Scientific Quarterly Journal of Geosciences

Scientific Quarterly Journal of Geosciences

Mechanism of Deformation and the Associated Microstructures in the Basic Mylonitic Rocks, NW Urumieh

Document Type : Original Research Paper

Authors
K. Mohammadiha 1
M. Sabzehie 2
M. Ghahraie pour 1
J. Radfar 1
1 Master of Science, Geological Survey of Iran, Tehran, Iran
2 PhD., Geological Survey of Iran, Tehran, Iran
10.22071/gsj.2012.54020
Abstract
A large widespread outcrop of granitoid - mylonitic gabbros complexes is observed in northeastern part of Serow, NW Iran. Those rocks were considered as Precambrian gneiss and metamorphic rocks (Haghipour and Aghanabati, 1977), or alternatively, a complex of acidic to basic igneous rocks which have undergone intense deformation and dynamic metamorphism by shearing (Mohammadiha, 2000; Mohammadi Torkabad, 2001). The basic mylonitic rocks in the studied area are simply composed of plagioclase, hornblende, actinolite, chlorite, and epidote. They display minor remains of primary pyroxenes which are largely replaced by amphibole. Feldspars have been altered to epidote, and secondary plagioclase (more sodic) and roughly sericite. There are some gabbros with clastic and lentiform fabric which were not affected by dynamic deformation in the shear zone. Cataclastic flow, micro fracturing, dislocation creep, recovery, diffusion creep, grain boundary sliding and pressure dissolution are the dominant deformation mechanisms influenced the complexes. The consequent structures are foliation, lineation, undoluse extinction, porphyroclasts with core-mantle structure, micro fractures parallel and unparallel with brecciation, mechanical twining, mica fish structure, banded differentiated structure and kinked foliation. We conclude that the whole observed evidences demonstrate a major dynamic deformation in a brecciated zone in the studied area. 
Keywords
Basic mylonitic rocks
deformation
Brecciated zones
Metamorphism
Urumieh
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Scientific Quarterly Journal of Geosciences
Volume 22, Issue 85
Autumn 2013
Pages 47-54