滇西北甘孜-理塘构造带放射虫地层、硅质岩地球化学及其构造古地理意义  

Radiolarian Fauna and Geochemical Characters of the Cherts from Garz-Litang Tectonic Belt and Its Tectono-Paleogeographic Significance

作　　者：杨文强[1] 冯庆来[1] 刘桂春[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,武汉430074

出　　处：《地质学报》2010年第1期78-89,共12页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号40372105;40772143);中国地质大学地质过程与矿产资源国家重点实验室MOST基金资助成果

摘　　要：滇西北香格里拉地区上三叠统哈工组由砂岩、粉砂岩和泥岩组成,并发育大量的沉积混杂岩块。硅质混杂岩块中含有大量的放射虫及竹节石生物化石。放射虫自中泥盆世到中三叠世均有分布,竹节石时代为中泥盆世。不同时代的硅质岩均为生物成因硅质岩,其Al2O3/(Al2O3+Fe2O3)比值介于0.58～0.96之间。北美页岩标准化的稀土模式比较平坦,具弱的Ce负异常或明显的正异常,Eu异常不明显,总体表现为大陆边缘型硅质岩的特征。生物组合和地球化学特征说明甘孜-理塘盆地自早泥盆世裂开。根据硅质岩和硅质泥岩的稀土元素特征,该盆地演化经历了中泥盆世至早石炭世早期缓慢扩张的构造活动期和早石炭世晚期至早三叠世的快速扩张期,以及中三叠世晚期的向西俯冲阶段。晚三叠世,甚至侏罗纪,该盆地仍然发育有深水沉积环境。The Upper Triassic Hagong Formation distributed in the Shangri-La area,northwestern Yunnan consists of terrestrial conglomerate,sandstone,siltstone,and mudstone,in which a great number of chaotic blocks were developed.The Chert chaotic blocks yield Middle Devonian to Middle Triassic radiolarian fauna,as well as Middle Devonian tantaculites.All the chert chaotic blocks with various ages are biogenic with Al2O3/（Al2O3＋Fe2O3） ratios from 0.58 to 0.96.NASC normalized REE patterns for the cherts are relatively flat with weak negative or obvious positive Ce anomaly and no Eu anomaly,which implies the continental margin basin of depositional environment.The plankton assemblage of radiolarian and tentaculites and the geochemical features indicate that the Garz-Litang basin should have formed before Middle Devonian.The evolution of Garz-Litang basin could be divided into two stages according to the REE characters,slowly spreading stage from Middle Devonian to early Early Carboniferous and fast spreading and subduction stage from late Early Carboniferous to Middle Triassic.The basin provided a deep-water sedimentary environment in Late Triassic,even Jurassic.

关 键 词：放射虫 甘孜-理塘构造带 沉积混杂岩 构造古地理 泥盆系 

分 类 号：Q915[天文地球—古生物学与地层学]