内蒙古阿拉善右旗塔木素地区酸性侵入岩锆石U-Pb年龄与地球化学特征

内蒙古阿拉善地块北缘塔木素地区酸性侵入岩发育，主要岩性为黑云母花岗岩、花岗闪长岩、二长花岗岩、英云闪长岩，其中花岗闪长岩、英云闪长岩、二长花岗岩构成塔木素地区侵入岩的主体，岩体侵入晚石炭世—早二叠世阿木山组，又被白垩系、侏罗系不整合覆盖，区域上呈近东西向展布。采用LA-ICP-MS技术，测得内蒙古阿拉善右旗塔木素地区的塔木素二长花岗岩和笋布尔英云闪长岩中锆石的206Pb/238U年龄分别为264.2±3.3Ma和273.0±3.3Ma，这2个年龄被解释为各自的侵位年龄，即二者均形成于中二叠世。花岗闪长岩、二长花岗岩和英云闪长岩在SiO2-K2O图解中落入钙碱系列和高钾钙碱性系列，A/CNK值分别为0.874~1.01、1.06~1.54和0.91~1.03；Ba、Rb、Th、K等大离子亲石元素富集，Nb、Ta、P、Ti等高场强元素相对亏损；稀土元素总量分别介于156.99×10-6~212.87×10-6、126.92×10-6~212.98×10-6和128.13×10-6~214.5×10-6之间，均呈负Eu异常；在构造环境Rb-（Yb+Nb）和Rb-（Yb+Ta）判别图解中均落入火山弧花岗岩区。结合区域背景分析，阿拉善北缘在早二叠世时可能存在与弧物质有关的岩浆活动。

LA-ICP-MS zircon U-Pb dating and geochemistry of granitoids in Tamusu, Alxa Right Banner, Inner Mongolia

Acid and intermediate-acid intrusive rocks are widely distributed in Tamusu, northern Alxa massif. These rocks are mainly biotite granite, granodiorite, adamellite and tonalite, with the last three forming the main body of the intrusive rocks in Tamsag area. The massif, unconformably covered by Cretaceous and Jurassic strata, was intruded into Late Carboniferous-Early Permian Amushan Formation, and its regional distribution shows sub-latitudinal feature. The LA-ICP-MS zircon U-Pb ages of the monzonitic granite and tonalite in this region are respectively 264.2±3.3Ma and 273.0±3.3Ma. The granodiorite, monzonitic granite and tonalite are of calc-alkalic to high potassium calc-alkalic suite, characterized by A/CNK ratios of 0.874~1.01, 1.06~1.54, and 0.91~1.03, and ∑REE values of 156.99×10-6~212.87×10-6, 126.92×10-6~212.98×10-6 and 128.13×10-6~214.5×10-6, respectively. These intrusive rocks show a close affinity to island-arc granites in Rb-(Yb+Nb) and Rb-(Yb+Ta) diagrams, with enrichment of Ba, Rb, Th, K and other large ion lithophile elements, and depletion of Nb, Ta, P, Ti and other high field strength elements. It is considered that the northern margin of Alxa might still have had some arc-related magmatic activities during the Permian period.