Late Triassic granitic magmatism in the Eastern Qiangtang, Eastern Tibetan Plateau: Geochronology, petrogenesis and implications for the tectonic evolution of the Paleo-Tethys
Late Triassic granitic magmatism in the Eastern Qiangtang, Eastern Tibetan Plateau: Geochronology, petrogenesis and implications for the tectonic evolution of the Paleo-Tethys
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DOI：
10.1016/j.gr.2014.01.009
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发表时间：
2015-06
影响因子：
6.1
通讯作者：
Touping Peng;Guochun Zhao;W. Fan;Bingxia Peng;Yongsheng Mao
中科院分区：
文献类型：
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作者：
Touping Peng;Guochun Zhao;W. Fan;Bingxia Peng;Yongsheng Mao
青藏高原北方羌塘中部广泛出露三叠纪花岗岩。因此，他们为青藏高原的发展做出了重要贡献。本文通过对羌塘中部东大山岩基的锆石U-Pb定年、Hf同位素、全岩元素和Sr-Nd同位素分析，探讨了该岩基的成因和构造环境。LA-MC-ICP-MS锆石U-Pb结果表明，DDS岩基的侵位年龄为220.3 ± 0.7Ma。DDS中的花岗岩均具有高的A/CNK值（> 1.0），表现出类似于S型花岗岩的过铝质特征。稀土元素分馏模式（La/Yb）N= 6.98-13.9，Eu ~*/Eu = 0.51-0.67），εNd（t）和εNd（t）值均为负值，Nd和Hf模式年龄亏损，表明DDS花岗质岩浆以壳源为主，可能为古元古代基底（即太古宙基底），结合区域研究，新的地球化学资料和年代学结果表明，晚三叠世岩浆活动形成于后碰撞构造环境。中生代岩浆岩的空间分布格局，与羌塘中部高压变质岩的折返作用相结合，形成了板片断裂模式，导致碰撞后伸展和软流圈上涌，引起中下地壳大规模部分熔融，产生大量长英质岩浆。因此，羌塘盆地晚三叠世后碰撞岩浆作用的发生，特别是高压榴辉岩和蓝片岩的折返及其在晚三叠世火山碎屑岩底部的存在，这清楚地表明古特提斯洋的最终闭合以及与之相关的冈瓦纳-直到中三叠世早期，才完成了西羌塘和东羌塘盆地的演化。
Triassic granites are widely exposed in the central Qiangtang, northern Tibetan Plateau. They, therefore, made an important contribution to the growth of the Tibetan Plateau. In this paper, we present zircon U–Pb dating and Hf isotopic results, and whole-rock elemental and Sr–Nd isotopic analyses of the Dongdashan (DDS) batholith in the central Qiangtang in order to understand their petrogenesis and tectonic setting. LA-MC-ICP-MS zircon U–Pb results show that the DDS batholith was emplaced at 220.3 ± 0.7 Ma. All the granites in the DDS possess high A/CNK values (> 1.0) and display peraluminous characteristics, similar to S-type granite. Their strongly fractionated REE patterns ((La/Yb)N= 6.98–13.9) with conspicuous negative Eu anomalies (Eu*/Eu = 0.51–0.67), together with negative εNd(t) and εNd(t) values, and depleted Nd and Hf model ages, suggest that the DDS granitic magma had a dominantly crustal source, likely the Paleoproterozoic basement (i.e., the Ningduo and Caoqu group metasediments) in the area.In combination with regional studies, our new geochemical data and geochronological results demonstrate that the Late Triassic magmatism was generated in a post-collisional tectonic setting. The spatial distribution pattern of the Mesozoic igneous rocks, coupled with the exhumation of high-pressure metamorphic rocks in the central Qiangtang, favors a slab breakoff model, which resulted in post-collisional extension and asthenospheric upwelling that induced large-scale partial melting of the middle-lower crust to produce voluminous amounts of felsic magma. Therefore, the occurrence of the Late Triassic post-collisional magmatism, and particularly the exhumation of high-pressure eclogites and blueschists as well as their presence in the lowermost portion of the Late Triassic volcanoclastics in the Qiangtang basin, clearly indicate that the final closure of the of Paleo-Tethys Ocean and associated continent–continent collision between the Gondwana-derived Western Qiangtang and Eastern Qiangtang terranes had not been completed until the early mid-Triassic.