Mesozoic extensional tectonics in eastern Asia:: The south Liaodong Peninsula metamorphic core complex (NE China)

In the North China block, the south Liaodong Peninsula massif is an elliptical metamorphic core complex (MCC) with a long axis trending NE-SW. In cross- section view, it is asymmetric, with a steeply dipping northwestern flank and a gently dipping southeastern flank. It consists of three lithotectonic units: a gneissic migmatite unit, a Paleoto Meso-Proterozoic micaschist-slate unit, and a Neoproterozoic to Mesozoic sedimentary cover. Three deformation events related to extensional tectonics are distinguished in the study area: D-1 is a ductile deformation related to the exhumation of the MCC; the following event, D-2, corresponds to the development of recumbent folds formed during the early exhumation of the MCC; and the youngest event, D-3, corresponds to brittle normal faulting that controlled the opening of a Cretaceous continental half-graben basin. A pre-D-1 event characterized as northward verging is interpreted as the result of N-S shortening that occurred in the Late Triassic during the final stages of the collision between the North and South China blocks. The ductile and brittle structures were developed coevally, with synkinematic plutonism and formation of half-grabens. New 40Ar/39Ar and U/Pb Cretaceous ages obtained from the mylonitic granodiorite, gneissic migmatite, orthogneiss, and granite indicate that the south Liaodong Peninsula MCC is contemporaneous with other Cretaceous extensional structures, such as numerous syntectonic plutons bounded by ductile normal faults, MCC, and half-graben basins, described in eastern China. Among the several hypotheses proposed to account for the Mesozoic extension along the eastern margin of Eurasia, lithosphere convective removal appears to be the most likely.