Coesite eclogites and diamond-bearing ultrahigh-pressure (UHP) metamorphic rocks along ancient plate boundaries were mostly derived from quartz-and carbonate-bearing rocks originally formed close to the earth's surface. ...
Hacker B.R.; Calvert A.; Zhang R.Y.; Ernst W.G.; Liou J.G.(2003)
The diamond-bearing, ultrahigh-pressure Kokchetav Massif recrystallized at eclogite-facies conditions deep in the mantle at 180-km depth at 535 F 3 Ma, and yet new 40 Ar/ 39 Ar ages suggest that it may have been exhumed ...