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Petrogenetic evolution of the Zhuopan potassic alkaline complex, western Yunnan, SW China: Implications for heterogeneous metasomatism of lithospheric mantle beneath Simao and western Yangtze block
Lithos ( IF 3.5 ) Pub Date : 2021-07-10 , DOI: 10.1016/j.lithos.2021.106354
Zhuang Miao 1 , Zhidan Zhao 1 , Yaoling Niu 1, 2, 3 , Hangshan Lei 1 , Xin Tong 1 , Jingkai Wu 1 , Yiyun Yang 1 , Dong Liu 1 , Qing Wang 1 , Di-Cheng Zhu 1 , Guochen Dong 1 , Su Zhou 1
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Potassic alkaline rocks are instrumental in unveiling the composition and geodynamic evolution of mantle lithosphere. The Zhuopan alkaline complex, located in the western Simao block, SW China, exhibits features of high potassium, enrichment in LILEs, and depletion in HFSEs. These same elemental features and SrNd isotopic compositions are also evident in the coeval clinopyroxenitic and syenitic rocks, indicating a comagmatic origin. In this paper, we present new data and discuss the petrogenesis of these rocks. We show that magmas parental to the Zhuopan alkaline complex are derived from highly enriched clinopyroxene-rich lithospheric mantle. These alkaline magmas emplaced in shallow crustal level and experienced crustal assimilation during ascent and through magma chamber processes. Pyroxenite is of cumulitic origin dominated by clinopyroxene and apatite. It formed at an early stage and received more effective crustal contamination. Pyroxene syenite, syenite and nepheline syenite are compositional mixture of variably evolved melt with incompletely segregated liquidus phases (e.g., clinopyroxene, biotite, alkali-feldspar, apatite, nepheline). An important observation is that the Dy/Yb ratio, LILE and LREE abundances of the Zhuopan complex are significantly higher than those of the contemporaneous mafic volcanic rocks in the western Yangtze block, reflecting different sources and source histories. The lithospheric mantle beneath Simao and western Yangtze blocks must have been heterogeneously metasomatized by oceanic subduction-related fluids and melts. Particularly, the mantle source for the Zhuopan alkaline rocks exhibits feature of carbonatite metasomatism. This is further supported by our modeling where melts derived from marine carbonate play a crucial role.

中文翻译:

云南西部卓盘钾碱性杂岩体的岩石成因演化:对思茅和扬子地块西部岩石圈地幔非均质交代作用的启示

钾碱性岩有助于揭示地幔岩石圈的组成和地球动力学演化。卓盘碱性杂岩体位于思茅区块西部,具有高钾、LILE富集、HFSE贫化的特点。这些相同的元素特征和 SrNd 同位素组成在同时代的单斜辉石岩和正长岩中也很明显,表明其起源为彗岩浆。在本文中,我们提供了新数据并讨论了这些岩石的岩石成因。我们发现,卓盘碱性杂岩的母岩浆源自高度富集的单斜辉石岩石圈地幔。这些碱性岩浆位于地壳浅层,并在上升过程中和通过岩浆室过程经历了地壳同化。辉石岩是积云状成因,主要成分是单斜辉石和磷灰石。它形成较早,受到更有效的地壳污染。辉石正长岩、正长岩和霞石正长岩是不同演化熔体与不完全偏析液相的组成混合物(例如,单斜辉石、黑云母、碱长石、磷灰石、霞石)。一个重要的观察结果是,卓盘杂岩的Dy/Yb比值、LILE和LREE丰度显着高于扬子西部地块同生基性火山岩,反映了不同的物源和物源史。思茅和扬子地块西部下方的岩石圈地幔一定是受到了与大洋俯冲相关的流体和熔体的非均质交代作用。特别是卓盘碱性岩的地幔源区表现出碳酸岩交代作用特征。我们的模型进一步支持了这一点,其中来自海洋碳酸盐的熔体发挥着至关重要的作用。
更新日期:2021-07-10
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