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Teng, Fang-Zhen. "Lithium isotopic systematics of the continental crust." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/3215.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Geology. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Souquière, François. "Mechanics of earthquakes in the continental crust." Besançon, 2010. http://www.theses.fr/2010BESA2047.
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This thesis aims at deciphering the complex and polyphase seismic deformation associated with two major pseudotachylyte-bearing fault zones, the pre-mesozoic Outer Hebrides Fault (OHF) in northwest Scotland, and the Mesozoic to Cenozoic Canavese fault zone and adjacent Ivrea zone in the Italian Alps. For both areas, the deformation was analysed from the field scale to scanning electron microscope scale to scanning electron microscope scale. In addition, Ar:Ar absolute dating was performed on Italian pseudotachylytes. The first part of this thesis shows that the OHF in the south Uist-Barra area is clearly segmented: the northern Stulabhal segment is characterized by quartz-feldspar gneisses (QF gneisses) in the foot wall and by two –pyroxene gneisses (Corodale gneisses) in the hanging-wall. The southern Eriskay segment is characterized by QF gneisses both in the hanging wal. Moreover, the Stulabhal segment is underlined by a continuous and mappable, several meters thick, pseudotachylyte sole at the base of the hanging wall, and by diffuse pseudotachylyte fault vein in the footwall, while the Eriksay segment consists of several faults outlined by pseudotachylyte-rich zones whose thickness never exceeds 1 m. […]In the second part of this thesis, we clarify the spatial and temporal distribution of pseudotachylyte in the Val Sesia area of the Ivrea zone. Pseudotachylytesin the Balmuccia periotite tectonic lens were formed during at least two periods:before Permian times and lateCretaceous to Tertiary. Pseudotachylytes in gabbroic rocks are randomly distributed over two-kilometrer-wide belt and were formed in the early Cretaceous. Pseudotachylytes in paragneisses distributed near the Canavese fault were formed in Eocene Times and are probably related to the thrusting of the Sesia zone over the Ivrea zone. This polyphase formation accompanied the exhumation of the Ivrea crust. […] This comparative analysis between the two fault zones brings information pertaining to the mechanical behavior of the continental crust.
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Ma, Xiaofei. "USArray Imaging of North American Continental Crust." DigitalCommons@USU, 2017. https://digitalcommons.usu.edu/etd/6904.
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The layered structure and bulk composition of continental crust contains important clues about its history of mountain-building, about its magmatic evolution, and about dynamical processes that continue to happen now. Geophysical and geological features such as gravity anomalies, surface topography, lithospheric strength and the deformation that drives the earthquake cycle are all directly related to deep crustal chemistry and the movement of materials through the crust that alter that chemistry.
The North American continental crust records billions of years of history of tectonic and dynamical changes. The western U.S. is currently experiencing a diverse array of dynamical processes including modification by the Yellowstone hotspot, shortening and extension related to Pacific coast subduction and transform boundary shear, and plate interior seismicity driven by flow of the lower crust and upper mantle. The midcontinent and eastern U.S. is mostly stable but records a history of ancient continental collision and rifting.
EarthScope’s USArray seismic deployment has collected massive amounts of data across the entire United States that illuminates the deep continental crust, lithosphere and deeper mantle. This study uses EarthScope data to investigate the thickness and composition of the continental crust, including properties of its upper and lower layers. One-layer and two-layer models of crustal properties exhibit interesting relationships to the history of North American continental formation and recent tectonic activities that promise to significantly improve our understanding of the deep processes that shape the Earth’s surface. Model results show that seismic velocity ratios are unusually low in the lower crust under the western U.S. Cordillera. Further modeling of how chemistry affects the seismic velocity ratio at temperatures and pressures found in the lower crust suggests that low seismic velocity ratios occur when water is mixed into the mineral matrix, and the combination of high temperature and water may point to small amounts of melt in the lower crust of Cordillera.
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Lancaster, Penelope Jane. "Secular evolution of the continental crust through detrital zircon." Thesis, University of Bristol, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.529845.
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Spencer, Christopher J. "Generation and preservation of continental crust in collisional orogenic systems." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/11966.
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The continental crust is the archive of Earth history. Much of what we know about the development of Earth is learned from the continental crust, and it is within the crust that many natural resources are found. Hence, understanding its formation and evolution is a key aspect to a deeper knowledge of the Earth system. This thesis is a study of the processes that have formed and shaped the distribution of continental crust, with specific focus on crustal development associated with the Rodinian supercontinent and the Grenville Orogeny spanning ca. 1200 to 900 Ma. Specifically it addresses an aspect of the incompleteness of the record of continental crust formation. The preserved continental crust is punctuated with periods of lesser and greater frequency of geologic features, e.g., the temporal distribution of the ages of mineral deposits, juvenile granitoids, eclogites, granulites, and the U-Pb crystallization ages of zircons now preserved in modern and ancient sediments (see Gastil, 1960; Barley and Groves, 1992; Condie, 1998; Campbell and Allen, 2008; Brown, 2007; Bradley, 2011). In addition, interpretive features in the geologic record also have an apparent episodic distribution such as passive margins (Bradley, 2011) and supercontinents (Condie, 1998). The episodic nature of these geologic phenomena implies either an episodic formation or preferential preservation of continental crust. These two end member models have been explained through a number of geologic processes such as eruption of superplumes, global disruption of thermal structure of the mantle, assembly of supercontinents, collisional orogenesis. Through the chapters outlined below, this thesis explores the connection of these episodic geologic events with key isotopic signals, principally U-Pb, Hf, and O isotopes in zircon supplemented by sedimentology, structural geology, and igneous geochemistry. It comprises a series of chapters developed around manuscripts prepared for publication.
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Bauer, Ann M. Ph D. Massachusetts Institute of Technology. "Archean continental crust formation and the rise of atmospheric oxygen." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113798.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017.Page 376 blank. Cataloged from PDF version of thesis.
Includes bibliographical references.
This thesis examines critical aspects of the terrestrial environment that have resulted in a habitable planetary surface: the establishment of the continental crust and the progressive rise of an oxygenated atmosphere. The volume of continental crust on the earliest Earth is a critical parameter for constraining the chemical evolution of major terrestrial reservoirs, and radiogenic isotope signatures document this varying geochemical character. Chapter 1 presents a Lu-Hf and U-Pb isotopic characterization of zircons from the 4.0-2.9 Ga Acasta Gneiss Complex (AGC) and documents the magmatic extraction history of this domain, including changes in source compositions. These results are compared with a complementary dataset obtained using solution methods in Chapter 2. The integration of these results demonstrates the utility of performing coupled solution- and laser-based analyses on the same zircon populations to parse out U-Pb and Lu-Hf systematics. Zircons from many of these orthogneisses exhibit isotopic complexity due to the combined effects of accumulated radiation damage and repeated metamorphic episodes. For this reason, it is best to subsample zircon grains to isolate domains of distinct age and isotopic composition. In order to obtain suitable precision for subsampled domains, it was necessary to develop analytical techniques (Chapter 3) suited to small-volume analysis of the U-Pb and Lu-Hf isotope systems in zircon (via both laser ablation and solution analysis). In contrast to the whole rock Nd isotopic record of the AGC, the zircon Hf isotopic record does not indicate that rocks within the AGC were derived from a strongly depleted mantle. In order to evaluate the polymetamorphic evolution of these rocks, in Chapter 4 1 present a combined U-Pb and Sm-Nd isotope and trace element study of MREE-rich accessory minerals. In Chapter 5, I investigate sedimentary pyrite formation pathways and the oxygenation history of the late Archean atmosphere using combined sulfur and iron isotope signals as recorded in distinct morphologies of pyrite. This work represents a critical step in deconstructing the pathways of S-MIF production, transfer and preservation in the sedimentary record. Collectively, these studies contribute to our understanding of the establishment and evolution of the early continental crust and an oxygenated atmosphere.
by Ann M. Bauer.
Ph. D.
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Dougherty-Page, Jon Stanley. "The evolution of the Archaean continental crust of Northern Zimbabwe." Thesis, Open University, 1994. http://oro.open.ac.uk/54877/.
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Granitoid clasts preserved in Late Archaean conglomerates indicate the presence of continental crust in Northern Zimbabwe prior to the ≈ 2.7 to ≈ 2.6Ga "event" which terminated with the stabilisation of the Zimbabwe Craton. The "Kober Technique" (Kober, 1986, 1987) of direct thermal ionisation of zircons has been set up in order to investigate the geochronological record preserved in such clasts. Conglomerates were sampled from two localities, Shamva, within the central part of Northern Zimbabwe, and Chinhoyi, at the north-western boundary of the craton. The results from both localities demonstrate the presence of continental crust in Northern Zimbabwe with a long and complex history prior to the Late Archaean "event". The minimum age of continental crust in the Shamva region is 3.34 Ga (Sm-Nd model age),with further episodes of granitiod intrusion indicated by zircon crystallisation at 3/197 ± 10 Ma, 2,925 ± 10 Ma, and 2,800 ± 20 Ma (Pb-Pb zircon). The Chinhoyi region has a shorter, simpler history, with the earliest recorded continental crust at 2,875 ± 3 Ma and later intrusions of granitoids at 2/800 ± 20 Ma, and2,720 ± 6 Ma (Pb-Pb zircon). Chemically, the early crust was dominated by sodic, Tonalite Trondhjemite-Granodiorite granitoids, whose formation may be modelled by the partial melting of metabasalts with residual hornblende and/or garnet. By contrast, the granitoids formed during the Late Archaean "event" which culminated in the stabilisation of the craton, dominantly follow calc-alkalinetrends, and their formation may be modelled by the fractionation of basaltic magmas (combined with assimilation- of pre-existing continental material) or intra-crustal remelting. This major switch in the origins (and hence chemistry) of granitoids may be attributed to mantle plume activity, the onset of which is recorded by the presence of greens tone belt volcanics derived from anomalously hot mantle, dated at' 2,713 ± 15 Ma (U-Pb zircon Jelsma, 1993).
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Chang, Jefferson Castillo. "Seismic evidence and tectonic significance of an intracrustal reflector beneath the inner California continental borderland and peninsular ranges." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2008. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Quas-Cohen, Alexandra Catherine. "Norwegian orthopyroxene eclogites : petrogenesis and implications for metasomatism and crust-mantle interactions during subduction of continental crust." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/norwegian-orthopyroxene-eclogites-petrogenesis-and-implications-for-metasomatism-and-crustmantle-interactions-during-subduction-of-continental-crust(d7951acf-8fda-454b-b0a8-5fd28f8750da).html.
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This study investigates the ultrahigh pressure (UHP) metamorphic and metasomatic processes involved in the transient subduction-exhumation of continental crust to over 100km depths during a collisional orogeny and the implications for the evolution of the continental crust and crust-mantle interaction at depth. The study focuses on garnet websterites (orthopyroxene eclogites) and zoned, clinopyroxenite-garnetite veining features present in a range of eclogite-facies, crustal metamafic-ultramafic bodies hosted within the Western Gneiss Region (WGR), western Norway. The structural occurrences and textures of some of these crustal garnet websterites are seemingly unique to the WGR but little research has focused on their origin or from a metasomatic perspective. Based on field and petrographic observations, a metasomatic origin is attributed to vein-associated garnet websterites at Kolmannskog, Myrbærneset and Svartberget. A metamorphic origin is attributed to body domains at Nybø, Kolmannskog, Båtneset and Myrbærneset and a combined metamorphic-metasomatic origin is attributed to garnet websterite body domains at Årsheimneset and Remøysunde and inferred at Grytting and Eiksunddal. UHP P-T conditions are obtained from garnet websterites of ~3.7GPa, 740°C at Nybø, ~3.1GPa, 670°C at Grytting, ~3.5GPa, 700°C at Årsheimneset, ~3.6GPa, 815°C at Remøysunde, ~3.0GPa, 750°C at Kolmannskog and ~3.85GPa, 790°C at Svartberget. On this basis, it is proposed the Nordøyane UHP domain be extended eastwards to incorporate the Kolmannskog locality which lies outside its currently defined boundary. Constructed P-T paths suggest the northern Nordøyane UHP domain experienced ~100°C higher temperatures than the southern Nordfjord-Stadlandet UHP domain but experienced similar pressures implying a lower regional P-T gradient than previously established. P-T paths also suggest UHP, vein-forming metasomatism occurred prior to peak temperatures. U-Pb isotopic dating of zircon and monazites in garnetite vein cores dates UHP metasomatism at 414±5.6Ma at Årsheimneset and 410±2.6Ma at Svartberget. The fluid responsible for UHP metasomatism is considered to be a Si-Al-K-H2O-rich supercritical liquid produced in the surrounding country rock associated with the breakdown of phengite with a Na-LILE-LREE-HFSE-P enrichment signature. The major element composition of the fluid added to the Svartberget body is calculated to be 48-60% SiO¬2, 17-27% Al2O3, 3-11% K2O, <10% MgO, CaO and FeO, 3-6% Na2O, <4% P2O5¬, <1% TiO2 and MnO with an overall, undersaturated-saturated sialic, syenitic character hybridised through interaction with the garnet peridotite body margins. The continental fluid-mafic-ultramafic rock systems studied imply a zoned metasomatic unit forms at the interface between subducted continental crust and above mantle wedge at depths of ≥120-130km and along any fluid pathways penetrating into the mantle transferring abundant alkalis, water and trace elements into the mantle. Fluid-mantle interaction is proposed to form abundant biotite and amphibole and zones of garnet websterite, biotite websterite and biotite clinopyroxenite with lenses of eclogite and/or accessory phase (rutile, zircon, monazite, apatite, xenotime)-rich garnetite ±glimmerite selvages where residual fluids accumulate. Subcontinental mantle metasomatism may be associated with UHP, supercritical liquids derived from subducted, eclogite-facies, continental crust rather than oceanic crust as the continental crust is a greater source of the Si, alkalis, trace elements and water which characterise mantle metasomatism.
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Mercer, Celestine Nicole. "Mineralogical indicators of magmatic and hydrothermal processes in continental arc crust /." Connect to title online (Scholars' Bank) Connect to title online (ProQuest), 2009. http://hdl.handle.net/1794/10250.
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Degli, Alessandrini Giulia. "Deformation mechanisms and strain localization in the mafic continental lower crust." Thesis, University of Plymouth, 2018. http://hdl.handle.net/10026.1/12799.
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The rheology and strength of the lower crust play a key role in lithosphere dynamics, influencing the orogenic cycle and how plate tectonics work. Despite their geological importance, the processes that cause weakening of the lower crust and strain localization are still poorly understood. Through microstructural analysis of naturally deformed samples, this PhD aims to investigate how weakening and strain localization occurs in the mafic continental lower crust. Mafic granulites are analysed from two unrelated continental lower crustal shear zones which share comparable mineralogical assemblages and high-grade deformation conditions (T > 700 °C and P > 6 Kbar): the Seiland Igneous Province in northern Norway (case-study 1) and the Finero mafic complex in the Italian Southern Alps (case-study 2). Case-study 1 investigates a metagabbroic dyke embedded in a lower crustal metasedimentary shear zone undergoing partial melting. Shearing of the dyke was accompanied by infiltration of felsic melt from the adjacent partially molten metapelites. Findings of case-study 1 show that weakening of dry and strong mafic rocks can result from melt infiltration from nearby partially molten metasediments. The infiltrated melt triggers melt-rock reactions and nucleation of a fine-grained (< 10 µm average grain size) polyphase matrix. This fine-grained mixture deforms by diffusion creep, causing significant rheological weakening. Case-study 2 investigates a lower crustal shear zone in a compositionally-layered mafic complex made of amphibole-rich and amphibole-poor metagabbros. Findings of case-study 2 show that during prograde metamorphism (T > 800 °C), the presence of amphibole undergoing dehydration melting reactions is key to weakening and strain localization. Dehydration of amphibole generates fine-grained symplectic intergrowths of pyroxene + plagioclase. These reaction products form an interconnected network of fine-grained (< 20 µm average grain size) polyphase material that deforms by diffusion creep, causing strain partitioning and localization in amphibole-rich layers. Those layers without amphibole fail to produce an interconnected network of fine grained material. In this layers, plagioclase deforms by dislocation creep, and pyroxene by microfracturing and neocrystallization. Overall, this PhD research highlights that weakening and strain localization in the mafic lower crust is governed by high-T mineral and chemical reactions that drastically reduce grain size and trigger diffusion creep.
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Ducea, Mihai N., George W. Bergantz, James L. Crowley, and Juan Otamendi. "Ultrafast magmatic buildup and diversification to produce continental crust during subduction." GEOLOGICAL SOC AMER, INC, 2017. http://hdl.handle.net/10150/623057.
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The processes and fluxes that produce the distinct compositional structure of Earth's continental crust by subduction remain controversial. The rates of oceanic crust production, in contrast, are well quantified and are generally believed to be faster than those responsible for building magmatic systems in subduction settings. Here we show that a recently recognized crustal section, the 30-km-thick Ordovician Sierra Valle Fertil-Sierra Famatina complex in Argentina, was built magmatically within only similar to 4 m.y. More than half of the crustal section represents additions from the mantle, and is preserved as mafic igneous rocks and maficultramafic cumulates; the remainder is tonalite to granodiorite with evidence for widespread assimilation from highly melted metasedimentary units. U-Pb zircon geochronology reveals that the construction of the arc was not a simple bottom-up construction process. This continuous exposure of the arc crust allows the quantification of field constrained magmatic addition rates of 300-400 km(3) km(-1) m.y.(-1). These rates are similar to those determined for modern slow-spreading mid-ocean ridges and are of the same magnitude as magmatic addition rates required to build certain large segments of the continental masses such as the Arabian-Nubian shield, among others. The implication is that significant convective removal of arc roots is required over time in order to build the modern continental crust via subduction-related magmatism.
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Mansur, Adam T. "Age, composition, and origin of the lower continental crust, northern Tanzania." College Park, Md.: University of Maryland, 2008. http://hdl.handle.net/1903/8993.
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Thesis (M.S.) -- University of Maryland, College Park, 2008.Thesis research directed by: Dept. of Geology. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Mercer, Celestine Nicole 1979. "Mineralogical indicators of magmatic and hydrothermal processes in continental arc crust." Thesis, University of Oregon, 2009. http://hdl.handle.net/1794/10250.
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xviii, 177 p. : ill., maps. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.This dissertation explores several important consequences of H 2 O-rich fluids in magmatic and ore-forming systems within continental arc crust. North Sister, a stratovolcano in the Oregon High Cascades, provides a window into magma generation processes in the deep crust. Eruption of a remarkably limited basaltic andesite composition over the lifespan of this volcano may reflect last equilibration of mantle derived magma within a deep crustal hot zone. High pressure, water-undersaturated phase equilibrium experiments show that an anhydrous, augite-rich gabbro at ∼12 kbar (40 km depth) and ∼ 1175°C is the most probable lithology with which North Sister basaltic andesite with ∼3.5 wt% H 2 O last equilibrated within the deep crust before erupting. While magma often erupts at the planets surface as at North Sister, a greater volume never reaches the surface and solidifies within the upper crust. Exsolution of magmatic fluids is an inevitable consequence of crystallization of hydrous crustal magmas. The fate of these fluids is the focus of the remainder of this dissertation. Modeling of CO 2 and H 2 O variations during crystallization of granitic magma reveals that exsolution of a large mass of fluid occurs only after CO 2 is largely degassed, creating ideal conditions for hydrofracturing and formation of porphyry copper deposits. CO 2 and H 2 O solubility relations suggest that H 2 O-rich magma was required to produce the porphyry-Cu-Mo deposit at Butte, Montana, which may explain its distinctively deep generation. Electron microprobe analyses of Ti in quartz and Zr in rutile in samples from Butte yield porphyry magma temperatures (630-770°C) that overlap substantially with hydrothermal vein temperatures (<430-750°C). Veins display large temperature ranges (50-250°C) that signify variable degrees of cooling of hot magmatic fluids upon contact with cooler wall rock during vein growth. Modeling of Ti diffusion in quartz suggests that individual dikes and veins likely cooled over short timescales (10s-1000s years), indicating that porphyry systems may evolve by episodic magmatic fluid injections with discrete thermal spikes. Modeling of Ti diffusion in quartz combined with electron backscatter diffraction maps show that small hydrothermal quartz veins likely formed by epitaxial growth. This dissertation includes co-authored material both previously published and in preparation for submission.
Committee in charge: A. Dana Johnston, Chairperson, Geological Sciences; Mark Reed, Member, Geological Sciences; Paul Wallace, Member, Geological Sciences; Richard P. Taylor, Outside Member, Physics
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Betka, Paul. "Structural and Kinematic Evolution of the Lower Crust." ScholarWorks @ UVM, 2008. http://scholarworks.uvm.edu/graddis/22.
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Abstract Three dimensional finite strain and kinematic data from the Resolution Island Shear Zone, Fiordland, New Zealand record the progressive evolution of a lower crustal metamorphic core complex. The Resolution Island Shear Zone is a mid-Cretaceous (~114-90 Ma) extensional shear zone that juxtaposes high-pressure (P~17-19 kbar) garnet-granulite and eclogite facies orthogneiss from the lower crust against mid-crustal (P~6-8 kbar) orthogneiss and paragneiss along a low-angle upper amphibolite facies ductile normal fault. In the lower plate of the Resolution Island Shear Zone the high-pressure garnetgranulite and eclogite facies gneissic foliations (S1) are attenuated by granulite facies extensional shear zone foliations (S2). Retrograde metamorphism marked by the breakdown of omphacite and garnet to amphibole and feldspar in S2 foliation records the unloading of the lower plate during extension. Continued extension localized strain into weaker amphibole and feldspar-bearing lithologies. Upper amphibolite facies shear zones anastomose around rigid lenses that preserve the S1 and S2 fabric. Upper amphibolite facies shear zone fabrics (S3/L3) that envelop these pods display a regional-scale domeand- basin pattern. These shear zones coalesce and form the Resolution Island Shear Zone. Coeval with the formation of the Resolution Island Shear Zone, a conjugate, southwest dipping, and lesser magnitude shear zone termed the Wet Jacket Shear Zone developed in the upper plate of the Resolution Island Shear Zone. Three-dimensional strain analyses from S3/L3 fabric in the Resolution Island Shear Zone show prolate-shaped strain ellipsoids. Stretching axes (X) from measured finite strain ellipsoids trend northeast and southwest and are subparallel to L3 mineral stretching lineations. Shortening axes (Y, Z) are subhorizontal and subvertical, respectively, and rotate through the YZ plane of the finite strain ellipsoid. This pattern reflects the dome-and-basin geometry displayed by anastomosing S3 foliations and indicates the Resolution Island Shear Zone developed in the field of constriction. Threedimensional kinematic results indicate a coaxial-dominated rotation of stretching lineations toward the X-axis in both the XZ and XY planes of the finite strain ellipsoid. Results suggest that a lower crustal metamorphic core complex developed in a constrictional strain field with components of coaxial-dominated subvertical and subhorizontal shortening. Mid-Cretaceous (~114-90 Ma) extensional structures exposed in Fiordland, including the Resolution Island, Wet Jacket, Mount Irene and Doubtful Sound shear zones and the Paparoa metamorphic core complex allows the reconstruction of a crustal column that describes the geometry of mid-Cretaceous continental rifting of Gondwana. The overall symmetry of crustal-scale structures during continental extension suggests kinematic links between flow in the lower crust and the geometry and mode of continental extension. This result is consistent with numerical models of lithospheric rifting that predict the lower crust has a primary control on the style of continental extension.
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Marr, Catherine. "The free-air gravity anomaly edge effect and the mechanical properties of the lithosphere." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337522.
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Jackson, Matthew David. "The generation, segregation and mobilisation of granitic melt in the continental crust." Thesis, University of Liverpool, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364199.
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Peddy, Carolyn Paige. "Synthetic-aperture and near-vertical deep reflexion studies of the continental crust." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357906.
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Edwards, Caroline Marion Hawkey. "A comparison of arc evolution on continental and oceanic crust, Sunda Arc, Indonesia." Thesis, Royal Holloway, University of London, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361452.
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Piccolo, Andrea [Verfasser]. "Continental crust production during the early Earth: Constraints from geodynamic models / Andrea Piccolo." Mainz : Universitätsbibliothek Mainz, 2019. http://d-nb.info/1188356739/34.
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Miladinova, Irena [Verfasser]. "The subduction of continental crust - insights from eclogite geochronology and petrology / Irena Miladinova." Bonn : Universitäts- und Landesbibliothek Bonn, 2019. http://d-nb.info/119183204X/34.
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Laurie, Angelique. "The formation of Earth’s early felsic continental crust by water-present eclogite melting." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80214.
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Thesis (PhD)--Stellenbosch University, 2013.ENGLISH ABSTRACT: The sodic and leucocratic Tonalite, Trondhjemite and Granodiorite (TTG) granitoid series of rocks characterise Paleo- to Meso- Archaean felsic continental crust, yet are uncommon in the post-Archaean rock record. Consequently, petrogenetic studies on these rocks provide valuable insight into the creation and evolution of Earth’s early continental crust. The highpressure (HP)-type of Archaean TTG magmas are particularly important in this regard as their geochemistry requires that they are formed by high-pressure melting of a garnet-rich eclogitic source. This has been interpreted as evidence for the formation of these magmas by anatexis of the upper portions of slabs within Archaean subduction zones. In general, TTG magmas have been assumed to arise through fluid-absent partial melting of metamafic source rocks. Therefore, very little experimental data on fluid-present eclogite melting to produce Archaean TTG exist, despite the fact that water drives magmatism in modern arcs. Consequently, this study experimentally investigates the role of fluid-present partial melting of eclogite-facies metabasaltic rock in the production of Paleo- to Meso-Archaean HP-type TTG melts. Experiments are conducted between 1.6 GPa and 3.0 GPa and 700 ºC and 900 ºC using natural and synthetic eclogite, and gel starting materials of low-K2O basaltic composition. Partial melting of the natural and synthetic eclogite occurred between 850 ºC and 870 ºC at pressures above 1.8 GPa, and the melting reaction is characterised by the breakdown of sodic clinopyroxene, quartz and water: Qtz + Cpx1 + H2O ± Grt1 = Melt + Cpx2 ± Grt2. The experimental melts have the compositions of sodic peraluminous trondhjemites and have compositions that are similar to the major, trace and rare earth element composition of HPtype Archaean TTG. This study suggests that fluid-present eclogite melting is a viable petrogenetic model for this component of Paleo- to Meso-Archaean TTG crust. The nature of the wet low-K2O eclogite-facies metamafic rock solidus has been experimentally defined and inflects towards higher temperatures at the position of the plagioclase-out reaction. Therefore, the results indicate that a crystalline starting material is necessary to define this solidus to avoid metastable melting beyond temperatures of the Pl + H2O + Qtz solidus at pressures above plagioclase stability. Furthermore, this study uses numerical and metamorphic models to demonstrate that for reasonable Archaean mantle wedge temperatures within a potential Archaean subduction zone, the bulk of the water produced by metamorphic reactions within the slabs is captured by an anatectic zone near the slab surface. Therefore, this geodynamic model may account for HP-type Archaean TTG production and additionally provides constraints for likely Archaean subduction. The shape of the relevant fluid-present solidus is similar to the shape of the pressure-temperature paths followed by upper levels of the proposed Archaean subducting slab, which makes water-fluxed slab anatexis is very dependant on the temperature in the mantle wedge. I propose that cooling of the upper mantle by only a small amount during the late Archaean ended fluid-present melting of the slab. This allowed slab water to migrate into the wedge and produce intermediate composition magmatism which has since been associated with subduction zones.
AFRIKAANSE OPSOMMING: Die reeks natruimhoudende en leukokraties Tonaliet, Trondhjemiet en Granodioriet (TTG) felsiese stollingsgesteentes is kenmerkend in die Paleo- tot Meso-Argeïkum felsiese kontinentale kors, maar is ongewoon in die post-Argeïese rots rekord. Gevolglik, petrogenetiese studies op hierdie rotse verskaf waardevolle insig in die skepping en evolusie van die aarde se vroeë kontinentale kors. Die hoë-druk (HD)-tipe van die Argeïkum TTG magmas is veral belangrik in hierdie verband as hulle geochemie vereis dat hulle gevorm word deur hoë druk smelting van 'n granaat-ryk eklogitiese bron. Dit word interpreteer as bewys vir die vorming van hierdie magmas deur smelting van die boonste gedeeltes van die blaaie in Argeïese subduksie sones. TTG magmas in die algemeen, is veronderstel om op te staan deur middel van water-afwesig gedeeltelike smelting van metamafiese bron rotse. Daarom bestaan baie min eksperimentele data op water-teenwoordig eklogiet smelting om Argeïkum TTG te produseer, ten spyte van die feit dat water magmatisme dryf in moderne boë. Gevolglik is hierdie studie ‘n eksperimentele ondersoek in die rol van water-teenwoordig gedeeltelike smelting van eklogiet-fasies metamafiese rots in die produksie van Paleo- tot Meso-Argeïkum HD-tipe TTG smelte. Eksperimente word uitgevoer tussen 1.6 GPa en 3.0 GPa en 700 ºC en 900 ºC met behulp van natuurlike en sintetiese eklogiet, en gel begin materiaal van lae-K2O basaltiese samestelling. Gedeeltelike smelting van die natuurlike en sintetiese eklogiet het plaasgevind tussen 850 ºC en 870 ºC te druk bo 1.8 GPa, en die smeltings reaksie is gekenmerk deur die afbreek van natruimhoudende klinopirokseen, kwarts en water: Qtz + Cpx1 + H2O ± Grt1 = Smelt + Cpx2 ± Grt2. Die eksperimentele smelte het die komposisies van natruimhoudende trondhjemites en is soortgelyk aan die hoof-, spoor- en seldsame aard element samestelling van HD-tipe Argeïkum TTG. Hierdie studie dui daarop dat water-teenwoordig eklogiet smelting 'n lewensvatbare petrogenetiese model is vir hierdie komponent van Paleo- tot Meso-Argeïkum TTG kors. Die aard van die nat lae-K2O eklogietfasies metamafiese rock solidus is eksperimenteel gedefinieër en beweeg na hoër temperature by die posisie van die plagioklaas-out reaksie. Daarom dui die resultate daarop dat 'n kristallyne materiaal nodig is om hierdie solidus te definieër en metastabiele smelting buite temperature van die Pl + H2O + Qtz solidus druk bo plagioklaas stabiliteit te vermy. Verder maak hierdie studie gebruik van numeriese en metamorfiese modelle om aan te dui dat die grootste deel van die water geproduseer deur metamorfiese reaksies binne die blaaie bestaan vir redelike Argeïkum mantel wig temperature binne 'n potensiële Argeïkum subduksie sone, en word opgevang deur 'n smelting sone naby die blad oppervlak. Daarom kan hierdie geodinamies model rekenskap gee vir HD-tipe Argeïkum TTG produksie en dit bied ook die beperkinge vir waarskynlik Argeïese subduksie. Die vorm van die betrokke waterteenwoordig solidus is soortgelyk aan die vorm van die druk-temperatuur paaie gevolg deur die boonste vlakke van die voorgestelde Argeïkum subderende blad, wat water-vloeiing blad smeltingbaie afhanklik maak van die temperatuur in die mantel wig. Ons stel voor dat afkoeling van die boonste mantel met slegs 'n klein hoeveelheid gedurende die laat Argeïese, die water-vloeiing smelting van die blad beëindig. Dit het toegelaat dat die blad water in die wig migreer en intermediêre samestelling magmatisme produseer wat sedert geassosieer word met subduksie sones.
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Emo, Robert B. "Probing the lower continental crust with the petrology and geochemistry of Queensland xenoliths." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/232622/1/Robert%20Bernard_Emo_Thesis.pdf.
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This thesis investigated the poorly constrained composition and evolution of the lower continental crust in Queensland through geochemistry, geochronology, and petrological modelling. The analysis of deep crustal rocks brought to the surface by explosive volcanism shows that the lower crust in Queensland is nearly devoid of many geologically significant trace elements. The modelling demonstrates that this lower crust formed through solid-melt interactions at the base of the crust. The combined data show that this depleted, hybridised crust could be more common than previously recognised and that hybridisation is likely a major driver of continent formation.
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Fauconnier, Julien. "Anisotropie, fusion partielle et déformation de la croûte continentale : étude expérimentale et observations de terrain." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066560/document.
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La localisation de la déformation est une caractéristique nécessaire de la tectonique. Pour localiser la déformation, une roche doit subir un affaiblissement. Le processus affaiblissant principal des roches est l'interconnexion de phases faibles. Dans le cas de la croûte continentale, les phases faibles étant le plus souvent responsables de la localisation sont les micas et les liquides silicatés résultant de la fusion partielle. Bien qu'il existe des études expérimentales sur la rhéologie des micas, il y a très peu d'études sur l'impact des micas sur la localisation dans les conditions de la croûte continentale inférieure. De même, les précédentes études expérimentales montrent l'effet de la fusion partielle sur la résistance des roches mais elles utilisent toutes un matériel de départ isotrope. Or la croûte subissant la fusion partielle dans les orogènes est susceptible d'être préalablement déformée et donc anisotrope. Dans le but d'apporter de nouvelles données sur le comportement mécanique et les microstructures de la croûte continentale anisotrope, ainsi que sur l'effet des micas sur la localisation de la déformation, cette thèse propose de réaliser une série d’expériences en presse de Griggs. Cette approche expérimentale est aussi couplée à un travail de terrain sur la zone de faille de Møre og Trøndelag (Norvège). Cette structure étant un zone de cisaillement d'échelle crustale dont la cinématique est partiellement synchrone de la fusion partielle, elle est adaptée à l'étude naturelle des relations entre fusion partielle et déformationStrain localization is a necessary feature of tectonic. To be able to localize deformation, rocks must undergo weakening. The main weakening process is weak phase interconnection. For continental crust, weak phases that are the most often responsible of strain localization are micas and melt. Although previous experimental studies exist about rheological properties of micas, none are about the effect of micas on the strain localization in the lower continental crust conditions. Previous experimental studies about the effect of partial melting were always done with isotropic starting material. But continental crust which undergo partial melting is very likely to be deformed before melting and therefore to be highly anisotropic. In the aim to bring new data about mechanical behavior and microstructures of anisotropic continental crust, as well as the effect of micas on strain localization, this thesis propose to conduct a series of experiments in a Griggs apparatus. This experimental approach is also coupled with field work on the Møre og Trøndelag Fault Zone (Norway). This crustal scale shear zone was partially synchronous with partial melting and therefore is well suited for studying relation ship between deformation and partial melting
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Hague, Philip John. "A study of the lower crust using wide-angle multi-channel seismic data." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314019.
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Garçon, Marion. "Variabilité chimique et isotopique créée par les processus sédimentaires dans les sédiments de rivière Himalayennes." Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENU031/document.
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Les compositions isotopiques en Nd, Hf, Pb et Sr des sédiments de rivière sont souvent considérées comme étant représentatives de celles de leurs roches sources. Elles sont donc largement utilisées pour tracer la provenance des sédiments ou pour moyenner les compositions isotopiques des lithologies drainées. L'influence des processus sédimentaires sur les compositions isotopiques de ces sédiments est cependant mal connue. L'objectif de l'étude présentée ici est de caractériser l'ampleur de la variabilité isotopique pouvant être générée par les processus de tri minéralogique au cours du transport des sédiments dans le milieu fluviatile. Pour ce faire, nous avons analysé les concentrations en éléments traces et les compositions isotopiques en Nd, Hf, Pb et Sr dans différents types de sédiments de rivière (bedload, suspended load, bank) échantillonnés à plusieurs endroits dans le système fluviatile du Ganges qui draine une partie de l'orogène Himalayenne. Nous avons également mesuré les compositions chimiques et isotopiques de nombreuses fractions minérales et granulométriques séparées de ces sédiments afin de mieux comprendre l'influence de chaque espèce minérale dans le budget isotopique total d'un sédiment de rivière. Dans le cas où les lithologies drainées sont essentiellement cristallines et sédimentaires, nous montrons que les isotopes du Nd dans les sédiments de rivière sont très peu affectés par les processus de tri minéralogique puisqu'ils sont toujours contrôlés par les mêmes minéraux, à savoir la monazite et l'allanite. Au contraire, les systèmes isotopiques de l'Hf, du Pb et du Sr s'avèrent particulièrement touchés par les processus de tri minéralogique. Les isotopes de l'Hf et du Pb sont tous deux affectés par un effet zircon qui génère de larges variations isotopiques entre les sédiments de fond de rivières et ceux transportés en suspension. Pour le Sr, les variations observées entre les différents types de sédiments résultent des proportions variables de micas et feldspath-K qu'ils contiennent. Dans le cas où les principales lithologies drainées présentent de forts contrastes d'érodabilité i.e. basaltes versus roches cristallines, nous montrons que les effets combinés de l'érosion différentielle dans le bassin de drainage et du tri sédimentaire dans la colonne d'eau sont responsables d'importantes variations isotopiques en Nd, Hf et Pb entre les sédiments de fond de rivière et ceux transportés en suspension. Nos calculs suggèrent que les produits d'érosion basaltique, relativement fins, sont préférentiellement transportés en suspension, proche de la surface de l'eau, alors que les produits d'érosion des roches plus cristallines sont préférentiellement concentrés dans les sédiments de fond de rivière. Enfin, nous suggérons que les variations isotopiques observées entre les différents types de sédiments transportés par les rivières sur les continents pourraient avoir d'importantes implications pour les systématiques isotopiques des sédiments océaniques terrigènes et sur l'évolution à long terme du réservoir mantellique si ces derniers sont recyclés au niveau des zones de subductionNd, Hf, Pb and Sr isotopic compositions of river sediments are often considered to be representative of those of their source rocks. Thus, they are widely used to trace sediment provenance or to average the isotopic compositions of the drained lithologies. The influence of sedimentary processes on the isotopic composition of these sediments is however poorly known. The aim of the present study is to characterize the extent of the isotopic variability that can be generated by mineral sorting process during sediment transport in fluvial system. To do this, we analyzed trace element concentrations and Nd, Hf, Pb and Sr isotopic compositions in river bank, bedload and suspended load sampled at several locations in the Ganga fluvial system draining part of the Himalayan orogen. We also measured the chemical and isotopic compositions of numerous mineral and granulometric fractions separated from these sediments to better understand the contribution of each mineral species to the bulk isotopic budget of river sediments. When the drained lithologies are mainly crystalline and sedimentary, we show that Nd isotopes are very little affected by mineral sorting processes because, whatever the sediment type, those isotopes are always controlled by the same minerals i.e. monazite and allanite. In contrast, Hf, Pb and Sr isotopic systems are significantly affected by mineral sorting processes. Both Hf and Pb isotopes are affected by a zircon effect that generates large isotopic variations between bedload and suspended load. For Sr, variations between the different sediment types more likely result from variable proportions of K-feldspar and mica. When the main drained lithologies are characterized by strong differences in erodibility i.e. basalts versus crystalline rocks, we show that the combined effects of differential erosion in the drainage basin and sediment sorting in the water column are responsible for significant Nd, Pb and Hf isotopic variations between bedload and suspended load. Our calculations suggest that basaltic erosion products are preferentially transported in suspension, near the water surface, whereas the erosion products of more crystalline rocks are preferentially concentrated in bottom sediments. Finally, we suggest that the isotopic variations observed between bedload and suspended load on continents may have important implications for the isotopic systematics of oceanic terrigenous sediments and the long-term evolution of the mantle if these latters are recycled in subduction zones
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Tafur, Lorena Andrea. "Mineral Equilibrium Constraints on the Feasibility of Diffusively-Fluxed Melting in the Continental Crust." Master's thesis, Faculty of Science, 2019. http://hdl.handle.net/11427/31280.
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Generation of granitic magma predominantly occurs by melting through the breakdown of hydrous minerals. However, melting due to the influx of water has been recognised in anatectic amphibolite-facies composite grey gneisses, metagreywackes and low-pressure metapelites, and has consequently been proposed as an alternative mechanism for granite generation and crustal differentiation. Water-fluxed melting is recognised by voluminous melt production at relatively low temperature, where hydrous minerals are stable and anhydrous minerals are preferentially consumed during melting. Mineral equilibrium modelling to determine the P–T conditions, melt volumes, melting reactions and viable fluid sources reveal that water-present melting in all target lithologies is confined to the wet solidus and does not extend to temperatures higher than 700–710 ◦C. Melting at suprasolidus conditions does not involve the mechanical flow of a free water phase. Instead, the process is driven by diffusion of H2O along chemical potential gradients and is therefore more appropriately described as diffusively-fluxed melting. Diffusively-fluxed melting is not restricted to specific compositions or P–T conditions, although it is more efficient at lower pressure and in lithologies with a low hydrous mineral content. Melting reactions in all lithologies primarily consume quartz and feldspars to yield 5–6 mol.% melt for each mol.% of H2O added. aH2O remains constant at ∼0.70–0.77 during progressive melting as long as alkali feldspar is present. Once alkali feldspar is exhausted, plagioclase becomes the main reagent, producing more tonalitic melt compositions with gradually higher aH2O. Melting will initiate and proceed as long as a µH2O gradient exists between the fluid source and target lithology. Our calculations show that an ordinary magma, such as an I-type magma with typical, undersaturated H2O content, has a µH2O high enough to be a viable fluid source, allowing diffusively-fluxed melting to produce melt volumes and fertility comparable to that of dehydration melting. However, voluminous melt production requires a considerable volume of H2O, which necessitates a focussed fluid source such as a magma conduit or melt-bearing shear zone. Any other magmatic fluid source will undergo a similar amount of crystallisation as the melt fraction produced in the target rock, such that there will be no net melt production. Considering that shear-zone hosted magma conduits are relatively rare, diffusively-fluxed melting appears to only be viable in a small fraction of the anatectic orogenic crust. Therefore, whereas it may play a significant role in locally raising melt volumes and modifying magma chemistry through mingling and hybridisation, it does not appear to, of itself, be able to meaningfully contribute to crustal differentiation.
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Fauconnier, Julien. "Anisotropie, fusion partielle et déformation de la croûte continentale : étude expérimentale et observations de terrain." Electronic Thesis or Diss., Paris 6, 2016. http://www.theses.fr/2016PA066560.
Full textAbstract:
La localisation de la déformation est une caractéristique nécessaire de la tectonique. Pour localiser la déformation, une roche doit subir un affaiblissement. Le processus affaiblissant principal des roches est l'interconnexion de phases faibles. Dans le cas de la croûte continentale, les phases faibles étant le plus souvent responsables de la localisation sont les micas et les liquides silicatés résultant de la fusion partielle. Bien qu'il existe des études expérimentales sur la rhéologie des micas, il y a très peu d'études sur l'impact des micas sur la localisation dans les conditions de la croûte continentale inférieure. De même, les précédentes études expérimentales montrent l'effet de la fusion partielle sur la résistance des roches mais elles utilisent toutes un matériel de départ isotrope. Or la croûte subissant la fusion partielle dans les orogènes est susceptible d'être préalablement déformée et donc anisotrope. Dans le but d'apporter de nouvelles données sur le comportement mécanique et les microstructures de la croûte continentale anisotrope, ainsi que sur l'effet des micas sur la localisation de la déformation, cette thèse propose de réaliser une série d’expériences en presse de Griggs. Cette approche expérimentale est aussi couplée à un travail de terrain sur la zone de faille de Møre og Trøndelag (Norvège). Cette structure étant un zone de cisaillement d'échelle crustale dont la cinématique est partiellement synchrone de la fusion partielle, elle est adaptée à l'étude naturelle des relations entre fusion partielle et déformationStrain localization is a necessary feature of tectonic. To be able to localize deformation, rocks must undergo weakening. The main weakening process is weak phase interconnection. For continental crust, weak phases that are the most often responsible of strain localization are micas and melt. Although previous experimental studies exist about rheological properties of micas, none are about the effect of micas on the strain localization in the lower continental crust conditions. Previous experimental studies about the effect of partial melting were always done with isotropic starting material. But continental crust which undergo partial melting is very likely to be deformed before melting and therefore to be highly anisotropic. In the aim to bring new data about mechanical behavior and microstructures of anisotropic continental crust, as well as the effect of micas on strain localization, this thesis propose to conduct a series of experiments in a Griggs apparatus. This experimental approach is also coupled with field work on the Møre og Trøndelag Fault Zone (Norway). This crustal scale shear zone was partially synchronous with partial melting and therefore is well suited for studying relation ship between deformation and partial melting
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Barovich, Karin Marie. "Behavior of lutetium-hafnium, samarium-neodymium and rubidium-strontium isotopic systems during processes affecting continental crust." Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/185602.
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Combined Lu-Hf, Sm-Nd and Rb-Sr isotopic studies of continental crustal rocks were undertaken to assess the relative effects of secondary crustal processes on isotopic systematics of whole-rock systems. The processes studied include ductile deformation, and three cases of hydrothermal alteration, involving fluids of varying composition. The Rb-Sr system proved to be easily disturbed during all secondary processes, while Sm-Nd and Lu-Hf systems were, for the most part, resilient. These results show that Nd or Hf isotopic information obtained from old rocks that have undergone typical crustal deformational and alteration events can be counted on to be equally reliable. Nd and Hf isotopic analyses were performed on four suites of Early Archean felsic gneiss complexes from Greenland, Labrador, Swaziland, and Michigan to explore questions associated with Early Archean crustal growth. The Sm-Nd isotopic data yield initial ∊(Nd) values that are mostly consistent with published age data for the suites. Calculations show limited scatter may be attributed to subtle changes in the Sm/Nd ratio or Nd isotopic composition. The Hf isotopic results are more variable and complex than the Nd results. The relevance of the studies on isotopic mobility in the first part of this work is that they have demonstrated that Nd and Hf isotopes are equally resilient during a range of secondary crustal processes. Given the robustness of the Nd isotopic data from the Archean samples, however, it seems unreasonable to attribute the much wider variation in Hf isotopic data to post-Archean isotopic disturbances. Differences in initial Hf isotopic ratios from differing magma sources seem called for. Nd and Hf whole-rock analyses of a Late Archean pristine garnet-bearing granitoid complex from northern Canada point out the importance of garnet in fractionating Lu/Hf ratios, and in developing anomalous ∊(Hf) signatures in potential source regions. Calculations show that even short-lived upper mantle/lower crustal heterogeneities, products of previous partial melting events involving garnet fractionation, can develop the range of positive and negative ∊(Hf) values seen in the Early Archean samples.
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Savage, Paul S. "Silicon isotopes and the development of the Earth." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:ff7a692d-910c-4d22-8087-263f6c0b5f75.
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Silicon (Si) isotopes have been extensively studied in low temperature environments but the science of Si isotopes in igneous material has been comparatively ignored. This is because the degree of isotopic fractionation at high temperatures is relatively small, making the accurate measurement of these variations extremely challenging. Using state-of-the-art analytical techniques and instrumentation, which deliver high levels of precision, the objective of this research is to rectify this omission. Specifically, this study aims to investigate whether there are systematic Si isotope variations within, and provide robust Si isotopic compositions for, the major silicate reservoirs on Earth. To this end, a broad range of mantle and crustal lithologies, sourced globally and from various tectonic regimes, have been analysed using high resolution MC-ICP-MS. Analyses indicate that the Si isotopic compositions of mantle-derived mafic and ultramafic material are extremely homogeneous. These data are used to calculate a Bulk Silicate Earth (BSE) average of δ30Si = -0.29 ± 0.08 ‰ (2 s.d.). The degree of Si isotopic fractionation as a result of magmatic differentiation has also been assessed, and found to be small but resolvable between basalt and rhyolitic end-members. Finally, this research shows that, although igneous rocks and sediments derived from the continental crust can be relatively heterogeneous with respect to Si isotopes, bulk averages calculated for the upper, middle and lower continental crust are all very similar to that of BSE. Providing robust estimates for these reservoirs has greatly improved our knowledge of the behaviour of Si isotopes in silicate lithologies and provides a framework for further Si isotopic investigations of such material.
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Stremtan, Ciprian Cosmin. "Mantle-crust Interaction in Granite Petrogenesis in Post-collisional Settings: Insights from the Danubian Variscan Plutons of the Romanian Southern Carpathians." Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5624.
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The issue of granite petrogenesis plays a key role in our overall understanding of the growth and differentiation of continents, as well as in our ability to unravel the tectonic histories of orogenic belts. Granites are ubiquitous magmatic products found in almost all tectonic settings: oceanic and continental rifts (i.e., plagiogranites - extreme basalt differentiates), active continental margins (e.g,. the granitic batholiths of central and southern Andes), continent-continent collision zones (e.g., the orogenic batholiths of the Himalayas, Western Anatolia), post-collisional settings (e.g., the Variscan provinces of Europe), complex within-plates settings (e.g., Limmo massif, Afar, Ethiopia). Furthermore, granitoids are characterized by considerable petrological and geochemical heterogeneity, as they can form from a vast array of sources: sediments (e.g., pelites, arkoses, psammites), metamorphic rocks (e.g., (mica)schists, gneisses, etc.), and igneous rocks (e.g. andesites, dacites, tonalites, etc.). Aside from fertile sources (i.e., protoliths), granite petrogenesis is dependent upon two critical parameters: temperature (to promote melting of the protoliths) and water availability - either as freely available aqueous solutions/vapors (e.g., water input in subduction zones); or water released via dehydration melting of hydrous minerals (e.g., micas, amphiboles). The presence of water in protoliths depresses the melting temperature of mineral components and provides the environment for redistribution of chemical components.
Understanding the origins of granitic rocks presents unique challenges, given that in many of the tectonic settings where granites are encountered, it is clear that their modes of formation can involve a spectrum of igneous and metamorphic processes that are not readily accessible for examination, either through the study of modern environments or via analogy to "classical" localities. The petrogenesis and emplacement of granites in post-collisional tectonic settings is one of the thornier challenges, as these rocks appear to be derived via thermal and magmatic processes within highly deformed and compositionally diverse continental crust for which we lack a clear understanding. A number of unconventional and difficult-to-test mechanisms have been posited to drive crustal heating, melting, and subsequent pluton post-collisional emplacement. Although large volumes of granitic magmas have been emplaced in post-collisional settings, the complexities of the processes active in such settings make it challenging to put forward testable models that effectively combine available geochemical, petrologic, and geophysical data. Models for granite genesis away from plate margins (by means of crustal thickening, thermal blanketing, and internal heating from radioactive decay of 40K, 230Th, 235U, and 238U; delamination of the crustal lithosphere and juxtaposition of hot mantle melts at the base of the crust; underplating of mantle melts; or slab brake-off and upwelling of mantle melts) have been successfully applied in comparatively young orogenic regions, such as the Himalayas, the Carpathians, and Turkey. These models have proven challenging to employ in older orogenic belts, given their sometimes intricate tectonic and metamorphic histories, and the loss of pertinent evidence due to the effects of post-emplacement tectonic reworking, and often extensive alteration and erosion.
A series of ancient but fresh, age-correlative granitic plutons are exposed in Alpine nappes on the flanks of the Carpathians Mountains in southwestern Romania. These granites, all mapped as intruding the Neoproterozoic basement of the Danubian tectonic terrane, were emplaced during the post-collisional stages of two world-scale orogenies: an older, Pan-African event (~600 Ma) and a younger, Variscan event (~330- 280 Ma). My dissertation is focused on the study of late Variscan post-collisional plutons and associated sub-volcanic dykes, as they are tremendous tools for understanding and quantifying the mantle-crust interaction in post-collisional environments and the overall evolution of the continental crust during the Variscan orogeny.
Originally believed to be Proterozoic in age, zircon U/Pb dating showed that the plutons are much younger (Chapter 1 - Post-collisional Late Variscan magmatism in the Danubian domain (South Carpathians, Romania) documented by zircon U/Pb LA-ICP-MS) and correspond to the latest stages of the Variscan orogeny, as recorded elsewhere in the European Variscan provinces. The granitic plutons are relatively small and are generally concordant with the structures preserved by the country rocks. The extraordinary petrological and geochemical heterogeneities, even at pluton scale (Chapter 2 - Petrology and geochemistry of the Late Variscan post-collisional Furătura granitic pluton South. Carpathian Mts. (Romania)) argue against unique protoliths and simple evolutionary processes (e.g., closed-system fractional crystallization; anatexis). Trace elemental data for the Furătura pluton shows that the melts were formed in equilibrium with a garnet-amphibole restite, under pressure-temperature conditions deeper than the plagioclase stability field, implying that the melting took place at depths in excess of 40 km in the continental crust. Stable and radiogenic isotope data suggest that a protolith was of (possibly enriched) mantle affinities, and that the melts were subsequently contaminated in various degrees by deep crustal lithologies. In comparison, other post-collisional Variscan plutons from the Danubian domain (Chapter 4 - The role of the continental crust and lithospheric mantle in Variscan post-collisional magmatism - insights from Muntele Mic, Ogradena, Cherbelezu, Sfârdinu, and Culmea Cernei plutons (Romanian Southern Carpathians)) have trace elemental compositions that suggest they were formed at different levels in the crust, under P-T conditions corresponding to both garnet-amphibole and plagioclase stability fields. Some of the plutons lack mantle geochemical signatures and their isotopic compositions are indicative of substantial involvement of both lower- and upper-crustal rocks in their formation and subsequent evolution. On the other hand, plutons emplaced during the same time interval and most likely in close geographical proximity have trace elemental and isotopic compositions indicating strong input from previously enriched mantle components which experienced various degrees of assimilation fractionation-crystallization and/or assimilation of continental crust material during their evolution. This variability in both protoliths and processes responsible for the formation of the granites, coupled with the presence of mantle signatures in late-orogenic post-collisional melts are strong evidence to support delamination as means of providing both the mantle-derived input and energy required for generation of granitoids in the crust. The pronounced variation in petrological and chemical compositions of synchronous plutons suggests that delamination in the Danubian domain was not a single, large scale event that affected the entire crust, but rather a collection of disparate, spatially and chronologically limited event, that affected the Variscan crust during the latest stages of the orogeny.
This hypothesis is further tested on a series of sub-volcanic dykes (the Motru Dyke Swarm) crosscutting the entire Danubian basement (Chapter 3 - Post-collisional magmatism associated with Variscan orogeny in the Danubian Domain (Romanian Southern Carpathians): the Motru Dyke Swarm). Initially, the emplacement age of these dykes was assumed as "pre-Silurian" but our mapping has showed that they intrude components of the Danubian domain that shared a documented common history not earlier than the Carboniferous. Furthermore, the dykes are in intrusive relationship with two of the Danubian Variscan plutons, thus arguing for an early Permian emplacement age. Geochemical data show extraordinary heterogeneities in the dykes' composition and record both mantle and crust involvement in their formation. The dykes were emplaced at much shallower depths in the crust, as compared with the granitic plutons. Still, their isotopic compositions clearly indicate that they sampled both lower- and upper-crustal compositions during their evolution. This means that after the crustal thickening episodes that define continent-continent collisions, during the latest stages of the Variscan orogeny, the crust became progressively thinner, as a way to compensate for its metastable state. Thinning of the crust is greatly favored by delamination of the lithosphere. A delamination event, which usually postdates the cessation of continental collision or prolonged crustal shortening, involves the geologically rapid foundering of negatively buoyant lithosphere comprised of mantle and (potentially) lower crust into underlying hotter and less dense asthenosphere. Such a process will remove the lithospheric mantle (and potentially segments of the lower crust) along pre-existing lineaments or mechanical flaws, and juxtapose hot upwelling asthenosphere against the base of the crust, leading to partial melting.
Field, petrological, and geochemical data presented in my dissertation document pronounced variations in the overall composition of synchronous plutons and dykes, and further suggest that delamination in the Danubian domain was an active process. This bears great importance in our understanding of the evolution of the crust and argues that mantle-crust interactions are responsible for the generation of continental crust even in the latest stages of an orogen.
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Favaro, Silvia [Verfasser]. "Response of orogenic crust to indentation by Adriatic continental lithosphere – Tauern Window, Eastern Alps (Austria) / Silvia Favaro." Berlin : Freie Universität Berlin, 2016. http://d-nb.info/1107011574/34.
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Konrad-Schmolke, Matthias. "Insights into subduction and exhumation mechanisms of continental crust an example from the Sesia Zone (Western Alps) /." [S.l.] : [s.n.], 2006. http://www.diss.fu-berlin.de/2006/112/index.html.
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Johnson, Nicholas Edward. "Magnetotelluric studies of the crust and upper mantle in a zone of active continental breakup, Afar, Ethiopia." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7739.
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The Afar region of Ethiopia is slowly being torn apart by the Red Sea, Gulf of Aden and Main Ethiopian rifts which all meet at this remote, barren corner of Africa. Prior to rifting, volcanism probably started here some 30 million years ago, marked by the arrival of the Afar mantle plume and subsequent eruption of kilometres thick flood basalts. To the north and east the Red Sea and Gulf of Aden rifts have already progressed to become sea-floor spreading centres where new oceanic crust is produced. Active spreading on the Red Sea rift takes a landward step west into Eritrean Afar at approximately 15oN, after which divergence between the Nubian and Arabian tectonic plates is localised into 60 km long, 20 km wide magmatic segments that undergo periodic rifting cycles. This part of Afar is a unique natural laboratory where the process of transition from continental rifting to sea floor spreading can be studied. In September 2005 a dramatic rifting episode began on one such segment of the Red Sea rift in Afar (the Dabbahu magmatic segment), whereby a 60 km long dyke containing an estimated 2.5 km3 magma was intruded in just two weeks, allowing opening of up to 8 m. Since then a further 13 smaller dykes have been intruded, some with fissural eruptions of basaltic lava. Subsidence observed via geodetic observations can only account for a small fraction of the magma supply required to in ate the dykes, suggesting a deep crustal or upper mantle source must exist. The magnetotelluric (MT) method is a passive geophysical technique, used to probe the Earth to reveal subsurface conductivity. The presence of fluids can dramatically increase conductivity by orders of magnitude making the MT method ideally suited to detecting them. MT data collected from 22 sites on profiles near to and crossing the active rift are analysed and interpreted in conjunction with seismic and petrological constraints. They reveal for the first time, the existence of both a mid to lower-crustal magma chamber directly below the rift, and an o -axis zone of partial melt well within the mantle. The volume of melt contained within the crust and upper mantle below the Dabbahu segment is estimated to be at least 350 km3; enough to supply the rift at current spreading rates for almost 30 thousand years, assuming that both melt containing regions supply the rift. Vast amounts of highly conductive material, suggesting the existence of pure melt in places, are also required in the shallow crust close to Dabbahu volcano which lies at the northern end of the segment. Further data collected on the currently inactive Hararo segment which is the next one to the south of Dabbahu, show a smaller zone of partial melt that appears to be pooling at the Moho, inferred seismically to be at about 22 km, but little or no melt is required within the mid-crust. The minimum amount of melt estimated to be contained here is just 21 km3; an order of magnitude less than on the Dabbahu segment, but similar to estimates for melt within the crust found below the rift axis in the continental Main Ethiopian rift. This, along with other morphological evidence, suggests that this rift segment is less mature than the Dabbahu segment to the north, rather than it simply being at a different stage of a rifting cycle. A wide spread layer of highly conductive sediments up to 2 km thick has been imaged at most locations. This was unexpected on the Dabbahu segment where the surface of the Earth is dominated by heavily faulted basalts erupted from fissures, which are seen as a resistive uppermost layer several hundred metres thick. The high conductivity of the sediments is attributed to high heat flow and the presence of brines.
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Tipper, Edward Thomas. "The isotopic fingerprint of calcium and magnesium : from the alteration of the continental crust to global budgets." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614219.
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Jones, Rosemary Ellen. "Subduction zone processes and continental crust formation in the southern Central Andes : insights from geochemistry and geochronology." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/9672.
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Subduction zones, such as the Andean convergent margin, are the sites at which new continental crust is generated, and where subducting material is either recycled to the crust via arc magmatism or transferred to the deep mantle. The composition of arc magmas and associated new continental crust reflects variable contributions from mantle, crustal and subducted reservoirs. Insights into crustal growth and recycling processes in the southern Central Andes, specifically in the Pampean flat-slab segment, have been gained by utilising a range of petrological, geochronological and geochemical techniques. These techniques have been applied to a suite of Late Cretaceous (~73 Ma) to Late Miocene (~6 Ma) intrusive (granitoids) and extrusive (basalts to rhyolites) arc rocks collected from an east - west transect across the Andean Cordillera. The oxygen and hafnium isotopic composition of the accessory mineral zircon allows mantle-derived melts contaminated with older, upper continental crustal to be identified. Boron isotopic compositions of melt inclusions, combined with concentrations of certain incompatible trace elements, can be used to assess the source and influence of fluids derived from subducting material on the melt source region. The southern Central Andes provides a particularly interesting area to study these processes as the thickness of the continental crust has increased significantly over the course of the Cenozoic (from ~35 km to >50 km) and the angle of the subducting Nazca plate has shallowed since ~18 Ma, causing the position of the volcanic arc to migrate to the east. In order to unravel the complexities involved with constraining the contributions to arc magmas at an active continental margin, a range of geochronological, geochemical, and geothermobarometric techniques, including high resolution, micro-analysis of mineral phases and melt inclusions, have been applied. High resolution, U-Pb dating of magmatic zircon has improved regional stratigraphy in the Pampean flat-slab segment (between ~29 and 32 °S) and provided an accurate temporal constraint for geochemical and geothermobarometric data. The results of in-situ O and Lu-Hf isotope analysis of zircon show both distinct temporal and spatial variations across the Andean arc. The observed isotopic variability is attributed to variable contamination of mantle-derived melts with distinct Andean basement terranes, which vary east – west in composition and age. ‘Mantle-like’ δ18O(zircon) values, juvenile initial ƐHf(zircon) values and a lack of inherited, xenocrystic zircon cores, suggests the Late Cretaceous (~73 Ma) to Eocene (~39 Ma) plutons located in the Principal Cordillera of Chile, experienced very little interaction with the upper continental crust. Amphibole – plagioclase geothermobarometry indicates these calc-alkaline granitoids, which form extensive north – south trending belts, were emplaced at shallow depths in the crust (~4 – 5 km). Therefore the Late Cretaceous to Late Eocene is interpreted as a period of significant upper crustal growth. The isotopic variability in the Late Oligocene (~26 Ma) to Late Miocene (~6 Ma) arc magmatic rocks demonstrates that during thickening of the continental crust and migration of the Andean arc to the east, arc magmas assimilated Late Paleozoic to Early Mesozoic basement. In addition, arc magmas erupted/emplaced in the Argentinean Precordillera (i.e. farthest east from the trench) assimilated a Grenville-aged (~ 1330 – 1030 Ma) basement. The youngest arc magmas (~6 Ma) erupted in the Frontal Cordillera also show evidence for the assimilation of this ancient basement terrane, potentially signalling under-thrusting beneath the Frontal Cordillera. Overall, the later part of the Cenozoic represents a period of crustal reworking. Boron concentrations and isotope ratios measured in pyroxene hosted melt inclusions and for the first time in zircon hosted melt inclusions, are higher than the values expected for the mantle wedge and show significant variations with time. The source of the Paleocene (~61 Ma) arc magmas were influenced by fluids primarily derived from altered oceanic crust. Lower δ11B values and boron concentrations obtained for Oligocene (25 – 23 Ma) arc magmatic rocks reflects a diminished influence of slab-derived fluids reflecting a greater depth to the top of the slab. Fluids derived from serpentinite influenced the source of the arc magmas after ~19.5 Ma. This has been linked with the intersection of the Juan Fernández Ridge, a volcanic seamount chain associated with hydrated and serpentinised oceanic lithosphere.
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Stevenson, Ross Kelley. "Implications for the evolution of continental crust from hafnium isotope systematics of detrital zircons in Archean sandstones." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184895.
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The fractionation of zircons by sedimentary processes into continental margin sandstone deposits results in a biased preservation of pre-existing continental crust in the form of zircon in those sequences. This provides a unique opportunity to distinguish between the contrasting theories of episodic growth versus constant volume of continental crust over geologic time through Hf isotope ratios of detrital zircons. ¹⁷⁶Hf/¹⁷⁷Hf ratios were determined for detrital zircon fractions from 2.6-3.0 Ga old sedimentary sequences from the Canadian Shield, North Atlantic, Wyoming, and Kaapvaal Cratons. Hf T(CHUR) ages are less than 3.0 Ga and ε(Hf) values are positive or slightly negative at the time of deposition for most of the Malene, Canadian Shield, Wyoming and upper portions of the Kaapvaal sediments. Notable exceptions are basal samples of the Pongola (3.32 Ga), Dominion (3.11 Ga) and Witwatersrand (3.13 Ga), an arkose from Michigan (3.20 Ga) and one Malene sample (2.97 Ga), all of which either unconformably overlie or are closely associated with pre-3.0 Ga crust. Nd data for shales from the same sequences in the Canadian Shield and Kaapvaal sequences mimic the Hf results. The late Archean sequences appear to be dominated by zircon populations of late Archean age. Hf model ages, from pre-3.0 Ga strata (Upernavik of Labrador and quartzites from Montana), range from 3.1 to 3.6 Ga and are broadly consistent with ages of coexisting volcanics or intrusives, suggesting little inheritance of significantly older material. 2.0-2.5 Ga old quartzites from the Canadian Shield, Wyoming and South Africa have 2.58 to 2.84 Ga model Hf ages indicative of a large expanse of late Archean crust exposed at the time of deposition. The data strongly suggest inheritance of pre-3.0 Ga zircons only in areas where pre-3.0 Ga old crust exists today, and imply that the quantity of continental crust prior to 3.0 Ga ago was not much greater in extent than the pre-3.0 Ga crust exposed today. Small amounts of continental crust prior to 3.0 Ga ago and rapid addition of continental crust between 2.5 and 3.0 Ga ago are consistent with the episodic growth theory of crustal evolution.
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Ingram, Michael. "4d Strain Path Recorded In The Lower Crust During The Transition From Convergence To Continental Rifting, Doubtful Sound, Fiordland, New Zealand." ScholarWorks @ UVM, 2017. http://scholarworks.uvm.edu/graddis/683.
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ABSTRACT
Doubtful Sound, in SW New Zealand, exposes an exhumed section of lower crust that represents the root of an Early Cretaceous magmatic arc. Here, the lower crust underwent a change from contraction to extension and these tectonic cycles are fundamental to the growth of continental crust. Mafic-intermediate granulite gneisses occur below the extensional Doubtful Sound shear zone (DSSZ) which records the retrogression and transposition of granulite fabrics at the upper amphibolite facies. I compared 3D rock fabrics, microstructures and textures within and below the DSSZ to determine the processes involved in the shift from contraction to extension and to infer the sequential processes of transforming L>S granulites to L=S amphibolites.
Below the DSSZ, dehydration zones around felsic veins and leucosome in migmatitic orthogneiss record granulite facies metamorphism. Aggregates of clinopyroxene (cpx) and orthopyroxene (opx) that are rimmed by garnet (grt) and interstitial melt are set in a plagioclase (pl) matrix. Peritectic grt, pl-grt symplectites, beads of pl along grain boundaries, and elongate, inclusion-free pl reflect the anatexis. Pl exhibits a crystal preferred orientation (CPO) and evidence of subgrain rotational recrystallization and grain boundary migration, indicating subsolidus deformation outlasted melting. Mafic aggregates are boudinaged and opx developed subgrains. During peak metamorphism high strain was partitioned to locations enriched in melt, producing L>S fabrics and an upward trajectory in the strain path. A comparison of mineral grain shapes indicates that pl accommodated most of the strain. Granulite-amphibolite transitional rocks inside the DSSZ record a heterogeneous retrogression of the granulites to a polyphase metamorphic assemblage of hornblende (hbl), biotite (bt), and fine pl. Also preserved is the resetting of high strain L>S granulite to low strain, L=S amphibolite. Folia of porphyroblastic hbl + bt progressively penetrate the pl matrix via solution mass transfer. Porphyroblastic pl in the rock matrix becomes increasingly transposed to gneissic layering. A path of decreasing gradient from high strain L>S granulite to low strain L=S amphibolite reflects the development of the DSSZ fabric, growth of new minerals and onset to deformation at the amphibolite facies. Inside the DSSZ, amphibolites show an increasing strain gradient from low strain L=S amphibolite to high strain L=S amphibolite. Pl aggregates lack a CPO and are mostly annealed but preserve grain boundary migration microstructures. Hbl is recrystallized and forms asymmetric fish. Evidence of high fluid activity and reaction softening within the DSSZ include increased hbl + bt and bt beards on pl relative to rocks outside the DSSZ.
My observations suggest that magma, heat, and melting initially weakened the lower crust, facilitating the development of high strain zones with L>S fabrics. Partially molten regions deformed by suprasolidus flow and solid portions deformed mostly by dislocation creep in pl and boudinage of cpx + opx. Later, the lower crust was weakened and high strain fabrics were reset from overprinting and transposition as retrogression progressed and low strain L=S fabrics formed. During extension there was an upward trajectory in the strain path to high strain L=S fabrics within the DSSZ, where hbl and bt accommodated more strain. My results illustrate the importance of 1) melting, cooling, and hydration in controlling strain partitioning and the rheological evolution of lower crustal shear zones, and 2) the importance of integrating microstructural and fabric analysis to determine strain paths.
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Wandres, Marcel Charles Anekant. "Provenance study of the Torlesse Terranes and implications for the origin of the continental crust of eastern New Zealand." Thesis, University of Canterbury. Geological Sciences, 2002. http://hdl.handle.net/10092/5730.
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The Torlesse terranes - part of the New Zealand Eastern Province - are accretionary complexes that comprise an enormous volume of quartzofeldspathic sandstones and mudstones with subsidiary conglomerates plus minor oceanic assemblages. Two terranes are recognised in the South Island, the Permian to Late Triassic Rakaia terrane and the Late Jurassic to Early Cretaceous Pahau terrane. Recent studies in detrital petrology and geochemistry have been important in establishing the broad type of source for these two terranes. All studies point to a continental arc/cratonic provenance and various source areas have been proposed. This thesis provides the best evidence yet that the Pahau terrane is locally derived and that an Antarctic source for the Rakaia sediments must be (re)considered.
A detailed sampling program and geochronological, geochemical and Sr-Nd isotope analyses of igneous clasts from seven Torlesse terrane conglomerates, in conjunction with SHRIMP U-Pb detrital zircon ages from three Torlesse sandstones, have helped to broadly characterise the igneous protosources for the Pahau and Rakaia terranes. The conglomerate locations were chosen to represent the full stratigraphic range of both terranes, and the geographical distribution of the conglomerates mimics an approximate inboard to outboard transect of the two terranes with respect to the Panthalassan margin of Gondwana.
Igneous clasts from the Aptian (Mount Saul and Ethelton) and Albian (Kekerengu) Pahau terrane conglomerates are predominantly volcanic and hypersolvus, calc-alkaline, metaluminous to weakly peraluminous and display a general geochemical concordance that suggests a similar petrogenesis. SHRIMP U-Pb zircon ages of these clasts range from 128-123 Ma and from 147-135 Ma. These clasts are indistinguishable in age (except for the younger group), chemical composition, and petrogenesis from the felsic members of the calc-alkaline I-type granitoids of the Darran Suite, whereas alkaline rhyolitic clasts correlate best with the Electric Granite. The age range of all clasts overlaps with detrital zircon ages of the conglomerate matrix from Ethelton, indicating that Late Jurassic to Early Cretaceous magmatism was penecontemporaneous with the sedimentation of the Pahau terrane. The youngest detrital zircon from the Ethelton conglomerate matrix gives an age of 112±2 Ma that constrains the minimum age of magmatism in the source region.
An Early Jurassic calc-alkaline, weakly peraluminous rhyolite clast from Kekerengu (188±3 Ma) correlates with the calc-alkaline, weakly peraluminous to peraluminous Bounty Island Granite.
SHRIMP U-Pb zircon ages of Rakaia terrane igneous clasts define three distinct groups. The first group, Permian to Middle Triassic, ranges in age from 292-243 Ma with two subgroups recognisable, a minor one ranging in age from 292-277 Ma and a major one from 258-243 Ma. All these clasts are confined to the Kazanian Te Moana, the Dorashamian McKenzie Pass, and the Carnian Lake Hill conglomerates. The calc-alkaline to high-K calcalkaline, metaluminous to peraluminous clasts range in composition from andesites to rhyolites and their intrusive equivalents. Adakitic, mylonitic and gneissic clasts are especially common at Lake Hill.
Carboniferous, calc-alkaline, metaluminous to weakly peraluminous clasts are confined to the (?)Permian Boundary Creek conglomerate, ranging in age from 356-325 Ma, constituting the second group. Pooled individual zircon ages from igneous' clasts from the Boundary Creek conglomerate point towards a possible presence of Carboniferous sediments within the Haast Schist.
The third group consists of two Cambrian clasts, a monzogranite from Te Moana (497±8 Ma) and a dacite from Lake Hill (c. 517 Ma). These two clasts indicate that Cambrian plutons and volcanics were a protosource that provided detritus to the Rakaia depocentres. Cambrian magmatism was confined to the New Zealand Western Province and its Australian and Antarctic correlatives as well as the Transantarctic Mountains and their Australian correlatives. The presence of the Cambrian clasts indicates an autochthonous setting of the Rakaia depocentres with respect to the Gondwana margin as early as the Kazanian.
Detrital zircon age distributions from the Anisian Kurow Hill and Balmacaan Stream Rakaia sandstones identify a Permian to Triassic arc source as the main contributor of detritus to the Rakaia sedimentary basin. Geochronology, geochemistry and Sr-Nd isotopes of Rakaia igneous clasts correlate broadly with those of Permian to Triassic plutons and volcanics from the Antarctic sector of the Panthalassan margin of Gondwana.
Sandstone clasts from two Rakaia and two Pahau conglomerates were collected to investigate the recycling of the older Rakaia rocks. Petrography and geochemistry of Pahau terrane clasts indicate that at the time of the Pahau sedimentation Permian to early Late Triassic Rakaia rocks were exposed and recycled into the Pahau basin. Recycling of the Rakaia sediments into the Pahau terrane is also supported by the detrital zircon age data from this and other studies. Furthermore, the similarities of petrographic and geochemical data between sandstone clasts from the Rakaia terrane and Rakaia sandstones suggest that clasts were derived by autocannibalistic reworking of older, consolidated, Rakaia sediments.
Geochronology, geochemistry and Sr-Nd isotopes of igneous clasts from the Pahau terrane identify the Median Tectonic Zone (Darran Suite and Electric Granite) as a detritus contributor to the Pahau depositional basin. Based on sandstone and sandstone clast geochronology, geochemistry and Sr-Nd isotopes, the recycling of the older inboard Rakaia and Caples terranes into the Pahau basin is demonstrated. A multi- source model is proposed in which the uplifted Rakaia and Caples terranes as well as an active volcanic arc contributed detritus to the Pahau sedimentary basin.
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Couzinié, Simon. "Evolution of the continental crust and significance of the zircon record, a case study from the French Massif Central." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSES035.
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La formation de la croute continentale est une des conséquences majeures de la différenciation de la Terre. Les avancées récentes dans la compréhension de ce phénomène résultent de l’amélioration des techniques analytiques permettant la mesure in situ des compositions isotopiques en U-Pb-Hf-O de grains de zircon, minéral abondant dans les roches crustales. Cette étude reconstitue l’histoire du segment de croute affleurant dans l’est du Massif Central français (MCF), portion de la chaine Varisque d’Europe de l’Ouest, dans le but d’évaluer les limites d’utilisation des zircons pour retracer l’évolution crustale. L’origine et la signification géodynamique des principales unités lithologiques du MCF ont été étudiées en combinant les approches classiques de la pétrologie avec des données isotopiques U-Pb-Hf-O acquises sur zircon. Deux incohérences majeures existent entre nos résultats et les conclusions tirées de l’étude des zircons considérés hors de leur contexte pétrologique, approche généralement suivie pour analyser l’évolution crustale. Les âges modèles calculés à partir des données Hf suggèrent une importante croissance crustale au Mésoproterozoique dans le MCF, en contradiction avec le fait que 60% de la croute locale soit d’âge Néoproterozoïque. De plus, 5 à 10% de la croute du MCF a été formée durant l’orogènese Varisque sans que cela ne soit enregistré par le zircon. Dans les deux cas, ces incohérences résultent du caractère hybride des signatures isotopiques portées par les zircons. Celles-ci ne peuvent être correctement détectées et interprétées qu’en disposant de données pétrologiques complémentaires sur les roches contenant les grains analysésThe formation of the continental crust is a major consequence of Earth differentiation. Understanding how the crust formed and evolved through time is paramount to locate the vast mineral deposits hosted therein and address its influence on the global climate, ultimately affecting the development of terrestrial life. Recent advances on the topic of continental crust evolution benefited from improvements of analytical techniques enabling in situ measurements of U-Pb- Hf-O isotope compositions in zircon, a widespread accessory mineral of continental igneous rocks. The time constrains derived from the U-Pb chronometer coupled with the petrogenetic information retrieved from Hf-O isotope signatures are currently used to unravel the diversity and succession of magmatic events affecting the continental crust at the regional and global scales. This study reconstructs the evolutionary path followed by the crust segment today exposed in the eastern part of the French Massif Central (FMC), a portion of the Variscan belt of Western Europe, with the aim to investigate the potential flaws of the zircon record of crust evolution. In this scope, the origin and geodynamic significance of the constituent FMC lithological units are tackled by combining conventional petrological observations with zircon U-Pb-Hf-O isotope data. The results obtained following this integrated approach are then confronted to the conclusions that would have been drawn solely from zircon isotopic signatures, taken out of their petrological context, as is commonly performed in studies investigating crust evolution. The oldest rocks of the FMC correspond to Ediacaran (590_550 Ma) meta-sediments deposited in back-arc basins along the northern Gondwana margin. Such basins were fed by a mixed detritus originating from the adjacent Cadomian magmatic arc and a distal Gondwana source, presumably the Sahara Metacraton. Partial melting of these meta-sediments at the Ediacaran/Cambrian boundary led to voluminous S-type granitic magmatism, pinpointing a first major crust reworking event in the FMC. The origin of anatexis likely stems from the transient thickening of the hot, back-arc crust caused by the flattening of the Cadomian subduction. Subordinate melting of the depleted backarc mantle at that time is also documented. During the Lower Paleozoic, rifting of the northern Gondwana provoked coeval crust and (limited) mantle melting. Mantle-derived igneous rocks show markedly diverse trace element and isotopic signatures, consistent with a very heterogeneous mantle source pervasively modi_ed by the Cadomian subduction. Finally, the Variscan collision resulted in crustal melting as evidenced by the emplacement of S-type granites and the formation of migmatite domes, the spatial distribution of which being partly controlled by the crustal architecture inherited from pre-orogenic events. Synchronous intrusion of mafic mantle-derived magmas and their differentiates testify for Variscan post-collisional new continental crust production in the FMC. Two major inconsistencies exist between these results and the zircon record. First, zircon Hf model ages would point to substantial Mesoproterozoic crust formation in the FMC whereas more than 60% of the crust is actually Neoproterozoic in age. Second, new additions to the continental crust volume during the Variscan orogeny are not recorded even though 5 to 10% of the exposed crust formed at that time. The origin of both discrepancies inherently lies in the mixed isotopic signature carried by many zircon grains. Such equivocal information can only be detected when additional petrological constrains on the zircon host rocks are available and provide guidance in interpreting the zircon record of crust evolution
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Graessner, Thorsten. "Thermal evolution of the continental crust of Calabria during the Hercynian orogeny constraints from metamorphic phase equilibria and isotopic dating /." [S.l. : s.n.], 1999. http://e-diss.uni-kiel.de/diss=/d327.pdf.
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Iwaniw, Andrew Mark. "Evidence of recycling of Archaean continental crust : a geochemical and Nd-Sr isotope study of Gawler Craton Granitoids, South Australia /." Title page, contents and abstract only, 2000. http://web4.library.adelaide.edu.au/theses/09SB/09sbi9663.pdf.
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Cole, Philip Bruce. "Anisotropy of the zone of exhumed continental mantle and the structure of the earliest formed oceanic crust west of Iberia." Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288464.
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Gray, Benjamin M. "The origin of cyclical high- and low-Cr basalts with continental crust trace element signatures in the Kalkarindji Large Igneous Province." Thesis, Queensland University of Technology, 2015. https://eprints.qut.edu.au/81995/1/Benjamin_Gray_Thesis.pdf.
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The 510 million year old Kalkarindji Large Igneous Province correlates in time with the first major extinction event after the Cambrian explosion of life. Large igneous provinces correlate with all major mass extinction events in the last 500 million years. The genetic link between large igneous provinces and mass extinction remains unclear. My work is a contribution towards understanding magmatic processes involved in the generation of Large Igneous Provinces. I concentrate on the origin of variation in Cr in magmas and have developed a model in which high temperature melts intrude into and assimilate large amounts of upper continental crust.
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Luo, Gang Liu Mian. "Dynamic links between short-term deformation and long-term tectonics a finite element study /." Diss., Columbia, Mo. : University of Missouri--Columbia, 2009. http://hdl.handle.net/10355/6966.
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Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 26, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Mian Liu. Vita. Includes bibliographical references.
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ANTONICELLI, MARTA. "Evolution of mantle melts intruding the lower continental crust: constraints from the Rocca d’Argimonia ultramafic sequence (Ivrea Mafic Complex, southern Alps)." Doctoral thesis, Università degli studi di Pavia, 2021. http://hdl.handle.net/11571/1431715.
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Delleani, F. "DEFORMATION AND METAMORPHISM RELATIONSHIPS IN ACID AND FEMIC PROTHOLITHS OF THE AUSTROALINE CONTINENTAL CRUST SUBDUCTED AND EXHUMED IN THERMAL REGIME SEVERELY DEPRESSED." Doctoral thesis, Università degli Studi di Milano, 2013. http://hdl.handle.net/2434/216120.
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Intrusives of pre-Alpine age and their high grade country rocks, subducted-exhumed in Alpine times, has been studied with petro-structural methods, applied after quality mapping. In this subduction environment, focus was oriented on interaction of deformation and metamorphic transformation progress, in areas offering a mosaic of different tectonometamorphic steps. Such apparently incoherent distribution of structural imprints, representing various discrete states of the tectonic sequence heterogeneously frozen in adjacent space, has been recomposed into a coherent progression of deformation events by means of foliation trajectory mapping. Such work guaranteed a petrographic analysis of the mineral support of sequentially ordered planar fabrics, used for thermobarometrical estimates of the deformative and metamorphic evolution. This evaluation has been performed in acid and femic protoliths intruded in the continental crust of the Sesia-Lanzio Zone in the internal Western Alps.
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Wellhäuser, Alexander [Verfasser], Gerhard [Akademischer Betreuer] Wörner, Gerhard [Gutachter] Wörner, Tracy A. [Gutachter] Rushmer, Jonas [Gutachter] Kley, Andreas [Gutachter] Pack, Burkhard [Gutachter] Schmidt, and Simon [Gutachter] Turner. "Generating early continental crust / Alexander Wellhäuser ; Gutachter: Gerhard Wörner, Tracy A/ Rushmer, Jonas Kley, Andreas Pack, Burkhard Schmidt, Simon Turner ; Betreuer: Gerhard Wörner." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://d-nb.info/1213520525/34.
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Schlindwein, Vera. "Architecture and evolution of the continental crust of East Greenland from integrated geophysical studies = Aufbau und Entwicklungsgeschichte der kontinentalen Kruste Ostgrönlands aus integrierten geophysikalischen Untersuchungen /." Bremerhaven : Alfred-Wegener-Inst. für Polar- und Meeresforschung, 1998. http://www.gbv.de/dms/bs/toc/245800581.pdf.
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Chao, Tzu-Kai Kevin. "Temporal changes of shear wave velocity and anisotropy in the shallow crust induced by the 10/22/1999 m6.4 Chia-yi, Taiwan earthquake." Thesis, Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28088.
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Temporal changes of seismic velocity and anisotropy in the shallow crust are quantified using local earthquakes recorded at a 200-m-deep borehole station CHY in Taiwan. This station is located directly above the hypocenter of the 10/22/1999, M6.4 Chia-Yi earthquake. Three-component seismograms recorded at this station show clear direct (up-going) and surface-reflected (down-going) P- and S-waves, and S-wave splitting signals. The two-way travel times in the top 200 m is obtained by measuring the time delays between the up-going and down-going waves in the auto-correlation function. The S-wave travel times measured in two horizontal components increase by ~1-2% at the time of Chia-Yi main shock, and followed by a logarithmic recovery, while the temporal changes of S-wave splitting and P-wave are less than 1% and are not statistically significant. We obtain similar results by grouping earthquakes into clusters according to their locations and waveform similarities. This suggests that the observed temporal changes are not very sensitive to the seismic ray path below CHY, but are mostly controlled by the variation of material property in the top 200 m of the crust. We propose that strong ground motions of the Chia-Yi main shock cause transient openings of fluid-filled microcracks and increases the porosity in the near-surface layers, followed by a relatively long healing process. Because we observe no clear changes in the shear wave anisotropy, we infer that the co-seismic damages do not have a preferred orientation. Our results also show a gradual increase of time delays for both the fast and slow S-waves in the previous 7 years before the Chia-Yi main shock. Such changes might be caused by variations of water table, sediment packing or other surficial processes.