First identification of Late Mesozoic intraplate magmatism in the Chinese North Tianshan: Implications for the orogenic architecture and crustal evolution

Fujun Wang, Zhiyuan He, Rongfeng Ge, Meng Luo, Bihai Zheng, Zhiyong Zhang, Rongsong Tian, Yuanyuan Cao, Wenbin Zhu
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Abstract

The formation and dynamics of granitoids in an intra-continental setting are crucial for understanding the architecture and evolution of continental crust. Here, we report geochronological, geochemical, and Sr-Nd-Hf isotopic data for newly discovered late Mesozoic granitic intrusions in the Tianshan belt, northwestern China. These granitoids are I-type granites derived from an igneous precursor and were emplaced during ∼145-132 Ma. They have positive ε Nd (t) values and young Nd model ages, together with relatively low Sr/Y ratios, indicating that they might have originated from partial melting of the juvenile lower crust. There is a prominent decoupling between zircon Hf and bulk rock Nd isotopes, which may have resulted from the early crystallization of Ti-rich minerals. These granitic intrusions also display subduction-related geochemical characteristics, which are likely inherited from the Paleozoic crustal sources that were metasomatized by subduction-related fluids. We conclude that these late Mesozoic granitoids were emplaced in an intra-continental setting, and were likely triggered by thermal relaxation due to crustal shortening and thickening. These data further imply that the Tianshan has changed into crustal reworking during the Mesozoic from its prominent crustal growth in the Paleozoic. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change Supplementary material: https://doi.org/10.6084/m9.figshare.c.7167890
首次发现中国北天山晚中生代板内岩浆活动:对造山构造和地壳演化的启示
大陆内部花岗岩的形成和动力学对于了解大陆地壳的结构和演化至关重要。在此,我们报告了在中国西北部天山带新发现的中生代晚期花岗岩侵入体的地质年代、地球化学和Sr-Nd-Hf同位素数据。这些花岗岩是由火成岩前驱体演化而来的I型花岗岩,形成于145-132Ma之间。它们具有正的ε钕(t)值和年轻的钕模型年龄,以及相对较低的锶/钇比值,表明它们可能起源于年轻下地壳的部分熔融。锆石 Hf 与大块岩石 Nd 同位素之间存在明显的脱钩现象,这可能是富钛矿物早期结晶的结果。这些花岗岩侵入体还显示出与俯冲有关的地球化学特征,这些特征很可能是从古生代地壳来源继承下来的,它们被与俯冲有关的流体变质。我们的结论是,这些中生代晚期的花岗岩是在大陆内部环境中形成的,很可能是由地壳缩短和增厚引起的热松弛引发的。这些数据进一步表明,天山在中生代已从古生代突出的地壳增长转变为地壳再加工。 专题文集:本文是中生代和新生代构造、地貌和气候变化文集的一部分,可在以下网址查阅: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change 补充材料: https://doi.org/10.6084/m9.figshare.c.7167890
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