Geochemistry and petrogenesis of the Paleoproterozoic orthogneisses and granitoids of the Banded Gneissic Complex,central Rajasthan,NW India:Implications for crustal reworking processes  

作　　者：Iftikhar Ahmad T.P.Abdul Latheef M.E.A.Mondal Ismail S.Hamidullah Kamaal Parvez 

机构地区：[1]Department of Geology,Aligarh Muslim University,Aligarh,U.P 202002,India [2]Department of Earth Sciences,Indian Institute of Technology Roorkee,Roorkee 247667,India

出　　处：《Acta Geochimica》2023年第2期373-386,共14页地球化学学报（英文）

基　　金：supported by the Science and Engineering Research Board(SERB),Government of India,New Delhi,under a Major Research Project(File No.CRG/2019/000088)sanctioned to MEAM.

摘　　要：Granitoids and orthogneisses(1.7 Ga)from the northern part of the Banded Gneissic Complex(BGC-II domain),Aravalli Craton(NW India)are geochemically analyzed to understand the geodynamic condition and crustal evolution processes.The samples are metaluminous to peraluminous(molar A/CNK:0.74±2.12),and characterized by Eu-anomaly ranging from 0.17 to 1.06,Fe_(2)O_(3)^(T)/(Fe_(2)O_(3)^(T)+MgO)from 0.8 to 0.9 and high magmatic zircon saturation temperature(>830°C)which are the features suggestive of A-type granite affinity.Tectonic discrimination diagrams classify the samples as post-collisional extensional A2-type granites.Geochemical characteristics along with trace element ratios[(Y/Nb)_(N)=0.15 to 4.33(avg.0.76),(Th/Nb)_(N)=4.63 to 255.47(avg.63.13),(Th/Ta)_(N)=1.37 to 9.84(avg.8.86),(Ce/Pb)_(N)=0.05 to 3.05(avg.1.43)]indicate that the rocks were derived from a plagioclase-rich and garnet-free crustal source under lowpressure conditions.Further,it is also proposed that tonalite-trondhjemite-granodiorite(TTG)rocks which occur dominantly in southern Rajasthan(BGC-I)are precursors and their partial melting led to the generation of the studied A-type granite samples.The studied samples also bear close geochemical similarity with A-type granites of similar age(1.7 Ga)near the Sakhun-Ladera region of northern BGC-II.The studied A-type granites are believed to be coeval to similar aged A-type granites of the Khetri and Alwar sub-basins of the North Delhi Fold Belt(NDFB).They are comparable in age and magmatic history to recorded A-type magmatism in North America and parts of the Chinese craton.The large geographical extents of synchronous A-type granites are proposed to be related to the Columbia Supercontinent assembly(ca.1.7 Ga;postcollisional granites).Thus,based on the studied extensional granites,we surmise that BGC-II was part of the Columbia Supercontinent.

关 键 词：Banded Gneissic Complex(BGC II) Aravalli Craton A-type granites Orthogneisses Rifting of Columbia 

分 类 号：P588.3[天文地球—岩石学] P597.3[天文地球—地质学] P542