Ultrarapid exhumation of ultrahigh-pressure diamond-bearing metasedimentary rocks of the Kokchetav Massif, Kazakhstan?

The diamond-bearing, ultrahigh-pressure Kokchetav Massif recrystallized at eclogite-facies conditions deep in the mantle at 180-km depth at 535 +/- 3 Ma, and yet new 40Ar/39Ar ages suggest that it may have been exhumed to crustal depths (as indicated by closure of mica to Ar loss) by similar to529 Ma. These data indicate a possible exhumation rate of tens of kilometers per million years, i.e., a rate that is comparable to rates of horizontal plate motion and subduction. (C) 2003 Elsevier B.V. All rights reserved.