Early Cretaceous exhumation of high-pressure metamorphic rocks of the Sistan Suture Zone, eastern Iran

The Sistan Suture Zone (SSZ) of eastern Iran is part of the Neo-Tethyan orogenic system and formed by convergence of the Central Iranian and Afghan microcontinents. Ar-Ar ages of ca. 125 Ma have been obtained front white micas and amphihole front variably overprinted high-pressure metabasites within the Ratuk Complex of the SSZ. The metabasites. which occur its fault-bounded lenses within it subduction melange, document peak-metamorphic conditions in eclogite or blueschist facies followed by near-isothermal decompression resulting in an epidote-amphibolite-facies overprint. Ar-40/Ar-39 step heating experiments were performed on a phengite + paragonite mixture from an eclogite, phengites front two amphibolites and paragonite from a blueschist 'best-fit' ages front these micas are. respectively. 122.8 +/- 2.2, 124 +/- 13, 116 +/- 19 and 139 +/- 19 Ma (2 sigma error). Barroisite from an amphibolite yielded an age of 124 +/- 10 Ma. The ages are interpreted its cooling ages that record the post-epidote-amphibolite stage in the exhumation of the rocks. Our results imply that both the high-pressure metamorphism and the epidote-amphibolite-facies overprint occurred prior to 125 Ma. subduction of oceanic lithosphere along the eastern margin of the Sistan Ocean had therefore begun by Barremian (Early Cretaceous) times. Copyright (C) 2008 John Wiley & Sons, Ltd.