Geochronology, geochemistry, and zircon Hf isotopes of the late Permian–early Triassic Wuma intrusions in the Erguna Block, northeast China: Petrogenesis and implications for tectonic setting and crustal growth

The Wuma magmatic suite is a group of large granite plutons and small diorite stocks in the Erguna Block, northeast China. These intrusions were emplaced along the Mongol–Okhotsk Suture Zone during the late Permian–early Triassic (253–248 Ma). Significant chemical and isotopic diversity within the granites and diorites suggests variable formation conditions and the involvement of multiple magmatic sources. The granitic intrusions are dominantly characterized by moderate to large, uniform light rare earth element enrichments and variable heavy rare earth element depletions. Zircons from the Wuma granites have eHf(t) values of −6.0 to 0.5 and TDM2 ages of 1.6–1.2 Ga, suggesting that these granitic magmas were generated by partial melting of Mesoproterozoic continental crust. The diorites are compositionally similar to Andean plutonic rocks with moderate light rare earth element and heavy rare earth element fractionations and likely formed by partial melting of a sediment-metasomatized mantle. The Wuma intrusions belong to the high-K calc-alkaline series and are characterized by a significant enrichment in large-ion lithophile elements (e.g., Rb, Ba, K, and U) and depletion of high-field strength elements (e.g., Nb, Ta, and Ti). These geochemical characteristics are typical of subduction-related magmatism, which can be linked to the southward subduction of the Mongol–Okhotsk oceanic plate. Combined with data from published studies, our Hf isotopic analyses indicate 4 main periods of crustal growth beneath the Erguna Block: Mesoarchean (3.0–2.8 Ga), Neoarchean–Paleoproterozoic (2.6–1.8 Ga), Meso- to Neoproterozoic (1.6–0.7 Ga), and Phanerozoic (mainly Ordovician and Late Triassic–Early Cretaceous).