Study of the Metamorphic Evolution of a Carbonate-Bearing Metaperidotite From the Sidironero Complex (Central Rhodope, Greece) Using P-T and P(t)-Xco2 Pseudosections

Abstract

The carbonate-bearing metaperidotite from Sidironero Complex, north of the Xanthi town is composed primarily of olivine and orthopyroxene megacrysts and of Ti-clinohumite, tremolite, chlorite, dolomite, magnesite, talc, antigorite and spinel group minerals. The metaperidotite underwent a prograde HP metamorphism probably isofacial with the neighboring amphibolitized eclogites. Calculated P-T and P(T)-X CO2 phase diagram sections (pseudosections) for the bulk rock composition showed that X CO2 in the fluid phase was extremely low (≤0.008) at the first stages of the metamorphism and increased up to 0.022 at the peak P-T conditions ~1.5 GPa and 6900 C. The prograde metamorphism probably started from a hydrated and carbonated assemblage including talc+chlo-rite+magnesite+dolomite and proceeded with tremolite and antigorite formation before olivine growth, and orthopyroxene formation after olivine growth . Matrix dolomite, breakdown of chlorite to Cr-spinel+olivine and of Ti-clinohumite to olivine+Mg-ilmenite occurred during decompression. The P-T path is constrained by the absence of clinopyroxene in the metaperidotite.