Geochemical transition from Cretaceous island arc basalt-like to oceanic island basalt-like basaltic rocks in the Jiurui district of the Yangtze Block, South China

Abstract

The Cretaceous volcanic-sedimentary succession in the Jiurui district of the Yangtze Block contains basalts that are interlayered with fine clastic rocks, conglomerate and breccia strata. Here, we present data of whole-rock40Ar–39Ar dating, major and trace elements, Sr–Nd–Pb isotopes, zircon U–Pb dating and Hf isotopes, and plagioclasetrace element analyses to constrain the petrogenesis and tectonic background of these basaltic rocks,. Two episodiceruptions (ca. 126 Ma and ca. 91 Ma) are recognized, and the early basaltsdisplay evident enriched source characteristics such as high incompatible and low compatible elements, negative Nb, Ta, and Ti, slightly positive Pb anomaly, negative εNd(t) and εHf(t) values, higher (87Sr/86Sr)i, andhigh incompatible elements in plagioclase,indicating anisland arc basalt-like nature. The younger basalts show low incompatible and high compatible elements, negative Rb, Pb, Nb, and Ta, positive Sr anomaly, positive εNd(t) values, lower (87Sr/86Sr)i, and low incompatible elements in the plagioclase, indicating an oceanic island basalt-like characteristic. The early ca. 126 Ma basalts were probably derived from a deeper and older enriched lithospheric mantleconsisting of rutile-bearing garnet pyroxenite or eclogite, whereas the younger ca. 91 Ma basalts were derived from a shallower and younger depletedasthenospheric mantle constituting peridotite, with limited amounts of enriched lithospheric mantlecomponent. The retreat and rollback of the paleo-Pacific slab and related lithospheric thinning and mantle composition transition processes probably occurred at ca. 126 Maand ca. 91 Ma in this inland region of the Yangtze Block in northwestern Jiangxi province.