Jurassic picritic and potassic mafic dyke swarms in eastern China: Evidence for thermal erosion of the lithospheric mantle during Paleo-Pacific subduction

Abstract

Paleo-Pacific subduction significantly impacted the structure and nature of the mantle in Eastern China. However, the thermal structure of the supra-subduction-zone mantle during the early stage of the Paleo-Pacific subduction has not been well constrained. Here, we present an integrated study involving field investigation, petrology, and geochemistry on two types of Jurassic (168–155 Ma) mafic dyke swarms in Western Liaoning, North China Craton (NCC), to trace the properties of the NCC mantle during the Jurassic. The picritic dyke swarms, trending NNW (330°–350°), show OIB-like geochemical signatures, with high mantle potential temperatures (Tp) ranging from 1498 ± 52°C to 1535 ± 56°C. These picritic dyke swarms are derived from high-degree of partial melting of the asthenospheric mantle by a hot and hydrous asthenospheric melts rising from the mantle transition zone above the subducted slab. In contrast, the Jurassic potassic mafic dyke swarms, trending NNW (325°–345°), were formed by partial melting of the metasomatized lithospheric mantle during the upwelling of the asthenospheric melts. We conclude that thermal erosion would be a major factor in the destruction of the lithospheric mantle beneath the NCC in the early stage of the Paleo-Pacific plate subduction.