The latest Neoarchean-Paleoproterozoic evolution of the Dunhuang block, eastern Tarim craton, northwestern China: Evidence from zircon U-Pb dating and Hf isotopic analyses

摘要

The Dunhuang block, in the easternmost segment of the Tarim craton, exposes Precambrian mafic granulite and felsic gneiss. To better understand the poorly known formation and evolution of the Tarim craton, we carried out detailed field-based petrological and geochronological investigations on the major lithologies of the Dunhuang block. U-Pb dating and Hf isotopic analyses on the mafic granulite and felsic gneiss (TTG gneiss) of the Dunhuang block reveal two distinct age populations: the Latest Neoarchaean (～2.5. Ga) and the Late Palaeoproterozoic (1.82-1.85. Ga). The zircon magmatic cores and metamorphic rims of tonalitic gneisses yield similar ages of ～2.5. Ga, supporting the existence of Archean rocks in the Dunhuang block. The short time interval between Latest Neoarchean magmatism and high-grade metamorphism suggests that they were related to the same Latest Neoarchean tectonothermal event. The ～2.5. Ga zircons show Hf-depleted mantle model ages between 2.55. Ga and 2.8. Ga with a peak at ～2.7. Ga, suggesting that ～2.7. Ga juvenile crust of the Dunhuang block was reworked during a 200-300. m.y. period at the end of the Neoarchean. The age of ～1.85. Ga obtained from the mafic granulites and felsic gneisses is interpreted as the age of high-pressure granulite facies metamorphism. Combined with the Hf isotopic data, these data suggest that the Dunhuang block experienced ～2.7. Ga crustal growth, a ～2.5. Ga magmatic-metamorphic event and a 1.82-1.85. Ga (HP) granulite facies metamorphic event. This sequence of events is very similar to that of the North China Craton, implying that the evolutionary history of the Dunhuang block was consistent with that of the North China Craton from the Neoarchean to Paleoproterozoic.