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 basicintermediate 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_2O_3(12.5-16.60 wt.%) and K_2O(0.60-3.63 wt.%).Further they are enriched in LREEs and ULEs(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.