Crustal thickening prior to 38 Ma in southern Tibet: Evidence from lower crust-derived adakitic magmatism in the Gangdese Batholith
Crustal thickening prior to 38 Ma in southern Tibet: Evidence from lower crust-derived adakitic magmatism in the Gangdese Batholith
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藏南38Ma前地壳增厚：来自冈底斯岩基下地壳埃达克岩浆作用的证据
DOI：
10.1016/j.gr.2011.07.004
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发表时间：
2012
影响因子：
6.1
通讯作者：
Liu, Yong-Sheng
中科院分区：
文献类型：
--
作者：
Guan, Qi;Yuan, Hong-Lin;Zhu, Di-Cheng;Zhao, Zhi-Dan;Dong, Guo-Chen;Zhang, Liang-Liang;Li, Xiao-Wei;Liu, Min;Mo, Xuan-Xue;Liu, Yong-Sheng
藏南新生代埃达克岩的岩石成因和地球动力学意义仍然是争论的话题。本文报道了藏南冈底斯岩基东部卧龙地区寄主花岗岩和镁铁质包体的年代学和地球化学资料。锆石LA-ICPMS测年结果表明，卧龙花岗岩与包体在38 Ma左右同步侵位。寄主花岗岩为中-高钾钙碱性偏铝质花岗岩(A/CNK=0.93-0.96)，富Al_2O_3(15.47-17.68%)，低MgO(0.67-1.18%)，相容元素丰度极低(如：Cr=3.87-8.36ppm，Ni=3.04-5.71ppm)，锶/Y比值高(127-217)，与典型埃达克岩相似。镁铁质包体(SiO_2=51.08-56.29%)的镁含量为3.83-5.02%，镁含量为48-50，具有负的Eu异常(δ，Eu=0.59-0.79)。卧龙花岗岩和包体具有相似的锶-钕同位素组成(初始87Sr/86Sr=0.7053~0.7055，εNd(T)=−2.7~−1.4)，但锆石εHf(T)值不同，变化范围为+6.0~+12.6。对冈底斯岩基埃达克质岩石资料的综合研究表明，卧龙埃达克质寄主花岗岩来源于增厚的下地壳部分熔融，而镁铁质包体的母岩浆很可能来自藏南岩石圈地幔。卧龙花岗岩类被解释为增厚的下地壳源熔体和岩石圈地幔源镁铁质熔体混合的结果，可能是对新特提斯洋板在50 Ma左右裂解的长期岩浆响应。结果表明，藏南地区地壳增厚发生在约38 Ma之前，并支持印亚碰撞一定发生在40 Ma之前的普遍观点。
The petrogenesis and geodynamic implications of the Cenozoic adakites in southern Tibet remain topics of debate. Here we report geochronological and geochemical data for host granites and mafic enclaves from Wolong in the eastern Gangdese Batholith, southern Tibet. Zircon LA-ICP-MS dating indicates that the Wolong host granites and enclaves were synchronously emplaced at ca. 38Ma. The host granites are medium- to high-K calc-alkaline, metaluminous (A/CNK=0.93–0.96), with high Al2O3(15.47–17.68%), low MgO (0.67–1.18%), very low abundances of compatible elements (e.g., Cr=3.87–8.36ppm, Ni=3.04–5.71ppm), and high Sr/Y ratios (127–217), similar to those typical of adakite. The mafic enclaves (SiO2=51.08–56.29%) have 3.83–5.02% MgO and an Mg#of 48–50, with negative Eu anomalies (δEu=0.59–0.79). The Wolong host granites and enclaves have similar Sr–Nd isotopic compositions (initial87Sr/86Sr=0.7053–0.7055, εNd(t)=−2.7 to −1.4), with varying zircon εHf(t) values, ranging from +6.0 to +12.6. A comprehensive study of the data available for adakitic rocks from the Gangdese Batholith indicates that the Wolong adakitic host granites were derived from partial melting of a thickened lower crust, while the parental magmas of the mafic enclaves were most likely derived from lithospheric mantle beneath southern Tibet. The Wolong granitoids are interpreted as the result of mixing between the thickened lower crust-derived melts and lithospheric mantle-derived mafic melts, which are likely the protracted magmatic response to the break-off of the Neo-Tethyan oceanic slab at about 50Ma. Our results suggest that the crustal thickening in southern Tibet occurred prior to ~38Ma, and support the general view that the India–Asia collision must have occurred before 40Ma.
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64.8
作者：
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通讯作者：
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