Diamond from the Dabie Shan Metamorphic Rocks and Its Implication for Tectonic Setting

Abstract

Diamond occurs in ultrahigh pressure metamorphic rocks from Dabie Shan, Anhui Province, eastern China. Diamond-bearing rocks include eclogite, gamet-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°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.

Delamination in collisional orogens: Thermomechanical modeling

“…Deep subduction of continental crust and subsequent exhumation are in agreement with previous models of collision zones Warren et al, 2008;Valera et al, 2008;Duretz et al, 2011]. Natural exposures of crustal UHP rocks corroborate early subduction to depths ≫100 km with subsequent rapid exhumation to shallower crustal levels, and are reported from a variety of localities, such as the Western Alps [e. g., Chopin, 1984], the Kazakh Kokchetav Massif [e.g., Shatsky et al, 1999;Hermann et al, 2001], the Variscan Belt [e.g., Bakun-Czubarov, 1991;Kotkova et al, 2011], the Western Gneiss Region of Norway [e.g., Lappin and Smith, 1978], or the Dabie Shan [e.g., Xu et al, 1992;Hacker et al, 2000]. The highest pressure estimates of up to 4.5 GPa [Lappin and Smith, 1978;Hermann et al, 2001] and the correlation of diamond stability and pressures of ca.…”

Dual sources of water overprinting on the low zircon δ18O metamorphic country rocks: Disequilibrium constrained through inverse modelling of partial reequilibration

“…The Dabie-Sulu orogen is characterized by the largest occurrence of the microdiamond- and/or coesite-bearing UHP metamorphic rocks worldwide1617181920. Triassic ages of 200 to 240 Ma were dated with distinctive geochronometers for the eclogite facies rocks and their exhumation cooling histories were accordingly quantified2122232425262728.…”

Isotopic disequilibrium in ultrahigh-pressure and retrograde metamorphism of eclogite and gneiss from the Chinese Continental Scientific Drilling in the Sulu orogen, China: evidence from mineral Nd–Sr–O isotopic composition

“…Numerous coesite-and diamond-bearing eclogite bodies crop out in different types of country rocks, including orthogneisses, metabasics, and marbles (e.g., Xu et al 1992Xu et al , 2003Xu et al , 2005. Geochemical studies have demonstrated that supracrustal material was subducted to mantle depth of more than 120 km, recrystallized within a short time span under UHP metamorphic condition and then was rapidly exhumed (e.g., Zheng et al 2003c).…”