黑龙江省东部双鸭山二长辉长岩的年代学、矿物学、结晶过程及其地质意义

Geochronology, mineralogy, crystallization process and tectonic implications of the Shuangyashan monzogabbro in eastern Heilongjiang Province.

双鸭山二长辉长岩侵位于中国黑龙江省双鸭山市东北部的下白垩统含煤地层内。岩相学证据表明,双鸭山二长辉长岩中的橄榄石、斜长石、单斜辉石和钛铁矿依次是岩浆早期结晶的矿物,而黑云母及少量细小的斜方辉石是演化的岩浆分别与早期结晶的钛铁矿、橄榄石反应的产物,最后的残余岩浆结晶形成了他形的钾长石,包裹其它矿物形成嵌晶结构。根据双鸭山二长辉长岩全岩成分做结晶过程的热力学模拟计算,估计的结晶过程与岩相学研究基本一致。黑云母K-Ar法和SHRIMP锆石U-Pb法的年龄测定结果一致表明,双鸭山二长辉长岩的侵位时代为98Ma,即晚白垩世早期。这一时期,中国东北地区东部、俄罗斯远东兴安岭-鄂霍茨克一带、和日本西南部可能都是当时欧亚大陆东部活动大陆边缘的组成部分,因而晚白垩世早期俯冲相关的岩浆活动在中国东北地区东部可能也是大量存在的。

The Shuangyashan monzogabbro occurs in the Lower Cretaceous coal-bearing strata in the Shuangyashan basin, eastern Heilongjiang Province, Northeast China. In the monzogabbro, olivine, plagioclase, clinopyroxene and ilmenite subsequently crystallized from magma, whereas biotite and minute orthopyroxene resulted from the reaction of evolved magma with the crystallized ilmenite and olivine, respectively. Finally, the residue magma crystallized as anhedral K-feldspar and enclosed all already crystallized minerals, showing the poikilitic texture. Thermodynamic simulation for crystallization process of the Shuangyashan monzogabbro shows the results are generally consistent with the petrographic observation. Biotite K-Ar and SHRIMP zircon U-Pb dating consistently yielded an early Lite Cretaceous age of 98Ma for the monzogabbro. In the Late Cretaceous, eastern Northeast China, Khingan-Okhotsk of Far East Russian, and Southeast. Japan together were in an active continental margin setting. The early We Cretaceous subduction-related magmatism may be widely distributed in eastern Northeast China.