四川攀枝花昔格达组及其下伏河流砾石的地球化学特征以及对物源的制约  

Geochemical characteristics of Xigeda lacustrine sediments,underlying fluvial gravels and its constraints on provenance related to Xigeda paleo-lake in Panzhihua area,Sichuan Province

作　　者：郑勇[1] 王亚军[1] 孔屏[1,2] 

机构地区：[1]中国科学院地质与地球物理研究所岩石圈演化国家重点实验室,北京100029 [2]中国科学院青藏高原研究所,北京100085

出　　处：《地质科学》2009年第3期1036-1051,共16页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家自然科学基金项目(编号:40721003;40573041)资助

摘　　要：位于扬子地块西缘的攀枝花地区昔格达组湖相沉积及其下伏河流相砾石比较发育。湖相沉积具有较高的SiO_2含量和Al_2O_3/SiO_2比值,显示其载体沉积物具有较高成熟度,表明经历了长距离的搬运。主元素、稀土(REE)和微量元素分析结果揭示昔格达组湖相沉积物源形成于典型的大陆岛弧构造背景,主要来自松潘—甘孜造山带义敦岛弧花岗岩区。Eu/La-Yb/La判别图与Zr/Y比值进一步证实昔格达组湖相沉积分别来自于金沙江上游及雅砻江上游,说明昔格达古湖形成时金沙江上游已被袭夺。昔格达组下伏河流相砾石REE、微量元素分析结果显示其形成于被动大陆边缘构造背景,说明其是由雅砻江经扬子板块边缘花岗岩区携载而来。昔格达组湖相沉积与其下伏河流相砾石的不同物源特征表明伴随着昔格达古湖的形成,金沙江河流经历了演化史上的巨变。Lacustrine sediments and underlying fluvial gravels related with Xigeda paleo-lake outcrop in the Panzhihua area,west of Yangtze platform. High concentrations of SiO2 and high SiO2/Al2O3 ratios with the lacustrine sediments suggest high maturity and long distance transportation. The geochemical characteristics of major, REE and trace elements allocate the provenance of lacustrine sediments to a continental island-arc environment, and most probably derived from the granitoid region of Yidun island arc in the Songpan-Ganze orogenic belt. Eu/La-Yb/La signatures and Zr/Y ratios provide further information on the provenance of the lacustrine sediments, from both catchments of the Jinsha River and the Yalong River. This suggests that the upstream of Jinsha River was captured during the period of Xigeda paleo-lake formation. The geochemical characteristics of REE and trace elements in the fluvial gravels underlying Xigeda lacustrine sediments suggest formation in a tectonic setting of passive continental margin, and most probably in the west part of Yangtze platform, in the catchment of Yalong River. The different provenance features between the lacustrine sediments and the underlying fluvial gravels imply a significant change of the course of the Jingsha River in the period of Xigeda paleo-lake formation.

关 键 词：攀枝花 昔格达组 河流相砾石 物源 金沙江 

分 类 号：P591[天文地球—地球化学]