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青藏高原西北缘红其拉甫岩体早白垩世晚期花岗闪长岩及闪长质岩墙成因:壳幔作用实例
李继永1,2
学位类型硕士
导师牛耀龄
2016-08-22
学位授予单位中国科学院大学
学位授予地点北京
学位专业海洋地质
关键词闪长质岩墙 花岗闪长岩 壳幔作用 青藏高原西北缘
摘要本文针对青藏高原西北缘红其拉甫岩体花岗闪长岩及闪长质岩墙进行了详细的年代学,矿物学,全岩主、微量元素和Sr-Nd-Hf同位素地球化学研究。花岗闪长岩和闪长质岩墙锆石U-Pb定年分别为~104 Ma和~100 Ma。闪长质岩墙岩性从中性向酸性演化,包括辉长闪长岩,闪长斑岩及花岗闪长斑岩,其矿物组成表现出不平衡特征,如斜长石,辉石及角闪石晶体成分变化。地球化学特征上,闪长质岩墙富集不相容元素(Ba,Rb,Th,U,K),Sr-Nd-Hf同位素表现出富集特征(87Sr/86Sri:0.7066 ~ 0.7071,εNd(t):-5.3 ~ -7.4,εHf(t):-3.6 ~ -6.2)。我们推断这些闪长质岩墙是被俯冲洋壳或沉积物所交代的地幔楔部分熔融结果,并伴随着辉石,角闪石及斜长石分离结晶,和下地壳混染的AFC(同化混染-分离结晶)过程。同时,幔源岩浆上升底侵,诱发下地壳熔融,形成具有地幔同位素印记的花岗闪长岩,相较闪长质岩墙,其同位素特征更富集(87Sr/86Sri:0.7087 ~ 0.7125,εNd(t):-9.5 ~ -11.6,εHf(t):-10.3 ~ -14.1)。结合区域地质构造背景,我们推测红其拉甫岩体是活动大陆边缘俯冲环境下壳幔作用的产物,岩浆活动持续了数百万年。同时表明什约克弧后盆地(Shyok Basin)的闭合时限,及科希斯坦-拉达克岛弧(Kohistan-Ladakh Arc)与喀喇昆仑地块(Karakoram Terrane)的碰撞很可能晚于~100 Ma。
其他摘要
We present a detailed study of geochronology, mineral chemistries, bulk-rock major and trace element abundances, and Sr-Nd-Hf isotope compositions of the granodiorite and associated dioritic dikes in the Hongqilafu pluton at the northwestern margin of the Tibetan Plateau. The granodiorite and dioritic dikes yielded zircon U-Pb ages of ~104 Ma and ~100 Ma, respectively. The dioritic dikes comprise varying lithologies of gabbroic diorite, diorite porphyry and granodiorite porphyry, exhibiting a compositional spectrum from intermediate to felsic rocks. Their mineral compositions display disequilibrium features such as large major element compositional variations of plagioclase, clinopyroxene and amphibole crystals. These dioritic dikes are enriched in incompatible elements (Ba, Rb, Th, U, K) and Sr-Nd-Hf isotopes (87Sr/86Sri: 0.7066 to 0.7071, εNd(t) : -5.3 to -7.4, εHf(t) : -3.6 to -6.2). We suggest that the dioritic dikes were most likely derived from partial melting of mantle wedge metasomatized by the subducted/subducting seafloor with a sediment component, followed by AFC processes with fractional crystallization of clinopyroxene, amphibole and plagioclase and assimilation of lower continental crust. The mantle-wedge derived magma parental to the dioritic dikes underplated and induced the lower continental crust to melt, forming the felsic crustal magma parental to the granodiorite with mantle melt signatures and having more enriched isotope compositions (87Sr/86Sri: 0.7087 to 0.7125, εNd(t) : -9.5 to -11.6, εHf(t) : -10.3 to -14.1) than those of the dioritic dikes. The Hongqilafu pluton is thus the product of mantle-crust interaction at an active continental margin subduction setting over the period of several million years. This understanding further indicates that the closure timing of the Shyok back-arc basin and the collision between the Kohistan-Ladakh Arc and the Karakoram Terrane may have taken place later than ~100 Ma.
 
学科领域同位素地球化学 ; 岩石学 ; 海洋地质学
语种中文
文献类型学位论文
条目标识符http://ir.qdio.ac.cn/handle/337002/130848
专题海洋地质与环境重点实验室
作者单位1.中国科学院海洋研究所
2.中国科学院大学
推荐引用方式
GB/T 7714
李继永. 青藏高原西北缘红其拉甫岩体早白垩世晚期花岗闪长岩及闪长质岩墙成因:壳幔作用实例[D]. 北京. 中国科学院大学,2016.
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