Petrogenesis of Caledonian-age granites in Southwest China : Implications for magmatic evolution and mineralization along the southern margin of the Youjiang Basin

A series of granitic plutons associated with Sn (Cu) polymetallic ore is developed in the Youjiang Basin, Southwest China, at the southwestern end of the South China Block. Study of the petrography, geochemistry, zircon U-Pb geochronology, and biotite mineral chemistry of the Qinjia granite pluton and the Hongnipo granite group show that both rock types are predominantly monzonitic granite, with a few being syenogranite. The zircon U-Pb ages of the late intrusions of the Qinjia granite pluton and the Hongnipo granite group are 421.3 +/- 2.7 Ma and 413.7 +/- 2.5 Ma, respectively. Both are I-type granites and show enrichment in large ion lithophile elements and light rare earth elements, depletion in high field strength elements and heavy rare earth elements, and significant negative Nb, Ta, and Ti anomalies. The magma system of the Hongnipo granite group is relatively richer in F and Cl and has a higher degree of magma differentiation than the Qinjia granite pluton. The Qinjia granite pluton exhibits promising metallogenic potential for the formation of Sn-Cu deposits. The Hongnipo granite group displays promising potential for Pb-Zn (Cu) mineralization, as well as a discernible potential for Sn mineralization. In light of the regional geological characteristics, we posit that the genesis of Caledonian granite along the southern margin of the Youjiang Basin is closely related to the evolutionary process of subduction- collisional and postcollisional extension of the Proto- Tethys Ocean, as exemplified by the Qinzhou- Hangzhou joint belt. The Qinjia granite isa composite rock mass that has been formed by three distinct stages of Caledonian-age ocean plate bidirectional subduction, syn- collisional extension, and postcollisional extension. The Hongnipo granite group was primarily formed during the postcollisional extensional phase of the late Caledonian age.