Petrogenesis and geodynamic implications of the Wanlicheng granites and hosted magmatic enclaves in Songpan-Garze orogen: Evidence from petrography and geochemistry.

Numerous Triassic granitic plutons are extensively developed in the Songpan-Garze orogen, and their petrogenesis is important for understanding the geodynamic settings of these granitic magma. The host granites show high content of SiO2 (69.43%~73.10%) and total alkaline and are weakly peraluminous rocks (A/CNK=1.01~1.12), belonging to high-K calc-alkaline to shoshonitic I-type granites. MMEs show low content of SiO2 (52.85%~59.50%) and Mg# (45~63) and are metaluminous high-K calc-alkaline monzodiorite or monzonite. The MMEs exhibit typical magmatic texture, with acicular apatite, zoned plagioclase, pupil-like quartz and other disequilibrium textures. Trace and rare earth elements studies show that the MMEs were derived from the crust-mantle mixing, i.e., underplated basaltic magma mixed with the overlying crustal felsic magma, and the mixed melt experienced the fractional crystallization of ilmenite and biotite. The host granites were derived from pure felsic crust, characterized by low ratios of Mg# (21~39), intermediate CaO/(MgO+TFeO), high ratios of K2O/Na2O and (Na2O+K2O)/(TFeO+MgO+TiO2), indicating that the source was dominated by metagraywacke. Combined with regional geological data, the authors hold that the large-scale granitic magmatism was controlled by basaltic magma underplating in a post-collisional extensional setting.