Modern-style tectonic cycle in earliest Proterozoic time: Petrogenesis of dioritic-granitic rocks from the Daqingshan–Wulashan Terrane, southern Yinshan Block, North China Craton

Archean granitoids provide us with an insight into the accretion and differentiation of early continental crust. We report the study of a dioritic to granitic rock association occurring in the Hongzhao region of the Daqingshan–Wulashan Terrane at the southern periphery of the Yinshan Block in western North China Craton. Zircon UPb dating reveals that the Hongzhao plutonic suite was emplaced within a short period (2.48–2.46 Ga) at the Archaean–Proterozoic transition. Four types of rocks have been identified based on their petrogeochemistry, which are K–rich diorite (KDG), Na–rich diorite (NDG), metaluminous monzogranite (MMG), and peraluminous syenogranite (PSG). First, the K–rich diorites are characterized by enrichment in both incompatible elements and transition elements with SiO2 contents of 63.4 to 57.2 wt%. Their dual geochemical character resembles the high–Ti sanukitoids, with strongly subchondritic isotopic compositions [εHf (t) = −0.8 to −5.6; εNd (t) =0.4 to −3.1] and high K2O/Na2O ratios (1.19–0.76), implying the contribution of older crustal materials in their origin. Combined with their high Y (46.9–17.9 ppm) and HREE (Yb = 4.35–1.62 ppm) abundances, the K–rich diorites were most likely derived from a mantle source previously enriched by melts from ancient terrigenous sediments at relatively lower pressures. Second, the Na-rich diorites show a crustal–derived, adakite affinity with moderate SiO2 (66.1–55.3 wt%) contents, high Na2O/K2O (8.51–3.17), Sr/Y (147–37), and (La/Yb)N (51–15) ratios, and low MgO (2.96–1.67 wt%), Cr (64–13 ppm), and Ni (38–6 ppm) contents. Na-rich diorites show evolved and homogeneous zircon εHf (t) (4.0–2.8) and whole–rock εNd (t) (3.6–1.2) values, indicating that they were most probably produced by partial melting of pre-existing mafic crust. Third, the metaluminous monzogranites exhibit high SiO2 contents and moderate REE fractionation with variably negative Eu anomalies. Evolved and homogeneous isotopic compositions [εHf (t) = 4.2 to 2.1 and εNd (t) = 1.7 to 1.6] suggest that the metaluminous monzogranites originated from partial melting of pre–existing continental rocks at shallow depth. Fourth, the peraluminous syenogranites show the highest SiO2 (77.3–68.6 wt%) contents and lowest CaO, ∑REE, and Y abundances, extremely high Sr/Y (up to 241), (La/Yb)N (up to 128) ratios, conspicuous positive Eu anomalies (Eu/Eu* = 6.49–0.91), and variable but negative–dominated εHf (t) (1.2 to −5.9) and εNd (t) (0.8 to −0.8) values