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    华夏地块加里东期构造事件:两类花岗岩的锆石U-Pb年代学和Lu-Hf同位素制约

    Caledonian tectonic event of Cathaysia block: Constraints on zircon U-Pb geochronology and Lu-Hf isotope for two kinds of granite

    • 摘要: 提要:为了更好地了解华夏地块加里东期构造事件,对武夷山—井冈山地区加里东期块状花岗岩和片麻状花岗岩进行锆石U-Pb年代学和Lu-Hf同位素研究。片麻状花岗岩的结晶年龄在415~440 Ma,块状花岗岩的结晶年龄为430~449 Ma。锆石εHf(t)值在-20~0之间(n=247),绝大多数在-10以下。二阶段Hf模式年龄tDMC在1.5~2.8 Ga。结合前人资料,两类花岗岩在形成时代、锆石Hf同位素和二阶段Hf模式年龄tDMC组成上相近,物质来源主要为不同时代地壳物质的再循环,没有显著的地幔物质加入。华夏地块加里东期构造热事件形成于陆内造山环境,430 Ma左右可能是加里东期造山带构造体制转换的时间,片麻状构造是同造山或后造山构造变形的结果。

       

      Abstract: Abstract: For better understanding the Caledonian tectonic event of Cathaysia block, this paper documents a set of new zircon U-Pb geochronological and Hf isotopic analytical results for the Caledonian massive and gneissic granites from Wuyishan-Jinggangshan area. Crystallization ages of gneissic granites range from 415 Ma to 440 Ma,crystallization ages of massive granites range from 430 Ma to 449 Ma. The εHf(t) values of zircons range from -20 to 0(n=247), most data below -10. The two stage Hf model ages (tDMC) range from 1.5 Ga to 2.8 Ga. Combined with previous data, the authors revealed that the formation age, zircon Hf isotopic form and two stage Hf model ages (tDMC) of the two kinds of granite are similar. Granites were derived from crustal source of different times, which recycled during Caledonian. In addition, the addition of juvenile mantle-derived magma was insignificant. The Caledonian tectothermal event of Cathaysia block took place within an intracontinental orogenic environment. Caledonian orogen may have transformed its tectonic regime at about 430Ma, and gneissic structure resulted from synorogenic or late-orogenic deformation.

       

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