Petrogenesis and tectonic implications of the Neoproterozoic mafic intrusions in the Bikou Terrane along the northwestern margin of the Yangtze Block, South China
Petrogenesis and tectonic implications of the Neoproterozoic mafic intrusions in the Bikou Terrane along the northwestern margin of the Yangtze Block, South China
复制标题
扬子地块西北缘碧口地体新元古代镁铁质侵入岩的岩石成因及构造意义
DOI：
10.1016/j.oregeorev.2021.104014
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发表时间：
2021
影响因子：
3.3
通讯作者：
He Shuai
中科院分区：
文献类型：
--
作者：
Hui Bo;Dong Yunpeng;Zhang Feifei;Sun Shengsi;He Shuai
扬子地块西北缘碧口地体的新元古代镁铁质侵入体记录了评价华南扬子地块构造演化的重要信息。然而，它们的岩石成因和构造意义仍然很少受到限制。在本文中，我们介绍了碧口地体辉长闪长岩和辉长岩锆石 U-Pb 年代学和全岩地球化学的综合研究结果。锆石 U-Pb 测年结果表明，这些辉长岩闪长岩和辉长岩样品是在大约 1997 年同时形成的。 880马。辉长闪长岩样品成分呈钙碱性，SiO2、Mg#、Ni、Cr 含量居中。它们富含 LREE，缺乏 HFSE（即 Nb、Ta、Zr 和 Hf）。它们具有较高的 Th/Yb 比值，而 Nb/Yb、Nb/La、Th/Nd、Th/Zr 和 U/Th 比值较低，表明它们源自由板片衍生熔体交代的地幔楔源的部分熔融。辉长岩样品通常被归类为亚碱性拉斑斑岩，并且 MgO、Mg#、Cr 和 Ni 的含量始终处于低至中等水平，并且 Th、U、Nb 和 Ta 浓度具有明显的峰值。它们显示出类似E-MORB的富集轻稀土元素，Nb/La、Ta/Yb、Th/La和Nb/Zr比例较低，Nb/Yb和Th/Yb比例中等，这表明它们很可能起源于上涌富集的软流圈地幔与地幔楔橄榄岩之间的相互作用。该机制可能是由俯冲相关环境中的板块回滚过程触发的。我们的新研究以及其他学者的现有观测结果支持了新元古代早期沿扬子地块西北缘存在持续俯冲相关的系统。
The Neoproterozoic mafic intrusions in the Bikou Terrane along the northwestern margin of the Yangtze Block record crucial information on evaluating the tectonic evolution of the Yangtze Block, South China. However, their petrogenesis and tectonic significance are still poorly constrained. In this paper, we present the results of a comprehensive study of zircon U–Pb geochronology and whole-rock geochemistry from the gabbro-diorites and gabbros of the Bikou Terrane. Zircon U–Pb dating results indicate that these gabbro-diorite and gabbro samples were formed coevally at ca. 880 Ma. The gabbro-diorite samples are calc-alkaline in composition and have intermediate contents of SiO2, Mg#, Ni, and Cr. They are enriched in LREEs, and depleted in HFSEs (i.e., Nb, Ta, Zr, and Hf). They have relatively high ratios of Th/Yb, and low ratios of Nb/Yb, Nb/La, Th/Nd, Th/Zr, and U/Th, indicating that they were derived from partial melting of a mantle wedge source metasomatized by slab-derived melts. The gabbro samples are commonly classified as sub-alkaline tholeiitic rocks, and have constantly low to medium values of MgO, Mg#, Cr, and Ni, with distinct spikes at Th, U, Nb and Ta concentrations. They show an E-MORB-like enriched LREEs, low ratios of Nb/La, Ta/Yb, Th/La, and Nb/Zr, and medium ratios of Nb/Yb and Th/Yb, implying that they were most probably originated from the interaction between the upwelling enriched asthenospheric mantle and the mantle wedge peridotite. This mechanism may be triggered by the slab rollback process in a subduction-related environment. Our new investigations, along with available observations from other scholars, support the persistent subduction-related system along the northwestern margin of the Yangtze Block during the early Neoproterozoic.