阿尔泰地区霍热木德克花岗岩体年代学、地球化学特征及构造意义

Chronological and geochemical characteristics and tectonic significance of Huoremudeke granitic pluton in Altay area of Xinjiang,China

中阿尔泰构造带出露大面积晚三叠世花岗岩,对其进行详细研究是了解阿尔泰造山带构造演化和陆壳增生过程的重要途径。本文对霍热木德克岩体进行详细的岩石学、锆石U-Pb年代学、岩石地球化学及Sr-Nd同位素研究。霍热木德克花岗岩体主要有粗粒二长花岗岩、细粒二长花岗岩和正长花岗岩。LA-ICP-MS锆石U-Pb年代学研究结果表明,其结晶年龄为(222.3±1.8)Ma(MSWD=1.6),为晚三叠世岩浆活动产物。地球化学研究表明,岩石具有高SiO_2、Al_2O_3、ALK,低TiO_2、MnO、MgO、P_2O_5的特征,轻稀土富集、轻重稀土分馏明显,具有Eu的负异常(δEu=0.37~0.50),富集大离子亲石元素、相对亏损高场强元素,显示出强过铝质S型花岗岩的特征,花岗岩具有负的εNd(t)(-3.7^-2.7)和较老的二阶段模式(T2DM)年龄(1.2~1.3Ga)。综合分析认为,霍热木德克花岗岩由富含白云母和黑云母的变泥质岩经历部分熔融形成,其源区有富钙斜长石、钛铁矿的残留,为同碰撞造山阶段挤压环境下地壳加厚而发生部分熔融的产物,形成于同碰撞构造环境。

The Huoremudeke granitic pluton occurs in the central part of the Altay Orogenic Belt （AOB）. The pluton is composed principally of coarse monzonitic granite, fine monzonitic granite and syenogranite. Detailed petrologic, geochronological, geochemical and Sr-Nd isotopic studies are carried out on the granitic rocks from the Huoremudeke pluton. Zircons analysis from the sampleyields a weighted average mean 206 Pb/238 U age of （222. 3±1. 8） Ma （MSWD=1. 6） ,representing the intruding age of the pluton. Geochemically,the granitic rocks are characterized by high SiO2, AlO3, ALK, and low TiO2 , MnO, MgO and P2O5 contents, with fractionated REE patterns and negative Eu anomalies （δEu = 0. 37 -0.50）. They show enrichment of LILE, and depletion of HFSE on the primitive mantle-normalized trace element diagrams and have high Sr isotopic compositions （ initial87Sr/86Sr = 0. 692 50-0. 704 11） and weakly negative εNd （t） values （ - 3. 7-- 2. 7）, with Nd modelages of 1. 2-1. 3 Ga. It is considered that the granite is probably derived from dehydration melting of biotite-bearing pelite and its source area has residual plagioclase and ilmenite. Combined with the tectonic evolution of the Altay, it is proposed that the Huoremudeke granitic pluton is formed in the syn-collision environment.