Granitoid rocks are universal in continental crust and are of special significance in understanding tectonic settings. This paper presents detailed zircon U-Pb dating, Hf isotope, whole-rock geochemistry, and Sr-Nd-Pb isotope analyses, and mineralogy of two Ordovician granitoid intrusions and one quartz diorite intrusion in Western Kunlun, NW Tibetan Plateau. The Yutian Complex is composed of diverse rock suites, including monzogabbros, quartz monzodiorites, monzogranites, and monzodioritic enclaves. These suites have similar rock formation ages (447–440 Ma) and minerals, e.g., amphibole grains from different suites belonging to pargasite. Moreover, they exhibit geochemical similarities, such as broadly parallel trace-element patterns characterized by enrichments in light rare earth elements and large ion lithophile elements, and depletions in high field strength elements, which are typical features of arc rocks. Furthermore, the studied samples display homogeneous zircon Hf values, e.g., εHf(t) = −1 to −3, and whole-rock isotopic compositions, e.g., εNd(t) = −4 to −6. Thus, they were most likely derived from a mantle wedge enriched by subducted sediments and fluids, which then evolved into different suites through fractional crystallization of hornblende and plagioclase. The ca. 440 Ma North Yutian quartz diorite intrusion, with an average of εHf(t) value of −6, was a product of the partial melting of mafic lower crust through slightly fractional crystallization of hornblende. In contrast, the ca. 470 Ma Aqiang granodiorite intrusion has εHf(t) values varying from −5 and −2, but it has heterogeneous petrological and geochemical features. It is considered to be a product of the partial melting of the overriding mantle wedge modified by fluids derived from the subducted Proto-Tethys slab and some mixed crustal materials. The Aqiang samples belong to the slightly fractionated I-type series, but they have variable alumina saturation index (ASI = molar Al2O3/[CaO – 3.33 × P2O5 + Na2O + K2O]) values (0.74–1.03) due to variable peraluminous biotite contents. The different suites in the Yutian Complex display low ASI values (<1) controlled by sources and fractional crystallization. The Yutian Complex and the North Yutian intrusion were emplaced during the southward subduction of the Proto-Tethys oceanic lithosphere, and the Aqiang intrusion was emplaced in response to the northward subduction.

中文翻译：

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青藏高原西部昆仑西部奥陶纪花岗岩的成岩作用：洞察特提斯海洋的演化

花岗岩岩石在大陆壳中普遍存在，对理解构造环境具有特殊意义。本文介绍了西北青藏高原西部昆仑地区两次锆石奥陶纪花岗岩侵入体和一个石英闪长岩侵入体的详细锆石U-Pb测年，Hf同位素，全岩地球化学和Sr-Nd-Pb同位素分析以及矿物学。于田综合体由各种岩石组合组成，包括辉石岩，石英辉闪石，辉光岩和辉闪岩群。这些套房具有相似的岩石形成年龄（447–440 Ma）和矿物，例如来自属于辉绿石的不同套房的闪石粒。此外，它们还表现出地球化学的相似性，例如广泛平行的痕量元素模式，其特征是富含轻稀土元素和大型离子亲石元素，和高场强元素的损耗，这是弧形岩石的典型特征。此外，研究样品显示出均质的锆石Hf值，例如εHf（t）= -1至-3，全岩石同位素组成，例如εNd（t）= -4至-6。因此，它们很可能源自俯冲沉积物和流体富集的地幔楔，然后通过角闪石和斜长石的部分结晶而演变成不同的组。的ca。440 Ma北于田石英闪长岩侵入体的平均εHf（t）值为-6，是黑角铁矿通过部分角晶状结晶结晶部分熔融的产物。相反，ca。470 Ma Aqiang花岗闪长岩侵入体的εHf（t）值介于-5和-2之间，但具有非均质的岩石和地球化学特征。它被认为是上覆地幔楔部分熔融的产物，地幔楔被俯冲的原始特提斯板片和某些混合地壳物质衍生的流体改性。Aqiang样品属于略微分级的I型系列，但是由于铝黑云母含量可变，它们的氧化铝饱和指数（ASI =摩尔Al2O3 / [CaO – 3.33×P2O5 + Na2O + K2O]）值（0.74-1.03）不等。 。于田综合体中的不同套件显示出较低的ASI值（<1），受源和分级结晶控制。在原始特提斯海洋岩石圈的南向俯冲过程中，建立了玉田复合体和北部的玉田侵入体，并响应北俯冲而形成了阿强侵入体。