Rheology and Petrofabrics of the Mantle Xenoliths from Huinan, China

Mantle xenoliths can provide important information toward the rheology of the underlying upper mantle in the past. Here we present detailed study into the rheology and petrofabrics of the spinel lherzolite in the Cenozoic basalts from the northeastern margin of the north China craton (NCC) located at Huinan, Jilin province of China. Mineral chemical compositions of the spinel lherzolite indicate an equilibrium temperature of 982~1085 ^oC. Dislocation oxidation decoration reveals that dislocation creep dominats its plastic deformation resulting in different kinds of dislocation structures. Deformation differential stress, estimated based on the size of the subgrains, is 21-37 MPa. Electron backscattered differaction (EBSD) analyses show that the lattice preferred orientations (LPOs) of the olivine are typical A-type fabrics implying a dry and low stress condition. The estimated strain rate and equivalent viscosity are three orders of magnitude lower than the estimations for the NCC indicating a strong weakening of the uppermost mantle. We hypothesize that the weakening may be resulted from the thinning of the NCC during the Cenozoic time.