延边“早海西期”棉田花岗岩和仲坪紫苏辉石闪长岩的单颗粒锆石U-Pb定年

Single Grain Zircon U-Pb Ages of the "Early Hercynian" Miantian Granites and Zhongping Hypersthene Diorite in the Yanbian Area

延边花岗岩是中国东北巨型花岗岩省的一部分。传统观点认为,该区花岗岩主要形成于古生代。但高精度的单颗粒锆石U-Pb定年显示,曾被认为是早海西期的棉田岩体和仲坪岩体形成于中生代,其侵位年龄分别为189±1 Ma、129±2 Ma,而不是以前认为的晚古生代。这一年代学结果同时还显示,两岩体是两期岩浆活动的产物,而并不是传统观点所认为的同源岩浆演化的产物。结合从延边地区部分原加里东期花岗岩中获得的中生代年代数据,认为华北地台与北侧佳木斯地块—兴凯地块间拼合历史的传统模式需要进一步修正。

The Yanbian granites, an important part of the giant granitic province in Northeast China, were previously thought of as Paleozoic plutons. A high-precision single grain zircon U-Pb isotopic dating, however, shows that the Miantian and Zhongping plutons, typical Early Hercynian granites, were emplaced in the Mesozoic. The two plutons studied are dated at 189±1 Ma and 129 ± 2 Ma respectively, which indicates that these two plutons were formed in two separated magmatic periods, not consistent with the previously thought that they were originated and evolved from the same magma. In combination with the Mesozoic age data of some Caledonian granites in this area, we propose that the traditional model about the collision between the North China craton and the Jiamusi-Xingkai massive should be modified.