Lithospheric and asthenospheric sources of lamprophyres in the Jiaodong Peninsula: A consequence of rapid lithospheric thinning beneath the North China Craton?

Abstract

Lithospheric thinning and destruction of the North China Craton have been topics of active discussion throughout the last two decades, but the specific processes associated with lithospheric thinning remains controversial. Here we report co-occurrence of low-Ti (TiO2<1.1wt.%, Ti/Y<270) and high-Ti (TiO2>2wt.%, Ti/Y>370) types of lamprophyres in the Jiaodong Peninsula, eastern North China Craton in order to address this issue. Low-Ti lamprophyres are depleted in HFSE and enriched in Pb, both typical subduction signatures. We suggest they were derived from partial melting of an ancient and enriched lithospheric mantle, which was previously modified by slab-derived hydrous fluids. In contrast, the high-Ti lamprophyre has trace element patterns similar to many oceanic basalts with depletion of Pb but little or no HFSE depletion. We infer that they originated from partial melting of a convective asthenospheric mantle. Zircon U–Pb dating shows that both types of lamprophyres intruded the eastern North China Craton about 121Myr ago. Their indistinguishable ages thus appear to record a rapid transition from lithospheric to asthenospheric mantle source, suggesting further that the lithosphere beneath the eastern North China Craton was removed, potentially delaminated ca. 121Myr ago beneath Jiaodong Peninsula. The detachment of cratonic lithosphere is likely related to continental arc-rifting which resulted from Palaeo-Pacific plate subduction in the Mesozoic.