Early Cretaceous oceanic island basalt-type magmatism in northern Guangdong: Implications for lithospheric thinning in the South China Block

South China Block (SCB) underwent a tectonic switch from compression to extension between Late Jurassic and Early Cretaceous, but the extension process has not been well understood. Here we report the Meiziwo lamprophyres in northern Guangdong formed at Early Cretaceous (ca. 136 Ma; 40Ar/39Ar dating) are characterized by oceanic island basalt (OIB)-like geochemical signatures and Pb enrichment, together with moderately high (87Sr/86Sr)i (0.70642-0.70766), positive εNd(t) (+4.6 to +5.1), intermediate (206Pb/204Pb)i (18.579-18.602), (207Pb/204Pb)i (15.727-15.733), (208Pb/204Pb)i (38.871-38.909). The lamprophyres were derived from an asthenosphere-dominated source, with recycled oceanic crust and terrigenous sediments contribution. In contrast, the previously reported ca. 154 Ma mafic dyke in eastern Guangdong, and the ca. 165-155 Ma A-type granite belt in southern Hunan and nearby regions, show arc-like signatures and unradiogenic Nd but moderately radiogenic Pb isotopes, suggesting magma derivation from a lithospheric mantle. Hence, the change from lithospheric to asthenospheric sources may be caused by progressive lithospheric extension and thinning associated with the rollback and tearing of the paleo-Pacific plate. The 136 Ma Meiziwo lamprophyres, together with the 140 Ma asthenosphere-derived OIB-like mafic rocks nearby, signify the petrologic response to regional extension in the South China Block from ca. 140 Ma onward.Supplementary material: Tables S1-S3 and Figures S1-S4 are available at https://doi.org/10.6084/m9.figshare.c.5953720.