Generation of coeval metaluminous and muscovite-bearing peraluminous granitoids in the same composite pluton in West Qinling, NE Tibetan Plateau
Generation of coeval metaluminous and muscovite-bearing peraluminous granitoids in the same composite pluton in West Qinling, NE Tibetan Plateau
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青藏高原东北部西秦岭同一复合岩体中同时代准铝质和含白云母花岗岩的生成
DOI：
10.1016/j.lithos.2019.06.034
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发表时间：
2019
期刊：
影响因子：
3.5
通讯作者：
Guo-Chen Dong
中科院分区：
文献类型：
--
作者：
Jun-Qiang Hu;Xiao-Wei Li;Ji-Feng Xu;Xuan-Xue Mo;Fang-Yue Wang;Hong-Xia Yu;Wei Shan;Hui-Xiang Xing;Xiong-Fei Huang;Guo-Chen Dong
关于（强）过铝质花岗岩的性质及其与同时代的准铝质花岗岩的关系存在相当大的争议。过铝质花岗岩的起源对于了解花岗岩岩石成因以及大陆地壳的形成和演化具有重要意义。这项研究揭示了青藏高原东北部西秦岭约243-242 Ma的郭马营复合岩体（GCP）中存在同生的准铝质花岗岩和含白云母的过铝质花岗岩。 GCP 中三叠世花岗岩类在岩石学和地球化学上可分为两类。 I 组样品的特点是 K2O/Na2O 比率稍高，并且是具有较低 Zr 饱和温度 (740–756 °C) 的正铝质样品。相比之下，第二组样品具有较低的 K2O/Na2O 比率，并且大部分为强过铝成分，Zr 饱和温度略高（762-778 °C）。两组具有相似的微量元素和Sr-Nd-Pb-Hf同位素组成，表明中下地壳起源于角闪岩残留物。准铝质花岗岩被解释为西秦岭下中下地壳角闪岩的部分熔融，而含白云母的过铝质花岗闪长岩也是由角闪岩源部分熔融生成的，并在源中添加了富含长石的成分。来自交代地幔楔源部分熔融的含水玄武岩熔体也被纳入岩浆糊中。据推测，不同的岩浆来源、夹带的包晶组合以及不同程度的前晶再循环共同对GCP的花岗质岩浆化学产生了影响。因此，我们的数据表明，含白云母的强过铝质花岗岩被广泛认为是再生变沉积岩的产物，也可能起源于以角闪岩为主的来源，并涉及富含长石的成分。
There is considerable controversy over the nature of (strongly) peraluminous granitoids and their relationship with coeval metaluminous granitoids. The origin of peraluminous granitoids is of great importance for an understanding of granite petrogenesis, as well as the formation and evolution of the continental crust. This study reveals the presence of contemporaneous metaluminous granitoids and muscovite-bearing peraluminous granitoids in the Guomaying composite pluton (GCP) at approximately 243–242 Ma in West Qinling in the NE Tibetan Plateau. The Middle Triassic granitoids in the GCP can be petrographically and geochemically divided into two groups. The group I samples are characterized by slightly higher K2O/Na2O ratios and are metaluminous with lower Zr-saturation temperatures (740–756 °C). In contrast, the group II samples have lower K2O/Na2O ratios and mostly strongly peraluminous compositions, with marginally higher Zr-saturation temperatures (762–778 °C). Both groups share similar trace elements and Sr–Nd–Pb–Hf isotopic compositions, pointing to middle to lower crustal origins with an amphibolitic residue. The metaluminous granitoids are interpreted as partial melting of amphibolites in the middle to lower crust beneath West Qinling, and the muscovite-bearing peraluminous granodiorites were also generated by partial melting of an amphibolitic source, with addition of a feldspar-rich component in the source. The hydrous basaltic melts derived from partial melting of a metasomatized mantle wedge source were also incorporated into the magma mush. It is inferred that disparate magma sources, entrained peritectic assemblages, and various degrees of antecryst recycling collectively exerted influence on the granitic magma chemistry of the GCP. Consequently, our data suggest that muscovite-bearing strongly peraluminous granitoids, which are widely regarded as the products of recycled metasedimentary rocks, can also originate from an amphibolite-dominated source with involvement of a feldspar-rich component.