--> ABSTRACT: The Palaeotethys Suture Zone in NE Iran: New Constraints on the Evolution of the Eo-Cimmerian Belt (Darius Programme), by Zanchi, Andrea; Berra, Fabrizio; Balini, Marco; Ghassemi, Mohammad R.; Heidarzadeh, Ghassem; Zanchetta, Stefano; #90135 (2011)

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The Palaeotethys Suture Zone in NE Iran: New Constraints on the Evolution of the Eo-Cimmerian Belt (Darius Programme)

Zanchi, Andrea 1; Berra, Fabrizio 2; Balini, Marco 2; Ghassemi, Mohammad R.2; Heidarzadeh, Ghassem 2; Zanchetta, Stefano 1
(1)Scienze Geologiche e Geotecnologie, Università degli studi di Milano-Bicocca, Milan, Italy. (2) Scienze della Terra, Università degli studi di Milano, Milan, Italy.

North Iran is a key-area for the Cimmerian orogeny, which is related to the Late Triassic collision of Iran with Eurasia and to the closure of the Palaeotethys. Recent analyses of the Cimmerian evolution have been performed on the Alborz, whereas studies in NE Iran are rare. Due to the importance of this region for the reconstruction of the Cimmerian event, a research project sponsored by the DARIUS PROGRAMME has been focused on the area east of Mashad (Fariman). Here, the occurrence of a thick succession of Permian andesitic to basaltic submarine lava flows interfingering with shallow water limestones and silicilastics arises several questions on the geodynamic significance of this peculiar rock association, previously interpreted as a Palaeotethys-related accretionary wedge. Problematic are also the Permian “ophiolites” of Darreh Anjir, which do not seem to represent typical oceanic crust remnants.

Detailed studies of this succession allowed us to substantially modify previous interpretations. The Permian units were deposited in a marine basin close to a volcanic area, where a large volume of lava flows was emplaced in submarine conditions. Deformational features are not typical of an accretionary wedge as neither disruption of the stratigraphy, nor penetrative shear zones and HP metamorphism have been found. Geochemical data suggest an arc-related setting developed on a continental crust. We thus interpret these units as remnants of a supra-subduction arc-related complex, grown during the Permian along the active Eurasian margin above a N-dipping subduction zone, where the Palaeotethys ocean was consumed.

North of this area, the intra-arc basin of Aghdarband records the Triassic history of the collision zone. The Triassic successions show a N-verging Cimmerian imbricate thrust fan developed in a retro-wedge position with respect to the main N-dipping collision zone located south of Mashad. The thrust fan interacts with a major ESE-WSW left-lateral fault zone, accommodating an important component of oblique convergence. All these structures are sealed by the Bajocian Kashaf Rud Fm., which indicates that the main deformation, affecting also Upper Triassic units, can be related to the Cimmerian events.

These new data add important information on the evolution of the pre Middle Jurassic history of the basement of the hydrocarbon rich Kopeh Dagh Mesozoic and Tertiary successions which are exposed in NE Iran and Turkmenistan.

 

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.