Many Late Mesozoic granites distribute in the Yidun island arc belt, SW China. However, in situ zircon U-Pb ages and Hf isotopic data of these granites have rarely been reported so far. As lately reported granite from the central segment of the Yidun island arc belt, the Xiasai granite has a close genetic relationship with the Xiasai Ag-Pb-Zn polymetallic deposit. This paper presents (1) laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb age for the Xiasai granite to determine precisely the time of the magmatism, (2) geochemical and Hf isotope data for the Xiasai granite to constrain the petrogenesis and tectonic setting. The LA-ICP-MS analyses of zircon from the Xiasai granite yielded a weighted mean206Pb/238U age of 103±1 Ma (MSWD=0.5), indicating that it was emplaced in the Early Cretaceous. Petrography and chemical compositions of the granites show that they belong to high-K calc-alkaline series and are characterized by high silicon, enrichment of alkaline and iron but depletion in calcium and magnesium. Their SiO2 and K2O+Na2O contents are 72.94%-74.98% and 7.56%-8.08%, respectively. The A/CNK values vary from 1.06 to 1.10, show a weak peraluminous affinity. The granitic rocks are enriched in high field strength elements (e.g. Zr and Hf) and large ion lithophile elements (e.g. U and Th) but depleted in Ba, Sr, P, and Ti. REEs are characterized by significant negative Eu anomalies (δEu=0.13-0.25) and exhibit right-inclined patterns with LREE enrichment but HREE depletion. Mineralogy and geochemistry of the rocks show an affinity to aluminous A-type granite, similar to other Late Cretaceous A-type granites such as the Rongyicuo, Lianlong and Ruorolong granites in the Yidun island arc belt. Zircon Hf isotopic compositions of the Xiasai granite are characterized byεHf(t) values varying from 2.7 to 0.6 and the two-stage model ages (TDM2) of 925 Ma to 1095 Ma, implying that different source materials have contributed to the magma genesis. Integrated geological, geochemical and isotopic data suggest that the Xiasai A-type granite is most likely generated via a two-stage process, including formation of parental magma by mixing of an asthenosphere-derived magma and a crustal-derived felsic magma in the deep crust, followed by intensive magmatic differentiation of the parental magma. These granites are likely to have been generated in a post-collisional extensional tectonic setting related to arc-continent collision during the Early Cretaceous.%义敦岛弧带晚中生代侵入岩体目前仍缺乏高精度的年代学数据制约,其成因也存在争论。作者首次在岛弧带中段夏塞银铅锌多金属矿区发现与成矿关系密切的黑云母二长花岗岩。本文对其开展了年代学、地球化学和 Hf 同位素分析,探讨成因及构造背景。LA-ICP-MS锆石U-Pb定年结果为103±1 Ma(MSWD=0.5),为早白垩世晚期岩浆活动产物。花岗岩属高钾钙碱性岩系,具有高硅、富碱和铁、贫钙和镁特征, SiO2含量为72.94%~74.98%, K2O+Na2O=7.56%~8.08%,铝饱和指数 A/CNK=1.06~1.10,属弱过铝质岩石。岩石富集 Zr、Hf 等高场强元素和 U、Th 等大离子亲石元素,明显亏损Ba和Sr。REE具有明显的Eu负异常(δEu=0.13~0.25),总体呈较陡右倾的LREE富集和HREE相对亏损特征。岩相学和地球化学显示其为铝质A型花岗岩。Hf同位素组成εHf(t)=–2.7~0.6,二阶段模式年龄TDM2=925~1095 Ma。地球化学及Hf同位素揭示夏塞岩体为软流圈地幔与壳源长英质岩浆混合成因,并经历了斜长石、正长石和褐帘石等矿物的分离结晶。夏塞花岗岩体具有后碰撞花岗岩特征,形成于早白垩世晚期弧-陆碰撞造山后伸展构造背景。
展开▼
