西大别~2.0 Ga变质花岗岩的发现及其Hf同位素特征

The discovery of~2.0 Ga metamorphosed granite in western Dabie Mountains and its Hf isotopic characteristics

扬子陆块广泛存在2.10~1.90 Ga构造热事件的年代学信息,然而在大别地区该时期的岩浆岩体尚未报道,本文在野外地质调查的基础上,对西大别金盘岩体的变质花岗岩开展了锆石年代学和Hf同位素分析。锆石U-Pb测年结果显示变质花岗岩的结晶年龄为(2022±17)Ma(MSWD=2.3),代表了大别造山带古元古代的岩浆活动记录。锆石的εHf(t)值(-10.6~-7.6)及其二阶模式年龄(2.96~3.12 Ga)表明该岩体来源于古老陆壳的再造。综合已有Hf同位素资料,扬子陆块北缘广泛发育2.95~3.18 Ga太古宙地壳,为该类花岗岩的岩浆形成提供了物源。金盘岩体形成于古元古代碰撞造山作用时期(2.03~1.93 Ga),可能指示了Columbia超大陆聚合在大别地区的响应。该~2.0 Ga花岗岩体的识别,为研究大别造山带早前寒武纪构造岩浆事件的演化序列提供了新的资料。

Geochronological data of 2.10-1.90 Ga tectonic thermal events in the Yangtze block are widely documented,but the magmatic rocks of this period in the Dabie area have not been reported.On the basis of field geological survey,the geochronological and zircon Hf isotopes of the metamorphic granite from the Jinpan pluton in western Dabie Mountains were analyzed.U-Pb dating of magmatic zircons from the metamorphic granite yielded age of(2022±17)Ma(MSWD=2.3),which represents Paleoproterozoic magmatic event in the Dabie orogenic belt.The negativeεHf(t)values(-10.6--7.6)and TDm^(2)ages(2.95-3.12 Ga)of zircons indicate that the Jinpan granite might be derived from the reconstruction of ancient continental crust.The previous Hf isotope results also indicate that the widely-distributed Archean continental crust(2.95-3.18 Ga)in the Yangtze Block provided material source for the magmatic evolution of the Jinpan metamorphic granite.The Jinpan pluton was formed in the period of Paleoproterozoic collisional orogeny(2.03-1.93 Ga),and it might be the response to the convergent of Columbia supercontinent.The identification of the~2.0 Ga granite provides a new evidence for the evolution of Precambrian tectonic-magmatic events in the Dabie orogenic belt.