Petrogenesis and geochemistry of the Late Carboniferous rear-arc (or back-arc) pillow basaltic lava in the Bogda Mountains, Chinese North Tianshan
Petrogenesis and geochemistry of the Late Carboniferous rear-arc (or back-arc) pillow basaltic lava in the Bogda Mountains, Chinese North Tianshan
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DOI：
10.1016/j.lithos.2015.11.024
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发表时间：
2016-02
期刊：
影响因子：
3.5
通讯作者：
W. Xie;Zhen-Yu Luo;Yigang Xu;Yibing Chen;L. Hong;Liang Ma;Qiang Ma
中科院分区：
文献类型：
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作者：
W. Xie;Zhen-Yu Luo;Yigang Xu;Yibing Chen;L. Hong;Liang Ma;Qiang Ma
中国天山造山带晚古生代的构造性质长期以来一直存在争议。为解决这一问题，对北天山博格达山齐家沟群晚石炭世枕状玄武质熔岩进行了年代学和地球化学的综合研究。对与枕状熔岩呈整合接触的英安岩凝结岩进行的锆石 SHRIMP U-Pb 测年表明，它们的喷发时间约为 311 Ma。枕芯和边缘显示出不同的岩石学和地球化学特征，表明岩浆后海底热液蚀变。然而，枕头芯和边缘都具有类 MORB 的 Sr-Nd-Hf 同位素和弧状微量元素成分。枕状熔岩中的单斜辉石和斜长石在成分上与塔里木地幔柱相关的镁铁质岩石的成分不同。这些观察结果，连同拉斑斑岩指数 (THI > 1) 和铁锰比 (53-57)，表明博格达枕状熔岩可能是由沉积物熔体交代的干燥、贫化的地幔源产生的。与伊豆—小笠宁弧后玄武岩相比，博格达晚石炭世玄武岩熔岩在主量、微量元素和矿物成分方面与伊豆—小笠宁弧后玄武岩（包括弧状弧后玄武岩）非常相似。这表明这些玄武岩可能是在弧后或弧后环境中形成的。
The tectonic nature of the Chinese Tianshan Orogen during the Late Paleozoic has been long disputed. With aims of providing constraints on this issue, an integrated study of geochronology and geochemistry has been carried out on the Late Carboniferous pillow basaltic lava of the Qijiagou Group from the Bogda Mountains, Chinese North Tianshan. Zircon SHRIMP U–Pb dating of a dacite ignimbrite, which is in conformable contact with the pillow lava, suggests that they were erupted at ~ 311 Ma. The pillow cores and rims show different petrological and geochemical characteristics, suggesting post-magmatic seafloor hydrothermal alteration. Nevertheless, both pillow cores and rims have the MORB-like Sr–Nd–Hf isotopes and arc-like trace element compositions. Clinopyroxene and plagioclase from the pillow lavas are compositionally different from those of the mafic rocks related to the Tarim mantle plume. These observations, together with the tholeiitic index (THI > 1) and the Fe/Mn ratios (53–57) of them, indicate that the Bogda pillow lavas may have been generated from a dry and depleted mantle source metasomatized by sediment-derived melts. Compared with basalts of the Izu–Bonin arc-back-arc system, the Bogda Late Carboniferous basaltic lavas show great resemblance to the Izu–Bonin rear-arc basalt (including the arc-like back-arc basalt) in terms of major and trace element and mineral compositions. It suggests that these basalts were likely formed in a rear-arc or back-arc environment.