Geochemistry and geochronology of the Mesozoic Lanong ophiolitic melange, northern Tibet: Implications for petrogenesis and tectonic evolution
Geochemistry and geochronology of the Mesozoic Lanong ophiolitic melange, northern Tibet: Implications for petrogenesis and tectonic evolution
复制标题
藏北中生代拉农蛇绿混杂岩的地球化学和年代学：对岩石成因和构造演化的启示
DOI：
10.1016/j.lithos.2017.09.003
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发表时间：
2017
期刊：
影响因子：
3.5
通讯作者：
Huang Qiang Tai
中科院分区：
文献类型：
--
作者：
Zhong Yun;Liu Wei Liang;Xia Bin;Liu Jing Nan;Guan Yao;Yin Zhen Xing;Huang Qiang Tai
拉弄蛇绿混杂岩是位于西藏北方班公湖-怒江缝合带中段的一个典型的蛇绿混杂岩。它主要由超镁铁岩和镁铁岩组成，其构造环境和形成时代的约束性较差。本文提供了拉弄蛇绿混杂岩中辉长岩、辉长粗玄岩、粗玄岩和玄武岩的新地球化学和LA-ICP-MS锆石U-Pb年龄数据。枕状玄武岩具有N-MORB（正常洋中脊玄武岩）的地球化学特征，锆石U-Pb年龄为147.6 ± 2.3Ma。它们是由尖晶石二辉橄榄岩组成的亏损地幔源的~ 20-30%部分熔融产生的。辉长岩、块状玄武岩和辉长粗玄岩样品的稀土元素配分模式为亏损型和“V”型，具有不同程度的类玻安岩地球化学特征，其锆石U-Pb年龄为149.1 ± 1.2Ma（辉长粗玄岩）。它们来自于一个显着的耐火地幔源重熔后，以前的玄武岩熔体提取一个或多个事件。这些镁铁质岩的地球化学数据表明，它们是在大陆弧前环境中发展的，岩浆来自亏损地幔源俯冲板片衍生的流体和熔体与轻微的地壳混染修改。另一方面，白云岩具有明显的似洋岛玄武岩（OIB）地球化学特征，其锆石U-Pb年龄为244.1 ± 3.0Ma。它们形成于大陆架斜坡上的裂谷环境中，起源于与一些古老的次大陆岩石圈地幔物质混合的亏损软流圈岩浆源的低程度部分熔融。结合前人的研究结果，认为拉弄蛇绿混杂岩可能是在中三叠世-早白垩世班公湖-怒江特提斯洋向南俯冲的过程中，在会聚的板块边缘形成的。也就是说，OIB状的粗粒岩可能反映了中三叠世的伸展裂谷环境，具有薄陆壳，辉长岩，辉长岩粗粒岩和玄武岩代表了晚侏罗世-早白垩世弧前盆地的后期阶段。
The Lanong ophiolitic mélange is a typical ophiolitic mélange in the middle section of the Bangong–Nujiang suture zone in northern Tibet. It mainly consists of ultramafic and mafic rocks, and its tectonic setting and formation age remain poorly constrained. In this paper, new geochemical and LA–ICP–MS (laser ablation–inductively coupled plasma mass spectrometer) zircon U–Pb age data obtained from gabbro, gabbro–dolerite, dolerite and basalt of the Lanong ophiolitic mélange are provided. The pillow basalts exhibit N-MORB (normal mid-ocean ridge basalt)-like geochemical features with a zircon U–Pb age of 147.6 ± 2.3 Ma. They were generated by ~ 20–30% partial melting of a depleted mantle source composed of spinel lherzolite. The gabbro, massive basalt and gabbro–dolerite samples are characterised by more depleted and “V”-shaped REE (rare earth element) patterns, and they exhibit variable degrees of boninite-like geochemical characteristics, with a zircon U–Pb age of 149.1 ± 1.2 Ma (gabbro-dolerite). They were derived from the remelting of a significantly refractory mantle source following one or more episodes of previous basaltic melt extraction. Geochemical data of these mafic rocks indicate that they were developed in a continental fore-arc setting, and magmas were derived from depleted mantle sources modified by subducted slab-derived fluids and melts with minor crustal contamination. On the other hand, the dolerites show distinct OIB (oceanic island basalt)-like geochemical features, with a zircon U–Pb age of 244.1 ± 3.0 Ma. They were formed in a rift setting on a continental shelf-slope and originated from a low degree of partial melting of a depleted asthenospheric magma source mixed with some ancient sub-continental lithospheric mantle materials. The signatures presented here, combined with the results of previous studies, suggest that the Lanong ophiolitic mélange probably developed in a convergent plate margin under the southward subduction of the Bangong–Nujiang Tethys Ocean beneath the Lhasa terrane during the Middle Triassic–Early Cretaceous. Namely, the OIB-like dolerites likely reflect an extensional rift setting featuring thin continental crust in the Middle Triassic, and the gabbros, gabbro–dolerites and basalts represent a later stage of a fore-arc basin during the Late Jurassic–Early Cretaceous.