Petrography of high temperature deformation in marginal parts of the Lakhshak granitoid intrusion, NW of Zahedan, Iran


The Lakhshak granitoid intrusion which is located in the northwest of Zahedan is a part of Zahedan-Saravan plutonic belt. This Oligo-Miocene in-trusion, intruded as an elongated pluton into the Eocene flysh type meta-sediments that in turn be-long to the Sistan suture zone, between Lut and Afghan blocks. The marginal granitoid rocks in the south and southwest of pluton have been plastically deformed during the emplacement of this pluton with approximately 400 m thick and show fabrics such as S-C structures. These rocks display a transition from strongly deformed fabrics at the margin to progressively less deformed fabrics to the center. Moreover, due to high temperature brittle deformations, igneous primary minerals, such as plagioclase and orthoclase, were broken and filled by some secondary high temperature minerals such as biotite and quartz. Seemingly, some melt was present during these deformations, as indicated by (1) presence of fine grains of quartz, feldspar and biotite aggregates grains in fracture-controlled open-ings in the primary feldspar crystals, (2) occurrence of quartz and feldspar grains within deformed biotite cleavages, (3) partial plagioclase replacements by quartz and K-feldspar intergrowth, (4) presence of the undeformed granophyric texture in the margin of deformed orthoclase crystals.