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  • 1
    Keywords: India ; Archean granitoids ; Indian cratons ; Archean supercontinents ; Archean tectonics ; early earth
    Notes: This book presents a synthesis of research into Archean Indian granitoids. This volume will provide an update of Archean granitoids from each Indian craton and will examine emplacement mechanisms, petrogenesis, temporal distributions, geodynamic settings and mineralization. The implications for Archean tectonics, changes in geodynamics and reconstructions of Archean supercontinents will also be highlighted. | 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
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  • 2
    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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  • 3
    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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  • 4
  • 5
    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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