FABRIC KINEMATICS OF ECLOGITE AND DEEP CONTINENTAL SUBDUCTION: EBSD STUDY OF ECLOGITE FROM THE MAIN HOLE OF THE CHINESE CONTINENTAL SCIENTIFIC DRILLING PROJECT

Abstract

The main hole of the Chinese Continental Scientific Drilling Project (CCSD-MH) is located in the Maobei eclogite complex, south Sulu UHP terrane. Eclogites from 0 ~ 600m in depth of the CCSD-MH are characterized by east-dipping foliation with moderate dip angle, S-N stretching lineation, "A" type shear fold and a series of smallVductile shear zones. Lattice-preferred orientations (LPO) of omphacite and garnet in 7 eclogite samples were measured using electron backscatter diffraction (EBSD) technique. Garnet appears to be randomly oriented whereas omphacite displays very strong LPO. The [001]-axes of omphacite are concentrated parallel or subparallel to the lineation, the (010)-poles and [100]-axes normal to the foliation, and [110]-poles form the girdle perpendicular to the foliation, implying that the dominant slip systems in omphacite are [001] (100) and 1/2 <11̄0>. Based on high-temperature deformation of clinopyroxene in laboratory, the Maobei eclogites experienced the dislocation creep at 800 ~ 900 C and UHP conditions. The asymmetry of omphacite LPO with respect to foliation and lineation reveals top-to-south shear sense in eclogites, which was formed during the northward deep subduction of the Yangtz plate beneath the North China plate. The reconstructed architecture of the Maobei eclogite complex is a sheared flow fold developed under UHP conditions. Therefore early petrofabrics preserved in eclogites can furnish important kinematic information on the relative plate motions in deep subduction zones.