Sequential syndeformational porphyroblast growth during low-pressure/high temperature contact regional metamorphism in the Ghandab region, NE Iran

Detailed microstructural analysis has been conducted in the Ghandab metamorphic Complex, which is one of the most important high temperature – low pressure regional contact metamorphism studied areas in Iran. Textural evidence suggests the sequence of growth of minerals with increasing metamorphic grade and during development of a crenulation foliation. The sequence of mineral growth is considered to be cordierite, andalusite, garnet, and sillimanite. The first foliation (S1) is preserved largely as inclusion trails in cordierite porphyroblasts. However, garnet and andalusite porphyroblasts are syndeformation crystals and grow during development of crenulation-foliation of S2. According to textural evidence, sillimanite produced late in the thermal history of metamorphism and deformation.