Late Mesozoic extensional tectonics in the North China block: a crustal response to subcontinental mantle removal?

摘要

In the North China block, Cretaceous extensional tectonics is expressed by numerous syntectonic plutons bounded by ductile normal faults and several metamorphic core complexes (MCC). Cretaceous half-grabens filled by continental terrigenous deposits are widespread. The examples of MCC from South Liaoning Peninsula, Yiwulüshan, Hohhot as well as the Yunmengshan syntectonic pluton spread along ca 2000 km suggest that the early Cretaceous extensional tectonics in the North China block is globally symmetric. The geodynamics setting of this continental-scale extension remains disputed. It is not satisfactorily explained by back-arc rifting related to the Paleo-Pacific subduction or crustal "unthickening". Mantle lithosphere removal is, however, considered. Upwelling of asthenosphere may be the origin of heat advection and fluid transfer from mantle to lower crust, thus triggerring the Cretaceous magmatism, crustal softening and diffuse continental stretching. Several possible lithosphere-scale models, such as convective removal of mantle lithosphere and detachment of a large piece of mantle, are discussed.