藏南彭错林硅质岩地球化学特征及沉积环境分析

藏南彭错林硅质岩地球化学特征及沉积环境分析

何俊国,周永章,杨志军,李红中,王晓悦

中山大学地球科学系/地球环境与地球资源研究中心,广州　510275

摘要:通过野外地质调查和系统的岩石化学、常量元素、微量元素以及稀土元素等研究,探讨了藏南彭错林硅质岩的地球化学特征及其沉积环境。研究表明,呈厚层状产出的绿色、棕褐色硅质岩具有较高的

SiO 2含量,局部受Fe 、Mn 矿化,Al/(Al +Fe +Mn )比值小,在Fe 2Mn 2Al 三角成因判别图解中,大部分硅质

岩样品落入热水沉积区域,微量元素Sr 、Zr 、Cu 、Zn 和Ba 含量较高,稀土元素∑REE 较低,Ce 负异常,Eu 正异常,北美页岩标准化后配分模式稍向左倾,体现出热水沉积特征;在沉积环境判别图100×Fe 2O 3/

SiO 22100×Al 2O 3/SiO 2、Fe 2O 3/(100-SiO 2)2Al 2O 3/(100-SiO 2)和Fe 2O 3/TiO 2-Al 2O 3/(Al 2O 3+Fe 2O 3)

中,硅质岩样品投影到洋中脊和深海区域,说明形成于大洋中脊和深海盆地环境;硅质岩常量和稀土参数变化特征图显示,在剖面中PCL 21、PCL 25和PCL 27采样位置更接近热液中心;硅质岩的形成与板块的汇聚消减产生的以洋中脊和海底热点为中心的洋壳热水系统有关。

关键词:硅质岩;热水沉积;洋中脊;藏南;彭错林;地球化学

中图分类号:P588.2 文献标识码:A 文章编号:167125888(2009)0621055211

收稿日期:2009205205

基金项目:国家自然科学基金项目(40573019);高等学校博士学科点专项科研基金项目(20040558050)

作者简介:何俊国(1968—

),男,陕西渭南人,博士,主要从事沉积地球化学和矿床地球化学的教学与研究,E 2mail :eeshjg @ 。

Study on G eochemical Characteristics and Depositional

Environment of Pengcuolin Chert ,Southern Tibet

H E J un 2guo ,ZHOU Y ong 2zhang ,YAN G Zhi 2jun ,L I Hong 2zhong ,WAN G Xiao 2Yue

Depart ment of Eart h Sciences/Center f or Eart h Envi ronment &Resources ,S un Yat 2sen Universit y ,Guangz hou 510275,China

Abstract :The geochemical characteristics and depo sitional environment of Pengcuolin chert are st udied based on t he field investigations and analysis on major element s ,trace element s and rare eart h element s.The massive chert is green and brown ,being high in SiO 2content ,locally enriched in Fe and Mn ,Al/(Al +Fe +Mn )ratio being low.In Fe 2Mn 2Al t riangle diagrams ,most chert samples fall into t he hydrot hermal region.Trace element s such as Sr ,Zr ,Cu ,Zn and Ba are higher and ΣREE is lower ,wit h Ce negative anomaly and Eu anomaly.Their NASC 2normalized REE distribution patterns are slightly left 2leaning ,indicating t heir hydrot hermal origin.In sedimentary environment discrimination di 2agrams such as 100×Fe 2O 3/SiO 22100×Al 2O 3/SiO 2,Fe 2O 3/(100-SiO 2)2Al 2O 3/(100-SiO 2)and Fe 2O 3/TiO 22Al 2O 3/(Al 2O 3+Fe 2O 3),chert samples fall into t he areas of t he mid 2ocean ridges or deep 2sea.In parameter variation diagrams ,samples of PCL 21,PCL 25and PCL 27are clo ser to t he hydrot her 2mal center.It is shown t hat t he Pengcuolin chert ,sout hern Tibet was formed by t he hydrot hermal sys 2tems at co nvergence and subduction sites of plates.

K ey w ords :chert ;hydrot hermal sedimentation ;mid 2ocean ridge ;sout hern Tibet ;Pengcuolin ;geo 2chemistry

　第39卷　第6期2009年11月 吉林大学学报(地球科学版)Journal of Jilin University (Earth Science Edition ) Vol.39　No.6Nov.2009