华北克拉通桑干地区高压麻粒岩的锆石SHRIMP U-Pb年龄及其地质含义

为了揭示华北克拉通桑干地区古元古代高压麻粒岩变质峰期时限,对选自该区的两个高压麻粒岩样品(DST02,XYS01)进行了锆石SHRIMP U-Pb测年。锆石样品的阴极发光图像显示为球形和无内部结构,Th/U比值变化为0.01~0.93。这些特征表明两样品的锆石应属于变质成因锆石。两样品的SHRIMP测年结果分别给出(1 792±12)Ma和(1 891±46)Ma。根据前人的年代学方面的研究成果,特别是未变质强过铝花岗岩中获得的1 900~1 850 Ma的锆石U-Pb年龄(郭敬辉等,2002)结果来看,本区高压麻粒岩峰期变质时代不会晚于此。因此本文获得的1 850~1 800 Ma的锆石SHRIMP U-Pb年龄应代表退变年龄。而(1 891±46)Ma的年龄限定了峰期高压变质年龄上限。

Zircon SHRIMP U-Pb age of the Paleoproterozoic high-pressure granulites from the Sanggan area, the North China Craton and its geologic implications

Zircons extracted from high-pressure granulite and strongly peraluminous granites from the Sanggan area of the North China Craton,have been investigated by integrating petrogenesis with U-Pb ages.The isometric internal structure and round shape of the zircons as revealed by cathodoluminescence,in combination with low Th/U ratios(0.01～0.93),indicate that they crystallized or recrystallized under metamorphic conditions and the ages obtained must be representative of the metamorphic age.Concordant U-Pb ages of((1 792±12) Ma)(8 points) and (1 891±46) Ma(19 points) were obtained from zircons of the sample DST02 and XYS01,respectively.Zircons U-Pb ages of 1 900~1 850 Ma obtained from unmetamorphosed strongly peraluminous granites,indicate that the upper limit of the peak metamorphic age could not be younger than(1 900) or(1 850) Ma.Therefore,the U-Pb ages of(1 792±12) Ma and(1 891±46) Ma are proposed to represents the time of retrograde and peak granulite metamorphic ages,respectively.