Cooling history of the Puttetti alkali syenite pluton,southern India |
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| Institution: | 1. V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia;2. Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia;1. Department of Geology, Saint Mary''s University, Halifax, NS B3H 3C3, Canada;2. Departmento de Geología Regional, Instituto de Geología, Universidad Nacional Autónoma de México, 04510 México, D.F., México;3. New Brunswick Department of Energy and Mines, Geological Surveys Branch, P.O. Box 50, Bathurst, NB E2A 3Z1, Canada;1. Tomsk State University, prosp. Lenina 36, Tomsk, 634050, Russia;2. Area de Geodinamica Interna Departamento de Geologia, Universidad de Salamanca, 37008, Salamanca, Spain;3. Senckenberg Naturhistorische Sammlungen Dresden, Museum für Mineralogie und Geologie, Königsbrücker Landstraße 159, 01109 Dresden, Germany |
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| Abstract: | The Puttetti alkali syenite pluton in southern India belongs to the suite of felsic magmatic intrusives emplaced during the Late Neoprotrozoic-Cambrian time during the final phase of amalgamation of the Gondwana supercontinent. In this study, we evaluate the cooling history of this pluton based on various isotopic systems. We present whole-rock Pb-Pb data on the syenite which yields an isochron age of 508±25Ma. Three phlogopite separates from the syenite pluton give K-Ar ages of 454.0±9.0, 448.5±8.9 and 445.6±8.8 Ma indicating cooling age at temperatures of ～415°C. U-Pb analyses of zircons from this syenite yielded an age of 572±2 Ma in a previous study. With U-Pb closure temperatures >800 o C, this age probably indicates the timing of emplacement of the Puttetti pluton. Collectively, we estimate from the isotopic age data and respective closure temperatures that the syenite body cooled at about 3.2 o C/Ma from about 800 o C to about 415 o C. The markedly low cooling rate of the syenite pluton, absence of chilled margin effects, and common occurrence of pyroxene, feldspar, phlogopite and zircons megacrysts in the rock indicate that the host granulites were at high temperatures during the emplacement of the syenite magma. The cooling history of Puttetti syenite estimated in this study is closely comparable with the 3–4 o C/Ma cooling rate estimated for a granite pluton in a previous study from Madagascar. Our study suggests protracted cooling rates for the late Pan-African intrusives emplaced within the Gondwana crust, with a long residence history in a hot crust bore they were exhumed to shallower levels. |
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