Two-stage magmatic events of the early Paleozoic in the eastern Hexi Corridor Belt, NW China: petrogenesis and tectonic implications

Abstract

The petrogenesis and geodynamic implications of the early Paleozoic magmatic events in the eastern Hexi Corridor Belt, NW China, remain poorly constrained. In this study, we present high-quality zircon U–Pb ages as well as geochemical and zircon Lu–Hf isotopic data for three early Paleozoic intrusive rocks from the Mafuxiazi area in the eastern Hexi Corridor Belt. The LA-ICP-MS U–Pb dating results suggest that there are two stages of magmatic activities during the late Ordovician (447 Ma) and late Silurian (426–423 Ma). The late Ordovician and late Silurian granitoids are predominated by metaluminous and belong to medium-K calc-alkaline and high-K calc-alkaline, respectively. Both two-stage granitoids have been identified as I-type granites. Geochemical characteristics show high Sr, low Y and Yb contents, and high La/Yb and Sr/Y ratios, with weakly negative or no significant Eu anomalies. However, the two-stage granitoids display different zircon Hf isotopic compositions, implying different source materials. The late Ordovician granitoids show negative to slightly positive zircon eHf(t) values of − 2.93~1.68 with crustal Hf model ages (TCDM) of 1318–1610 Ma, suggesting a mixed source from ancient crustal and mantle materials, whereas the late Silurian granitoids have a wide range of zircon eHf(t) values from − 27.34 to 3.00 (only three zircon grains show positive values) with older crustal Hf model ages (TCDM) of 1219–3117 Ma, indicating significantly ancient crustal contribution with limited mantle materials. Based on geochemical and geochronological data, accompanied with consideration of the regional geological setting, we suggest that the late Ordovician granitoids were most likely formed in a back-arc basin, whereas the late Silurian granitoids developed in a post-collision setting.