The Yenshanian-type twin granite belts in intracontinental compression-subduction environments in the northern part of East Qinlin area

Abstract

Calc-alkaline granites (excluding A- and M-type) could be divided into two petrogenic series, i.e., the syntexis series and the transformation series according to their genetic mechanisms. In the light of this classification we found that granites of these two series often aligne in paired zones parallel to contemporaneous B-type or intracontinental compression-subduction zones within ascended slabs, resulting in a regular zonal pattern together with subduction zones. Thus, they are defined as twin granite belts. According to the spatial relations between the granite belts and the subduction zones, the twin granite belts could be classified as A-, AB- and B-type. The zonation of granites of the two series in the northern part of the East Qinlin area could be cited as a typical example of A-type twin granite belts related to the Yenshanian intracontinental compression-subduction movement in the area In this paper the tectonic settings and petrogenic features of the twin granites belts in East Qinlin are systematically described, and a tectonic model for granitic magma genesis in intracontinental compression-subduction environments has been proposed. In this model the formation of A-type twin granite belts is closely connected with tectonic movements in terms of the principle, rule and dynamics of material differentiation in the lithosphere.