桂中都安钾镁煌斑岩金云母^(40)Ar/^(39)Ar年龄及其构造意义

Phlogopite ^(40)Ar/^(39)Ar dating of the lamproite veins in Du'an County,central Guangxi and its tectonic significance

右江褶皱带地处扬子陆块和华夏陆块的结合部位,区内广泛发育以基性-超基性岩墙群和超酸性岩脉为主的燕山晚期双峰式岩浆活动。对桂中都安地区的金云钾镁煌斑岩脉进行了金云母^(40)Ar/^(39)Ar法测年,斑晶和基质金云母样品均给出了较一致的坪年龄,分别为93.6±0.6Ma和92.9±0.6Ma,相应的等时线年龄分别为93.4±0.9Ma和92.7±0.8Ma,上述年龄代表了岩脉的侵位年龄。结合区内报道的同期年代学资料,进一步证明右江褶皱带及其周缘晚白垩世双峰式岩浆活动响应了华南地区燕山晚期的构造转换事件及随后大规模的岩石圈伸展减薄。

The Youjiang Fold Belt is located in the connection region between Yangtze Block and Cathaysia Block. It is characterized by Late Yanshanian bimodal magmatic activities and consists of basic-ultrabasic dyke swarms and ultra-acid rock veins.In this study, the phlogopite 40 Ar/39 Ar dating of phenocryst and matrix from phlogopite lamproite veins, which are located in the Du’an County of central Guangxi, yielded two plateau ages of 93.6±0.6 Ma, 92.9±0.6 Ma and two isochron ages of 93.4±0.9 Ma, 92.7±0.8 Ma, respectively. These ages are interpreted as the emplacement age for phlogopite lamproite veins. The new results obtained by the authors in junction with the coeval magmatic events further reveal that the voluminous Late Cretaceous bimodal magmatic activities occurred in the Youjiang Fold Belt as well as its peripheral regions in response to the Late Yanshanian tectonic transition and subsequent lithospheric thinning and extension in South China.