Charnockite and granite formation and influx of CO₂ at Kabbaldurga

Abstract

The discovery, at Kabbaldurga quarry, Karnataka, south India^1–3, of patches of charnockite apparently in an arrested state of development has refocused attention on the mechanism of charnockite formation. In particular, the relative roles of CO₂ and H₂O during high grade metamorphism and charnockite development can be studied in such an area. During an influx of a CO₂-rich volatile phase, H₂O may be liberated as a result of the reduction in the state of hydration by the breakdown of hydrous minerals⁴. The P–T conditions in which this occurs are important because, with an increase in XH₂O, conditions which may allow anatexis could be initiated in advance of such a CO₂-rich phase. Indeed, Weaver⁵ has suggested that the K-rich acid charnockites found at Pallavaram, Madras⁶, developed due to changes in volatile composition before the onset of charnockite conditions. The exposure at Kabbaldurga quarry is interpreted here as displaying evidence that such a process has taken place.