The operation of plate tectonics in Earth's middle age: Constraints from ∼1.4 Ga calc-alkaline arc magmatism in the southern CAOB

The Mesoproterozoic (1.6–1.0 Ga) era recorded the supercontinent transition from Nuna to Rodinia supercontinent. However, the global tectonic style within this age interval remains highly debated (plate tectonics vs lid tectonics), largely due to the occurrence of widespread continental rifting sequences, alkaline and anhydrous magmatism, along with high T/P metamorphism. We here systematically investigated the whole-rock geochemical, geochronological, and Nd-Hf isotopic characters of metamorphosed Mesoproterozoic granodiorite and monzogranite within the Alxa Block in the central segment of the southern CAOB. The field geology and obtained data indicate that they are typical of I-type granitoids emplaced at 1.43–1.40 Ga, with their parental magmas generated by partial melting of preexisted juvenile mafic crusts. These granitoids belong to the calc-alkaline and magnesian series, and are enriched in LREE and LILE. Moreover, their parental magma contains high magmatic H₂O contents (>7 %). The data patterns, combined with regional geology, indicate these granitoids are continental arc magmatic rocks. Our data, together with those published data in the microcontinental blocks of southern CAOB, argue that the protracted (1.51–1.40 Ga) calc-alkaline granitic magmatism in these blocks was generated in a continental marginal arc. This prolonged continental arc system coincides well with the Great Proterozoic Accretionary Orogen (GPAO) in the Mesoproterozoic and must have been formed outboard the GPAO. Furthermore, a review of global geological and geochemical data patterns favor widespread subduction on the periphery of Nuna and the operation of plate tectonics in the Mesoproterozoic.