柴北缘欧龙布鲁克地块东段古元古代基性麻粒岩:岩石学、锆石U-Pb年代学和Lu-Hf同位素证据

Paleoproterozoic mafic granulite in the eastern Oulongbuluke block of the North Qaidam Mountains: Evidence from petrology,zircon U-Pb dating and Hf isotope

在欧龙布鲁克地块东部地区的正片麻岩中识别出呈透镜状产出的基性麻粒岩,部分已转变为斜长角闪岩。其主要矿物组合为单斜辉石、斜方辉石、斜长石、角闪石等,为典型中低压麻粒岩相组合。锆石SHRIMP U-Pb定年得到基性麻粒岩1928±9Ma的变质年龄,片麻岩围岩得到了1927±20Ma的变质年龄,以及2368±5Ma、2377±7Ma的岩浆结晶年龄。片麻岩锆石Hf同位素数据显示变质锆石及岩浆锆石均具有相似的Hf同位素成分,其二阶段模式年龄为2590~2830Ma,显示其可能源于太古代地壳物质的再造。欧龙布鲁克地块古元古代岩浆及变质演化历史与塔里木克拉通及华北克拉通很高的相似性,预示着在古元古代三者可能具有一定的亲缘性。

Mafie granulite enclosed within orthogneiss is recognized in the eastern Oulongbuluke block.It mainly consists of clinopyroxene,orthopyroxene,plagioclase and amphibole,characteristic of low-medium pressure granulite facies assemblage.Zircon SHRIMP U-Pb dating of one mafic granulite yields an age of 1928 ± 9Ma,interpreted as Paleoproterozoic metamorphic age.Zircon SHRIMP U-Pb analyses from two orthogneiss samples give metamorphic age at 1927 ± 20Ma and magmatic crystallization ages at 2368 ± 5Ma and 2377 ± 7Ma,respectively.Zircon Hf isotopic data show that both the metamorphic and magmatic zircons from gneisses have similar 176Hf./177 Hf ratios with two-stage Hf model ages between 2590Ma and 2830Ma,indicating they could be derived from reworking of Archean crust.The Paleoproterozoic magmatic and metamorphic evolution history of the Oulongbuluke block exhibits high degree of similarity with those in the Tarim Craton and North China Craton.This implies that they have affinity in Paleoproterozoic.