江西九岭花岗岩类复式岩基锆石SHRIMP U-Pb年代学

SHRIMP U-Pb Zircon Geochronology of the Jiuling Granitic Complex Batholith in Jiangxi Province

江西九岭花岗岩体产于扬子地块东南缘,是我国华南的一个规模巨大的复式花岗岩基.该岩体一直被认为是在晋宁期、海西期和燕山期多期次岩浆侵入活动的产物.在对该复式岩基进行详细野外调查的基础上,开展了锆石SHRIMPUPb年龄测定,过去认为是晋宁期形成的花岗岩样品,测出的206Pb/238U年龄为(9828±8)Ma;而原来认为是海西期形成的甘坊岩体测出的年龄为(820±10)Ma,说明该区不存在海西期的花岗岩,结合其他新的年代学资料推测扬子板块内可能不存在加里东—海西期的岩体;原认为是燕山中期的样品测出的年龄为(151.4±2.4)Ma,研究结果与原来的一致.此外,还获得了1.4～1.9Ga的继承锆石的年龄,可能代表九岭新元古代花岗岩源岩的年龄.

The Jiuling granitic batholith in Jiangxi Province crops out at the southern margin of the Yangtze block, and it is the largest Neoproterozoic granitoid intrusion in South China. The granitic complex has long been considered to consist of Jinningian granites, Hercynian granites and Yanshanian granites. In this paper, a SHRIMP U-Pb zircon geochronological study on this complex has been performed on the basis of detailed field research. The ^206 pb/^238 U age of granite thought to be formed in the Neoproterozoic is （828±8）Ma, while the age of one sample from Ganfang granite thought to be formed in the Hercynian is （820±10）Ma, which suggests there is no Hercynian granite in this area. Combined with other new geochronological data, it seems that there is no proof of Caledonian-Hercynian magmatic activity within the Yangtze block, which may infer that there is no Caledonian-Hercynian intrusion in the interior of the Yangtze block. The age of a sample thought to be formed in the Yanshanian is （151.4±2. 4）Ma, which confirms previous results. A few inherited zircons record Mesoproterozoic age information, which may represent the ages of the granite source rocks.