鄂尔多斯盆地东部紫金山岩体SHRIMP测年地质意义  

GEOLOGICAL SIGNIFICANCE OF SHRIMP DATING OF ZIJINSHAN ALKALI COMPLEX IN THE EASTERN ORDOS BASIN,CHINA

作　　者：杨兴科[1] 晁会霞[1] 郑孟林 姚卫华[3] 杨旭升[1] 

机构地区：[1]长安大学成矿作用及其动力学开放实验室,陕西西安710054 [2]中国石油化工股份公司勘探开发研究院,北京100083 [3]中国石油长庆油田分公司勘探开发研究院,陕西西安710021

出　　处：《矿物岩石》2008年第1期54-63,共10页Mineralogy and Petrology

基　　金：国家973项目(编号:2003CB214601)

摘　　要：通过对鄂尔多斯盆地东部晋西挠褶带紫金山碱性杂岩体的地质特征、岩石学特征、岩石地球化学、稀土元素地球化学分析及U-Pb同位素SHRIMP测年等研究发现:该碱性杂岩体作为鄂尔多斯盆地东部燕山期岩浆侵入热力作用的代表,具有富碱、较富铁、贫镁、钙,SiO2不饱和或极不饱和,属碱性-过碱性系列。地球化学特征显示富碱、铁、贫镁;稀土元素含量高,无铕异常;岩浆侵入表现出明显的方向和多阶段性,可侵入二叠纪—三叠纪地层中。盆地东部火成岩同位素测年数据表明岩浆-热力作用高峰期在110Ma^150 Ma。测试样品中有21组锆石样品年龄介于125 Ma^132 Ma之间,说明主期岩浆活动热力事件时代为早白垩世,是盆地形成演化的中晚期发生构造转换(深部的隆升)相对应,与华北地区较普遍的早白垩世构造热事件一致。早白垩世强烈的构造热力变动导致该盆地东翼大面积的抬升隆起、吕梁软流圈上涌和晋西挠褶带的形成。SHRIMP测年还发现,除主期125 Ma^132 Ma岩浆热力事件外,有捕获的早期岩浆锆石反映的热力活动事件,构造演化分析显示多阶段热力作用特点。The magma thermal actions in Western Shanxi fold belt in the eastern Ordos basin is widely developed. On the basis of analysis of geological, petrologic and geochemical and REE study, the method of U-Pb isotopes by SHRIMP dating is used to unravel the magma thermal actions in the eastern basin. Zijinshan alkali complex is unsaturated or extremely unsaturated in SiO2 ,belonging to alkaline-peralkaline series. Its geochemistry is characteristic of alkali-rich,K- rich, Fe-rich, Mg-lean, with high content of rare earth elements, and without Eu abnormal. Statistic isotope dating of magma-thermodynamic process peak of igneous rocks in the eastern basin ranges from 110 Ma to 150 Ma. 21 groups of zircon dated 125 Ma-132 Ma,belonging to early Cretaceous. The complex has special tectonic setting which is the deep response to tectonic inversion and initial uplifting in the middle-later stag-e of basin evolution and is consistent with co-tectonic thermal event in North China. In early Cretaceous,intense tectonic-thermal activity leads to the large-scale uplift in the east of the basin,to the upwelling of Luliang asthenosphere, and the formation of Western Shanxi fold belt.

关 键 词：鄂尔多斯盆地 岩浆热力作用 构造事件 早白垩世 紫金山 SHRIMP测年 

分 类 号：P597[天文地球—地球化学] P588.15[天文地球—地质学]