An outline of very low-grade metabasites of Kamal Abad (west of Naein, Isfahan province)

Very low-grade metamorphism (hydrothermal metamorphism) in Kamal Abad (west of Naein) affects Eocene basalts, and led to the formation of: prehnite, malachite, azurite, zeolite (mesolite, scolecite and laumontite), quartz and calcite in cavities and fractures. Chlorite (brunsvigite), amphibole (ferro-actinolite) and saussurite appear as secondary phases in primary rock. Two series prehnite occurs in the study area: The first has high relief and interference color and the second has low relief and interference color. This may be due to difference in Fe3+ content in their crystallization structure. Using mineral chemistry as well as the abundance of hydrothermal minerals (prehnite, zeolite, quartz, calcite, malachite, azurite and laumontite), the nature of fluid should be enriched in Ca, Si, Al and OH and poor in Fe, Na, K, Mn and Cu. The very low-grade metamorphic minerals formed in neutral to slightly alkaline pH, low CO2, temperature of 150-350oC and less than 3 kbars pressure. The studies show prehnite-pumpellyite facies, zeolite facies and laumontite subfacies formed in the area. Moreover, the rate of alteration owing to the small volume of magmatic and hydrothermal solution is not high in the study area.