川西雀儿山花岗岩的地球化学和岩石成因

Geochemistry and Petrogenesis of Queershan Granitoids, Western Shichuan Province

位于川西义敦岛弧北端的雀儿山花岗岩体主要由岩体边部或者作为包体的花岗闪长岩、主体似斑状花岗岩和较晚的呈条带状或者脉状伟晶质、细晶质花岗岩组成。这些花岗质岩石表现了较宽的常量元素变化范围,属于高钾钙碱性到shoshonite亚铝到过铝质岩石系列,表现了较平坦式具有负Eu异常的稀土配分模式。在原始地幔标准化的多元素图解上所有这些岩石表现Rb、Th和K等大离子亲石元素强烈富集,Nb、Sr、P和Ti等元素明显亏损。Sm-Nd同位素分析结果表明似斑状花岗岩亏损地幔模式年龄tDM=1.23~1.61Ga,εNd(t)=-5.3^-6.3,细晶花岗岩脉tDM=2.30Ga,εNd(t)=-6.9。这些岩石的εNd(t)分布在康定杂岩的Nd同位素演化范围内和上部。岩石地球化学和Nd同位素特征研究揭示其花岗岩岩浆起源于上部地壳杂砂岩、砂页岩和泥质岩石的部分熔融,经历了早期阶段的铁镁质矿物和副矿物的分离结晶,晚期钾长石等卷入了分离结晶。雀儿山花岗质岩浆活动发生于同碰撞到碰撞后隆升构造背景。

Queershan granitoids, located in the most north of Yidun island arc belt, western Sichuan province consist chiefly of granodiorites distributing in the margin of the plutonic intrusion or as enclaves, porphyry-like granites as main lithology and later pegmatic and aplitic ganites as veins. These granitoids in the Queershan pluton have wider variation in major components and were attributed to high-K calc-alkaline and shoshonite series with per- to meta-aluminous geochemical characteristics, displaying flatted REE patterns with significant negative gu anomalies. On the primitive mantle normalized spider diagrams, Rb, Th and K LILEs are quite enrichment, but Nb, Sr, P and Ti obvious depletions. Sm-Nd isotopic analyses reveal these porphyry-like granite samples from Queershan granitoids with depletive mantle model ages, tDM = 1.23- 1.61Ga and εNd （t）=- 5. 3-- 6. 3, and the aplitic granite with tDM = 2. 30 Ga,εNd （t）=- 6. 9. The εNd （t） of all these granitoids distribute within and above the εNd （t） evolutionary range of the Proterozoic Kangding complex. Integrated the petrochemistry and Nd isotopic characteristics, the granitoid magma could derive from partial melting of continental upper crust materials of major greywackes, sillstones and pelitic rocks, undergoing earlier fractionation of mafic and accessory minerals, and later fractionation involving k-felspar. Tectonic discriminations reveal that these granitoids were must likely generated in the syn-colllision and post-collision uplifting processes