The early-middle Silurian Delite monzogranite and quartz syenite, East Kunlun Orogenic Belt, NW China: petrogenesis and implications for tectonic evolution of the Proto-Tethys

The tectonic evolution of the Proto-Tethys in the East Kunlun Orogenic Belt (EKOB) is controversial. Herein, new petrological, whole-rock geochemical, zircon U-Pb geochronological and zircon Lu-Hf isotopic data for early Paleozoic intrusive rocks in the Delite region are reported. LA-ICP-MS zircon U-Pb isotopic data show that the Delite monzogranite and quartz syenite were formed at 437.0 +/- 2.9 Ma and 424.8 +/- 2.2 Ma, respectively. The Delite monzogranite contains high SiO2, Al2O3 and K2O and A/CNK ratios, but low MgO and Mg# values (33-38). This study considers that the monzogranite is a typical S-type granite and originated from partial melting of ancient crustal clastic material (metagreywacke) in a syn-collision setting. The quartz syenite is K-rich and Mg-poor, with low Mg# values (36-41), exhibiting geochemical signatures of an alkalic syenite derived from partial melting of basaltic lower crust in a post-collision setting. Combining with the previous work, we suggest that in the middle part of the EKOB the Proto-Tethys closed at ca 437 Ma with a post-collisional setting after ca 427 Ma.