Two kinds of granulites (HT-HP and HT-UHT) in North China Craton:Their genetic relation and geotectonic implications.

Abstract

High-grade metamorphie rocks are extensively distributed in the North China Craton ( NCC ) , and study on high-temperature and high-pressure granulites ( HT-HP) and high- ultrahigh- temperature granulites ( HT-UHT) is a key issue to understanding the tectonic evolution of the Early Precambrian Earth. The HT-HP granulites are mainly garnet-bearing mafic granulites that are metamorphosed and deformed dykes enclosed in the orthogneisses. The HT-UHT rocks are metamorphosed pelites (khondalites) , and sapphirine and spinal in khondalite indicates metamorphie: temperature 900～1000℃. This paper deals with the occurrences, distribution, metamorphie conditions and history, isotopic ages of the two granulites, and emphasizes the following aspects; ①the peak metamorphie conditions and P-T paths with a relief of pressure for two granulites are similar; ②their metamorphie ages of the peak and followed decompressional stages are also similar; ③HT-HP and HT-UHT granulites probably occur in area distribution other than in linear distribution; ④high-grade granulites represent the Precambrain lowermost crust. Their metamorphie P/T gradients, uplifting rates, rigidities and protolith rock associations are significantly different from those of rocks in Phanerozoic orogenic belts. Therefore, the metamorphic geological setting and their original relation for the two granulites are most important in the future study.