K-rich granitoid magmatism at the Archean–Proterozoic transition in southern Jilin: Insights into the Neoarchean crustal evolution of the northeastern part of the North China Craton

Massive Neoarchean to early Paleoproterozoic K-rich granitoid rocks are widely distributed in the southern Jilin metamorphic basement terrane, which is located in the northeastern part of the North China Craton (NCC). Based on newly obtained petrological, geochemical and geochronological data, these K-rich granitoid rocks can be subdivided into: ~2.50Ga porphyritic monzogranites in the Jingyu–Tonghua area, and ~2.50–2.49Ga medium-grained and coarse-grained monzogranites and ~2.47Ga porphyritic quartz syenites in the Huadian–Jingyu area. The ~2.50Ga porphyritic monzogranites are characterized by rare earth element (REE) patterns with high (La/Yb)N and low (Gd/Yb)N ratios and weakly negative Eu anomalies, as well as zircon εHf(t2) values of +1.7 to +5.3 with TDM(Hf) values of 2748 to 2612Ma. These results suggest that the monzogranitic magma was produced under low-pressure conditions by partial melting of a heterogeneous crustal source, with residual plagioclase, hornblende, orthopyroxene, and clinopyroxene. The ~2.50–2.49Ga medium- to coarse-grained monzogranites show low MgO and CaO contents, Mg# values of 1–42 and zircon εHf(t2) values of −0.7 to +4.6, as well as TDM(Hf) values of 2847 to 2634Ma. These results indicate that these rocks were also generated from partial melting of pre-existing juvenile crustal materials that were enriched in potassium by either fluid alteration or surface processes at middle to lower crustal levels. The ~2.47Ga porphyritic quartz syenites have zircon εHf(t2) values of +2.8 to +5.6 and TDM(Hf) values of 2678 to 2571Ma; display the highest K2O concentrations of the rocks examined in this study; are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs); have low MgO contents and Mg# values; and display strongly differentiated chondrite-normalized REE patterns with no significant Eu anomalies. These results indicate that these rocks may have been produced by partial melting of juvenile mantle-derived basaltic rocks associated with recycled K-rich metasediments in the lower crust.