Paleoproterozoic crustal evolution of the Tarim Craton: Constrained by zircon U-Pb and Hf isotopes of meta-igneous rocks from Korla and Dunhuang

摘要

The Tarim Craton is one of three large cratons in China. Presently, there is only scant information concerning its crustal evolutionary history because most of the existing geochronological studies have lacked a combined isotopic analysis, especially an in situ Lu-Hf isotope analysis of zircon. In this study, Precambrian basement rocks from the Kuluketage and Dunhuang Blocks in the northeastern portion of the Tarim Craton have been analyzed for combined in situ laser ablation ICP-(MC)-MS zircon U-Pb and Lu-Hf isotopic analyses, as well as whole rock elements, to constrain their protoliths, forming ages and magma sources. Two magmatic events from the Kuluketage Block at ~2.4Ga and ~1.85Ga are revealed, and three stages of magmatic events are detected in the Dunhuang Block, i.e., ~2.0Ga, ~1.85 Ga and -1.75 Ga. The ~1.85 Ga magmatic rocks from both areas were derived from an isotopically similar crustal source under the same tectonic settings, suggesting that the Kuluketage and Dunhuang Blocks are part of the uniform Precambrian basement of the Tarim Craton. Zircon Hf model ages of the ~2.4 Ga magmatism indicate that the crust of the Tarim Craton may have been formed as early as the Paleoarchean period. The ~2.0Ga mafic rock from the Dunhuang Block was formed in an active continental margin setting, representing an important crustal growth event of the Tarim Craton in the mid-Paleoproterozoic that coincides with the global episode of crust formation during the assembly of the Columbia supercontinent. The ~1.85Ga event in the Kuluketage and Dunhuang Blocks primarily involved the reworking of the old crust and most likely related to the collisional event associated with the assembly of the Columbia supercontinent, while the ~1.75 Ga magmatism in the Dunhuang Block resulted from a mixture of the reworked Archean crust with juvenile magmas and was most likely related to a post-collisional episode.