Charnockite Formation and Early Precambrian Crust Evolution in Yishui Area, Shandong Province, China

摘要

Charnockite and granulite in Yishui area, Shandong Province are located in the middle part of the Tancheng-Lujiang fault zone, eastern China. Field studies have shown that the charnockites, derived from the adjacent granulites, are classified as three types: enderbite, garnet-enderbite and hypersthene-trondhjemite. In addition, two generations of minerals are present in the charnock- ites: the relic minerals such as garnet, hypersthene and clinopyroxene, and the neocrystallized minerals such as plagioclase and K-feldspar. The relic minerals occurring in the granulite facies stage were affected by the later partial melting. The relic minerals, irregular and usually ragged in shape, occupy the interstitial positions in the neocrystalline minerals. The neocrystalline minerals are usually euhedral-subhedral crystals. The study of petrology, mineralogy and geochemistry of charnokites concludes that the enderbite was formed by the anatexis of the two-pyroxene plagio- clase granulite, that the garnet-enderbite was formed by the anatexis or sillimanite garnet gneiss, and that the hypersthene-trondhjemite was formed by the anatexis of the leucocratic two-pyroxene plagioclase granulite. The U-Pb dating of the zircon indicates that the formation of the charnockite and granulite was related to the Archean-Proterozoic upwelling of a mantle plume (hot spot) around 2 500 Ma, in Yishui area, Shandong Province.