鄂尔多斯盆地西南边部超钾质岩及构造意义  

The ultra-potassic rocks on the southwestern margin of the Ordos basin and their tectonic significance

作　　者：张宏法[1] 包洪平 彭天朗[1] 王润三[1] 白海峰 马占荣 

机构地区：[1]大陆动力学国家重点实验室西北大学地质学系,陕西西安710069 [2]中石油长庆油田开发研究院,陕西西安710000

出　　处：《中国地质》2012年第5期1172-1182,共11页Geology in China

基　　金：大陆动力学实验室自主基金(DJ0813313);中石油长庆油田研究院"鄂尔多斯盆地周缘中生代岩浆活动与油气聚集的关系"(UJ631)共同资助

摘　　要：鄂尔多斯盆地西南边部出露的铜城超钾质岩,分布在甘肃省崇信县铜城镇以南的桃梢屲—庙滩一带,为浅成侵入岩墙,斑状结构,块状构造;岩性为霓辉黑榴二长斑岩与假白榴石斑岩。斑晶矿物成分以含白榴石、黑榴石、霓辉石及两种长石为特征;地球化学显示:主量元素以富集K2O、Al2O3、CaO而贫SiO2、MgO、TiO2、P2O5为特征,微量元素以富含大离子亲石元素(LILE)K、Rb、Sr、Ba、Pb而贫高场强元素(HFSE)Nb、Ta、Zr、Hf为特征,地幔起源环境可能为EMI型富集地幔;两种岩性锆石U-Pb年龄显示其形成年龄(110.8±1.0)Ma和(107.6±0.9)Ma,为早白垩世。因此笔者认为:早白垩世华北克拉通东部陆块发生岩石圈大幅减薄作用过程中,陆块西部岩石圈也有相应岩石圈减薄作用发生。Ultrapotassic dykes on the southwestern margin of the Ordos basin display massive structure and porphyritic texture.According to their mineral association,these rocks are mainly composed of aegirine augite ivernite and pseudoleucite porphyry,whereas the phenocrysts contain leucite,melanite,aegirine augite and some feldspar.These rocks have high K2O,Al2O3,CaO and low SiO2,MgO,TiO2 and P2O5 content.In the spider diagrams,they are enriched in K,Rb,Sr.Ba,Pb and depleted in Nb,Ta,Zr,Hf.Zircon U-Pb dating reveals that they have crystallization ages of（110.8±0.98）Ma and（107.6±0.92）Ma,respectively,belonging to Early-Cretaceous.It is held that these ultrapotassic rocks resulted from the lithosphere thinning process on the western margin of the Ordos basin.

关 键 词：超钾质岩 锆石U-PB 地球化学 中生界 岩石圈减薄 鄂尔多斯 西南边部 

分 类 号：P597.3[天文地球—地球化学]