Structural evolution and metamorphism of the southern margin of the central Iran micro-continent. The metamorphic complexes of the Neyriz region (Sanandaj-Sirjan Zone)

Category Tectonic & Seismotectonic
Group GSI.IR
Location 21th symposium on geosciences
Holding Date 24 May 2008

      The region of Neyriz presents metamorphic rocks thrust over the south-western Iran Tethyan ophiolites. The protoliths of the metasedimentary metamorphic rocks represent the Paleozoic age. Magmatic rocks (anatectic granitoids and mafic and ultramafic rocks) are included in these sequences. All of the rocks are affected by a fundamental deformation itself constituted by a shearing polyphase foliation present in gneissic-core domes, followed by a crenulation cleavage. The fundamental structures developed contemporaneously with a medium ?pressure metamorphism characterized by the syn-kinematic crystallization of kyanite and the beginning of the anatexis followed by the developpement of retrometamorphic parageneses.
   The Upper Triassic series unconformably cover the underlying deformed and metamorphic rocks that represent the Paleozoic and the Early Triassic. The major deformation is thus the Early-Kimmerian Orogeny. From this time, the gneissic domes started to rise in the upper levels of the crust. The kinematic of the structures indicates the diapiric characters of these antiformes.
   After the Mid-Permian the studied area represented the south Iranian passive margin, the central Iranian microcontinent being separated from the Gondowanian supercontinent by the Neo-Thethys opening. After the Upper Triassic the region became the active margin structurated by an accretionary prism. It resolved finally by the end of the Mesozoic in an orogenic prism after the closure of the Neo-Tethyan oceanic basin. At that time, the ancient southern Iranian margin with its metamorphic rocks was thrust upon the Tethyan ophiolites and farther away over the ancient arabo-gondwanian margin.

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