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A mid-Palaeozoic ocean–continent transition in the Mazongshan subduction–accretion complex, Beishan, NW China: new structural, chemical and age data constrain the petrogenesis and tectonic evolution
Geological Magazine ( IF 2.3 ) Pub Date : 2020-04-21 , DOI: 10.1017/s0016756820000114
J.-X. Wang , K.-X. Zhang , Brian F. Windley , B.-W. Song , X.-H. Kou , S.-D. Wang , L.-J. Wang

Accretionary orogens contain key evidence for the conversion of oceanic to continental crust. The late tectonic history and closure time of the Palaeo-Asian Ocean are recorded in the Mazongshan subduction–accretion complex in the southern Beishan margin of the Central Asian Orogenic Belt. We present new data on the structure, petrology, geochemistry and zircon U–Pb isotope ages of the Mazongshan subduction–accretion complex, which is a tectonic mélange with a block-in-matrix structure. The blocks are of serpentinized peridotite, basalt, gabbro, basaltic andesite, chert and seamount sediments within a matrix that is mainly composed of fore-arc-trench turbidites. U–Pb zircon ages of two gabbros are 454.6 ± 2.5 Ma and 434.1 ± 3.6 Ma, an andesite has a U–Pb zircon age of 451.3 ± 3.5 Ma and a tuffaceous slate has the youngest U–Pb zircon age of 353.6 ± 5.1 Ma. These new isotopic ages, combined with published data on ophiolitic mélanges from central Beishan, indicate that the subduction–accretion of Beishan in the southernmost Central Asian Orogenic Belt lasted until Late Ordovician – Early Carboniferous time. Structure and age data demonstrate that the younging direction of accretion was southwards and that the subduction zone dipped continuously to the north. Accordingly, these results record the conversion of oceanic to continental crust in the southern Beishan accretionary collage.

中文翻译:

北山马宗山俯冲-增生杂岩中古生代中古生代海陆过渡:新的构造、化学和年龄数据制约了成因和构造演化

增生造山带包含大洋地壳转变为大陆地壳的关键证据。中亚造山带北山南缘马宗山俯冲-增生杂岩记录了古亚洲洋晚期构造历史和闭合时间。我们提供了关于马宗山俯冲-增生杂岩的结构、岩石学、地球化学和锆石 U-Pb 同位素年龄的新数据,该杂岩是一种具有块状基质结构的构造混杂岩。块体为蛇纹岩化橄榄岩、玄武岩、辉长岩、玄武质安山岩、燧石和海山沉积物,基质主要由弧前沟浊积岩组成。两个辉长岩的 U-Pb 锆石年龄分别为 454.6 ± 2.5 Ma 和 434.1 ± 3.6 Ma,安山岩的 U-Pb 锆石年龄为 451.3 ± 3.5 Ma,凝灰质板岩最年轻的 U-Pb 锆石年龄为 353。6±5.1 毫安。这些新的同位素年龄,结合已发表的北山中部蛇绿混杂岩数据表明,中亚造山带最南端的北山俯冲-增生一直持续到晚奥陶世-早石炭世。构造和年龄数据表明,吸积年轻化方向为南,俯冲带不断向北倾斜。因此,这些结果记录了北山南部增生拼贴中海洋向大陆地壳的转变。构造和年龄数据表明,吸积年轻化方向为南,俯冲带不断向北倾斜。因此,这些结果记录了北山南部增生拼贴中海洋向大陆地壳的转变。构造和年龄数据表明,吸积年轻化方向为南,俯冲带不断向北倾斜。因此,这些结果记录了北山南部增生拼贴中海洋向大陆地壳的转变。
更新日期:2020-04-21
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