Detrital zircon U-Pb geochronology of Ordovician-Silurian strata in the northwestern platform of the Tarim Basin: Implications for provenance systems and tectonic evolution

The northern margin of the Tarim Block (NTB) is an essential tectonic unit for understanding the tectonicsedimentary system and geodynamic mechanisms of the Tarim Block and the surrounding region. Five Ordovician limestone samples and six Silurian sandstone samples were collected from the KepingBachu area, an early Paleozoic platform basin. Detrital zircon U-Pb chronology analysis shows that most of the early Paleozoic samples yield evident detrital zircon U-Pb age peaks of 454 Ma, 768/804 Ma, 976 Ma, 1818 Ma, and 2372 Ma. However, there was a 1000-940 Ma gap in the igneous rock records of the NTB, which means no magmatic provenance corresponding to the early Neoproterozoic detrital zircons with a peak age of ca. 976 Ma. Based on comparisons with potential provenance areas, the YiliCentral Tianshan Block (YCTB) may be the missing source, which was migrated to the NTB after the mid-Neoproterozoic orogenic event. The detrital zircon U-Pb age spectra of different regions in the NTB are significantly different. The early Paleozoic detrital zircons were abundant in the Ordovician strata in Keping-Bachu, but rare in Tabei and Quruqtagh. With the Hf isotopic compositions, the early Paleozoic detrital zircons came from the Southwest Tarim during the late Ordovician. Here, we present a bidirectional model for the provenance supply of the northwestern platform controlled by Tabei Uplift and Southwest Uplift. Moreover, the proportion of 480-420 Ma detrital zircons in Silurian strata gradually decreased from east to west, implying that the magmatic activity in the northern margin gradually weakened along the margin. By comparing the peak ages of early Paleozoic detrital zircons in the northwestern platform (435-434 Ma), Tabei (436 Ma), and Quruqtagh (454-450 Ma), we propose that the northeastern margin had transformed into an active continental margin in the late Ordovician, while the northwestern margin was later than it. (c) 2024 Published by Elsevier B.V. on behalf of International Association for Gondwana Research.