Petrogenesis and tectonic implications of 2.45 Ga potassic A-type granite in the Daqingshan area, Yinshan Block, North China Craton

Abstract

An Archean–Paleoproterozoic (A–P) A-type granite 15 km wide and 25 km long has been identified in the Daqingshan area south of the Yinshan Block (YB), North China Craton (NCC). Known as the Jinpen pluton, this body is the largest individual granite pluton in the Daqingshan area. Its crystallization ages of 2460–2450 Ma has been determined precisely using the secondary ion mass spectrometer (SIMS) zircon U–Pb method. The Jinpen pluton is lithologically homogeneous, consisting mainly of gneissic monzogranites with metaluminous affinity and high K2O/Na2O (1.08–2.06), Ga/Al, and Zr + Nb + Ce + Y values with high zircon saturation temperatures (Tzr) of 889–837 °C; these features are typical of A-type granite. Most samples contain enriched large ion lithophile elements (LILEs) and light rare earth elements (LREEs), high Y and Yb abundances with pronounced Eu negative anomalies, low Sr/Y and (La/Yb)N ratios, and low MgO, Cr, and Ni contents, implying a shallow crustal source for the pluton. Its whole-rock Nd isotope composition (εNd(t) = 2.5–0.6) and zircon Hf isotope composition (εHf(t) = 5.2–1.7, TDMC = 2.88–2.65 Ga) indicate that it mainly originated from pre-existing crustal materials. The zircon δ18O values of 6.58–5.71‰ suggest a crustal source of orthogneiss with little metasedimentary material. Previous studies have demonstrated that the YB experienced significant crustal growth at 2.8–2.7 Ga and further crustal reworking at about 2.5 Ga. This study reveals that the Jinpen potassic A-type granite was generated at 2.46–2.45 Ga by partial melting of pre-existing crustal materials at relatively low pressure (P) and high temperature (T) conditions symbolizing the first and essential cratonization of the lithospheric stabilization of the NCC.