江南造山带东段800~780Ma陆内裂谷岩浆活动--来自浙皖赣邻区约790Ma铝质A型花岗岩的证据

摘要

In this paper, the authors report geochronological and geochemical data obtained for Lingshan granite porphyries of the eastern Jiangnan Orogen in the Zhejiang-Anhui-Jiangxi border area. Zircon LA-ICP-MS U-Pb dating of Lingshan granite porphy⁃ries shows that these rocks were crystallized at 791.8 ± 2.6Ma. Lingshan granite porphyries are characterized by high Si, high TFeO/(TFeO+MgO)ratio, low Mg, Ca, Mn, and P, and peraluminous nature (A/CNK=1.04~1.18);REE data show that the granite por⁃phyries have high concentrations of Rb, Ga, Th, Zr, Y, but are depleted in Sr, P, Ti, Ba; additionally, the granite porphyries have high total REE concentrations and high LREE/HREE ratio, exhibiting strong negative Eu anomalies;these characteristics are consis⁃tent with features of the typical aluminous A-type granite. Geochemical analysis and results of previous researches show that the Ling⁃shan granite porphyries were formed in a continental rift environment, and most likely derived from partial melting of juvenile crust. In combination with the previous study, the authors hold that the magmatic activities that occurred between 800 and 780 Ma not on⁃ly played an important role in the formation of South China Neoproterozoic basin but also has important geological significance for the study of the tectonic environment during this period and calibration of sedimentary cycle during Banxi period.%对江南造山带东段浙皖赣邻区的灵山花岗斑岩进行了同位素年代学和岩石地球化学研究。LA-ICP-MS锆石U-Pb年龄测定结果表明，灵山花岗斑岩形成于791.8±2.6Ma。在岩石地球化学组成上，灵山花岗斑岩具有高Si，高TFeO/（TFeO+MgO）值，低Mg、Ca、Mn和P，显示出过铝质的特征（A/CNK=1.04~1.18）；微量元素富集Rb、Ga、Th、Zr、Y，贫Sr、P、Ti、Ba；稀土元素总量较高，轻、重稀土元素分异较明显，并表现出强烈的负Eu异常，这些特点与典型的铝质A型花岗岩一致。地球化学特征和前人研究成果表明，灵山花岗斑岩形成于陆内裂谷环境，最有可能来源于早期初生地壳的部分熔融。结合前人研究成果认为，800~780Ma的岩浆活动是华南新元古代一期重要的构造岩浆事件，该期岩浆活动不仅在华南新元古代盆地的形成过程中扮演了重要角色，而且在该时期构造环境的探讨、板溪期沉积旋回时限的标定等方面都发挥了重要作用。