藏南地区中生代硅质岩的地球化学特征及其成因意义  

Geochemical characteristics of Mesozoic chert from southern Tibet and its petrogenic implications.

作　　者：周永章[1,2] 付伟[1,2] 杨志军[1,2] 何俊国[1,2] 聂凤军[3] 李文[2] 赵文霞[1,2] 

机构地区：[1]中山大学地球环境与地球资源研究中心,广州510275 [2]中山大学地球科学系,广州510275 [3]中国地质科学院矿产资源研究所,北京100037

出　　处：《岩石学报》2008年第3期600-608,共9页Acta Petrologica Sinica

基　　金：国家科技部"973"项目(2002C13412606);国家自然科学基金(40573019);全国高等学校博士点基金(20040558050)

摘　　要：藏南地区中生代硅质岩包括蛇绿岩套硅质岩(与蛇绿岩共生)和非蛇绿岩套硅质岩两大类。本文重点分析日喀则地区彭错林、夏鲁以及泽当地区的罗布莎、江孜盆地宗卓组及四个剖面的硅质岩。其中,彭错林、夏鲁和罗布莎硅质岩与蛇绿岩共生,江孜盆地宗卓组为非蛇绿岩套硅质岩。分析表明:(1)藏南地区硅质岩剖面地球化学特征鲜明,具有一致性和多样性特点;(2)与蛇绿岩共生的彭错林、夏鲁、罗布莎硅质岩普遍具有高 Si、高 Fe、低 Al 特征,大部分微量元素相对于克拉克值亏损,稀土元素总量低,经北美页岩标准化后,Ce 异常明显或不明显,重稀土相对轻稀土富集。硅质泥岩的∑REE要明显高于硅质岩;(3)非蛇绿岩套宗卓组硅质岩SiO_2含量稍低,Al_2O_3.TiO_2则相反。V、Th、Hf、Ta 等不相容元素上亏损程度较小,部分样品含量可接近克拉克值。稀土总量相对较高,页岩标准化配分模式上体现为弱 Ce 正异常,负 Eu 异常,轻重稀土分异不明显的平坦型曲线图;(4)地球化学特征指示了,藏南地区硅质岩多数具有明显的热水沉积成因属性,同时有正常陆源组分的加入。其中,夏鲁硅质岩的热水沉积地球化学特征较为典型,而宗卓组硅质岩则表现出受陆源物质加入的影响显著的地球化学特点。There exist two kinds of chert, one associated with ophiolite, and other not in southern Tibet. This study mainly discusses cherts from the Pangcuolin, the Xialu, the Luobusha and the Jiangzi Zongcuo Formation profiles. Among them, those from the Pangcuolin, the Xialu and the Luobusha are associated with ophiolite, and the Jiangzi Zongcuo Formation are not. It is concluded that： （1） the cherts from Pangcuolin, Xialu and Luobusha are characterized by high content of SiO2 and TFe and low Al22O3, and depletion of most trace elements relative to their crust abundance. The REE is low in total content, with ambiguous Ce anomaly, ralatively rich HREE in the NASC-normalized REE abundance distribution pattern. The muddy chert is higher than normal chert in content of REE; （2） the chert from the Jiangzi Zongcuo Formation has a little lower content of SiO2, and evidently higher Al2O3, TiO2. Trace elements such as Ti, V, Th, Hf and Ta are less depleted in relation to their crust abundance. The REE is high in total content, with weakly positive Ce anomaly and negative Eu anamoly. The NASC-normalized REE abundance distribution pattern is flat. It is shown that most of the studied cherts are hydrothermally sedimentary origin, but with exitence of certain continental sources. Among them, the Xialu chert is typical of hydrothermally sedimentary origin, while the Jiangzi Zongcuo Formation chert is more evidently influenced in geochemical characteristics.

关 键 词：硅质岩 地球化学参数 稀土元素 热水成因 西藏南部 

分 类 号：P588.244[天文地球—岩石学]