南秦岭武当山群变质酸性火山岩锆石U-Pb年代学

对武当山群3个变质酸性火山岩样品的锆石U-Pb定年结果表明,武当山群变质酸性火山岩形成年龄为675.2±3.1 Ma,说明武当山群存在新元古代南华纪的地层组成.武当山群变质变形复杂,具多期岩浆活动,可能由不同时代火山岩和少量沉积岩组成,部分变质火山岩具有与耀岭河群火山岩和侵入到武当山群中的基性侵入岩相似的形成年龄,指示了武当山群变质酸性火山岩可能与基性侵入岩群和耀岭河群火山岩存在成因联系.基于现有同位素定年数据,武当山群火山岩数据具有年龄跨度大(太古宙至中生代)的显著特征,但总的趋势是新近取得的年龄数据多数比早期获得的数据要年轻.

Zircon U-Pb geochronology of the meta-acidic volcanic rocks from the Wudangshan Group, Southern Qinling Mountains, Central China

Zircon U-Pb ages of three meta-acidic volcanic rocks from the Wudangshan Group, Southern Qinling Mountains, Central China, dated by means of LA-MC-ICPMS are reported in this paper. The dating results show that the age of the meta-acidic volcanic rock is 675.2 ± 3.1 Ma (MSWD = 3.7), which constrains that the Wudangshan Group contains Nanhuan (Cryogenian) Period components. The Wudangshan Group is mainly composed of volcanic rocks of various ages and minor sedimentary rocks, demonstrating complex deformation and metamorphism and including poly-phases of magmatic rocks. Some meta-acidic volcanic rocks in the Wudangshan Group have similar age with the volcanic rock in the Yaolinghe Group and the basic intrusive rocks in the Wudangshan Group, indicating possible genetic relationship between the acidic volcanic rocks with the basic intrusive rocks in the Wudangshan Group and the Yaolinghe Group volcanic rock. Based on the available isotopic dating, it seems that the age span of the Wudangshan Group extends from the Archean to the Mesozoic, but the general trend is that most of the recently acquired age data are younger than those obtained earlier.