Late Neoarchean metavolcanic rocks from the Tonghua area, Southern Jilin Province, China: Constraints on the formation and evolution of the northeastern North China Craton

The Tonghua area is located on the northeastern edge of the Eastern Block of the North China Craton (NCC), and connects the Northern Liaoning Block (NLB) in the west and Southern Jilin Block (SJB) in the north. The greenstone sequences in this region are voluminous metavolcanic rocks, which mainly comprise amphibolite, pyroxene amphibolite, pyroxene/amphibole-plagioclase gneiss, and biotite-plagioclase gneiss. Here we present zircon cathodoluminescence images, U-Pb dates, and Lu-Hf isotope data, as well as whole-rock geochemical data for these rocks, in order to constrain the geodynamic evolution of the Neoarchean crust and mantle and define the crustal evolution process of the northeastern NCC. Zircons from these metavolcanic rocks can be divided into two groups, with one having a typical magmatic origin and the other a metamorphic recrystallization origin. Zircon U-Pb dating and Lu-Hf isotopic results show that the magmatic zircons have two peak ages, dated at ca. 2.60 Ga and ca. 2.52 Ga, with the former have epsilon(Hf) = +3.04 to + 9.24 and single-stage model ages (T-DM) of 2.80-2.54 Ga, the younger group have epsilon(Hf) values of + 2.41 to + 7.05 and T-DM values of 2.73-2.56 Ga. While the metamorphic zircons document consistent metamorphic ages at 2.47-2.53 Ga, suggesting a regional metamorphic event. Their framing into the regional background has allowed us to explore the complete Neoarchean tectonic-thermal event and further contrast the NLB and SJB in the chronology, as well as to reveal crustal growth (similar to 2.7 Ga, similar to 2.6-2.5 Ga) and reworking (similar to 2.53-2.47 Ga) history in the Neoarchean. The geochemical data indicate that the rocks were divided into three types, with affinities to mid-ocean ridge basalt (N-MORB), island arc tholeiites (IATs), and continental arc basalts (CABs). Taking into account the arc-related magmatism and the distribution of ancient crystalline basement (>= 2.7 Ga), it is proposed that a long-lived, active continental-margin setting may have evolved along the northeastern margin of the NCC during the late Neoarchean (similar to 2.5-2.6 Ga), which distinguishes the NLB and SJB. Moreover, the geochemical and Lu-Hf isotope mapping results also indicate that the NLB and SJB have different tectonic setting. We consider that the metavolcanic rocks from the Tonghua area are related to an arc-continent collision, and formed in a transitional inner-oceanic arc to active continental margin geodynamic setting during the late Neoarchean (2.6-2.5 Ga).