内蒙古阿拉善地块北缘沙拉扎山晚石炭世岩体地球化学特征与LA-ICP-MS锆石U-Pb年龄

采用LA-ICP-MS同位素测定技术，测得内蒙古阿拉善北缘沙拉扎山温都尔毛道黑云母花岗闪长岩锆石U-Pb年龄为301±2Ma，属于晚石炭世侵入岩。地球化学分析结果显示，该黑云母花岗闪长岩SiO2含量为67.23%~72.57%，K2O为1.14%~1.61%，Al2O3为14.92%~17.23%，具有过铝质（A/CNK=1.06~1.1）和钙碱性特征。岩石的稀土元素总量较低（38.86×10-6~74.39 ×10-6），轻稀土元素相对富集，Eu总体呈弱异常（δEu=0.9~1.3）。在原始地幔标准化图解中，岩石具有大离子亲石元素（Rb、Th、K）富集及高场强元素（Nb、Ta、P、Ti）亏损的特征，显示出I型花岗岩的特点。结合区域地质背景，该黑云母花岗闪长岩可能形成于俯冲背景，是洋壳板片与新生的壳源物质混合形成的产物，表明晚古生代沿着阿拉善地块北缘的俯冲至少始于301Ma。

Geochemistry and LA-ICP-MS zircon U-Pb age of Late Carboniferous Shalazhashan pluton on the northern margin of the Alxa Block,Inner Mongolia and their implications

The Wenduermaodao biotite granodiorite pluton is located in Shalazhashan on the northern margin of the Alxa Block. LA-ICP-MS U-Pb dating of zircons from the pluton yielded an age of 301±2Ma, which indicates that the pluton is a Late Carboniferous intrusion. According to the geochemical analysis, the Wenduermaodao pluton has high SiO2 (67.23%~72.57%), K2O(1.14 %~6.13%) and Al2O3(13.67%~17.29%), suggesting that it is calc-alkaline and peraluminous (A/CNK=0.98~1.10). This intrusion has low REE content (38.86×10-6~74.39×10-6) with a relative enrichment of LREE and week Eu anomalies (δEu=0.9~1.3). The primitive mantle normalized trace element patterns are characterized by the enrichment of the LILE (Rb, Th, K) and depletion of HFSE (Nb, Ta, P, Ti), showing the features of I-type granite. Combined with regional geology, the authors hold that the pluton was emplaced in a subduction setting and derived from mixed sources of oceanic crust and juvenile crust, and the subduction of Paleo Asian plate beneath the northern Alxa Block took place at 301Ma or earlier.