Geochemistry of ophiolite cherts from the Qinling orogenic belt and implications for their tectonic settings  

作　　者：ZHANG Chengli GAO Shan ZHANG Guowei GUO Anlin YUAN Honglin LIU Xiaoming WANG Jianqi 

机构地区：[1]The key Laboratory of Continental Dynamics,Ministry of Education,Department of Geology,Northwest University,Xian 710069 China [2]State Key Laboratory for Mineral Deposits Research,Nanjing University,Nanjing 210093,China [3]Department of Geochemistry,China University of Geosciences,Wuhan 430074,China

出　　处：《Science China Earth Sciences》2004年第4期329-337,共9页中国科学（地球科学英文版）

基　　金：This project was jointly supported by the NationalNatural Science Foundation of China (Grant Nos. 40372039,40032010-C, 40133020 and 49732080);the Foundations of Senior Visiting Scholarship of Colleges in Western areas and Backbone Teacher of Ministry of Education, China (Grant No. 2000-143).

摘　　要：Paleozoic cherts from the Mianl and the Erlangping ophiolite zones of the Qinling orogenic belt are characterized by low Si/Al ratios (52.14-683.52 in the Mianle cherts, 12.29-58.62 in the Erlangping cherts), Fe2O3 (0.01-0.35 and 0.02-1.24) and high Al2O3/(Al2O3+Fe2O3) ratios (0.82-0.99 and 0.83-0.99). The negative correlation between Si2O and Al2O3 in the cherts reflects the important role of terrigenous components. The Erlangping cherts have Lan/Cen=0.9-1.15 and Ce/Ce*=0.95-1.15 with low contents of V, Ni and Cu, consistent with those of cherts forming on the continental margin. In contrast, the Ce/Ce* ratios of the Mianle cherts range from 0.71 to 1.18 and Lan/Cen from 0.88 to 1.43 with slightly high V, Ni and Cu, which are similar to cherts found in the mid-ocean ridges and pelagic basins. Combined with the features of basic lavas associated with the cherts, it is suggested that during the Paleozoic, when the back-arc basin represented by the Erlangping ophiolite commenced shrinking in size in the mid-Ordovician, the southern Qinling was still in an extensional regime and finally grew into a new limited oceanic basin in the early Carboniferous.Paleozoic cherts from the Mianl and the Erlangping ophiolite zones of the Qinling orogenic belt are characterized by low Si/Al ratios (52.14-683.52 in the Mianle cherts, 12.29-58.62 in the Erlangping cherts), Fe2O3 (0.01-0.35 and 0.02-1.24) and high Al2O3/(Al2O3+Fe2O3) ratios (0.82-0.99 and 0.83-0.99). The negative correlation between Si2O and Al2O3 in the cherts reflects the important role of terrigenous components. The Erlangping cherts have Lan/Cen=0.9-1.15 and Ce/Ce*=0.95-1.15 with low contents of V, Ni and Cu, consistent with those of cherts forming on the continental margin. In contrast, the Ce/Ce* ratios of the Mianle cherts range from 0.71 to 1.18 and Lan/Cen from 0.88 to 1.43 with slightly high V, Ni and Cu, which are similar to cherts found in the mid-ocean ridges and pelagic basins. Combined with the features of basic lavas associated with the cherts, it is suggested that during the Paleozoic, when the back-arc basin represented by the Erlangping ophiolite commenced shrinking in size in the mid-Ordovician, the southern Qinling was still in an extensional regime and finally grew into a new limited oceanic basin in the early Carboniferous.

关 键 词：Qinling orogenic belt radiolarian cherts ophiolite m閘ange zone. 

分 类 号：P59[天文地球—地球化学]