Geochemistry of the Eocene Felsic Porphyric Rocks and High‐Mg Potassic Rocks along JARSZ: Implication for the Tectonic Evolution in Eastern Tibet
Geochemistry of the Eocene Felsic Porphyric Rocks and High‐Mg Potassic Rocks along JARSZ: Implication for the Tectonic Evolution in Eastern Tibet
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DOI：
10.1111/j.1755-6724.2010.00340.x
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发表时间：
2010-12
期刊：
影响因子：
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通讯作者：
Cheng Jianlin;Xu Jifeng;Wang Baodi;Kang Zhiqiang
中科院分区：
文献类型：
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作者：
Cheng Jianlin;Xu Jifeng;Wang Baodi;Kang Zhiqiang
始新世长英质斑岩和高镁钾质火山岩（HMPR）产于西藏东部金沙江-哀牢山-红河剪切带（JARSZ）。与普遍认为源自富集地幔的HMPR相比，长英质斑岩岩石的K2O含量相似，LREE和LILE富集，特别是放射性同位素（如Sr和Nd）特征与前者非常相似，这意味着长英质斑岩岩石的生成很可能与HMPR有关，尽管它们的主量和微量元素组成明显不同。藏东长英质斑岩与HMPR在时空分布上的密切关系以及相似的Sr-Nd特征表明它们可能是由相似的构造过程（事件）形成的。结合藏南和藏东的基性岩脉，我们认为藏南新特提斯板片北倾的断裂在50~40Ma期间引发了高镁钾质岩浆的形成。这导致通过下地壳中底侵HMPR的部分熔融或高镁钾质岩浆的分馏结晶来形成长英质斑岩岩浆。始新世板片的断裂也可能导致了与早期俯冲事件有关的丰富的成矿物质，从而导致了西藏东部 JARSZ 沿线斑岩矿床的形成。
Eocene felsic porphyric rocks and the high‐Mg potassic volcanic rocks (HMPR) occur along the Jinshajiang‐Ailao Shan‐Red River shear zone (JARSZ) in eastern Tibet. Compared with the HMPR, which are generally believed to be sourced from an enriched mantle, the felsic porphyric rocks show similar K2O contents, enrichment in LREE and LILE, particularly radiogenic isotope (e.g. Sr and Nd) features much similar to the former, implying generation of the felsic porphyric rocks most likely related to the HMPR, although they both have clearly different major and trace element compositions. The close relationship in spatial‐temporal distribution and similar Sr‐Nd characteristics between the felsic porphyric rocks and HMPR in eastern Tibet indicate that both of them were possibly formed by a similar tectonic process (event). Combining the basic dikes in southern and eastern Tibet, we suggest that the break‐off of north‐dipping Neo‐Tethyan slab in southern Tibet during 50–40 Ma, triggered formation of high‐Mg potassic magma. This led to developing felsic porphyric magma production by partial melting of underplating HMPR in the lower crust, or fractionation crystallization of the high‐Mg potassic magmas. The break‐off of slab in the Eocene may also have contributed to the abundant ore‐forming material related to earlier subduction events, resulting in formation of the porphyric deposits along JARSZ in eastern Tibet.