Petrogenesis of the Ramba leucogranite in the Tethyan Himalaya and constraints on the channel flow model
Petrogenesis of the Ramba leucogranite in the Tethyan Himalaya and constraints on the channel flow model
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特提斯喜马拉雅地区兰巴淡色花岗岩的岩石成因及河道水流模型的约束
DOI：
10.1016/j.lithos.2014.08.022
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发表时间：
2014-11
期刊：
影响因子：
3.5
通讯作者：
Chuan-Zhou Liu
中科院分区：
文献类型：
--
作者：
Fu-Yuan Wu;Wei-Qiang Ji;Jian-Gang Wang;Chuan-Zhou Liu
喜马拉雅期浅色花岗岩是认识喜马拉雅造山作用的地球动力学过程的关键。在这篇文章中，我们提出了岩石学，地质年代学和地球化学的结果，兰巴浅色花岗岩的作物在特提斯喜马拉雅山脉内的兰巴圆顶的中心。锆石、独居石和磷钇矿的U-（Th）-Pb定年揭示了兰巴穹隆约在1980年发生了三期淡色花岗岩岩浆活动。44 Ma，ca. 28、我和你8马，分别。CA。44、我和你28 Ma岩浆活动均以侵入穹隆边缘的强烈变形斑状二云母花岗岩片麻岩岩墙为代表。与古印度地壳物质相比，这些花岗质片麻岩具有较高的CaO和Sr含量，较高的Na/K、Sr/Y和较低的Rb/Sr比值，较低的87 Sr/86 Sr初始比值，但εNd（t）和εHf（t）值较高。这些结果表明，花岗岩片麻岩不是来自高喜马拉雅序列的变质沉积岩，而很可能是在增厚的地壳条件下的镁铁质岩石的部分熔融。CA。8 Ma浅色花岗岩由穹丘核部的二云母花岗岩岩体和穹丘边缘的含石榴子石花岗岩脉组成。主量元素和微量元素组成表明，这些中新世浅色花岗岩是典型的S型花岗岩，很可能是由变岩的白云母和/或黑云母脱水熔融形成的。含石榴子石花岗岩的TiO 2、TFeO、MgO和CaO含量相对较低，Rb含量和Rb/Sr比值较高，Eu负异常较强，表明其演化程度高于同时代的二云母花岗岩。此外，在Ramba浅色花岗岩中还发现了一些类似亚洲的物质，如中生代继承锆石和部分浅色花岗岩样品的Sr-Nd-Hf同位素组成相对亏损等。特提斯喜马拉雅浅色花岗岩的这些特征以前被认为是通道流模型的直接地质证据。然而，详细的年代学和地球化学研究的围岩表明，这些亚洲的物质最有可能来自围岩，而不是亚洲岩石圈，因此，他们可能不会被用来作为信道流模型的坚实证据。
The Himalayan leucogranites are critical for understanding the geodynamic process of Himalayan orogenesis. In this article, we present petrological, geochronological and geochemical results of the Ramba leucogranites that crop out in the center of the Ramba dome within the Tethyan Himalaya. U–(Th)–Pb dating of zircon, monazite and xenotime revealed three episodes of leucogranitic magmatism in the Ramba dome at ca. 44 Ma, ca. 28 Ma and ca. 8 Ma, respectively. The ca. 44 Ma and ca. 28 Ma magmatisms are both represented by strongly deformed porphyritic two-mica granite gneiss dykes that intruded into the margin of the dome. These granite gneisses have high CaO and Sr contents, relatively high Na/K, Sr/Y and low Rb/Sr ratios, and much lower initial87Sr/86Sr ratios but higher εNd(t) and εHf(t) values than the ancient Indian crustal material. These results indicate that the granite gneisses were not derived from metasedimentary rocks of the High Himalayan Sequence but most likely were derived from partial melting of mafic rocks at a thickened crustal condition. The ca. 8 Ma leucogranites consist of a two-mica granite pluton in the core of the dome and garnet-bearing granite dykes in the margin of the dome. Major and trace element compositions indicate that these Miocene leucogranites are typical S-type granites and were most likely derived from muscovite and/or biotite dehydration melting of metapelites. The relatively lower TiO2, TFeO, MgO and CaO contents, higher Rb concentration and Rb/Sr ratio, and more strongly negative Eu anomaly of the garnet-bearing granite indicate that it was more evolved than the coeval two-mica granite. The non-CHARAC (CHarge-And-Radius-Controlled) trace element behavior and the tetrad effect of the REE distribution of the garnet-bearing granite further suggest that it is a highly fractionated granite.Besides, our study detected some Asian-like materials in the Ramba leucogranites, such as Mesozoic-aged inherited zircons and the relatively depleted Sr–Nd–Hf isotopic compositions of some leucogranite samples. These features of leucogranites in the Tethyan Himalaya have been previously considered as direct geological evidence for the channel flow model. However, detailed geochronological and geochemical studies of the country rocks suggest that these Asian-like materials are most likely sourced from the country rock rather than the Asian lithosphere, thus they may not be used as solid evidence for the channel flow model.
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