Geochemical evolution of the Mangalwar Complex,Aravalli Craton,NW India:Insights from elemental and Nd-isotope geochemistry of the basement gneisses

作     者：Iftikhar Ahmad M.E.A.Mondal Rajneesh Bhutani M.Satyanarayanan 

作者机构：Department of GeologyAligarh Muslim UniversityAligarh 202002India Department of Earth SciencesPondicherry UniversityPuducherry 605014India CSIR-National Geophysical Research InstituteHyderabad 500007India 

出 版 物：《Geoscience Frontiers》 (地学前缘（英文版）)

年 卷 期：2018年第9卷第3期

页      面：931-942页

核心收录：

学科分类：07[理学] 

基　　金：A.M.U CSIR-NGRI Owl Research Institute University of Miami Society for Sedimentary Geology University Grants Commission University of Hyderabad National Physical Laboratory Himalayan Institute Hospital Trust 

主　　题：Aravalli Craton Mangalwar Complex Nd-isotope geochemistry Grey gneisses Sanukitoid High-K granitoids 

摘      要：The Banded Gneissic Complex(BGC) of the Aravalli Craton is divided into BGC-I and BGC-Ⅱ; the BGC-Ⅱ(central Rajasthan) is comprised of the Sandmata Complex and the Mangalwar Complex. We report elemental and Nd-isotope geochemistry of basement gneisses of the Mangalwar Complex and constrain its origin and evolution. Geochemically, the basement gneisses have been classified as low-SiO_2 gneisses(LSG) and high-SiO_2 gneisses(HSG). Both the LSG and HSG are potassic, calc-alkaline and peraluminous in nature. The LSG are enriched in incompatible(K, Sr, Ba, large ion lithophile elements) and compatible elements(MgO, Cr, and Ni). They display fractionated rare earth element patterns(***_N/Yb_N=12.1)with small Eu-anomaly(δEu=0.9), and exhibit negative anomalies of Nb and Ti in primitive mantlenormalized multi-element diagram. In terms of Nd-isotope geochemistry, the LSG are characterized by_(εNd)(t)=4.2 and depleted mantle model age of 3.3 Ga. To account for these geochemical characteristics we propose a three-stage petrogenetic model for the LSG:(1) fluids released from dehydration of subducting slab metasomatised the mantle-wedge;(2) the subducting slab underwent slab-breakoff causing upwelling and decompression melting of the asthenosphere during waning stage of subduction; and(3)upwelling asthenosphere provided the requisite heat for partial melting of the metasomatised mantlewedge leading to generation of the LSG parental magma. Asthenospheric upwelling also contributed in the LSG petrogenesis which is evident from its high Mg#(avg. 0.53). The LSG formed in this way are contemporary and chemically akin to sanukitoids of the BGC-I and Archean sanukitoids reported elsewhere. This provides a basis to consider the LSG as a part of the BGC-I. Contrary to the LSG, the HSG are depleted in compatible elements(MgO=avg. 1.1 wt.%; Cr=avg. 8 ppm; Ni=avg. 6 ppm) but enriched in incompatible elements(Sr=avg. 239 ppm, Ba=avg. 469 ppm). Its_(εNd)(t) values vary from-9.5 ***