Experimental constraints on the destruction mechanism of the North China Craton

Abstract

Craton destruction is a complex process involving both chemical and physical interactions between the crust and the mantle. Several mechanisms, including thermo-chemical erosion, delamination, lithosphere extension and subducting slab dehydration, have been proposed to explain the destruction of the North China Craton (NCC). We present constraints extrapolated directly from laboratory melt–peridotite reaction experiments, which demonstrate that the reaction between eclogite-derived melt and peridotite can lead to crystallization of low-Mg# pyroxenite and generation of high Mg# andesite, which is consistent with natural observations of the melt–peridotite reactions in the NCC. However, this reaction is a sluggish process under dry and hydrostatic conditions. It can be promoted significantly on a relatively large scale by the formation of melt-filled cracks/veins (melt+clinopyroxene) in peridotite under axial compression conditions or by the production of shear enhanced reaction zones (low Mg# olivine+orthopyroxene) under simple shear conditions. Our results also reveal that the lower crust of the NCC has a viscosity much lower than the upper crust and the unaltered dry upper mantle. These results suggest that 1) vertical tectonic deformation can facilitate large-scale melt–peridotite reaction and mantle refertilization; 2) weakening of the upper mantle by water is a prerequisite for eclogitilized lower crust to sink down through the otherwise strong lithospheric upper mantle. We propose a long-period, small-scale delamination model as a possible mechanism for the destruction of the interior of the North China Craton.