Paleo-Pacific Plate rollback triggered Early Cretaceous intermediate-felsic magmatism in the northern North China Craton

Abstract

Extensively developed Early Cretaceous intermediate-felsic rocks in the northern North China Craton (NCC), offer an opportunity to unravel the nature of Paleo-Pacific subduction and associated geodynamic processes by investigating their spatio-temporal characteristics and petrogenesis. Here we present geochemical and geochronological results of Early Cretaceous (118–115 Ma) trachyandesites and rhyolites from the eastern Hebei, northern NCC. The trachyandesites show low MgO (0.74–2.65 wt%) and Mg# (17–38), as well as enriched whole-rock Nd-Hf isotopic compositions (εNd(t) = -17.1 to -13.3, εHf(t) = -12.9 to -10.8), suggesting a probable origin of the enriched mafic lower crust. They also exhibit relative enrichment in LREE and flat in HREE. Trace element geochemical modeling results indicate that the trachyandesites likely formed through partial melting of the mafic lower crust at 790–820 °C and ca. 10 kbar (30–33 km). The rhyolites, characterized by higher SiO2 contents and similar εNd(t) (-17.4 to -15.5) and zircon εHf(t) values (-14.4 to -7.6) compared to the trachyandesites, probably represent the magmatic derivates of the trachyandesites. MELTS modeling results suggest that the rhyolites likely formed through fractional crystallization of the trachyandesitic magmas at ∼ 775 °C and 1–3 kbar. Integrating with previous studies, our study confirms that the Early Cretaceous intermediate-felsic magmatism across the northern NCC became younger from northwest to southeast. We propose that the change of the migration direction of these Early Cretaceous intermediate-felsic rocks is primarily attributed to slab rollback of the subducting Paleo-Pacific Plate.