When did the modern plate tectonics begin and how it evolved is an essential scientific question of Earth Science. UHP metamorphism happened since 600 Ma during cold subduction, while few Paleoproterozoic eclogites have been reported. The conversion of cold to hot subduction is an important indicator for the initiation of modern plate tectonics. Three narrow UHT pelitic granulite interlayers outcropped within HP mafic granulites in Chicheng, the Trans-North China Orogen. They have the same peak metamorphic age of ca. 1910 Ma. Here we report special melt inclusions in Chicheng UHT pelitic granulite. Confocal Raman Imaging shows that melt inclusions are composed of kumdykolite, kokchetavite and cristobalite, and they may form at high/ultra-high pressure with eclogite facies. The peak metamorphic temperature of the Chicheng pelitic granulite is 150 °C higher than the mafic granulite. The study shows that the Paleoproterozoic geotherm of the earth’s mantle turned from hot to cold, which implies the operation of modern plate tectonics probably was initiated in ca.1910 Ma.

Reference(s)

Ferrero, S., Ziemann, M.A., Angel, R.J., O’Brien, P.J. and Wunder, B., 2016. Kumdykolite, kokchetavite, and cristobalite crystallized in nanogranites from felsic granulites, Orlica-Snieznik Dome (Bohemian Massif): not evidence for ultrahigh-pressure conditions. Contributions to Mineralogy and Petrology, 171, pp.1-12.

Xu, C., Kynický, J., Song, W., Tao, R., Lü, Z., Li, Y., Yang, Y., Pohanka, M., Galiova, M.V., Zhang, L. and Fei, Y., 2018. Cold deep subduction recorded by remnants of a Paleoproterozoic carbonated slab. Nature Communications, 9(1), p.2790.