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

Abstract

The South China Block underwent a tectonic switch from compression to extension between the Late Jurassic and Early Cretaceous, but the extension process has not been well understood. Here we report that the Meiziwo lamprophyres in northern Guangdong, formed in the Early Cretaceous ( c. 136 Ma; 40 Ar/ 39 Ar dating), are characterized by ocean-island basalt (OIB)-like geochemical signatures and Pb enrichment, together with moderately high ( 87 Sr/ 86 Sr) i (0.70642–0.70766), positive ε Nd ( t ) (+4.6 to +5.1) and intermediate ( 206 Pb/ 204 Pb) i (18.579–18.602), ( 207 Pb/ 204 Pb) i (15.727–15.733) and ( 208 Pb/ 204 Pb) i (38.871–38.909). The lamprophyres were derived from an asthenosphere-dominated source, with contributions from recycled oceanic crust and terrigenous sediments. In contrast, the previously reported c. 154 Ma mafic dyke in eastern Guangdong and the c. 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 palaeo-Pacific plate. The 136 Ma Meiziwo lamprophyres, together with the 140 Ma asthenosphere-derived OIB-like mafic rocks nearby, signify the petrological response to regional extension in the South China Block from c. 140 Ma onward. Supplementary material: Tables S1–S3 and Figures S1–S4 are available at https://doi.org/10.6084/m9.figshare.c.5953720