P-T conditions of the Jandagh metapelitic schists, Northeastern Isfahan Province, Iran

The metapelitic schists of Jandagh or simply Jandagh metapelites can be divided into four groups based on mineral assemblages: (1) quartz-muscovite schists, (2) quartz-muscovite-biotite schists, (3) garnet-muscovite-chlorite schists, and (4) garnet-muscovite-staurolite schists. The Jandagh garnet-muscovite-chlorite schists show the first appearance of garnets. These garnets contain 58–76% almandine, 1–18% spessartine, and 8–20% grossular. Microprobe analysing across the garnets demonstrates an increase in Mg# from core to rim. This is a feature of the prograde metamorphism of metapelites. Well-preserved garnet growth zoning is a sign that metapelites were rapidly cooled and later metamorphic phases had no effect here. The appearance of staurolite in garnet-muscovite-chlorite schists signifies a beginning of the amphibolite facies. The absence of zoning in staurolite suggests that its formation and growth during prograde metamorphism occurred at a widely spaced isograde. Thermobarometric investigations show that the Jandagh metapelites were formed within a temperature range of 400–670°C and pressures of 2.0–6.5 kbar. These results are in agreement with the mineral paragenetic evidence and show the development of greenschist and amphibolite facies in the area studied.