地质学报2017，Vol.91Issue(10)：2322-2350,29.
扬子板块北缘早—中志留世硅质岩成因及古沉积环境的地球化学研究
Origin and Paleodepositional Environment of the Early-Middle Silurian Bedded Chert on the Northern Margin of the Yangtze Block:Evidence from Geochemical Study
摘要
Abstract
In this study,we performed an inorganic geochemical study of Early-Middle Silurian bedded organic C-enriched cherts in the region between northern Ruoergai (Zoigê) County and Diebu (Têwo) County,central China.The goal of this study is to determine the origin and paleodepositional environment of the chert beds and to establish a depositional model for the Yangchanggou Formation-Lalong Formation in the study area.An integrated study,involving petrographic analysis,scanning electron microscopy (SEM)analysis,major,trace and rare earth element analyses,organic carbon content analysis,and Si,and O isotopic analyses,has been performed on twenty-eight chert samples from the Yangchanggou Formation,Taer Formation and Lalong Formation of the Bailongjiang Group.Based on the petrographic,SEM,Fe/Ti,Al/(Al+Fe+Mn) (0.08～0.79;average 0.31),(Fe+Mn)/Ti (4.20 ～ 205.23;average 61.94),(La/Yb)N (0.12～1.41;average 0.54),δEu (0.81～3.36;average 1.55),ΣREE (7.59 ～ 253.48;average 82.90),Si isotope (-0.2‰～2.1‰;average 0.66‰),and O isotope (13.5‰～21.8‰) average 19.53‰) results and the diagenetic temperatures inverted from the O and Si isotopic data,the chert samples are primarily hydrothermal in origin,with some evidence of biogenic chert (based on the Si and O isotopic compositions).During the deposition of the Taer Formation,terrigenous material mixed with the paleo-seawater,promoting the growth of carbonate-producing organisms.Minor samples exhibit effect of terrigenous detrital material.Additionally,the petrographic,SEM,MnO2/TiO2,Al2O3/(Al2O3+Fe2O3)(0.11～0.84;average0.37),Al/(Al+Fe) (0.08～0.80;average0.33),Th/U,V(28.6×10-6～2261×10 6;average 454.42 × 10 6),Ti/V,δCe (0.65 ～ 1.58;average 1.01),and (La/Ce)N (0.60 ～ 1.314;average 0.97) results and the REE,TOC,and trace element (U,V,Mo,Cu,Ni) patterns indicate that the chert samples were deposited on a continental margin in an anoxic environment with strong hydrodynamic conditions.Portions of the chert samples have characteristics typical of mid-ocean ridge and ocean basin environments (i.e.,they are enriched in hydrothermal elements).In combination with previous research results,we conclude that the siliceous rock formed in a continental margin extensional environment on the northern margin of the Yangtze Block.This environment was characterized by well developed hydrothermal activity and anaerobic condition,which was conducive to enrichment of U,V,Mo,Cu,and Ni.The lower Paleozoic (Cambrian-Silurian) black shale in the northern margin of the Yangtze Block deposited in anoxic to reducing conditions in the extensional continent margin.关键词
硅质岩/成因/古构造环境/早—中志留世/扬子板块北缘Key words
Siliceous rock/origin/depositional environment/Early-Middle Silurian/northern margin of the Yangtze Block引用本文复制引用
张岩,漆富成,陈文,叶会寿..扬子板块北缘早—中志留世硅质岩成因及古沉积环境的地球化学研究[J].地质学报,2017,91(10):2322-2350,29.基金项目
本文为中国黑色岩系非常规铀资源矿集区成矿条件分析及资源预测评价(编号201493)、湘中地区黑色岩系非常规铀资源调查及远景评价(编号201768)、中国地质科学院基本科研业务费项目(编号YYWF201707)共同资助的成果. （编号201493）
