Constraining the timing of deep magmatic pulses from diamondiferous kimberlite and related rocks in the South China Continent and implications for diamond exploration

Abstract

Mantle-derived magmas provide windows to the deep earth, and precise dating of the deep magmatic rocks such as kimberlite and related lithologies is crucial to attaining a better understanding of the mantle evolution and mantle-crust interaction in conjunction with global geodynamic cycle. Here we report a geochronology investigation of the diamondiferous kimberlite and related rocks from the southeastern side of the Yangtze Craton in China with the aim to constrain the deep mantle magma emplacement patterns and mantle evolution through time. Ultrabasic magmatic events occurred intermittently between 492 and 441 Ma, as inferred from apatite U-Pb dating and phlogopite 40Ar-39Ar dating. Combined with the previous data, two pulses of diamondiferous magmatism (ca. 488 Ma and ca. 450 Ma) are identified. The emplacement ages and patterns of these deep-seated diamondiferous magmas are unrelated to the reported Pan-African tectonothermal event (peak at ca. 522 Ma), Kwangsian Orogeny (peak at ca. 435 Ma), and Emeishan plume event (peak at ca. 260 Ma) in the South China Continent. Instead, we infer that the kimberlite and associated rocks in the South China Continent may be related to the upwellings from the edges of the Large Low Shear Velocity Province located at the core-mantle boundary at that time. The lack of magmatic event during 760 to 460 Ma and the existence of the thick lithosphere (>175 km) beneath the South China Continent are suitable for lithospheric diamond formation during the Early Paleozoic. These data suggest that future diamond exploration should be focused on the kimberlites emplaced during the Cambrian–Ordovician transition on the southeastern side of the former Yangzte Craton.