High-Pressure Marbles from the Nahavand Area in the Sanandaj-Sirjan Metamorphic Belt, Iran

Marbles containing high-pressure mineral assemblage was found from the Sanandaj-Sirjan metamorphic belt in the Nahavand area in western Iran.  The high-pressure marbles occur as small bodies or lenses within pelitic schist layers and show compositional banding of carbonate- and silicate- rich bands.  Textural analysis revealed two metamorphic stages.  The early stage is testified by relicts of the minerals such as rounded jadeite-bearing diopside, epidote (clinozoisite), amphibole 1 (pargasite-edenite) and titanite 1. The second stage (main stage) documented to have phlogopite, chlorite, amphibole 2 (tremolite) and titanite 2. P-T-XCO2 estimates for the early stage of metamorphism give an average pressure, temperature and XCO2 of 13.5 kbar, 670 ºC and 0.35, whereas the second stage has been constrained at P=3.8 kbar, T=500 ºC and XCO2=0.45.  The high-pressure mineral assemblage documented in the Nahavand area, were formed during the subduction stage, while the second metamorphic blastesis were recorded during the exhumation event.