Dikes Deformation in Lakhshak Pluton: Microscopic Evidence from the Northeast of Zahedan, Southeastern Iran

Abstract

Based on geological classification of Iran, Oligocene Lakhshak pluton is situated in the Sistan suture zone that composed of siliciclastic and ophiolitic melanges. The Lakhshak pluton is a host of numerous northeast dikes intruded the siliciclastic sediments. The pluton is granodiorite, granite, diorite, quartz diorite in composition. The dikes occur along shear zones and show moderate to high deformations. Dikes are mainly diorite and granodiorite in composition and consist of plagioclase, biotite, hornblende and quartz. The deformation evidences are quartz microboudines, mica fish (especially in biotite), and fractures in minerals, inflation in quartz, asymmetric porphyroclasts, preferred orientation and rotation of minerals. These evidences show that the dikes suffered from brittle to ductile deformation. Dynamic recrystallization of quartz and feldspar grains is mainly similar as bulge type. Mylonitic structures in the dikes probably formed between 300 and 500°C. Oriented thin sections, three-dimensional block diagram and field studies show dextral shears in dikes.