Structures of mylonitic granites of the Yagan metamorphic core complex on Sino-Mongolian border??implications for its kinematics and chronology

The mylonitic granitic plutons are extended in line-shape (L) and parallel to the regional extensional shear foliation. After being unstrained, the primary shapes of these plutons are also nearly sheet-like (S). Their fabrics are of S-L or L type. Various kinds of shear marks indicate top-to-south shear. The plutons of various stages are different in deformation intensity; however, the foliation and lineation of these rocks have the same shear sense, which suggests progressive ductile shearing. The development mechanisms of the fabrics include magmatic flow, high-temperature solidstate flow and mid-low temperature solid-state flow. All this demonstrates that these plutons are probably early synextensional tectonic plutons. Their structural features and ages suggest that the low- and mid-crustal extensional detachments might have occurred at the early stage of the development of the metamorphic core complex in the early Mesozoic. These deformations are much deeper at levels and much older than those formed at the final formation stage.