Grenvillian orogeny in the Oulongbuluke Block, NW China: Constraints from an ∼1.1 Ga Andean-type arc magmatism and metamorphism

Abstract

A systematic petrologic, geochemical, and zircon U-Pb and Lu-Hf isotopic investigation of an ∼1.1 Ga arc magmatism and metamorphism was studied to evaluate the Grenvillian orogeny and assembly of Rodinia in the Oulongbuluke Block in NW China. The peak metamorphic P-T conditions of the paragneiss were restricted to 4.8–5.8 kbar and 652–700 °C based on P-T pseudosection and conventional geothermobarometry. Zircon U-Pb ages of 1132 ± 33 Ma, 1118 ± 9 Ma, and 1124 ± 12 Ma were determined for the metabasite, augen granitic gneiss, and paragneiss, respectively, indicating magmatic intrusion and a metamorphism event in the late Mesoproterozoic. The metabasites exhibited enrichment of light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) and depletion of heavy rare earth elements (HREEs) and high-field-strength elements (HFSEs), resembling the geochemical characteristics of Andean arc magmatism. The whole-rock geochemistry and in-situ zircon εHf(t) values of 4.3 and 11.2 suggested that the protolithic mafic magma originated from a subduction-modified lithospheric mantle. The low zircon εHf(t) values of −5.2 and −0.5 also suggested that the calc-alkaline augen granitic gneisses were derived from the partial melting of a late Paleoproterozoic crustal source. The ∼1.1 Ga arc-related magmatism and metamorphism in the Oulongbuluke Block indicated the occurence of a tectonic-thermal event in an Andean-type active continental margin in the late Mesoproterozoic. In this regard, the Oulongbuluke Block was likely temporarily connected to the Qilian Block and Tarim Craton, forming a single continuous block with similar Grenville age during the late Mesoproterozoic to early Neoproterozoic (1.1–0.9 Ga).