Petrogenesis of ca. 1.95 Ga S-type granites from the Helanshan Complex in the Khondalite Belt, North China Craton and its tectonic implications

The Helanshan Complex is dominated by Palaeoproterozoic S-type granites and pelitic granulites, recording anatexis of metasedimentary rocks and the formed the Khondalite Belt. LA–ICP–MS zircon U–Pb dating yields a crystallization age of 1956 ± 29 Ma for the monzogranite, coeval with the pelitic granulites (1945 ± 33 Ma). The ca. 1.95 Ga monzogranites within the Helanshan Complex are characterized by the presence of peraluminous minerals garnet, and exhibit elevated SiO2 contents (64.49–74.65 wt.%) and A/CNK ratios (1.08–1.75), which classify them as S-type granites. They show higher TiO2, Fe2O3T, and MgO than the experimental melts, but are lower than the pelitic granulites from the area. Whole-rock Nd isotopic data and geochemical modelling indicate that the extensive compositional variation of the granites is controlled by the entrainment of the restites and residual minerals, rather than by mantle-derived input. Integrated with regional data, two periods (ca. 1.95 Ga and 1.93–1.90 Ga) of granitoids are formed by different tectonic processes. The ca. 1.95 Ga S-type granites are purely sediment-derived, whereas some of the ca. 1.93–1.90 Ga S-type granitoids were formed by mixing sediment-derived and mantle-derived magmas. This record reveals a tectonic transition in the Khondalite Belt from syn-collisional compression to post-collisional extension during ca. 1.95–1.93 Ga.