Late Paleozoic to Mesozoic extension in southwestern Fujian Province, South?China: Geochemical, geochronological and Hf isotopic constraints from?basic-intermediate dykes

摘要

The tectonic evolution of SE China block since late Paleozoic remains debated. Here we present a new set of zircon U-Pb geochronological, Lu-Hf isotopic data and whole-rock geochemistry for two stages of basic-intermediate dykes from the southwestern Fujian. The samples were collected from the NE-trending (mainly diabases) and NW-trending (mainly diabasic diorites) dykes and yielded zircon U-Pb ages of 315?and 141?Ma, with ε Hf ( t ) values of??8.90 to 7.49 and??23.39 to??7.15 (corresponding to T DM2 values of 850 to 1890?Ma and 737 to 2670?Ma), respectively. Geochemically these rocks are characterized by low TiO 2 (0.91–1.73?wt.%) and MgO (3.04–7.96?wt.%), and high Al 2 O 3 (12.5–16.60?wt.%) and K 2 O (0.60–3.63?wt.%). Further they are enriched in LREEs and LILEs (Rb, Ba, Th and K), but depleted in HFSEs (Nb, Ta and Zr). The tectonic discrimination analysis revealed that the dykes were formed in an intraplate extensional environment. However, the NW trending dykes show crust-mantle mixed composition, which indicate an extensional tectonic setting with evidence for crustal contamination. The SE China block experienced two main stages of extensional tectonics from late Carboniferous to early Cretaceous. The tectonic evolution of the SE China block from late Devonian to Cretaceous is also evaluated. Graphical abstract Display Omitted Highlights ? Zircon U-Pb ages of 315?Ma and 141?Ma. ? The Hf isotopic features indicate enriched mantle reservoir and crust-mantle mixing. ? Late Devonian-early Triassic and late Jurassic-early Cretaceous extension.