THE AGE OF METAMORPHISM OF DIAMONDIFEROUS ROCKS DETERMINED WITH SHRIMP DATING OF ZIRCON
J. Hermann, D. Rubatto, A.V. Korsakov*, and V.S. Shatsky**
Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia
* Institute of Mineralogy and Petrography, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
** Affiliate of Institute of Mineralogy and Petrography, Siberian Branch of the RAS,
43 ul. Russkaya, Novosibirsk, 630058, Russia
Keywords: Diamond, zircon, U-Pb dating, SHRIMP, Kokchetav
Pages: 511-518
Abstract
In situ dating of zircon domains with a Sensitive High Resolution Ion Microprobe (SHRIMP) has been proved to be the best way to determine the age of peak metamorphic conditions in the diamondiferous, deeply subducted Kokchetav rocks. Three independent studies obtained within error-consistent results, providing evidence for peak metamorphic conditions at about 530 Ma. These studies demonstrated through mineral inclusions that the dated zircon crystals formed under peak metamorphic conditions, within the diamond stability field. Mineral inclusions indicate that zircon formed not only at the metamorphic peak, but also during the retrograde evolution under granulite- to amphibolite-facies conditions. The ages of the retrograde zircon domains are within error not distinguishable from the age of peak metamorphism. This provides evidence for very fast exhumation rates of minimum 1.8 cm/yr from diamond to granulite-facies metamorphism and high cooling rates > 40
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