内蒙古莫若格钦地区二长闪长岩锆石SHRIMP U-Pb年龄及其地质意义

Zircon SHRIMP U-Pb age of Monuogechin monzodiorite of Inner Mongolia and its geological significance

内蒙古莫若格钦铅锌矿预查区是中蒙边界地区南戈壁-东乌旗铜多金属成矿带中部新发现的一处铅锌矿化区。矿床地质特征研究表明,区内发育的二长闪长岩与铅锌多金属矿床的形成有密切的时空、成因关系。为了揭示成矿规律,笔者对二长闪长岩进行单颗粒锆石SHRIMP U-Pb定年,获得206Pb/238U加权平均年龄为（312.6±4.1）Ma（MSWD=0.76）,该年龄与二连-东乌地区晚石炭世岩浆活动事件（介于300~315 Ma）相对应,与白音乌拉—东乌珠穆沁旗岩带的花岗岩年龄（300~315）Ma一致。结合区域地质研究成果,初步确定莫若格钦二长闪长岩是晚石炭世弧间裂谷伸展作用下地壳挤压增厚局部熔融的产物。上述成果为研究南戈壁-东乌旗地区晚石炭世岩浆侵位活动以及铅锌铜钼多金属矿产找矿方向研究提供了重要证据。

Located in the South Gobi-Dong Ujimqin Banner metallogenic belt of the China-Mongolia border and its neighboring areas,the Monuogechin lead-zinc pre-investigation area is a newly-discovered lead-zinc polymetallic deposit.The exposed monzodiorite has an intimate relationship with the Monuogechin lead-zinc pre-investigation area.In order to determine the accurate age of the Monuogechin monzodiorite,the authors employed the zircon SHRIMP U-Pb isotope dating technology and obtained the age of（312.6±4.1） Ma（MSWD=0.76）,indica-ting Hercynian.This age is essentially in agreement with the event of magmatism in the east of the Erenhot-Dong Ujimqin Banner volcanic-magmatic belt（from 300 Ma to 315 Ma） and the age of granites in the South Gobi-Dong Ujimqin Banner copper polymetallic ore-forming belt.Combined with regional data,it is suggested that the Erenhot-Dong Ujimqin Banner Late Carboniferous monzodiorite resulted from the crustal thickening melting of the intraarc rift tensional system.This age provides important evidence for Late Carboniferous magmatism and helps guide the work related to lead-zinc molybdenum-copper polymetallic ore exploration in China-Mongolia border and its neighboring areas.