湘川地区上震旦—下寒武统硅岩的锶同位素特征  

CHARACTERISTICS OF STRONTIUM ISOTOPIC COMPOSITIONS OF THE LATE SINIAN-EARLY CAMBRIAN CHERTS FROM THE XIANGCHUAN DISTRICT AND ITS ORIGINS

作　　者：唐世荣[1] 王东安[2] 叶连俊[2] 

机构地区：[1]浙江农业大学环境与资源学院土化系 [2]中国科学院地质研究所

出　　处：《桂林工学院学报》1998年第1期16-21,共6页Journal of Guilin University of Technology

基　　金：国家自然科学基金

摘　　要：该区上震旦统—下寒武统层状硅岩发育。从该区采集到的硅岩样品中选取９个硅岩样品进行Ｒｂ，Ｓｒ同位素分析结果表明，硅岩的Ｒｂ含量为１．１３８×１０－６～３１．６９８×１０－６，平均９．５７９×１０－６，Ｒｂ／Ｓｒ值为０．１４～１．５３，平均０．６４９。在８７Ｓｒ／８６Ｓｒ－８７Ｒｂ／８６Ｓｒ等时线图上，９个硅岩样品点基本位于一条直线上，相关系数γ＝０．９６７９，呈极显著相关，硅岩的（８７Ｓｒ／８６Ｓｒ）ｉ＝０．７０９５５０。表明形成硅岩的物质来源可能具有多源性，包括陆源、热水来源和火山来源。硅岩的Ｒｂ－Ｓｒ等时线年龄为６１３Ｍａ左右，与用其它方法所得的年龄如硅岩的生物地层年龄基本相近。反映本区硅岩为原生沉积产物，其硅质物质的有序化作用发生在沉积－成岩阶段。Late Sinian-early Cambrian bedded cherts are well developed in the district. Nine late Sinian-early Cambrian chert samples were selected for analysis of rubidium and strontium isotopic compositions. Our study results show that the cherts contain rubidium contents ranging from 1.138 to 31.698 mg/kg and averaging 9.579 mg/kg with Rb/Sr ratios of 0.14 to 1.53 and average ratio 0.649. A good correlation were observed on the 87 Rb～ 87 Sr isochron diagram yielding a Rb-Sr age of 613.8209 Ma with an initial 87 Sr/ 86 Sr ratio of 0.709550 for all samples. This age is closed to that determined using other methods such as biostratigraphy. All those lines of evidence suggest that cherts were primary and formed through silica recrystalization during the sedimentary-diagenetic stage and that the silica might be derived from multiple sources including continental, hydrothermal and volcanic ones.

关 键 词：锶同位素 硅 上震旦统 岩石成因 下寒武统 

分 类 号：P588.244[天文地球—岩石学] P597[天文地球—地质学]