Paleoproterozoic emplacement and Cambrian ultrahigh-temperature metamorphism of a layered magmatic intrusion from the Central Madurai Block,southern India:From Columbia to Gondwana  

作　　者：Bing Yu M.Santosh Ming-Xian Wang Cheng-Xue Yang 

机构地区：[1]School of Earth Sciences and Resources,China University of Geosciences Beijing,No.29 Xueyuan Road,Haidian District,Beijing 100083,China [2]Department of Earth Science,University of Adelaide,Adelaide,SA 5005,Australia

出　　处：《Geoscience Frontiers》2022年第1期28-45,共18页地学前缘（英文版）

基　　金：funded by Foreign Expert grants to M.Santosh from the China University of Geosciences(Beijing)。

摘　　要：The Madurai Block in the Southern Granulite Terrane(SGT)of Peninsular India is one of the largest crustal blocks within the Neoproterozoic Gondwana assembly.This block is composed of three sub-blocks:the Neoarchean Northern Madurai block,Paleoproterozoic Central Madurai block and the dominantly Neoproterozoic Southern Madurai Block.The margins of these blocks are well-known for the occurrence of ultrahigh-temperature(UHT)granulite facies rocks mostly represented by Mg-Al metasediments.Here we report a dismembered layered mafic–ultramafic intrusion occurring in association with Mg-Al granulites from the classic locality of Ganguvarpatti in the Central Madurai Block.The major rock types of the layered intrusion include spinel orthopyroxenite,garnet-bearing gabbro,gabbro and gabbroic anorthosite showing rhythmic stratification and cumulate texture.The orthopyroxene-cordierite granulite from the associated Mg-Al layer is composed of spinel,cordierite and orthopyroxene.The pyroxene in both rock units is high-Al orthopyroxene formed under UHT metamorphic conditions.Conventional thermobarometry yields near-peak metamorphic conditions of 9.5–10 kbar pressure and a minimum temperature of 980℃.We computed P–T pseudosections and contoured for the compositional as well as modal isopleths of the major mineral phases,which yield temperature above 1000℃.FMAS petrogenetic grid,Al-in-orthopyroxene isopleth,conventional thermobarometry and calculated pseudosection reveal a clockwise pressure–temperature(P–T)path and near isothermal decompression.The U–Pb data on zircon grains from the layered magmatic suite indicate emplacement of the protolith at ca.2.0 Ga and the metamorphic overgrowths yield weighted ^(206)Pb/^(238)U mean ages ca.520 Ma.Monazite from the garnet-bearing gabbro and Opx-Crd granulite yielded ^(206)Pb/^(238)U weighted mean ages of ca.532 Ma and 523 Ma marking the timing of metamorphism.We correlate the layered intrusion to a Paleoproterozoic suprasubduction zone setting,defining the Ganguvarpatti ar

关 键 词：Mafic-ultramafic layered intrusion Ultrahigh-temperature metamorphism Zircon and monazite geochronology Central Madurai Block Southern Granulite Terrane 

分 类 号：P588.3[天文地球—岩石学]