DIAMOND FROM THE DABIE-SHAN METAMORPHIC ROCKS AND ITS IMPLICATION FOR TECTONIC SETTING

Diamond occurs in ultrahigh pressure metamorphic rocks from Dabie Shan, Anhui Province, eastern China. Diamond-bearing rocks include eclogite, garnet-pyroxenite, and jadeitite. Diamond occurs in a mineral assemblage with coesite and jadeite. The diamonds and diamondiferous rocks of Dabie Shan are interpreted to be the products of ultrahigh pressure metamorphism in the underthrust basement of the Yangtze continental plate during the early Mesozoic, at greater than 4.0 gigapascals and 900-degrees-C. This interpretation is based on the distribution of rock units, the stability field of diamond, and isotopic data indicating a crustal origin for the rocks. Most diamonds occur as euhedral inclusions in garnets and are 10 to 60 micrometers across, although some are up to 700 micrometers across.