伊犁盆地南缘中下侏罗统碎屑岩地球化学特征及对物源制约  

Geochemical Characteristic of the Lower and Middle Jurassic Clastic Rocks in the Southern Margin of the Yili Basin,Xinjiang and its Constraints on Provenance

作　　者：侯明才[1,2] 江文剑[1] 倪师军[1,2] 黄虎[1,2] 罗文[1] 石鑫[1] 缪宗利 

机构地区：[1]成都理工大学沉积地质研究院,成都610059 [2]油气藏地质与开发工程国家重点实验室成都理工大学,成都610059

出　　处：《地质学报》2016年第12期3337-3351,共15页Acta Geologica Sinica

基　　金：科技部"973计划""中国北方巨型砂岩铀成矿带陆相盆地沉积环境与大规模成矿作用"(编号:2015CB453001)项目资助的成果

摘　　要：对可地浸砂岩铀矿找矿和评价而言，明确赋铀砂体的物源是关键。伊犁盆地南缘中下侏罗统为重要砂岩型铀矿赋矿层位。来自盆地南缘坎乡苏阿苏沟中下侏罗统剖面碎屑岩岩石学及地球化学特征分析，对该套碎屑岩物源区特征及构造环境进行研究。下侏罗统八道湾组以杂色砾岩、含砾粗砂岩为主，颗粒具有较差的分选性和磨圆度。砾岩中可见块状层理，正粒序层理，砂岩中可见大型板状层理，砂岩主要为岩屑砂岩，岩屑成分主要为硅质岩屑和流纹岩岩屑；下侏罗统三工河组以细砂岩，粉砂岩，泥岩为主，细粉砂岩中可见沙纹层理，泥岩中可见到水平层理；中侏罗统西山窑组主要发育含砾粗砂岩-砂岩-泥岩组合，砂岩中发育大型槽状层理，平行层理，泥岩可见水平层理；来自该剖面19件样品的地球化学测试数据显示，该套碎屑岩具有较高的SiO2（53.01%~85.52%，平均值为71.22%）和Al2O3（7.45~23.83%，平均值为13.96%），低TFe2O3＋MgO（0.95~10.77%，平均值为3.64%）和TiO2（0.20~1.32%，平均值为0.74%），其微量元素和稀土元素组成与上地壳相似，轻稀土富集，重稀土较平坦，铕亏损较明显。微量元素和稀土元素特征显示其物源来源于上地壳长英质岩石，母岩沉积构造背景为与大陆岛弧相关沉积盆地。结合前人资料，认为伊犁盆地南缘中下侏罗统物源可能来源于石炭系大陆岛弧环境下形成的岩石。The Middle and Lower Jurassic in the southernYili basin is an important sandstone type uranium bearing sequence. This study carried out systematic analysis for lithological and geochemical features of the the Middle and Lower Jurassic clastic rocks in the southern Yili basin to understand its province features and tectonic environment. The results show that most sandstones are litharenite with low maturity, poor sorting and psephicity. Detritus consists mainly of siliceous and rhyolite fragments. It indicates the deposition of sandstone is close to the provenance. The fine grained clastic rocks has high SiO2 （ranging from 53.01% to 85.52%, Avg.71.22%） and Al2O3（ranging from 7.45% to 23.83%, Avg.13.96%）, and low content of TFe2O3＋MgO （ranging from 0.95% to 10.77%, Avg.3.64%） and TiO2 （ranging from 0.20% to 1.32%, Avg. 0.74%）.The trace elements and rare earth elements characteristics of fine clastic rocks are similar to the upper crust. Light rare earth elements are enriched, the distribution model of heavy rare earth elements is flat. The anomalous value of Eu is negative. The trace elements and rare earth elements characteristics of fine clastic rocks suggest that the parent rocks were derived from felsic rocks in the upper crust and deposited in a tectonic setting related to continental arc. Combined with previous research data,it can be concluded that the clastic rocks in the lower and middle Jurassic in the southern margin of the Yili basin may be derived from the Carboniferous rocks in continental arc environment.

关 键 词：中下侏罗统 碎屑岩 物源 地球化学 伊犁盆地 

分 类 号：P619.14[天文地球—矿床学]