Is There Paleoproterozoic Eclogite Facie Rock in Alxa along the Northern Margin of the North China Craton?

Eclogite facies rocks in orogenic belts are important to understand the orogenic process. However, it is challenging to recognize such rock type especially in the Paleoproterozoic time because of extensive post-formation reworking or overprinting processes. Here, I revisit the Paleoproterozoic garnet-websterite in the Alxa region, and use phase equilibria modeling to reconstruct its pressure–temperature path. The samples undergone eclogite facies metamorphism at 800–840 °C/1.6–1.9 GPa, and were later overprinted by high-temperature metamorphism at 920–980 °C/0.7–0.85 GPa. The presence of Paleoproterozoic eclogite facies rocks in the Alxa region adds to the growing body of evidence supporting the operation of modern-style plate tectonics during this era. The abrupt occurrence of eclogite facies rocks globally since Paleoproterozoic suggests that the Earth transited into “cold” subduction era. Because of the secular cooling of the Earth, the “cold” subduction thermal conditions have transitioned from 375 °C/GPa in the Paleoproterozoic era to current conditions of about 150 °C/GPa.