扬子克拉通西缘康定杂岩中花岗质岩石的成因及其构造意义  

Petrogenesis of granitoid rocks in the Kangding Complex, western margin of the Yangtze Craton and its tectonic significance.

作　　者：刘树文[1] 闫全人[2] 李秋根[1] 王宗起[2] 

机构地区：[1]北京大学造山带与地壳演化教育部重点实验室,北京大学地球与空间科学学院,北京100871 [2]中国地质科学院地质研究所,北京100037

出　　处：《岩石学报》2009年第8期1883-1896,共14页Acta Petrologica Sinica

基　　金：国家自然科学基金面上项目(40872120);国家重大基础研究项目(2002CB412608)资助成果

摘　　要：扬子克拉通西缘康定杂岩中的片麻状花岗岩主要由英云闪长岩、花岗闪长岩、灰白色细粒二长花岗岩和少量的粉红色粗粒二长花岗岩组成。其中英云闪长岩和花岗闪长岩形成于797～795Ma,灰白色细粒二长花岗岩SHRIMP锆石定年产生一个^(206)Pb/^(238)U权重平均767±24Ma,被解释为该期花岗质岩浆的结晶年龄。英云闪长岩、花岗闪长岩和灰白色细粒二长花岗岩和其中的闪长岩包体表现为右斜式稀土配分模式,具有很高的(La/Yb)_N比值,无Eu异常,在原始地幔标准化的多元素蜘蛛网状图上表现了明显的Nb、Ta、P和Ti负异常。而粉红色粗粒二长花岗岩却表现了平坦的稀土配分模式,具有强烈的负Eu异常和强烈的Nh、Ta、Sr、P和Ti负异常,但是富集大离子亲石元素。所有这些片麻状花岗岩具有ε_(Nd)(t)=-0.57～+5.67,绝大部分样品ε_(Nd)(t)>0。结合地质学、岩石学、地球化学和Sm-Nd同位素特征,康定杂岩中英云闪长岩、花岗闪长岩和灰白色细粒二长花岗岩形成于来自亏损地幔的初生地壳玄武质岩石和相关的杂砂岩在高压条件下的部分熔融,而粉红色粗粒二长花岗岩的岩浆导源于表壳岩低压条件下的部分熔融。结合这些片麻状花岗岩的岩石成因和构造鉴别,表明扬子克拉通西缘康定杂岩中新元古代片麻状花岗岩形成于安第斯型活动大陆边缘。Gneissic granitoid rock suite in the Kangding Complex, located in western margin of the Yangtze Craton, comprises mainly tonalite, granodiorite, hoar fine-grained monzogranite with a little of pink coarse-grained monzogranite. SHRIMP zircon U-Pb isotopic dating revealed that the tonalite and granodiorite emplaced at 797 similar to 795Ma, and a new SHRIMP zircon U-Pb chronological data yield a weighted average age of (206)Pb/(238)U age of 767 +/- 24Ma for a hoar fine-grained monzogranite (sample Kd-18), interpreted as emplacement age of the hoar fine-grained monzogranite. Tonalites, granodiorites, hoar fine-grained monzogranites, comprising dioritic enclaves in the gneissic granitoids, are characterized by right-inclined chondrite-normalized REE patterns with high (La/Yb)(N) values and without Eu anomalies, and significantly negative Nb, Ta, P and Ti in primitive mantle normalized multi-element spider diagrams. Whereas, pink coarse-grained monzogranites show flat chondrite-normalized REE patterns, strongly negative Eu and Nb, Ta, Sr, P and Ti anomalies but LILEs enrichment. Sm-Nd isotopes analyses reveal that the granitoids have epsilon(Nd) (t) = -0.57 similar to +5.67, and most of the samples epsilon(Nd) (t) > 0. Integrated features of geology, petrology to petrochemistry and Sm-Nd isotopes, the magma of the tonalite, granodiorite and hoar fine-grained monzogranite may be derived from partial melting of juvenile basaltic rocks and greywacks with depleted mantle affinity under high pressure condition, and the magma of the pink coarse-grained monzogranite could come from supracrust materials at the relative lower pressure condition. Petrogenesis of these granitoids, combining with tectonic discrimination, suggests that the Neoproterozoic Kanding Complex in the western margin of the Yangtze Craton could be produced in a tectonic setting of the subduction-related active continental margin.

关 键 词：扬子克拉通西缘 康定杂岩 花岗质岩石 成因 构造意义 Kangding Complex TECTONIC significance Yangtze Craton 二长花岗岩 英云闪长岩 片麻状花岗岩 花岗闪长岩 稀土配分模式 SHRIMP chronological data 细粒 部分熔融 TECTONIC setting negative Sm-Nd 

分 类 号：P58[天文地球—岩石学]