Origin of paleosubduction-modified mantle for Late Cretaceous (~100 Ma) diabase in northern Guangdong, South China: Geochronological and geochemical evidence

Abstract

Cretaceous mafic rocks mainly occur along the coast of South China. In comparison, coeval mafic rocks are distributed only sporadically in the inland region, and their petrogenesis and tectonic setting have not been well documented so far. Here we report a detailed study on 40Ar/39Ar dating, elemental geochemistry and Sr-Nd-Pb isotopes for the Yaoling diabases in northern Guangdong, South China. The Yaoling diabases yield a Late Cretaceous (101 ± 1 Ma) 40Ar/39Ar age. These rocks have variable (87Sr/86Sr)i (0.705023–0.709847), relatively uniform εNd(t) (+2.45 to +3.88) and intermediate (206Pb/204Pb)i (18.586–18.692), (207Pb/204Pb)i (15.743–15.764) and (208Pb/204Pb)i (38.300–39.137). These rocks exhibit geochemical affinity to both within-plate and arc magmatism, i.e., relatively high TiO2, Nb and Zr contents, and negative Nb anomalies with (Nb/La)PM of 0.65–0.82. Such dual features indicate that the Yaoling diabases were most likely generated through partial melting of a previously metasomatized lithospheric mantle at a shallow depth (75–85 km), and modified by crystal fractionation. It is likely that the ancient metasomatism may have occurred during the Neoproterozoic oceanic subduction beneath the Cathaysia Block. We suggest that the Yaoling diabases formed in an intraplate extension setting associated with asthenospheric upwelling, possibly in response to the far-field stress that propagated from the paleo-Pacific subduction during the Late Cretaceous (ca. 100 Ma).