Origin of vein graphite in high-grade metamorphic terrains

Abstract

The role of CO2 in the creation of a refractory base of granulite by metamorphism has received increasing attention by geologists investigating sub-crustal phenomena. A voluminous source of mantle-derived CO2 has been postulated for the phenomenon of granulite formation. Recent studies on the granulite terrain of Sri Lanka has clearly shown that it is only an upper crustal section and that it had been subjected to a much smaller influx of CO2 than hitherto envisaged. The close association of graphite with the granulites and the recent discovery of grain-boundary graphite in the lower crust implies graphite as a major source of CO2. Recent reports on the discovery of alluvial diamonds within the granulite belt of the Highland Complex of Sri Lanka where graphite is abundant possibly indicates penetration of the graphite-diamond inversion line.