SUBSOLIDUS PHASE TRANSITIONS OF THE CARBONATE COMPONENT OF STRONTIUM-BARIUM CARBONATITE

Abstract

Carbonatites associated with alkalic rock complexes in India and in the USSR in the Murun pluton have a unique carbonate component. Though dominated by calcite (59 to 63 mole percent), it also is unusually high in strontianite (6 to 15) and especially in witherite (27 to 31). One of the distinguishing and most interesting features of strontium-barium carbonatite is the metastability of its primary carbonate phases, which underwent successive, stage-by-stage exsolution with more stable minerals, as the bodies cooled. These solid-phase transitions should provide information on the mode of emplacement of such bodies and on their subsequent postcrystallization transformations. By microprobe and X-ray analysis of separate phases we were able to expose the complex pattern of evolution of carbonates in the rocks studied.