桂东南古罗和王姜冲钾玄质辉长岩的成因:地球化学、锆石U-Pb年代学及Hf同位素特征制约

古罗和王姜冲岩体产于扬子地块与华夏地块拼合带的西南段,对剖析华南区域构造演化过程具有重要的地质意义。古罗和王姜冲岩体主要由辉长岩及少量的闪长岩组成。LA-ICP-MS锆石U-Pb年代学分析表明,古罗和王姜冲辉长岩的侵位结晶时限分别为(163±1) Ma和(158±1) Ma,属于燕山期岩浆活动的产物。岩石无Nb、Ta负异常,具有板内钾玄岩系列特征,锆石的ε_Hf(t)值主要集中在0.7~8.3之间,其二阶段Hf模式年龄($T_{DM_{2}}$)为672~1 168 Ma,暗示其源区主要为新元古代—中元古代岩石圈地幔。综合地球化学、锆石Hf同位素组成特征及区域地质资料,认为古罗和王姜冲岩体是在板内伸展-减薄环境主要由亏损的软流圈地幔和富集的岩石圈地幔岩浆混合形成,且在上升过程中受到壳源组分混染。

Petrogenesis of the Guluo and Wangjiangchong Shoshonite-gabbro in Southeastern Guangxi Province: Constraints from Petrochemistry,Zircon U-Pb Age and Hf Isotope

The Guluo and Wangjiangchong plutons are located in the southwestern section of the suture between the Yangtze and Cathaysia blocks. They are important in revealing the tectonic evolution of South China. The plutons are composed dominantly of gabbro with minor diorite. The zircon U-Pb ages of the Guluo and Wangjiangchong plutons are (163 ± 1) Ma and (158 ± 1) Ma, respectively. The rocks show no negative Nb-Ta anomalies and intraplate potassic basalt affinity. The zircon ε_Hf(t) values (0.7-8.3) and T_DM2 (672-1,168 Ma) are indicative of a Neoproterozoic lithospheric mantle source. Integrating the regional geology, whole-rock geochemistry and zircon Hf isotopes studies, we suggest that the Guluo and Wangjiangchong plutons were formed in an intraplate extensional setting, via mixing between materials from the depleted asthenospheric mantle and the enriched lithospheric mantle, and contaminated by crustal materials during the magma ascent.