四川龙门山北段唐王寨-仰天窝向斜麻柳村辉绿岩斜锆石U-Pb同位素定年及其地质意义  

Baddeleyite U-Pb geochronology of Maliucun diabase from Tangwangzhai-Yangtianwo syncline in the northern segment of Longmen Mountain, Sichuan, and its geological significance

作　　者：沈淑鑫 贾东[1] 曾庆 谢忱 资金平 张勇[1] 胡晶 SHEN Shuxin;JIA Dong;ZENG Qing;XIE Chen;ZI Jinping;ZHANG Yong;HU Jing(School of Earth Science ＆ Engineering, Nanjing University, Nanjing 210023, Jiangsu, China;Exploration and Development Research Institute of PetroChina Southwest Oil ＆ Gasfield Company, Chengdu 610041, Sichuan, China)

机构地区：[1]南京大学地球科学与工程学院,江苏南京210023 [2]中国石油西南油气田公司勘探开发研究院,四川成都610041

出　　处：《地质通报》2018年第5期840-852,共13页Geological Bulletin of China

基　　金：国家重大科技专项<前陆冲断带及复杂构造区地质过程;深层结构与储层特征>(编号:2016ZX05003-001);<含油气盆地深层构造研究>(编号:2017ZX005008-001)

摘　　要：为确定龙门山北段唐王寨-仰天窝向斜内发育的NE向辉绿岩脉的侵位时代、构造背景,探讨其是否与峨眉山地幔柱活动相关,对向斜内麻柳村处的辉绿岩样品进行了斜锆石LA-ICP-MS U-Pb同位素测年、主量和微量元素分析。结果表明,辉绿岩斜锆石U-Pb同位素年龄为261.1±1.8Ma;属于高钛型拉斑玄武岩,高铝(13.39%~14.02%)、高铁(13.88%~14.67%)、低镁(4.43%~4.56%),富集大离子亲石元素和轻稀土元素,Nb/La=0.84~0.85、Th/Ta=2.40~2.45、Ta/Hf>0.25,具有与洋岛玄武岩相似的地球化学特征,Nb-Ta略微负异常,暗示其可能源于富集型地幔并受到少量陆壳物质混染,形成于大陆板内环境。与峨眉山玄武岩质火成岩对比发现,两者具有高度一致的形成时代及相似的地球化学特征。据此认为,该区辉绿岩为峨眉山地幔柱活动的产物,峨眉山玄武质岩浆的活动已经波及至龙门山北段及川西北地区,可能影响了该区的生物环境及油气成藏。To confirm the emplacement age and tectonic setting of the NE-striking diabase dykes developed in the TangwangzhaiYangtianwo syncline of northern Longmen Mountain as well as to reveal whether or not the diabases were associated with the Emeishan mantle plume activity, the authors investigated U-Pb baddeleyite age, major element content and trace element abundances of the diabase samples collected from the Maliucun area within the syncline. The results showed that the diabases yielded a baddeleyite concordant U-Pb age of 261.1±1.8 Ma; they belong to the high-Ti（Ti/Y500） tholeiitic series, and are characterized by high Al（13.39%~14.02%）, high Fe（13.88%~14.02%）, and low Mg（4.43%~4.56%） values as will as enrichment of the large iron lithophile elements and light rare earth elements; coupled with the data Nb/La（0.84~0.85）, Th/Ta（2.40~2.45）, and Ta/Hf0.25,the features of the diabases are similar to the geochemical characteristics of ocean island basalt; the slightly negative anomaly of Nb-Ta indicates that they were probably derived from the enriched mantle with minor contamination by crust materials. A comparison with the Emeishan basaltic rocks shows that they are consistent highly with each other in ages and geochemical characteristics. It is considered that the diabases were formed by Emeishan mantle plume activity and the activity of Emeishan basaltic magma was spread to the northern sec-tion of Longmen Mountain and northwestern Sichuan, which had an impact on the biotic environment and hydrocarbon accumulation of this area.

关 键 词：辉绿岩 斜锆石U-Pb年龄 峨眉山地幔柱 唐王寨-仰天窝向斜 

分 类 号：P597.3[天文地球—地球化学] P588.12[天文地球—地质学]