大兴安岭十二站晚古生代后造山花岗岩的特征及其地质意义

东北大兴安岭地区的十二站岩体主要由钾长花岗岩、二长花岗岩组成。钾长花岗岩的锆石LA-ICP-MS U-Pb定年结果为298Ma,属于晚古生代岩浆活动的产物。十二站岩体岩石化学以高钾(4.82%~6.06%)为特征,属于高钾钙碱性系列,富集大离子亲石元素(LREE和Rb、Th、K等)而亏损高场强元素(Nb、Ta、P、Ti等),显示后造山花岗岩的特征,是兴安地块与松嫩地块碰撞拼合后后造山阶段的产物。岩体的Hf 同位素将大兴安岭北部兴安地块的地壳增生时间限定在显生宙,而额尔古纳地块地壳增生主要发生在新元古代—显生宙,暗示两地块具有不同的早期地壳演化历史。

Characteristics and geological implications of the Late Paleozoic post-orogenic Shierzhan granite in the Great xing'an Range

The Shierzhan intrusion, located in the Great Xing'an Range of northeastern China, is mainly composed of syenogranite and monzogranite. Zircon U-Pb age obtained by LA-ICP-MS analyses from the syenogranite is 298Ma, suggesting that it is the result of Late Paleozoic magmatic activities. Petrochemically, the Shierzhan granite is characterized by high K (K2O 4.82%~6.06%), and therefore belongs to shoshonite series. It is enriched in LILE (LREE, Rb, Th, and K) and depleted in HFSE (Nb, Ta, P, and Ti), showing characteristics of post-orogenic granites. It is proposed that this pluton was likely the product of post-orogenic evolution after the collision of Xing'an and Songnen massifs. Zircon Hf isotopic data of the granite suggest that crustal growth of Xing'an massif in northern Great Xing'an Range occurred in the Phanerozoic, which is much different from that of the Eerguna massif which diaplayes crustal formation age of Neoprotozoic to Phanerozoic. Therefore, the Xing'an and Eerguna massifs have different early crustal evolution histories.