青藏高原南羌塘荣玛晚侏罗世闪长岩：班公湖—怒江特提斯洋向北俯冲产物

冉皞; 王根厚; 梁晓; 郑艺龙; 久米多吉

青藏高原南羌塘荣玛晚侏罗世闪长岩：班公湖—怒江特提斯洋向北俯冲产物

The Late Jurassic diorite in Rongma area, southern Qiangtang terrane, Tibetan Plateau: Product of northward subduction of the Bangong Co-Nujiang River Tethys Ocean

摘要

摘要: 班公湖—怒江特提斯洋的演化一直以来备受关注，对于其俯冲极性存在不同认识。报道在青藏高原南羌塘荣玛地区新发现的晚侏罗世闪长岩年代学、地球化学和锆石Hf同位素特征。LA-MC-ICP-MS锆石U-Pb年龄结果表明，岩石形成于149.7 ±0.8Ma，时代为晚侏罗世。岩石呈富碱，低MgO、TFeO、CaO，富集轻稀土元素和Rb、Th、U、K等元素，亏损Ta、Nb、P、Ti等元素。锆石εHf(t)值为正值，并且具有较大的变化范围（+4.26~+9.29），指示岩浆来源于幔源和壳源岩浆的混合。结合区域地质背景认为，荣玛地区晚侏罗世闪长岩为班公湖—怒江特提斯洋向北俯冲所引起的幔源和壳源岩浆混合作用的产物。

Abstract: The evolution of the Bangong Co-Nujiang River Tethys Ocean has long aroused much interest among geologists. The polarity of its subduction remains a topic of much controversy. This paper reports the geochronology, geochemistry and zircon Hf isotopic data of the Late Jurassic diorite in Rongma area, southern Qiangtang terrane, Tibetan Plateau. The LA-MC-ICP-MS U-Pb dating of zircons yielded an age of 149.7±0.8Ma. The Late Jurassic diorite is characterized by rich alkali metals, poor MgO, TFeO, CaO, enrichment of LREE as well as Rb, Th, U, K elements and depletion of Ta, Nb, P, Ti elements. The positive zircon εHf(t) with the wide range (+4.26~+9.29) indicates the mixing of mantle and crust magma. These new data, together with the geological background, indicate that the Late Jurassic diorite in Rongma area was formed by mixing of mantle and crust magma in response to northward subduction of the Bangong Co-Nujiang River Tethys Ocean.

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