江西武功山穹隆复式花岗岩的锆石U-Pb年代学研究

Zircon U-Pb Isotopic Chronology of the Wugongshan Dome Compound Granite in Jiangxi Province

采用锆石U-Pb法对武功山穹隆复式花岗岩中广泛分布的花岗质岩石开展精细定年研究,结果表明:山庄、张佳坊和武功山岩体的锆石U-Pb年龄分别为460.5±1.5 Ma、427.9±1.2 Ma和428.0±1.0-462.3±2.3 Ma,属早古生代晚期花岗岩;而雅山、温汤和明月山等岩体的锆石U-Pb年龄分别为161.0±1.0 Ma、143.8±1.6 Ma和126.3±6.4.Ma,属晚侏罗世-早白垩世花岗岩。因此认为武功山穹隆复式花岗岩中花岗岩分属早古生代晚期及晚侏罗世-早白垩世岩浆活动产物。从一个侧面说明华南地区大地构造演化过程中可能存在早古生代晚期构造一岩浆作用事件及晚侏罗世-早白垩世构造-岩浆作用事件,为华南大地构造演化研究提供了新的依据。结合前人在武功山地区花岗质片麻岩中白云母40Ar/39Ar法定年(225-233 Ma)资料,说明本区韧性变形形成于晚i叠世,可能意味着武功山伸展构造的启动时间,而晚侏罗世-早白垩世花岗岩浆的形成及向上运移,使周围的岩石软化乃至部分熔融,使得围岩环境更有利于伸展构造发展,并在早白垩世最终形成武功山花岗岩穹隆伸展构造。

There are many granite plutons in the Wugongshan dome compound granite. Fine U-Pb dating of zircons show that the Shanzhuang granite, Zhangjiafang granite and Wugongshan granite have zircon ages of 460. 5±1. 5 Ma, 427. 9±1. 2 Ma and 428. 0±1. 0～ 462. 3 ±2. 3 Ma respectively, belonging to the late Early Paleozoie. The Yanshan granite, Wentang granite and Mingyueshan granite have zircon ages of 161.0±1.0 Ma, 143. 8 ±1. 6 Ma, 126. 3 ±6. 4 Ma respectively, belonging to the late Jurassic-early Cretaceous. Therefore, the authors believe that the granite of the Wugongshan dome compound granite is the product of the late Early Paleozoie and late Jurassic-early Cretaceous magmatism. These data can indicate from another angle that there might be late Early Paleozoie tectonic-thermal events and late Jurassic-early Cretaceous tectonic-thermal events, which provides new evidence for the researches of geotectonie evolution of South China. Considering also ^40Ar/^39Ar dating of muscovite from granitic gneiss （225～233 Ma）, these data show that the ductile distortion was formed during the late Triassic which may be the startup of extensional tectonics. The formation and upwelling of late Jurassic-early Cretaceous magmas made the wall rocks softening and partial melting, which help the development of extensional tectonics in wall rocks, and the granitic dome extensional tectonics was finally formed during the Cretaceous in Wugongshan.