Zircon U–Pb geochronology and Hf isotopic constraints on the petrogenesis of Early Triassic granites in the Wulonggou area of the Eastern Kunlun Orogen, Northwest China
Zircon U–Pb geochronology and Hf isotopic constraints on the petrogenesis of Early Triassic granites in the Wulonggou area of the Eastern Kunlun Orogen, Northwest China
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DOI：
10.1080/00206814.2015.1029541
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发表时间：
2015-04
影响因子：
2.6
通讯作者：
Q. Ding;Fei Liu;Wei Yan
中科院分区：
文献类型：
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作者：
Q. Ding;Fei Liu;Wei Yan
五龙沟地区东北部广泛分布的花岗质侵入体，曾被认为是在新元古代侵位于古元古代金水口群中。本文详细介绍了乌龙沟地区乌龙沟花岗闪长岩和小丫口花岗岩的LA-ICP-MS锆石U-Pb年代学、主量元素和微量元素地球化学、锆石Hf同位素组成。3个花岗闪长岩样品获得247 ± 2、248 ± 1和249 ± 1 Ma的锆石U-Pb年龄，1个花岗岩样品获得246 ± 3 Ma的锆石U-Pb年龄。该花岗闪长岩样品是具有0.90-0.96的氧化铝饱和指数以及5.49- 6.14wt%的中至高碱含量的准矾土，低Zr+Nb+Ce+Y含量和低Fe_2O_3/MgO比值，指示I型典型岛弧岩浆源区。花岗岩为过铝质，铝饱和指数为1.02-1.03，Sr含量为305.00- 374.00ppm，Sr/Y比值为17.68 ~ 28.77，（La/Yb）N值为16.98-25.07，HREE含量较低（Yb = 1.10-2.00 ppm），低Y（13.00-21.10 ppm），表明为埃达克岩类岩石。所有花岗闪长岩样品的锆石εHf（t）值范围为−2.9至+3.9，花岗岩样品的锆石εHf（t）值范围为−7.8至+3.2。这些Hf同位素数据表明，早三叠世花岗岩是来自于部分熔融的镁铁质中元古代下地壳，虽然古地壳同化的程度可能更高的小丫口花岗岩。在这里，我们建议，CA。246-248 Ma岩浆是在古特提斯洋板块向北俯冲过程中形成的。
Widespread granitic intrusions in the northeast part of the Wulonggou area were previously thought to be emplaced into the Palaeoproterozoic Jinshuikou Group during the Neoproterozoic. This contribution presents detailed LA-ICP-MS zircon U–Pb geochronology, major and trace element geochemistry, and zircon Hf isotope systematic on the Wulonggou Granodiorite and Xiaoyakou Granite from the Wulonggou area. Three granodiorite samples yielded U–Pb zircon ages of 247 ± 2, 248 ± 1, and 249 ± 1 Ma, and one granite sample yielded U–Pb zircon age of 246 ± 3 Ma. The granodiorite samples are metaluminous with an alumina saturation index of 0.90–0.96, as well as intermediate- to high-alkali contents of 5.49–6.14 wt.%, and low Zr+Nb+Ce+Y contents, and low Fe2O3T/MgO ratios, which suggest an I-type classical island arc magmatic source. The granite samples are peraluminous with an alumina saturation index of 1.02–1.03, Sr content of 305.00–374.00 ppm, Sr/Y ratios of between 17.68 and 28.77, (La/Yb)N values of 16.98–25.07, low HREEs (Yb = 1.10–2.00 ppm), and low Y (13.00–21.10 ppm), which suggest adakite-like rocks. All granodiorite samples have zircons εHf(t) values ranging from −2.9 to +3.9, and granite samples have zircon εHf(t) values ranging from −7.8 to +3.2. These Hf isotopic data suggest that the Early Triassic granites were derived from the partial melting of a mafic Mesoproterozoic lower crust, although the degree of ancient crustal assimilation may be higher for the Xiaoyakou Granite. It is suggested here that the ca. 246–248 Ma magma was generated during the northward subduction of the Palaeo-Tethys oceanic plate.