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  • 1
    Keywords: India ; Archean granitoids ; Indian cratons ; Archean supercontinents ; Archean tectonics ; early earth
    Description / Table of Contents: 8 January 2019 --- Deformation-driven emplacement-differentiation in the Closepet Pluton, Dharwar Craton, South India: an alternative view / Abhijit Bhattacharya / Geological Society, London, Special Publications, 489, https://doi.org/10.1144/SP489-2019-315 --- Mineral-fluid interactions in the late Archean Closepet granite batholith, Dharwar craton, southern India / Ewa Slaby, Katarzyna Gros, Hans-Jürgen Förster, Alicja Wudarska, Łukasz Birski, Morihisa Hamada, Jens Götze, Hervé Martin, Mudlappa Jayananda, Jean-François Moyen and Izabela Moszumańska / Geological Society, London, Special Publications, 489, https://doi.org/10.1144/SP489-2019-287 --- Dissecting through the metallogenic potentials of older granitoids - case studies from Bastar and Eastern Dharwar cratons India / Dinesh Pandit, Sourabh Bhattacharya and Mruganka Kumar Panigrahi / Geological Society, London, Special Publications, 489, https://doi.org/10.1144/SP489-2019-342 --- Archaean granitoids of Bastar craton, Central India / M. E. A. Mondal, M. Faruque Hussain and Talat Ahmad / Geological Society, London, Special Publications, 489, https://doi.org/10.1144/SP489-2019-311
    Edition: online first
    Language: English
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  • 2
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    Geological Society of America (GSA)
    In: Geology
    Publication Date: 2014-01-28
    Description: How the Earth’s earliest crust was formed and when present-day plate tectonics (i.e., subduction) and life commenced remain fundamental questions in Earth sciences. Whereas the bulk composition of the crust is similar to that of rocks generated in subduction settings, it does not necessarily follow that melting and crust formation require subduction. Many workers suggest that subduction may have only commenced toward the end of the Archean or later. Here we observe that both the stratigraphy and geochemistry of rocks found in Quebec, Canada, that have been variously argued to be 4.4 or 3.8 Ga in age, closely match those from the modern-day Izu-Bonin-Mariana forearc. We suggest that this geochemical stratigraphy might provide a more robust test of ancient tectonic setting than individual chemical or isotopic signatures in rocks or detrital minerals. If correct, the match suggests that at least some form of subduction may have been operating as early as the Hadean or Eoarchean. This could have provided an ideal location for the development of first life.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
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  • 3
    Publication Date: 2012-03-01
    Description: This paper discusses the deformation pattern of the Murchison Greenstone Belt, which is located in the northeastern Kaapvaal Craton, South Africa. The belt strikes northeast to southwest, is surrounded by gneisses and granitoids, and contains Meso-Archaean metavolcanics and metasediments. It is narrow, strongly deformed, and deeply rooted in the centre with a bulk keel geometry. Regional fabrics consist of a sub-vertical foliation at a low angle to the belt strike and bears steeply plunging lineations. From available data and our observations, we constructed a map of the foliation trajectories. The map reveals the following: the deformations are distributed, both the belt and the northern bounding gneisses are deformed together in a ductile way, and the plutons were emplaced during regional deformation. The overall structural pattern, together with the existence of contemporaneous intrusive and extrusive rocks outcropping at the surface, supports a vertical tectonic model, with burial of the upper crustal rocks within the underlying weak material during horizontal crustal shortening. The occurrence of leucogranite intrusions is consistent with the melting of buried sediments belonging to the belt at depth. Finally, ages available on syn-kinematic granitoids (2.97 to 2.77 Ga) suggest a long-lasting tectonic process.
    Print ISSN: 1012-0750
    Topics: Geosciences
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  • 4
  • 5
    Publication Date: 2011-12-23
    Description: Growth and regrowth textures, trace element and oxygen isotope compositions, and water content or species have been studied in alkali feldspars from the late Archaean Closepet igneous bodies. Feldspar crystals grew from mixed magmas that are characterized by a high degree of homogenization. The 3D depiction of trace element distribution indicates that the crystallization process was followed by interaction with fluids. The magmatic system involved in feldspar formation shows non-linear dynamics. The interaction with fluids is also deterministic, but in contrast to magmatic crystallization, it shows an increasing persistency in element behaviour. The degree of persistency of the element activities in both processes has been calculated using the Hurst exponent. The recrystallization (regrowth) process induced by fluids proceeded along crystal fractures and cleavages, causing selective enrichment in large ion lithophile elements (light rare earth elements), Pb, Y, and in various water species. It did not change the feldspar oxygen isotope signature. In turn, the incorporation of hydrogen species into feldspar domains reduced Al–O – –Al defect densities in the structure, decreasing their luminescence. Water speciation shows persistent behaviour during heating, the process being reversible at least up to 600°C. Carbonate crystals with a mantle isotope signature are associated with the re-equilibrated feldspar domains. The feldspar compositions, the abundance of water species in them and the refractory nature of the residuum after heating, the unchanged oxygen isotopes and the mantle signature of co-precipitated carbonates testify that the observed recrystallization has taken place at temperatures above 600°C with H 2 O–CO 2 fertile, mantle-derived fluids. The paper draws special attention to some methodological aspects of the problem. The multi-method approach used here (major element, trace element and isotope geochemistry, infra-red, cathodoluminescence, 3D depiction of geochemical data and fractal statistics) may help to recognize and separate the various processes throughout the alteration history of the pluton.
    Print ISSN: 0022-3530
    Electronic ISSN: 1460-2415
    Topics: Geosciences
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  • 6
    Publication Date: 2019
    Description: 〈p〉Modern quantitative phase equilibria modelling allows the calculation of the stable phase assemblage of a rock system given its pressure, temperature and bulk composition. A new software tool (Rcrust) has been developed that allows the modelling of points in pressure–temperature–bulk composition space in which bulk compositional changes can be passed from point to point as the system evolves. This new methodology enables quantitative process-oriented investigation of the evolution of rocks. Procedures are outlined here for using this tool to model: 1) the control of the water content of a subsolidus system based on available pore space; 2) triggering of melt loss events when a critical melt volume threshold is exceeded, while allowing a portion of melt retention; 3) entrainment of crystals during segregation and ascent of granitic magmas from its source; 4) modification of the composition of granite magmas due to fractional crystallization and 5) progressive availability (through dissolution) of slow diffusing species and their control on the effective bulk composition of a system. These cases collectively illustrate thermodynamically constrained methods for modelling systems that involve mass transfer.〈/p〉 〈p〉Supplementary material at 〈a href="https://doi.org/10.6084/m9.figshare.c.4388291"〉https://doi.org/10.6084/m9.figshare.c.4388291〈/a〉〈/p〉
    Print ISSN: 0375-6440
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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  • 7
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    Geological Society of London
    Publication Date: 2019
    Description: 〈p〉The origin of large I-type batholiths remains a disputed topic. One model states that I-type granites form by partial melting of older crustal lithologies (amphibolites or intermediate igneous rocks). In another view, granite are trapped rhyolitic liquids occurring at the end of fractionation trends defining a basalt-andesite-dacite-rhyolite series.〈/p〉 〈p〉This paper explores the thermal implications of both scenarios, using a heat balance model that abstracts the heat production and consumption during crustal melting. Heat is consumed by melting and by losses through the surface (conductive or advective, as a result of eruption). It is supplied as a basal conductive heat flux, as internal heat production, or as advective heat carried by an influx of hot basalt into the crust.〈/p〉 〈p〉Using this abstract approach, it is possible to explore the role different parameters have on the balance of granites formed by differentiation of basalts or by crustal melting. Two end-member situations appear equally favorable to generate large volumes of granites: (i) short-lived environments dominated by high basaltic flux, where granites result mostly from basalt differentiation. (ii) long-lived systems with no or minimal basalt flux, with granites resulting chiefly of crustal melting.〈/p〉 〈p〉Supplementary material at 〈a href="https://doi.org/10.6084/m9.figshare.c.4386545"〉https://doi.org/10.6084/m9.figshare.c.4386545〈/a〉〈/p〉
    Print ISSN: 0375-6440
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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  • 8
    Publication Date: 2019
    Description: 〈p〉Whole-rock geochemistry represents a powerful tool in deciphering petrogenesis of magmatic suites, including granitoids, that can be used to formulate and test hypotheses qualitatively and often also quantitatively. Typically, it can rule out impossible/improbable scenarios and further constrain the process inferred on geological and petrological grounds. With the current explosion of high-precision data, both newly acquired and retrieved from extensive databases, the whole-rock geochemistry-based petrogenetic modelling of igneous rocks will gain further importance. Especially promising is its combination with thermodynamic modelling into a single, coherent and comprehensive software, using the R and Python languages.〈/p〉 〈p〉Supplementary material at 〈a href="https://doi.org/10.6084/m9.figshare.c.4386692"〉https://doi.org/10.6084/m9.figshare.c.4386692〈/a〉〈/p〉
    Print ISSN: 0375-6440
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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  • 9
    Publication Date: 2019
    Description: 〈p〉This paper descibes the petrology, geochemistry and petrogenesis of Archaean granitoids. Archaean granites define a continuum of compositions, between several end-members: (i) magmas that originated by partial melting of a range of crustal sources, from amphibolites to metasediments ("C-type" granitoids); (ii) magmas that formed by partial melting of an enriched mantle source, the most common agent of enrichment being felsic (TTG) melts. Differences in the degree of metasomatim results in different primitive liquids for these "M-type" granitoids.〈/p〉 〈p〉Mixed sources, differentiation and interactions between different melts resulted in a continuous range of compositions, defined by variable proportions of each end-member.〈/p〉 〈p〉During the Archaean, evolved crustal sources (sediments or felsic crust) and metasomatized mantle sources become increasingly more important, mirroring the progressive maturation of crustal segments, and the stabilization of the global tectonic system.〈/p〉
    Print ISSN: 0375-6440
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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  • 10
    Publication Date: 2019
    Description: 〈p〉The chemical composition of different rocks as well as volatile-bearing and volatile-free minerals has been used to assess the presence of fluids in the Closepet batholith and to estimate the intensity of the fluid–rock interactions. The data were processed using polytopic vector analysis (PVA). Additional data include measurements of water content in the structure of volatile-free minerals and an examination of growth textures. The composition of mineral domains indicated formation/transformation processes with common fluid–mineral interactions. In general, the results suggested that the processes occurred in a ternary system. Two end-members were likely magmas and the third was enriched in fluids. In contrast, analysis of the apatite domains indicated that they likely formed/transformed in a more complex, four-component system. This system was fluid-rich and included hybrid magma with a large mafic component. PVA implies that the fluids do not appear to come from one source, given their close affinity and partial association with mantle-derived fluids. A dynamic tectonic setting promoting heat influx and redistribution, and interaction of fluids suggests that the formation/transformation processes of minerals and rocks occurred in a hot-spot like environment.〈/p〉 〈p〉〈b〉Supplementary material:〈/b〉 〈a href="https://doi.org/10.6084/m9.figshare.c.4356926"〉Fig. S1 (〈b〉a〈/b〉) Representative raw-, (〈b〉b〈/b〉) fitted- and (〈b〉c〈/b〉) deconvolved-IR spectrum; 〈inter-ref locator="https://doi.org/10.6084/m9.figshare.c.4356926" locator-type="url"〉Table S1〈/inter-ref〉 Whole rock analyses of Closepet granite available at 〈inter-ref locator="https://doi.org/10.6084/m9.figshare.c.4356926" locator-type="url"〉https://doi.org/10.6084/m9.figshare.c.4356926〈/inter-ref〉〈/a〉〈/p〉
    Print ISSN: 0375-6440
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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