'Pseudo-Charnockites' from the Greenstone Terrain of Northeast Dharwar Craton

Patches and oriented zones of 'pseudo-charnockites', similar in appearance to incipient charnockites from the granulite transition zones, are reported for the first time from the pink granites of Gadwal and Kurnool areas in the low-grade metamorphic terrain of northeast Dharwar craton. With a mineral assemblage of quartz, feldspars, micas and amphiboles showing varying degrees of alteration to chlorite and sericite, these zones preserve the signature of hydration following peak metamorphism. Though aqueous brine inclusions (average 6 wt % NaCl equivalent) constitute the dominant fluid phase in the granite and the retrograde zones, the occurrence of coexisting monophase inclusions with a near-pure carbonic fluid (density 0.70-0.80g/cm3) in the retrograde zones invoke special attention. Though carbonic inclusions generally typify dehydration reactions, it is suggested that retrograde reactions of the type which produced the pseudo-charnockite horizons could also result in the entrapment of nearpure CO₂ of moderate to low densities. The carbonic inclusions have apparently resulted from the immiscible separation of a mixed carbonic-aqueous fluid which exsolved into brine and CO₂ upon decompression following the rapid uplift of the Eastern Block along the Chitradurga boundary fault, concomitant with the copious intrusion of younger granitoids.