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

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 degrees C followed by decompression to 6.0 +/- 0.5 kbar and 840 +/- 40 degrees 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.

Automated summary

The Paleoproterozoic era is a critical period for understanding global geodynamic regimes and plate tectonic processes. However, detailed studies on pressure-temperature-time paths of Paleoproterozoic metamorphic rocks are limited. In this study, zircon U-Pb geochronology was used to identify a prolonged Paleoproterozoic metamorphism in the Kongling Complex of the northern Yangtze Block. The results contradict previous hypotheses and suggest a typical warm subduction/collision in the Paleoproterozoic plate tectonic regime.