Tectonics and Geodynamics

Structural and microstructural investigation of Hoz Valley shear zone: with emphasis on preferred orientation of quartz c-axis Fabric, NW Zagros (Iran)

Azizi A.¹, Quanbari H.²

¹Islamic Azad University, Aligudarz branch, Aligudarz, Iran; ²Department of Earth Science, Science and Research Branch, Islamic Azad University, Fars, Iran.

[e-mail]; [e-mail]

HOZ VALLEY shear zone is located in the northwest of Zagros Mountain in the west of Iran. This zone is a port of the Sanandaj–Sirjan Polyphase metamorphic zone. This region rocks are formed under high-pressure and low-temperature metamorphic conditions. They are mostly schist, phyllite, quartz mylonite and quartz-feldspar mylonite. Field and laboratory work included analysis of oriented thin sections for microstructural indicators and specially, preferred orientation of Quartz C-axis fabric. These studies indicated three phases of deformation including D1, D2 and D3 in this region. D1 and D2 deformation phases were responsible for the formation of the S1-foliations, the L1-lineations, thrust faults (along zagros), quartz veins (parallel to S1 foliation and L1 lineation) and the formation of the S2-foliations, the L2-lineations (by creating microfolds),folding in quartz veins, respectively. During D3 phase of deformation has been created structures such as cutting fractures of all of the former structures and preferred orientation of Quartz C-axis fabric. Created deformations have been formed in medium-temperature condition (400 to 500 Cº). In this condition, the displacement creep is dominant and pyramid slip<a> {m} is important. This stage of Structure properties is consisting of flattened old crystals, dominant recovery and recrystalizated structures. By the way, evidence of deformation is completely clear as shortening in SW-NE direction associated with right- oblique convergence in structures and microstructures of region. According to this, deformation model is simple shear with right- oblique convergence, which is consistent with suggested models for regions with oblique convergence.

Fig. Structural geologic map of HOZ VALLEY shear zone – NW Zagros, location and stereographic projections of several quartz C-axes has been indicated on it.

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