The Sistan Suture Zone, eastern Iran: the exhumation history of oceanic HP/LT rocks and the geological significance of presumed granulite-facies mélange rocks.

• Applicants: Professor Dr. Michael Bröcker; Professor Dr. Frank Lisker
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 279126319

This proposal seeks funding for field-based research activities that aim at establishing a solid petrological, geochemical and geochronologic foundation for in-depth understanding of mélange rocks from the Sistan Suture Zone (SSZ), Iran. The study area provides the excellent opportunity to examine in detail the exhumation history of oceanic HP/LT rocks and their retrograde derivatives. The planned research activities will focus on key aspects of the SSZ evolution that demand more detailed attention: the thermal regime and the exhumation history. The proposal suggests activities which will integrate field activities, petrology, bulk-rock geochemistry, isotope geochemistry and geochronology. It is planned to apply Rb-Sr geochronology for dating the amphibolite and/or greenschist-facies event, and to use U-Pb zircon and monazite dating to determine ages recorded in presumed granulites and in chlorite schists. Fission-track (zircon, apatite) and (U-Th-Sm)/He (apatite) analyses will provide information for subsequent cooling stages. Bulk-rock geochemical and Sr-Nd isotope data will be used to fully characterize the studied sample suite. Taken together such data is a prerequisite for in-depth understanding of the geologic histories recorded by various mélange rocks that will help gaining insights into the specific subduction zone style and exhumation mechanisms. Emphasis will be placed on the following questions: Is the closure of the Sistan ocean associated with a hot subduction setting? What are the timescales and rates of exhumation? Did exhumation occur in a single short-lived event or in discontinuous episodes over a protracted time span? Which processes control exhumation? Answering of these questions will provide a test of tectonic concepts predicting fast and discontinuous exhumation for such settings. The newly gained knowledge will allow to link the cooling path and kinematic development of the SSZ to other Neotethyan suture zones, and to assess the mechanisms of suture zone dynamics. This project will advance the understanding of the subduction-exhumation events recorded in the Sistan suture and has the potential to provide further insight into the evolution of accretionary complexes.

• DFG Programme: Research Grants
• International Connection: Iran
• Cooperation Partner: Dr. Gholamreza Fotoohi Rad