内蒙古固阳地区侵入渣尔泰群中新元古代早期辉长岩岩床的发现及其意义

华北克拉通由于新元古代早期构造-岩浆活动的地质记录较少,制约了对其新元古代时期构造演化的认识。本文对内蒙古中部固阳地区侵位于渣尔泰群阿古鲁沟组中3个变辉长岩岩床样品进行了锆石LA-ICP-MS U-Pb年代学测试,显示其侵位年龄为-925 Ma,表明华北克拉通北缘存在新元古代早期的岩浆活动。该岩床与同时期华北克拉通中部-925 Ma的基性岩墙群(大石沟岩墙)和东南部945-890 Ma的基性岩床群(徐淮-辽东-沙里院岩床)具有相似的岩石地球化学特征和重叠的Nd同位素组成,表明其可能是新元古代早期华北克拉通中—东部发育的大规模基性岩浆活动事件在克拉通北缘的响应,但其规模相对华北克拉通东南缘明显较小。华北克拉通北缘新元古代早期基性岩浆活动的发现,为深入了解华北克拉通北缘新元古代构造演化及其与罗迪尼亚超大陆的关系提供了重要线索。

Identification of an early Neoproterozoic gabbro sill emplaced into the Zha'ertai Group in the Guyang area,Inner Mongolia and its geological significance

The evolution of North China Craton(NCC) during the early Neoproterozoic period remains unclear or controversial due to limited exposures of Neoproterozoic tectonism and magmatism. In this contribution, we identified an early Neoproterozoic gabbro sill emplaced into the Agulugou Formation within the Zha’ertai Group in Guyang area, central Inner Mongolia in northern margin of the NCC. Zircon LA-ICP-MS U-Pb dating on three metagabbro samples yields emplacement ages of -925 Ma, indicating existence of early Neoproterozoic mafic magmatic activities in the northern margin of the NCC. The early Neoproterozoic metagabbro sill in the Guyang area exhibits similar geochemical characteristics and overlapped Nd isotopic compositions to those of the -925 Ma mafic dyke swarm(Dashigou dykes) in the central NCC and the 945-890 Ma mafic sill swarms(Xuhuai-Liaodong-Sariwon diabase sills) in the southeastern NCC. The -925 Ma metagabbro sill emplaced into the Zha’ertai Group in the Guyang area is most likely the northwestern extension of the 945-890 Ma mafic magmatism in the central and eastern NCC. However, compared with the 945-890 Ma mafic magmatism in the central and eastern NCC that were considered to be related to breakup of the NCC from other continents in the Rodinia supercontinent, the areal extent and volume of the -925 Ma mafic magmatism is very small, indicating that the northern margin of the NCC was far from the plume and breakup center during the early Neoproterozoic. Our identification of the -925 Ma metagabbro sill in the northern NCC provides new evidence for Neoproterozoic evolution and involvement of the NCC in the Rodinia supercontinent.