STUDY OF THE PROPERTIES OF SYNTECTONIC PORPHYROBLASTS IN DABEIWU AREA,JIANGXI PROVINCE

The syntectonic porphyroblasts of pyrite and siderite in the ductile shear zone developed in epimetamorphic clastic rocks in Dabeiwu area are the products and marks of ductile shear deformation during progressive metamorphism.The porphyroblasts being of syntectonic origin have attained the following features:their growth is correlated with deformation intensity,content of sericite and size of the crystal,and the porphyroblasts have their distinct crystal forms and retain the schistosity of groundmass.From the rotation of the pophyroblasts,the authors reconstruct the evolution of Dabeiwu ductile shear zone:from left-lateral reverse-slip through flattening deformation to right-lateral normal-slip.