Petrology of coarse calcitic marble from parts of eastern ghats province, India

Abstract

The coarse grained calcitic marble rocks from part of Eastern Ghats Province have been studied to decipher the petrological evolution. The white coloured calcitic marble consists of grey coloured band(s). The white coloured part (association (a)) is rich in carbonate phases containing abundant coarse calcite crystals and minor dolomite with biotite, olivine, spinel, amphibole, apatite, graphite and iron sulphide. The grey coloured band (association (b)) has modally higher abundance of silicate phases over carbonates. Association (b) contains calcite, biotite, clinopyroxene, plagioclase and apatite (± graphite). Overall granoblastic texture and crystal plastic deformation reveal that the rocks are deformed and metamorphosed. Calcite contains minor amount of Mg, which decreases from core to rim (Xmg = 0.002–0.06). Silicate phases are compositionally close to the Mg end member. Reaction textures and modelling in C-space suggest that Mg-bearing calcite + biotite ± silica developed the peak metamorphic assemblages of (i) forsterite, calcite, spinel and (ii) diopside, anorthite (+ calcite) respectively for association (a) and (b). Dolomite exsolution in Mg-bearing calcite and formation of secondary amphibole, biotite and serpentine after olive and pyroxene document the retrograde history of metamorphism. Solvus thermometry using reintegrated composition of exsolved dolomite and host calcite records peak metamorphic temperature above 850°C. However, matrix calcite composition estimates down temperature of ~500OC, which suggests a retrograde cooling event. Peak pressure could not be estimated due to absence of any suitable geobarometry. Therefore, this study shows that the coarse grained marble rock suffered deformation – metamorphism in granulite facies condition above 850°C followed by a cooling event with drop in temperature of at least 350OC.