Geochronology, geochemistry, and zircon Hf isotopic compositions of Mesozoic intermediate-felsic intrusions in central Tibet: Petrogenetic and tectonic implications
Geochronology, geochemistry, and zircon Hf isotopic compositions of Mesozoic intermediate-felsic intrusions in central Tibet: Petrogenetic and tectonic implications
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DOI：
10.1016/j.lithos.2014.03.025
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发表时间：
2014-06
期刊：
影响因子：
3.5
通讯作者：
Jinxiang Li;K. Qin;Guangming Li;J. Richards;Junxing Zhao;Mingjian Cao
中科院分区：
文献类型：
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作者：
Jinxiang Li;K. Qin;Guangming Li;J. Richards;Junxing Zhao;Mingjian Cao
藏中羌塘南缘广泛分布着中生代中长英质侵入岩。锆石U-Pb定年表明，这些侵入体形成于侏罗纪（169-150 Ma）和白垩纪（127-113 Ma）两个时期。它们大多属于高钾钙碱性系列，并显示出强烈富集大离子亲石元素（如，Cs、Rb和K），Nb、Ta和Ti的亏损，以及原始地幔标准化图上的负Ba异常。P2 O 5含量随着SiO2含量的增加而减少，Th含量随着Rb含量的增加而增加，与I型岩浆的演化趋势一致。这些侵入体的锆石εHf（t）值范围很广，介于− 19.4到11.2之间，包括SiO2含量相似的岩石，表明地幔和羌塘地壳来源的贡献不同。侏罗纪侵入体中的细粒镁铁质至中等火成包体与寄主岩石具有相似的锆石U-Pb年龄和相似或略高的锆石εHf（t）值，表明包体岩浆源自深部混合岩浆，并注入上地壳岩浆室中更演化的岩浆中。岩浆混合也得到了个别侏罗纪和白垩纪侵入体和侏罗纪包体中广泛的锆石Hf同位素组成（εHf（t）=-19.4至2.5）的支持。侏罗纪-白垩纪岩浆可能形成于170 ~ 110 Ma班公湖-怒江洋俯冲过程中的大陆弧环境，并在板块上地壳中通过MASH过程演化。
Mesozoic intermediate–felsic intrusions are widely distributed in the southern Qiangtang terrane, central Tibet. Zircon U–Pb dating shows that these intrusions formed in two periods in the Jurassic (169–150 Ma) and Cretaceous (127–113 Ma). They mostly belong to the high-K calc-alkaline series, and show strong enrichments in large ion lithophile elements (e.g., Cs, Rb, and K), depletions in Nb, Ta, and Ti, and negative Ba anomalies on primitive mantle-normalized diagrams. P2O5contents decrease with increasing SiO2content, and Th contents increase with increasing Rb content, consistent with the evolution trend of I-type magmas. These intrusions show a wide range of zircon εHf(t) values from − 19.4 to 11.2, including in rocks with similar SiO2contents, suggesting variable contributions from mantle and Qiangtang crustal sources. Fine-grained mafic to intermediate igneous enclaves in Jurassic intrusions have similar zircon U–Pb ages and similar or slightly higher zircon εHf(t) values to the host rocks, suggesting that the enclave magmas were derived from mixed magmas at depth and injected into more evolved magmas in upper crustal magma chambers. Magma mixing is also supported by the wide range of zircon Hf isotopic compositions (εHf(t) = − 19.4 to 2.5) from within individual Jurassic and Cretaceous intrusions, and Jurassic enclaves. The Jurassic–Cretaceous magmas likely formed in a continental arc setting during subduction of the Bangong–Nujiang ocean between 170 and 110 Ma, and evolved in the upper plate crust by MASH processes.