystallization sequence of biotite before hornblende (and lack of pyroxenes) suggests the initial granitic magma contained less than 4 wt% H₂0 at temperatures less than 780°C. U-Pb, Pb-Pb, Rb-Sr and oxygen isotope studies indicate the terrane intruded by the Turtle pluton is 1.8 Ga, that the Turtle pluton crystallized at 130 Ma, that the Target Granite and garnet aplites are about 100 Ma, and that these intrusions were derived from different sources. Models based on isotopic data suggest the rhyolitic end member magma of the Turtle pluton was derived from mafic igneous rocks, and was not derived from sampled Proterozoic country rocks. Similarity of common Sr and Pb isotopic ratios of these rocks to other Mesozoic intrusions in the Colorado River Region suggest the Turtle pluton and Target Granite have affinities like rocks to the east, including the Whipple Mountains and plutons of western Arizona. P-T-t history of the southern Turtle Mountains implies uplift well into the upper crust by Late Cretaceous time so that the heating and deformation events of the Late Cretaceous and Tertiary observed in flanking ranges did not affect the study area.Ph. D.
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Elliott, Timothy Richard. "Element fractionation in the petrogenesis of ocean island basalts." Thesis, Open University, 1991. http://oro.open.ac.uk/57323/.
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Analytical techniques have been developed to measure the very small [230ThP32Th] atomic ratios (3-8x10-6) typical of basaltic lavas using a single focussing mass spectrometer. Compared to conventional alpha-counting methods, the technique presented typically gives a 2-5 fold improvement in reproducibility of 230 Th/232Th ratios, and furthermore uses -5x less sample, has a simpler chemical prepartion and a data aquisition time -100x shorter. The above technique was used in investigating a suite of historic (< 1000a) basanites from La Palma, Canaries. The lavas have undergone significant post melt segregration processes, involving residence in deep (>4kbar) magma chambers, that are inferred to persist for at least 30ka. The basanites show geochemical variations related to differences in the degree of partial melting, that are estimated to be between 0.3-2%. Rare earth element (REE) modelling suggests clinopyroxene, rather than garnet control during melting, contrary to expectations from recent geophysical models (McKenzie & O'Nions, in press). The La Palma mantle source is inferred to be LREE enriched, K& Rb depleted, and shows many incompatible element ratios characteristic of 'himu' basalts (Weaver 1991). In contrast, the 206pb/204pb ratios of the La Palma basanites (19.6±0.05) are lower than the isotopically defined'high p' basalts (Zindler & Hart 1986) which suggests that the La Palma source is geochemically similar, but younger than a typical 'high t' source. A suite of young (< 10,000a) high MgO tholeiites from Iceland show order of magnitude variations in highly incompatible element concentrations that correlate with FeO contents. Variations within these lavas is primarily attributable to sampling of instantaneous melts from different depths within a dynamic melting column. However, additional correlations of radiogenic isotope ratios with major and trace element contents highlights mixing of various plume melts with some 20% mid-ocean ridge basalt, derived from melting of upper mantle material entrained during plume upwelling.
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Davies, Marc Kerry. "The origin and petrogenesis of the Ethiopian flood basalts." Thesis, Open University, 2008. http://oro.open.ac.uk/54645/.
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The volcanic rocks of the Afro-Arabian volcanic province chart the nature and evolution of the mantle plume source responsible for a major continental flood basalt event and the manner in which it interacted with the lithosphere over the course of continental separation. The flood basalts of the Ethiopian Plateau constitute the larger part of this province and are associated with melting in the head of the Afar Plume. High-Ti picrites from the eastern part of the NW Plateau are among the earliest uncontaminated outpourings of flood volcanism; their compositions are therefore considered to be close to that of the primary melt. These are exposed in a stratigraphically coherent sequence with variably porphyritic high-Ti olivine-rich basalts and ankaramites, which together provide a continuous record of volcanism reflecting a transition from high- to low-flux magmatism. Phase-relations differ fromthose in other tholeiitic flood basalts in that clinopyroxene and magnetite crystallisebefore plagioclase. This is typical of ferropicrites and reflects a high-Fe-Ti-, and low AI-source. The olivine phenocrysts exhibit a range of morphologies and compositions which reflect fractionation and magma-mixing at varying depths prior to eruption, and the introduction of water into the magmas at shallow levels is evident from pervasive iddingsitization. The lavas have similar major element chemistry to MORB but show higher concentrations of incompatible elements inherited from a HIMU-type lithospheric component. and enrichments in LREE relative to HREE which reflect the presence of residual garnet in the source. The picrites and ankaramites have lower AI2O3 and higher K2O, P2O5, TiO2 and Fe2O3(tot) contents than any reported lavas with equivalent MgO content from other flood basalt provinces. These least evolved lavas were derived from oxidised (QFM+1), deep-seated magmas generated by different degrees of partial melting of the primary melt, whereas the olivine basalt magmas evolved by crystal fractionation at a shallow level from a melt similar in composition to the ankaramites. The MgO content of the primary melt calculated from the most Mg-rich olivines (Fo90) is between 17 and 18 %, and it is likely that this ponded at the base of the crust where it evolved at pressures near to 1.2 GPa. Primary melt fractions of 3 - 6 % were generated in the plume at pressures of 4 - 5 GPa and temperatures in excess of 1600 °C, implying that melting occurred beneath thick (120- 150 km) lithosphere prior to extension. Sub-chondritic initial 187Os/188Os ratios (0.125 - 0.126) indicate derivation from a depleted mantle source, and high 3He/4He (18.6 Ra) and solar-like Ne isotopic ratios imply an origin in undegassed mantle.
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Kwiecien, William. "The geology, geochemistry and petrogenesis of the Monsildale granodiorite." Thesis, Queensland University of Technology, 1996. https://eprints.qut.edu.au/36947/1/36947_Kwiecien_1996.pdf.
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Monsildale Granodiorite is a small (36 km2 ) Permo-Triassic intra-terrane composite pluton intruding sediments of the Early Permian Marumba Beds of the North D'Aguilar Block in the Central New England Orogen. It comprises two phases, an older and more felsic northern phase and a younger more mafic southern phase. Geochemistry and geochronology indicate the pluton formed by at least 5 time-separated magmatic events.
The southern phase comprises gabbro (14%), diorite (26%) and granodiorite (60%), with a temporal interval from gabbro (245±3 Ma), diorite (234 ±3 Ma) to granodiorite (232 ±3 Ma). Trace element geochemistry clearly supports a polymagmatic origin for the southern phase intrusion as the data define separate and unique trend lines for each of the rock types. Major element variation diagrams show diorite and granodiorite plot along a well defined curve with a strong calc-alkalic differentiation trend but diorite data are consistently more scattered. In marked contrast, gabbros plot as a discrete population characterised by a pronounced scatter, a feature which largely reflects their cumulate nature.
Textural features and geochemistry indicate the southern phase gabbro samples are largely cumulate fractionates and do not represent a fractionating magma. A low 87 Sr/86Sr ratio of 0.703279 (2 cr = ±0.0015), a 143Nd/144Nd ratio 0.512866 (2 cr = ±0.0017) and low Rb abundances ( < 2 - 35 ppm) indicate the Monsildale gabbro was derived from a depleted mantle source without significant crustal contribution during emplacement. Hornblende geobarometry indicates gabbro crystallised at pressures ranging from 5.56 - 3.21 kilobars. All gabbros are depleted in Nb(< 2-4 ppm) and Zr (19-58 ppm) and are enriched in LIL elements relative to MORB, signatures which are characteristic of a volcanic arc environment. Low abundances of incompatible high field strength elements, low rare earth element (REE) abundances and a relatively small degree of light REE enrichment are all indicative of a tholeiitic source. It is proposed the tholeiitic gabbros formed in response to rifting associated with the Esk Trough formation.
Southern phase diorite and granodiorite display a typical calc-alkalic differentiation trend, but trace element data clearly contrast different fractionation trends shown by diorite and granodiorite and indicate the two rock types are not genetically related. Major and trace element geochemistry indicate they both formed in a volcanic arc environment. Emplacement of southern phase diorite at 234 ±3 Ma and granodiorite at 232 ±3 Ma corresponds to a crustal compressional event in the North D'Aguilar Block in the Middle Triassic interval from 240 Ma to 230 Ma. Diorite and granodiorite are postulated to have formed by partial melting of an enriched crustal source rather than a depleted mantle source which is considered responsible for the tholeiitic gabbros. Variation in chemical composition of diorite is predominantly attributed to fractional crystallization of clinopyroxene, plagioclase and biotite. Variation in chemical composition of granodiorite is attributed to fractional crystallization of hornblende, plagioclase and biotite. Hornblende geobarometry indicates diorite crystallised at pressures ranging from 1.25 to 0.28 kilobars and granodiorite crystallised at lower pressures ranging from 1.2 kilobars for the most mafic rocks to 0.13 kilobars for the most felsic rocks.
The older northern phase is predominantly granite-granodiorite (95%) with minor diorite, quartz diorite, tonalite (4.5%) and very minor gabbro (0.5%). Gabbro, diorite and granodiorite from the northern phase are geochemically and petrographically distinct from the southern phases. Granodiorite (253 ±3 Ma) from the northern phase is peraluminous, ilmenite-bearing and has higher Fe2+fFe3+ ratios than the southern phase granodiorite which is metaluminous and magnetite-bearing. Biotite contains up to 0.09% atoms Al per 22 oxygen atoms in 6-fold coordination, a feature of S-type granites. Low strontium levels discriminate between all northern phase rocks ( < 300 ppm) and southern phase rocks (400-1200 ppm). Hornblende and biotite are iron-rich in the northern phase granodiorite and magnesium-rich in southern phase granodiorite.
The emplacement of northern phase granodiorite at 253 ±3 Ma corresponds to a crustal contraction event in the North D'Aguilar Block as evidenced by the shallow to moderate westward dipping Claddagh Thrust (::::: 260 Ma). The peraluminous nature of these ilmenite-bearing reduced rocks (high Fe2+/Fe3+ ratios) is interpreted to reflect a supracrustal or sedimentary protolith. They formed as a result of crustal contraction in the Mid-to Late Permian.
Trace element geochemistry indicates the northern phase gabbro, diorite and granodiorite may be genetically related. All rocks from the northern phase have undergone extensive cataclastic deformation.
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Babu, E. V. S. S. K. "Petrological studies on the Chimakurti gabbro-anorthosite-olivine-clinopyroxenite complex and its contact aureole, India." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243040.
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Costa, Felipe Grandjean da. "Petrogenese do granodiorito Fazenda Gavião : registro de uma colisão arco-continente no greenstone belt do Rio Itapicuru, Craton do São Francisco, Bahia." [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/287283.
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Orientador: Elson Paiva de OliveiraDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociencias
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Resumo: O greenstone belt do Rio Itapicuru é uma seqüência vulcano-sedimentar paleoproterozóica cortada por uma série de corpos plutônicos com idades entre 2160-2070 Ma. O Granodiorito Fazenda Gavião (GFG) é um corpo intrusivo em metabasaltos da porção ocidental do greenstone, próximo ao contato com o embasamento arqueano. Este pluton tem textura fanerítica média e hornblenda como mineral máfico dominante. Uma característica de campo é a presença de enclaves máficos magmáticos e diques máficos sinmagmáticos com evidências da mistura física de magmas (magma mingling). A analise geoquímica classifica o Granodiorito Fazenda Gavião como uma rocha intermediária (SiO2~63 wt%), com composição de granodiorito a quartzo-monzodiorito, da série cálcioalcalina de médio a alto-K, metaluminoso, espectro Terras Raras fracionado (razão (La/Yb)N = 22.81), alto Sr (900-800 ppm), alto Ba (1000-1500 ppm), e alta razão Sr/Y. Comparando com a geoquímica de outros plutons da área, o GFG apresenta assinatura dos elementos traço similar aos plutons alcalinos, sugerindo uma provável ¿consangüinidade¿ magmática entre estes plutons. A característica geoquímica dos diques máficos (appinitos) associados ao GFG é similar ao granodiorito em questão, porém com uma maior abundancia em Ba, Sr, MgO, Ni, Cr, K2O, e Terras Raras leves, sugerindo que estes diques são originados da fusão parcial de uma fonte mantélica enriquecida. O GFG apresenta semelhanças com rochas adakíticas e plutons TTGs, mas diferente destas rochas, apresenta maior conteúdo em K2O. É possível que o GFG foi originado pela fusão parcial de crosta máfica (crosta inferior?) (com granada e sem plagioclásio no resíduo) em função do acúmulo de magma máfico na base desta crosta (underplating of mafic magmas). O magma félsico gerado, provavelmente se misturou com uma pequena porcentagem do magma máfico, como é sugerido pelas feições de magma mingling observadas em campo. O GFG com idade de 2106 + 6 Ma (U-Pb SHRIMP em zircões) é mais jovem do que o magmatismo TTG/cálcio-alcalino (2163-2127 Ma) e é contemporâneo ao magmatismo potássicoultrapotássico (ca. 2110-2105 Ma) presente no contato embasamento-greenstone. O modelo de evolução geológica desenvolvido nesta dissertação sugere que os plutons ricos-em-K do greenstone belt do Rio Itapicuru são o registro da colisão de um arco oceânico com uma margem continental em ~2110-2105 Ma, precedendo outro evento colisional com retrabalhamento crustal em ~2080-2070 Ma
Abstract: The Rio Itapicuru greenstone belt is a gold-bearing Palaeoproterozoic volcanic-sedimentary sequence intruded by several granitic plutons in the time interval 2160-2070 Ma. The Fazenda Gavião granodiorite (FGG) is one of a set of plutons emplaced along the western boundary of the greenstone belt with the Archaean basement complex. The FGG is largely composed of a homogeneous coarse-grained hornblende granodiorite, occasionally crosscut by appinitic mafic dykes. Minor mafic enclaves and amphibolite xenoliths are common close to the contact with the host metabasalts. The FGG is a metaluminous medium-K to high-K calc-alkaline body with relatively constant silica abundances (SiO2 ~ 63-66 wt %). It shows fractionated REE patterns (LaN/YbN ~22), high Sr (900-800 ppm), high Ba (1000- 1500 ppm), and high Sr/Y ratios. Comparing with the geochemistry of other plutons of the area, the trace elements signature of the FGG suggests a probable magmatic consanguinity between this pluton and the alkaline plutons of the area. Similar geochemical characteristics of the FGG are observed in the associated appinitic dykes, which show relatively higher abundances of Ba, Sr, MgO, Ni, Cr, K2O, and the light rare earth elements, suggesting they derived from partial melts of an enriched mantle source. The FGG shares several geochemical characteristics with adakites and TTG plutons, but unlike these series it shows relatively higher K2O abundance. It is suggested here that the FGG originated from partial melts of the mafic lower crust (with garnet and no plagioclase in the residue) possibly triggered by underplating of mantle-derived, enriched mafic magmas, of which the appinitic mafic dykes may be a representative remnant. The granitic melt mixed with minor amounts of the appinitic magma, as suggest by magma mingling. The 2106 + 6 Ma-old (UPb SHRIMP in zircons) FGG is younger in age than the early (2163-2127 Ma) TTG/calcalkaline arc plutons of the greenstone, and is close-related in time to the young potassicultrapotassic plutons (ca. 2110-2105 Ma) emplaced along the basement-greenstone boundary. We suggest that the K-rich plutons in the Rio Itapicuru greenstone belt are the records of island arc-continent collision at ~2110-2105 Ma, preceding major continental rework and collision at ~2080-2070 Ma
Mestrado
Geologia e Recursos Naturais
Mestre em Geociências
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Chan, Heung Ngai. "Petrogenesis and tectonic evolution of Yarlung Tsangpo ophiolites, south Tibet." Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491339.
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Ophiolite complexes emplaced onto the Indian passive margin sequence in southwest Tibet represent the largest thrust sheet of the Neo-Tethyan oceanic crust and mantle that is preserved along the Yarlung Tsangpo Suture Zone (YTSZ). Field observations, petrological, geochemical and geochronological studies have revealed the supra-subduction zone (SSZ) type ophiolitic rocks formed in two different time frames, c. 127-124 Ma and c. ?4 Ma. The Early Cretaceous suite comprises voluminous mantle rocks, with subordinate mafic and ultramafic intrusions, while plutonic rocks are exposed locally. A shear zone complex probably representing a transform fault zone is also present. Geochemical analysis shows that the crustal rocks evolved from MORB-like to IAT to boninitic magmatism. The Late Cretaceous suite is represented by limited exposures of basaltic lavas, which have MORB-like geochemical compositions. Petrographic and geochemical evidence indicates that the majority of the mantle rocks are residues after extraction of MORB-type magma, which subsequently reacted with boninitic melts in a SSZ. Sub-ophiolite melange zones contain diverse rock types set in a serpentinte or mudstone matrix. Amongst a variety of lithologies, mid Jurassic and mid Cretaceous radiolarian cherts are exposed. Alkaline seamount volcanic rocks of inferred mid Cretaceous age were also found interbedded with cherts or overlain by limestones. Ophiolitic tholeiitic rocks were also included in the melange zones, two of which have 4°Ar_39Ar whole rock ages of c. 86 and 106 Ma. Evidence from the ophiolites and associated melange zones suggests that an intra-oceanic subduction zone initiated in the Early Cretaceous in this part of Neo-Tethyan Ocean. This SSZ system continued at least for c. 40 Ma, from the Early Cretaceous to Late Cretaceous.
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DesRoches, Valérie. "Petrogenesis of the pyroxenite units in the Muskox intrusion, N.W.T." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=22495.
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The layered series of the Muskox Intrusion can be divided into four megacyclic units on the basis of field mapping, each beginning with a thick olivine cumulate and succeeded up section by a variety of pyroxenitic and gabbroic cumulates. A systematic change in the order of appearance of orthopyroxene in the pyroxenite units of the layered series is correlated with a decrease in Mg no. (Mg/Mg + $ Sigma$Fe in cation units) at which clinopyroxene joins olivine on the liquidus, and spike-like increases in LIL/HFS ratios, which require that the composition of the magma of the Muskox Intrusion changed through time across the layered series. Mixing of residual liquid with primary liquids replenishing the chamber can explain the upsection decrease in the Mg no. of clinopyroxene at the base of successive pyroxenite units, but this mechanism cannot account for increased ratios of LIL to HFS incompatible elements observed in the olwebsterite of Megacycle #3 and the first websterite of Megacycle #4, because these ratios are not significantly fractionated by closed-system crystal fractionation. Contamination of the parental magma with melts from the paragneiss country rocks can reproduce the observed increase in the ratios of K/Ti and K/Zr. The gabbroic layers of Megacycle #1, #2, and #3 are especially enriched in LIL/HFS ratios, indicating the presence of a highly contaminated magma layer above the uncontaminated magma which crystallized much of the ultramafic series. The spike-like enrichment in LIL/HFS ratios in the pyroxenites suggests that episodic events of mixing occurred between an evolving uncontaminated magma and a highly contaminated magma, accumulated at the roof of the magma chamber.
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Cadman, Andrew Christopher. "The petrogenesis and emplacement of Proterozoic dyke swarms in Labrador." Thesis, University of Leicester, 1992. http://hdl.handle.net/2381/34998.
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The Archaean Hopedale Block, in the southern Nain Province of Labrador, Canada, is host to three generations of mafic intrusions of Proterozoic age; the 2.2 Ga Kikkertavak, the 1.6 Ga Kokkorvik and the 1.3 Ga Harp dyke swarms. Also present are two ultrabasic dyke types: firstly pyroxenites interpreted as coeval with the Kikkertavak swarm, and secondly 'high titanium dykes' with opaque-rich compositions of uncertain age. Many Kikkertavak (and Harp) intrusions show highly differentiated phyric textures attributed to rhythmic changes in flow conditions during solidification. Modelling of intradyke geochemical variation shows this can be largely correlated with phenocryst differentiation processes. Other textures indicate more extreme flow variations associated with composite intrusion. Analysis of Kikkertavak dyke morphologies and measurements of magma palaeo-flow directions using anisotropy of magnetic susceptibility suggests that the crack propagation direction during dyke emplacement may be decoupled from the preserved flow direction. However similar measurements on the Kokkorvik sheets suggests that decoupling does not occur in shallow-angle intrusions. Approaching the southern boundary of the Hopedale Block, Kikkertavak dykes show increasing tectonic, petrographic and geochemical alteration. The principle effects are mobile element depletion and redistribution, notably on the dyke margins. Fractional crystallisation, crustal contamination and partial melting processes alone are inadequate at explaining primary geochemical variation in both Kikkertavak and Harp swarms. Instead variation occurs mainly due to the melting of heterogeneous mantle sources. The iron-rich compositions of many Kikkertavak dykes is postulated to result from the underplating into the subcontinental mantle during subduction of mafic ocean plateau material. The geochemical signature of many Harp dykes may result from mixing with similar iron-rich mantle sources with alkaline partial melts added to the continental lithosphere. The geochemistry and emplacement style of other Proterozoic dyke swarms suggest that the mafic underplating model may be more generally applicable.
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Hodges, Sean Patrick. "Petrogenesis of the phonolitic rocks of the Velay oriental, France." Thesis, University of Oxford, 1991. http://ora.ox.ac.uk/objects/uuid:1d8c0fe8-9f9e-4348-9c4c-21174aa56e70.
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The Velay oriental (Massif Central, France) is a basaltic plateau with abundant viscous phonolite extrusions. The plateau lavas grade from alkali basalt to mugearite, but intermediate compositions are volumetrically scarce. Pyroclastics are absent. The most complete plateau sections are in the south, while in the north intermediate lavas appear only as viscous, phenocryst-rich extrusions. The plateau lavas were erupted between 11.7Ma and 7.6Ma, the southern phonolites 8.5Ma- 6.5Ma and new data show that the northern phonolites were erupted between 13.3Ma and 10.5Ma. Basement uplift occurred during the plateau-building stage, due to the emplacement of magma chambers. Intermediate lavas are scarce because they remained in the magma chambers due to their density, whereas phonolite was able to rise hydrostatically. The magma chambers were within 5km of the surface. Phonolites are divided into miaskitic and agpaiitic types on the basis of their chemistry and petrography. They evolved from the basalt by crystal settling in the magma chambers, whereas the aphyric plateau lavas evolved by plating crystals onto their conduit walls as they flowed towards the surface. Sr-isotopes show that the basalt-phonolite series is uncontaminated, whereas the northern intermediate lavas evolved by assimilation-fractional-crystallisation. A suite of cumulate nodules was recovered from a pyroclastic unit, which is probably younger than the Velay Miocene lavas. They are related to the northern intermediate lavas, and belong to the "Group II" class of nodules. Geothermobarometry suggests that both the cumulates and the northern intermediate lavas crystallised at a depth of 15-20km and probably became contaminated due to the smaller temperature difference between the geotherm and granite solidus at that depth. The vast majority of the Velay lavas are identical to alkalic ocean-island lavas, geochemically unaffected by their passage through the lithosphere, but with their relative proportions at the surface controlled by the density contrast between the basalt and basement granite.
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Aldanmaz, Ercan. "Petrogenesis of Late Cenozoic collision volcanism in Western Anatolia, Turkey." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4658/.
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Western Anatolia exhibits a record of almost all stages of a collision event and its related magmatic processes. Following an Eocene continent-arc collision, Western Anatolia region experienced a complete cycle of thickening and orogenic collapse. The early stage of collision- related volcanism, which was most evident during the Early Miocene (<21 Ma), produced a considerable volume of lavas and pyroclastic deposits covering a broad compositional range from basaltic andesites to rhyolites. The volcanic activity continued into the Middle Miocene with a gradual change in eruptive style and rock compositions. The Middle Miocene activity, formed in relation to localised extensional basins and was dominated by lava flows and dykes of basalts to andesites composition. Both the Early-Middle Miocene rocks have calc-alkaline and shoshonitic character. The late stage volcanism, from 11.0 to 8.3 Ma, was marked by alkali basalts and basanites erupted along the localised extensional zones. The Early-Middle Miocene volcanic rocks exhibit enrichment in LILE and LREE relative to the HFSE (characterised by negative Nb and Ta anomalies) and are characterised by high (^87)Sr/(^86)Sr and low (^143)Nd/(^144)Nd (-ɛno) ratios. These characteristics indicate a mantle lithospheric source region carrying a subduction component inherited from a pre-collision subduction event. Perturbation of this subduction-metasomatised lithosphere by delamination of the thermal boundary layer is the likely mechanism for the initiation of the post-collision magmatism. Trace elements systematics suggest that the Early-Middle Miocene series underwent a hydrous crystallisation (dominated by pargasitic amphibole) in deep crustal magma chambers. Subsequent crystallisation in shallower magma chambers follows two different trends: (1) anhydrous (pyroxene + plagioclase-dominated; and (2) hydrous (edenitic amphibole + plagioclase + pyroxene dominated).Trace element and isotope modelling shows that the Early-Middle Miocene rocks have been affected by assimilation combined with fractional crystallisation processes, and that the effects of assimilation decrease gradually from the Early Miocene into the Middle Miocene. This indicates a progressive crustal thinning related to the extensional tectonics that prevailed from the latest Early Miocene onwards. In contrast to the Early-Middle Miocene rocks, the Late Miocene alkaline rocks are characterised by low (^87)Sr/(^86)Sr and high (^143)Nd/(^144)Nd (+ɛnd) ratios and have OIB-type like trace element patterns characterised by enrichment in LILE, HFSE and L-MREE, and a slight depletion in HREE, relative to the N-MORB compositions. REE inversion modelling indicates that these rocks formed by partial melting (with degrees of ~2 to -10%) of a spinel + garnet Iherzolite source. Trace element and isotopic systematics are consistent with decompression melting of an enriched mantle asthenospheric source.
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Moodley, Jason Anthony. "Petrogenesis of the Bysteek and Koenap Formation Migmatites, Central Namaqualand." Thesis, Rhodes University, 2013. http://hdl.handle.net/10962/d1001574.
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The Mesoproterozoic rocks of the Bysteek and Koenap Formations of the Arribees Group are exposed within a NW-SE striking antiformal structure comprised of mafic granulites and metapelitic diatexites, and a number of marble and calc-silicate rock layers. The mafic granulites of the Bysteek Formation show a typological variety of anatectic features, including nebulitic, stromatitic mesosomes, melanosomes, quartz syenitic leucocratic vein networks and syenitic pools. Melanosomes consist of hedenbergitic to diopside-rich clinopyroxene (XMg: 0.40), anorthitic plagioclase (An90), with some quartz, minor apatite and titanite. Anatexis was caused by biotite dehydration melting and formed a melt of probably granitic composition. The leucosome composition ranges from either alkali-feldspar-granitic to plagioclase rich or granitic. This variation is interpreted as a result of variable extraction of melt from the source to granitic pools. The diatexites of the Koenap Formation are most likely of metapelitic or meta-greywacke origin. They are texturally variable but always contain high modal contents of alkali feldspar and quartz which generally form magmatic textures. Almandine-rich garnet (XMg: 0.18-0.25), cordierite (XMg: 0.71) form secondary biotite, sillimanite and magnetite during retrograde breakdown. Thermodynamic modelling of mafic granulite compositions suggests peak P-T conditions of ~865 °C and 8.6 kbar. Occasionally, garnet rich in ferric iron (XAdr: 0.55) forms by plagioclase-clinopyroxene breakdown under oxidising conditions at ~6 kilobar and ~ 800 °C. At the same stage amphibole forms in some melanosomes. P-T estimations for the diatexites based on thermodynamic modelling suggest the equilibration of the assemblage garnet, cordierite, alkali feldspar and melt at ~860 °C and 5.5 kbar. Conditions comparable to the peak pressure in the mafic granulites could not be established. However, since the diatexites and the mafic granulites are closely related in the field and no evidence of juxtaposition after the thermal peak exists, the P-T record of the diatexites might be incomplete
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Corbett, Helen Elizabeth. "Petrogenesis of the Tusas Mountain Granite, north-central New Mexico." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1343318854.
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Lewis, C. L. E. "Petrogenesis and thermal history of the Kunlun batholith, northern Tibet." Thesis, Open University, 1988. http://oro.open.ac.uk/54368/.
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The Kunlun Terrane is the most northerly of the several microplates that comprise the Tibetan Plateau. Geochronological data from the Kunlun batholith defines three distinct periods of intrusion at 390 Ma, 250 Ma and 190 Ma. A model is presented whereby the Devonian intrusions are considered to be related to a collision event between the Kunlun and Tarim Terranes, which were part of Gondwanaland and situated in the southern hemisphere at this time. It is proposed that in the region of the 1985 Tibet Geotraverse route, the Golmud Fault represents the Kunlun- Qinling suture line along which the two plates collided. Break-up of this part of Gondwanaland, which proabably also included the Qiangtang, Lhasa and Indian plates, occurred during the Permian along the Zangbo and Jinsha suture lines. Continental rifting was followed by a prolonged period of northward subduction of the Qiangtang Terrane beneath the Kunlun Terrane. This resulted in formation of the Permian batholith, and the massive Songban-Ganzi accretionary prism. Subduction culminated in collision at about 200 Ma. Post tectonic granites were emplaced around 190 Ma. Initial Sr ratios for the granitoids range from .7074 to .7130, and support the geochemical modelling which suggests that they have been derived from melting midcrustal sources. Only the Devonian Wanbaogou pluton may have resulted from anatexis of upper crustal sediments. A reset biotite age of 120 Ma from a pluton cut by the Xidatan Fault, supports sedimentalogical evidence which indicates a major reactivation of thrust faults in the area, as a result of collision between the Lhasa and Qiangtang Terranes during the Cretaceous. Apatite fission track ages from plutons north of the Golmud Fault also document this uplift event. A 100 Ma period of quiescence ensued, during which the Kunlun Terrane cooled extremely slowly until a state of thermal equilibration was reached. The collision of India with Tibet at 45 Ma thickened the Tibetan crust and resulted in further reactivation of faults in the Kunlun Terrane. Apatites from the granites between the Golmud and Xidatan faults give mixed ages around 20 Ma. It is calculated that uplift in this region, as a result of the Himalayan collision, could have been as recent as 8 Ma.
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Seligman, Angela. "Oxygen and hydrogen investigation of volcanic rocks: Petrogenesis to paleoclimate." Thesis, University of Oregon, 2016. http://hdl.handle.net/1794/20547.
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Knowledge of the isotopic evolution of volcanic eruptions is essential to volcanologists, geochemists, and paleoclimatologists. I isotopically evaluate the evolution of magmas from their initial formation, to eruption, and then to their alteration during the diffusion of environmental waters into volcanic glass. I focus first on the formation and evolution of large, caldera-forming eruptions from both Gorely volcano in Kamchatka, Russia and 30–40 Ma caldera forming eruptions through Oregon in the United States of America. I utilize oxygen (δ18O), hafnium (εHf), strontium (87Sr/86Sr), and neodymium (143Nd/144Nd) isotopes to document the creation of caldera-forming eruptions at these eruptive centers through the melting of surrounding crust. I also use U-Pb and 40Ar/39Ar to document the timescales of the formation of these large-volume silicic eruptions.
Following eruption, the volcanic glass in tephra and ash can slowly take in environmental water. It is thought that the hydrogen isotopic ratio (δD) of these waters can be used to determine paleoenvironments from the time that the volcanic glass was deposited. The latter portion of my dissertation focuses on the use of hydrogen isotopes of environmentally hydrated volcanic glass to determine paleoenvironments, and the calibration of the TCEA to analyze oxygen isotopes of hydrated volcanic glass. I first focus on the rate of diffusion of water at ambient temperature to better understand the time frame necessary to hydrate volcanic glass for use as a paleoenvironmental indicator. I also document the hydrogen isotopic ratios that result from the diffusion of water into volcanic glass, which is documented as a decrease in δD with an increase in secondary hydration in all regions worldwide except equatorial. Finally, I focus on the earliest stages of diffusion of water into volcanic glass by analyzing tephra deposits that were collected within days of the 1980 eruptions of Mount St. Helens as well as tephra deposits recently collected in 2015 to identify changes in water concentration and hydrogen isotopic ratios over an ~35 year period.
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Essex, Richard M. "Age and petrogenesis of the Striped Rock granite pluton : Blue Ridge province, southwestern Virginia /." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-03302010-020037/.
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Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992.3 maps in back pocket. Vita. Abstract. Includes bibliographical references (leaves 83-89). Also available via the Internet.
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Ruggiero, Alberto. "A unidade Maria Preta : geologia, geoquimica e petrogenese de rochas vulcanicas e sub-vulcanicas intermediarais a felsicas no "Greenstone Belt" do rio Itapicuru, Bahia." [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/287255.
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Orientador: Elson Paiva de OliveiraDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociencias
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Resumo: Novos dados geoquímicos nas rochas vulcânicas andesíticas e dacíticas da Unidade Maria Preta (UMP), Greenstone Belt do Rio Itapicuru, revelaram a presença de dois grupos geoquímicos distintos: um de rochas com afinidade adakítica e outro com caráter cálcio-alcalino. A suíte adakítica (ADK), localizada nas porções oeste da UMP, é caracterizada pelos altos valores de Sr/Y (Sr ~900 ppm, Y~5ppm); Na2O ~ 4,5ppm (K2O/Na2O ~0,3). É caracterizada também pelo enriquecimento de LILE (elementos litófilos de alto raio iônico) relativos aos HFSE (elementos de elevado potencial iônico) e também pelo moderado fracionamento dos elementos terras-raras (La/Yb ~ 12). A suíte cálcio-alcalina (CA) apresenta baixas razões Sr/Y (Sr ~ 170 ppm, Y~ 22 ppm), menor fracionamento de elementos terras-raras (La/Yb ~8) e anomalias negativas de Eu. No entanto apresenta maiores concentrações de elementos incompatíveis (Y ~22ppm, Zr ~142ppm, Th ~6ppm) e também Cr e Ni. Foi revelado, através de modelagem geoquímica que as duas suítes não se relacionam por cristalização fracionada. Contudo a suíte Adk apresenta indícios de cristalização fracionada de hornblenda enquanto que na CA a cristalização fracionada de plagioclásio desempenhou papel importante. O ambiente mais provável para a formação das rochas vulcânicas cálcioalcalinas é fusão em baixas profundidades da cunha do manto metassomatizado por fluídos liberados a partir de uma crosta oceânica subductada, seguida por fracionamento de plagioclásio. A geoquímica dos adakitos requer fusão de meta-basaltos hidratados em pressões elevadas, onde granada+hornblenda são estáveis e constituem o restito da fusão. Em geral, as rochas adakíticas apresentam indícios de pouca interação do magma original com uma coluna de manto peridotitico, como visto em adakitos atuais, dados os baixos valores de Cr e Ni em relação aos adakitos cenozóicos. A suíte cálcio-alcalina apresenta menores valores de fugacidade de oxigênio no sítio de extração do magma (entre -3 e -1 FMQ). Ao contrário, os adakitos apresentam maiores valores (entre -1 e +0,5 FMQ), semelhantes aos valores encontrados em adakitos modernos formados por fusão de crosta oceânica subductada. Dados de isótopos de Sm-Nd forneceram idades modelo TDM para a suíte adakítica de 2.213 a 2.010 Ma, com valores de eNdT de +3,9 a +1,7. A suíte cálcio-alcalina revelou idades modelo mais antigas, entre 2.330 e 2.279 Ma e menores valores de eNdT de +0,7 a + 1,3. Estes valores indicam magmatismo juvenil para ambas as suítes, porém com maior tempo residência crustal para a fonte das rochas cálcio-alcalinas, ou interação do magma com crosta mais antiga. Datação U-P SHRIMP em andesito adakítico revelou idade de cristalização de 2.081 ±9 Ma e a presença de zircões herdados arqueanos (3364, 3017, 3064 Ma), evidenciando que o magma gerado em zona de subducção interagiu com crosta arqueana, provavelmente o embasamento do Greenstone Belt do Rio Itapicuru, sugerindo então um provável arco continental como origem da Unidade Maria Preta. Esses dados sugerem que o vulcanismo intermediário a félsico do Greenstone Belt do Rio Itapicuru foi formado ou teve relação direta com subducção. Esta possivelmente teve uma vergência de leste para oeste, evidenciada pela zonalidade na geoquímica das rochas vulcânicas (adakitos à oeste e cálcio-alcalinas a leste).
Abstract: New geochemical data on andesites and dacites of the Maria Preta Unit, Rio Itapicuru Greenstone Belt, revealed two distinct geochemical groups: one of adakitic affinity and another of typical calc-alkaline. The adakitic suite, localized west in the unit, is characterized by high values of Sr/Y and Ti/YN >1. It shows enrichment in LFSE (Low Field Strength Elements) relative to HFSE (High Field Strength Elements) and a moderate rare earth element fractionation. The calc-alkaline suite (CA) shows low Sr/Y ratios, less rare earth elements fractionation and negative Eu anomalies. On the other hand it shows higher incompatible elements abundances (Y, Zr, Th) and high Cr and Ni concentrations. The two suites cannot be linked by fractional crystallization and are derived from different sources (distinct initial Nd ratios). The most probable setting for the formation of CA is partial melting of mantle peridotite modified by hydrous fluids released from a subducting slab, followed by low pressure plagioclase fractionation. The adakite geochemical features require partial melting of hydrous metabasalts at depths high enough to stabilize garnet+hornblende as the residual phase. This suite does not reveal significant interactions with the mantle, as shown by its lower Cr and Ni values than Cenozoic adakites. For an assumed 2170 Ma age, the Sm-Nd isotope data show higher eNd(t) for the adakites (+4,8 to +2,5) than for the calc-alkaline suite (+1,9 to +1,4). These data indicate a juvenile source for the UMP volcanic rocks. U-Pb SHRIMP dating indicates a crystallization age of 2,081 ± 9 Ma for the adakitic volcanic. Inherited Archean zircons (3364, 3017, 3064 Ma) evidence a magma generated at a subduction zone followed by interaction with Archean lithosphere, probably the basement of the Rio Itapicuru Greenstone Belt. The calc-alkaline suite shows low oxygen fugacities at the magma extraction site (between -3 e -1 FMQ). On the other side, the adakites shows higher values (between -1 e +0,5 FMQ), similar to modern adakites formed by a subducting slab melt. This results suggests that the UMP volcanism was formed or was directly connected to a subduction. The geographic position of the two suites, i.e. adakites to the west of the calc-alkaline volcanics, suggests subduction of an oceanic plate to the west.
Mestrado
Geologia e Recursos Naturais
Mestre em Geociências
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Pembroke, James William. "The recognition and significance of magma mixing in granites." Thesis, Oxford Brookes University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364075.
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Skae, Andrew. "The petrology of the Buckland volcanic province, Central Queensland, Australia." Thesis, University of Oxford, 1998. http://ora.ox.ac.uk/objects/uuid:e2a73f94-5e7b-4c3e-98e5-bd052dbf3205.
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Brown, P. J. "Petrogenesis of Ni-Cu ore bodies, their host rocks and country rocks at Selebi-Phikwe, Eastern Botswana." Thesis, University of Southampton, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381153.
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Fraser, K. J. "Petrogenesis of kimberlites from South Africa and lamproites from Western Australia and North America." Thesis, Open University, 1987. http://oro.open.ac.uk/54611/.
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Group 2 kimberlites from South Africa, and lamproites from Western Australia and North America are relatively unfractionated mantle-derived igneous rocks, situated on or close to ancient cratonic areas. They are characterised by high trace element contents, while the range in N d and Sr isotopes encompasses much of that reported for various upper and lower crustal rocks. It is argued that these features are not due to crustal contamination during magma ascent, rather they are source and extraction phenomena. The mantle source regions of these rocks were ancient (~ 1.0 to 2.5 Ga) and variably trace element enriched. Preservation of such regions within the mantle is most probable in the relatively 'cold' and 'rigid' subcontinental mantle lithosphere, which is believed to have been isolated from the convecting asthenosphere for a long time. The source regions of the kimberlites and lamproites were situated at various depths within the subcontinental mantle lithosphere, from within the amphibole stability field « 100 km) to within the diamond stability field (> 150 km). Low degrees of partial melting « 1 %), together with volatile composition and depth of melting, have significantly influenced the composition of the resultant kimberlite and lamproite magmas. Those magmas that originated from within the diamond stability field contain abundant entrained and dis aggregated mantle peridotite. This feature is related to melt migration and rapid ascent to the surface, from these mantle depths. The Sr, Nd and Pb isotope data record evidence of variable, but related trace element enrichment styles. The origin of these trace elements is either from recycled continental crust (e.g. pelagic sediment), or from intra-mantle processes (e.g. the migration and crystallisation of small volume silicate melts with variable volatile compositions). The available data are insufficient to determine between the models and further work in this area is required.
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Patridge, Karyn Ann. "Geochemistry and petrogenesis of John Day ash flows near Prineville, Oregon." Pullman, Wash. : Washington State University, 2010. http://www.dissertations.wsu.edu/Thesis/Spring2010/k_patridge_042110.pdf.
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Thesis (M.S. in geology)--Washington State University, May 2010.Title from PDF title page (viewed on July 9, 2010). "School of Earth and Environmental Sciences." Includes bibliographical references (p. 105-117).
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de, Oliveira Elson Paiva. "Petrogenesis of mafic-ultramafic rocks from the Precambrian Curaca terrane, Brazil." Thesis, University of Leicester, 1990. http://hdl.handle.net/2381/35079.
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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.
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Jobin-Bevans, L. Scott. "Geology, mineral chemistry and petrogenesis of the Pipestone Lake anorthosite complex." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq23356.pdf.
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Liu, Mian. "Migmatization and volcanic petrogenesis in the La Grande greenstone belt, Quebec." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63353.
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Ward, Susan E. "The petrogenesis of the Mesoproterozoic mafic dykes and sills of Zimbabwe." Thesis, University of Portsmouth, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.444475.
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The assembly of the Mesoproterozoic super-continent Rodinia of southern Africa is evidenced by the fonnation of supracrustal belts and related granitic magmatism mainly between 1400 and 900 Ma and known collectively throughout Africa as the Kibaran event. As these new crustal segments were being fonned, the ancient cratons were flexed and, in some regions, fractured. The associated intracratonic mafic magmatism is preserved as mafic dyke swanns in certain parts of southern Africa. Three dyke swarms, namely the Kamativi, Mutare and Guruve are believed to be of "Kibaran" age (although their age constraints are, as yet, unknown). The Umkondo sills are also of Kibaran age having been dated at 1105 ± 2Ma. The geochemistry of these three dyke swanns indicates that whilst they are ostensibly unremarkable continental tholeiites, they do in fact comprise dykes of rather different compositions. Three distinct subgroups are identified within the Kamativi dykes, six subgroups within the Mutare dykes and six subgroups within the Guruve dykes. The recognition of these subgroups suggests that the term "swarm" cannot be used when referring to these intrusive suites until the age constraints of the different subgroups within a suite are defmed. The Umkondo sills have a unifonn geochemistry and are very different and easily recognisable from the older (~1.8 Ga) Mashonaland sills in that they have a higher Si02 content, lower Fe203 and Ti02, content with lower TilZr and TiN ratios than the Mashonaland sills. The differences in the geochemistry of the Kamativi, Mutare and Guruve subgroups and the Umkondo sills has led to the recognition of three distinct magma types. A relatively enriched, high-Ti source termed type I, a depleted low-Ti source tenned type II and type III which is a relatively depleted low-Ti source with selective trace element, subduction-related enrichment. The similarities between the type III dykes and the Umkondo sills indicate a craton-wide igneous event with melting from similar source mantle compositions. Distinct plume characteristics are not found within the geochemistry of the Zimbabwe intrusives, but this does not necessarily preclude a plume source. Crustal contamination may overprint plume signatures and result in the increase 87Sr/86Sr and corresponding decrease in 144Ndl143Nd ratios as seen in these dykes. As collisional tectonics along the western and southern margins of the Kalahari craton are indicated in the Namaqua-Natal Belt of South Africa, compressional stresses along the southern and western margins of the Kapvaal craton may have caused extension within the Zimbabwe craton. This resulted in the upwelling of hotter mantle material which induced melting of the subduction modified SCLM. This research has shown the importance of the geochemistry of dykes, in establishing whether they constitute separate "swanns", or relatively small batches of melt from different sources intruded penecontemporaneously.
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Mason, Paul Robert David. "Petrogenesis of subduction-related magmatic rocks from the East Carpathians, Romania." Thesis, Birkbeck (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307401.
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