2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 12
Presentation Time: 8:00 AM-6:00 PM

Shear zone control on the emplacement of Malayer granitoid complex, NW Iran

AHADNEJAD, Vahid, VALIZADEH, Mohammad Vali and ESMAEILY, Dariush, Department of Geology, College of Science, University of Tehran, Enqelab Ave., Tehran, Iran, Tehran, 0098, Iran, ahadnejad@khayam.ut.ac.ir

Malayer complex is injected into the early to middle Jurassic metasedimentary rocks that are consist of slate, phyllite and schist so called Hamadan phyllite in the Sanandaj-Sirjan Zone (SSZ). The Sanandj-Sirjan Zone is produced by oblique collisional event between Arabian plate and Central Iran microcontinent. The Malayer plutonic complex, in the Northern Sanandj-Sirjan Zone (Western Iran), is a composite, roped-shaped intrusive body, comprising alkali granite, syenogranite, monzogranite, granodiorite, tonalite with high-k calc-alkaline affinities and some little massives of basic-to-intermediate, gabbro and diorite that have different geological history. A persistent control on the emplacement of the various suites by a nearby oblique, strike-slip pressional is suggested by several features. Among them are: shapes of individual intrusions and their location in transpressional sites; metric to decimetric-thick sheets emplaced along shear bands, fold axial surfaces and transitions between viscous- to solid-state fabrics in the pluton, bearing the same orientation and kinematics as in their country rocks.

Intergrowth textures such as myrmekite and perthite, mylonitic granites, complex deformation and elongated shape imply injection of melt along the high-strain shear zone. In order to understand the relationships between metamorphic mineral growth and deformation in the Malayer igneous complex, studies of microstructural textures were conducted, focusing on porphyroblast-matrix relationships.

Microstructureal studies indicated that the injection of granitic magma into the country rocks is syn-tectonic.

Microgranitoid enclaves that are felsic to intermediate in chemical composition are common in this igneous body. Their shapes in the middle of body are irregular and in the corner are lenticular to rounded. The sigmoidal shape of the rocks indicate that the dextral transpression is the dominant tectonic regime in this region.