Genesis of Triassic Buziwannan Granites in the West Kunlun Orogen Belt, China: Constraints from in Situ Major, Trace and Sr Isotope Analyses of Plagioclase
Lin Wang, Peiwen Chen, Qingdong Zeng, Renchang Mi, Runsheng Han
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引用次数: 0
Abstract
Buziwannan granodiorite and monzogranite associated with gold–polymetallic mineralization are located in the West Kunlun Orogen Belt in northwest China. Granodiorite was emplaced earlier than monzogranite. To determine the genesis of plagioclase from two intrusions and their relation with mineralization, the major, trace elemental, and Sr isotopic compositions of plagioclase were determined through LA-ICP-MS and LA-MC-ICP-MS respectively. The results indicated that the plagioclase from granodiorite had a high-An (around 40%) core and low-An (around 33%) rim, while the plagioclase from monzogranite was uniform with an An value around 18%. The (87Sr/86Sr)i ratios of plagioclase decreased with decreasing An value, which may be caused by small-scale crustal contamination and/or magma mixing. The crystallization process of plagioclase is mainly accompanied by the exsolution of magmatic H2O, and the pressure changes caused by the loss of magma H2O. These magmatic fluids are rich in ore-forming elements, such as Au–Ag–Cu–Zn, and form skarn mineralization near the wall rocks. Because of the co-crystallization of plagioclase, hornblende, and biotite, as well as the addition of minor felsic magma with lower Sr isotopic composition, the plagioclase from monzogranite exhibits low and uniform An values. In addition, a large amount of magmatic H2O carrying ore-forming elements was released during the emplacement of granodiorite, which caused the monzogranite to lose its metallogenic potential.
摘要 与金多金属矿化有关的布子湾南花岗闪长岩和单斜花岗岩位于中国西北部的西昆仑造山带。花岗闪长岩的成因早于单斜花岗岩。为了确定两个侵入体中斜长岩的成因及其与成矿作用的关系,通过LA-ICP-MS和LA-MC-ICP-MS分别测定了斜长岩的主要元素、微量元素和锶同位素组成。结果表明,花岗闪长岩中的斜长岩具有高An(约40%)核心和低An(约33%)边缘,而单斜长岩中的斜长岩则很均匀,An值约为18%。斜长岩的(87Sr/86Sr)i 比值随 An 值的降低而降低,这可能是小规模地壳污染和/或岩浆混合造成的。斜长石的结晶过程主要伴随着岩浆 H2O 的溶出和岩浆 H2O 损失引起的压力变化。这些岩浆流体富含成矿元素,如金-银-铜-锌,并在壁岩附近形成矽卡岩矿化。由于斜长石、角闪石和斜长石的共晶体化,以及加入了少量 Sr 同位素组成较低的长纤维岩浆,来自单斜长花岗岩的斜长石表现出低而均匀的 An 值。此外,在花岗闪长岩的成岩过程中,大量携带成矿元素的岩浆 H2O 被释放出来,使单斜花岗岩失去了成矿潜力。
期刊介绍:
Petrology is a journal of magmatic, metamorphic, and experimental petrology, mineralogy, and geochemistry. The journal offers comprehensive information on all multidisciplinary aspects of theoretical, experimental, and applied petrology. By giving special consideration to studies on the petrography of different regions of the former Soviet Union, Petrology provides readers with a unique opportunity to refine their understanding of the geology of the vast territory of the Eurasian continent. The journal welcomes manuscripts from all countries in the English or Russian language.