冈底斯弧南缘侏罗纪火成岩时空分布和地球化学组成变化特征及其对地壳增生的指示  

Distribution and geochemical characteristics of Jurassic igneous rocks in the sourthern Gangdese Arc and their implications for crustal accretion

作　　者：黄飞 陈建林[1,2] 许继峰[4] HUANG Fei;CHEN Jian-lin;XU Ji-feng(State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China;CAS Center for Excellence in Deep Earth Science,Guangzhou 510640,China;University of Chinese Academy of Sciences,Beijing 100049,China;School of Earth Science and Resources,China University of Geosciences,Beijing 100083,China)

机构地区：[1]中国科学院广州地球化学研究所同位素地球化学国家重点实验室,广东广州510640 [2]中国科学院深地科学卓越创新中心,广东广州 [3]中国科学院大学,北京100049 [4]中国地质大学地球科学与资源学院,北京100083

出　　处：《地球化学》2020年第6期610-620,共11页Geochimica

基　　金：国家自然科学基金(41873037,92055206);国家第二次青藏高原综合科学考察(2019QZKK0703)。

摘　　要：冈底斯弧南缘广泛出露有中生代和新生代火成岩,是青藏高原火成岩最发育的地区之一,记录了新特提斯洋北向俯冲、消减和随后的印度大陆与欧亚大陆碰撞等地质过程。对中生代尤其是侏罗纪火成岩的研究对于理解新特提斯洋早期俯冲及青藏高原南缘早期增生具有显著意义。对位于冈底斯南缘平行于雅鲁藏布江缝合带东西向展布的侏罗纪火成岩年代学和地球化学数据进行了总结,结果表明:(1)侏罗纪岩浆活动高峰期集中于早中侏罗世(192~168 Ma);(2)侏罗纪岩浆作用主要活动范围位于雅鲁藏布江以北附近,在北纬29.48°以北相对缺乏中晚侏罗世岩浆活动,而且早侏罗世岩浆活动相对于南边也更加平静,且以酸性岩浆活动为主;(3)侏罗纪火成岩微量元素也呈一些规律性变化,如Ba/La、Ba/Th比值随着时代的演化呈现出递增的趋势,很可能表明板片来源流体贡献逐渐增加,Nb/Th和Nb/La由西向东均呈现递减趋势,表明地壳混染作用很可能逐渐增强;(4)侏罗纪火成岩的微量元素组成空间上的变化特征指示在早侏罗世早期冈底斯弧南缘就已经存在正常地壳厚度,并且随着新特提斯洋的北向俯冲,其有逐渐增厚的趋势。Mesozoic and Cenozoic igneous rocks are widely exposed in the southern part of the Gangdese Arc and record the subduction of the Neo-Tethys ocean,and subsequent collision between India and Eurasia.These Mesozoic igneous rocks,and Jurassic igneous rocks in particular,are important for understanding arc accretion and the early subduction characteristics of the Neo-Tethys Ocean.Based on previous chronological and geochemical research into the EW-trending Jurassic igneous rocks distributed along the southern Gangdese Arc,we found that:(1)Jurassic magmatic activity reached a peak between the early and middle Jurassic(192~168 Ma);(2)major Jurassic magmatism developed an EW-trending region between the northern Yaluzangbu sutures and 29.48°N;(3)trace element ratios of these Jurassic igneous rocks show consistent trends,such as Ba/La and Ba/Th ratios increasing over time,and Nb/Th and Nb/La ratios decreasing from west to east,possibly indicating increased fluid contribution from the slab and gradually strengthening assimilation of the crust,respectively;and(4)in the early Jurassic,the southern margin of the Gangdese Arc had a normal crustal thickness,which increased gradually with the northward subduction of the Neo-Tethys ocean.

关 键 词：侏罗纪 岩浆活动 地球化学 地壳增生 冈底斯弧 青藏高原 

分 类 号：P594[天文地球—地球化学] P595[天文地球—地质学]