湖南安化留茶坡硅质岩的REE地球化学特征及其意义  

REE geochemistry of the Liuchapo chert in Anhua, Hunan

作　　者：常华进[1,2,3] 储雪蕾[1,2] 冯连君[1,2] 黄晶[1,2,3] 张启锐[1] 

机构地区：[1]中国科学院地质与地球物理研究所,北京100029 [2]中国科学院矿产资源研究重点实验室,北京100029 [3]中国科学院研究生院,北京100049

出　　处：《中国地质》2008年第5期879-887,共9页Geology in China

基　　金：国家自然科学基金项目(40532012;40603021);中国科学院知识创新工程项目(KZCX3-SW-141)资助

摘　　要：湖南安化留茶坡硅质岩沉积在埃迪卡拉纪末期(551～542Ma)的深水盆地中,它们具有如下REE地球化学特征:和PAAS相比,∑REE含量很低(8.6×10-6～18×10-6,平均13.6×10-6),Y/Ho比值较高(33.6～43.9,平均37.4),接近现代海水的Y/Ho比值(44);正的La异常(LaN/CeN平均为1.46),中等负的Ce异常(平均0.65),弱的正Eu异常(平均1.1),正的Gd异常(平均1.07),正的Y异常(平均1.22),LREE和MREE相对于HREE亏损(LaN/YbN平均为0.17,GdN/YbN平均为0.45),显示出和现代海水相似的REE特征,而与海底热液流体及与热液有关的碧玉的REE特征明显不同。这些表明留茶坡硅质岩受陆源碎屑及热液流体的影响很小。留茶坡硅质岩是由风化作用大量带入海洋的溶解的硅质化学沉积而成的。生物作用促进了海水中溶解硅质的沉淀。The Liuchapo chert in Anhua County, Hunan Province, South China, was deposited in a terminal Ediacaran （551-542 Ma） deep-sea basin. It has the following REE geochemical characteristics： it has very low REE concentrations （range 8.6×10^-6-18×10^-6;average 13.6×10^-6） and high Y/Ho ratios （range 33.6-43.9; average 37.4）, indicating that the ratio is close to that of modem seawater. They are also characterized by positive La anomalies （LaN/CeN 1.46 on average）, moderate negative Ce anomalies （average 0.65）, weak positive Eu anomalies （average 1.1）, positive Gd anomalies （average 1.07）, positive Y anomaly （average 1.22） and depletion of LREE and MREE relative to HREE （LaN/YbN 0.17 on average;GdN/YbN 0.45 on average）. These characteristics are similar to those of modem seawater but notably different from those of hydrothermal fluids or jasper related to seafloor hydrothermal sulfide deposits, suggesting the influence of terrigenous detrital input and hydrothermal fluids on is trivial and negligible. The Liuchapo chert formed by chemical deposition of huge amount of dissolved silica that was produced by chemical weathering and brought to the sea. Biological processes promoted precipitation of dissolved silica in seawater.

关 键 词：硅质岩 海水 热液 REE 埃迪卡拉纪 留茶坡组 湖南 

分 类 号：P595[天文地球—地球化学] P534.31[天文地球—地质学]