A Neoarchean subduction recorded by the Eastern Hebei Precambrian basement, North China Craton: Geochemical fingerprints from metavolcanic rocks of the Saheqiao-Shangying-Qinglong supracrustal belt

Abstract

The Saheqiao-Shangying-Qinglong supracrustal belt (SSQB) in the northern Eastern Hebei Precambrian basement (EHPB) is located in the northern margin of the Eastern Block (EB) of the North China Craton (NCC). The Shangying terrane constitutes the middle segment of the SSQB and contains primarily metamorphic volcanics and plutonic tonalitic gneisses. The metamorphic volcanics mainly consist of pyroxene plagioclase amphibolites, garnet plagioclase amphibolites, biotite plagioclase amphibole gneisses, and amphibole plagioclase gneisses. Zircon U-Pb-Lu-Hf isotopic analyses reveal that the metavolcanic rocks from the Shangying terrane crystallized at ∼2506–2613Ma with TDM (Hf) values of ∼2541–2944Ma. These metamorphic volcanic rocks are subdivided into four groups based on their lithological and chemical features. Group I consists chiefly of tholeiites that are characterized by slightly light rare earth element (LREE) depleted patterns and flat multi-element spider diagrams, which are similar to back-arc basin basalt (BABB)-like rocks and were derived from the partial melting of the depleted mantle. The tholeiites in Group II have slightly fractionated rare earth element (REE) patterns without Nb anomalies, exhibit an affinity to Nb-enriched basalt (NEB)-like rocks, and were produced by the partial melting of HFSE-enriched mantle peridotites. Group III is composed of slightly LREE-enriched tholeiites with negative Nb-Ta anomalies that resemble island arc tholeiites. Group IV comprises calc-alkaline basalts and andesites with highly enriched LREEs and evident Nb, Ta and Ti depletions that are geochemically similar to the products of island arcs. The island arc tholeiites and calc-alkaline basalt-andesites originated from the partial melting of sub-arc mantle peridotites that were previously metasomatized by slab-derived fluids/melts with the fractional crystallization of ferromagnesian minerals. Collectively, the BABB-like rocks, the NEBs, arc tholeiites and calc-alkaline basalt-andesites recorded magmatism from a subduction regime. Similarly, NEB, arc tholeiite-andesite-dacites and back-arc related rocks were recognized in the Saheqiao and Qinglong areas in the western and eastern parts of the SSQB (R. Guo et al., 2013, 2015), which further supports the existence of a Neoarchean convergent margin in the Eastern Hebei Precambrian basement (EHPB). Compared to the northwestern EHPB, the southeastern EHPB underwent lower metamorphism, contains arc dacites/rhyolites and greater contributions of the ancient continental crust, implying that the southeastern EHPB might have been or near a back-arc setting. Thus, we conclude that the SSQB experienced a southeastward-dipping subduction, which is consistent with studies of the adjacent regions (e.g., Western Liaoning Province). When combining the ∼2.5–2.6Ga supracrustal rocks and plutonic granitoid gneisses with depleted mantle origins along the northern margin of the EB of the NCC, we concluded that ∼2.5–2.6Ga was a significant period for juvenile crustal growth and that lateral accretion played a dominant role in crustal growth.