Tectonic evolvement of metamorphic complexes at Jilin paleocontinental margin during the transition from late Archaean to early Proterozoic

摘要

The kinematics and dynamical process of tectonic evolvement of metamorphic complexes at the interim from late Archaean to early Proterozoic is one of the key problems in geosciences. For the disputation on the genesis of metamorphic complexes at the margin of Jilin palaeocontinent, this paper takes the example of Banshigou region, Jilin Province to discuss the dynamical evolution of palaeocontinent during the transition from late Archaean to early Proterozoic (2600—2000 Ma). On the time sequence, from center to palaeocontinental margin, it shows a series of dynamical movements including underplating, horizontal movement, subduc-tion, intraplate extension and separation. And its corresponding sequence of kinematical modes is as follows: vertical movement, horizontal movement, extension and shearing in contact zone, uplift-sliding movement in paleocontinental margin and interformational sliding, resulting in such tectonite sequence, tectonic gneiss, gneissic complex, gneissic complex-mylonite, mylonite and fracture cleavage-mylonite, which consist of the main body of metamorphic complexes. Their palaeostresses are: < 20, 20.40, 21.72, 28.80 and 30.8—69.8 MPa respectively. The deforma-tional metamorphic temperature is between hornblende and low-grade greenschist facies. The general deformational characters of Jilin palaeocontinent reflect a complete dynamic system of crust evolution, which indicates that the formation of the metamorphic complexes and the tectonic evolution are altered from vertical movement to compression to extension. It also indicates a continuous tectonic transformation from deep to shallow, and from ductile to brittle. The transformation between different dynamic mechanisms not only forms tectonic rocks, but also benefits the linking up, exchange and enrichment with rock-forming minerals and ore-forming elements. This research is helpful to classifying regional tectonic events and making further study on the evolution of palaeocontinental dynamics.