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Very Low-Grade Metamorphism of Clastic Rocks from the Meso-Neoproterozoic and the Paleozoic along the Profile Yueyang-Linxiang in Northeastern Hunan Province and Its Geological Implications

查看全文 作　　者：WANG [1,2]Hejing;YUAN [1]Lei;WANG [1]Ling;ZHOU [1]Zhao;AN [1]Jiali 高影响力作者 机构地区：[1]School of Earth and Space Sciences,Peking University;[2]Key Laboratory of Orogenic Belt and Crustal Evolution,Ministry of Education高影响力机构 出　　处：《Acta Geologica Sinica(English Edition)》索引2016年第90卷第5期,共11页高影响力期刊 基　　金：supported by the National Natural Science Foundation of China(Grant No 41372061 and 40821002) 摘　　要：This study uses illite crystallinity,chlorite crystallinity,illite polytypes,the b_0 cell-dimension of K-white mica,clay mineral assemblages and mineral geothermo-geobarometers to investigate the overprint of diagenesis and metamorphism on the Meso-Neoproterozoic and the Lower Paleozoic along the profile Yueyang-Linxiang in northeastern Hunan Province,China.Illite crystallinity Kbler index(KI) of the <2μm fractions ranges from 0.225 to 0.485°Δ2θ while chlorite crystallinity Arkai index(AI) ranges from 0.244 to 1.500°Δ2θ.This indicates that the Meso-Neoproterozoic and the Lower Paleozoic along the profile Yueyang-Linxiang were overprinted with diagenesis and anchi- to epimetamorphism.Peak metamorphic temperature is estimated with the IV site chlorite geothermometer roughly at 360℃.The b_0 cell dimension values of illites(K-mica) range from 0.9002 to 0.9054 nm and,on average,at 0.9030 nm for the Meso-Neoproterozoic.Based on cumulative frequency curves of illite(K-mica) b_0 cell dimension,the peak metamorphic pressure of the MesoNeoproterozoic along the profile Yueyang-Linxiang is derived of an intermediate pressure type.Most illites occur in the 2M_1 polytype and some of them in a mixture of 2M1+1M types especially those in the Paleozoic.This result partly agrees with the conclusion of the lower greenschist and greenschist facies of the Lengjiaxi and Banxi Groups.However,it is not agreed with the sedimentary cover from the Sinian to the Lower Paleozoic or from the Banxi Group to the Lower Paleozoic.Crustal thickening due to 'collision' between the Yangtze and Cathaysia blocks led to an increase in the thickness of the Meso-Neoproterozoic to ca.14 km and resulted in a temperature increase in those rocks due to burial.The very low grade to low grade metamorphism overprinting the Meso-Neoproterozoic implies that the so called 'Chiangnania or Jiangnan orogen' was no relative with the 'Grenvillian orogeney;instead,it might be a continuous amalgamation product between the Yangtze and Cathaysia blocks. 关 键 词：成岩作用 很低档变态 illite crystallinity MESO-NEOPROTEROZOIC 更低的 palaeozoic
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