A refined study of Paleoproterozoic high-pressure granulite-facies metamorphism in the Kongling complex of northern Yangtze block

Abstract

The Paleoproterozoic era is a critical tuning period for the transitions in global geodynamic regimes and plate tectonic processes. However, detailed pressure–temperature–time (P–T–t) paths of Paleoproterozoic metamorphic rocks worldwide are scarce, which hinders our understanding of deep thermal state and relevant tectonic processes at that time. Here, we identified a prolonged Paleoproterozoic (from ca. 2.05 Ga to ca. 2.0 Ga) metamorphism by zircon U–Pb geochronology of mafic granulite in the Kongling Complex of the northern Yangtze Block. The metamorphic zircon grains/domains show distinct weakly to strongly fractionated heavy rare earth elements (HREE), corresponding to competitive growth with or without garnet during the metamorphism. Mineral assemblages of orthopyroxene + plagioclase are distinctly found both within and around (as corona) garnet, indicating high-temperature decompression. P–T estimations from mineral compositions, chemical potential modeling and phase equilibrium modeling together yield a clockwise path with peak metamorphism at 10.0 ± 0.3 kbar and 860 ± 30 °C followed by decompression to 6.0 ± 0.5 kbar and 840 ± 40 °C in a period of about 50 Myr. This contradicts a Paleoproterozoic ultrahigh-pressure collision in northern Yangtze Block and may exemplify the assembly of micro-continents during formation of the Paleoproterozoic Columbia (Nuna) supercontinent. According to the available P-T paths of worldwide Paleoproterozoic metamorphism, we propose a typical warm subduction/collision in Paleoproterozoic plate tectonic regime.