Hornfelses from Paritu, Coromandel County

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Abstract
The Paritu Plutonics (diorites, quartz-diorites, and granodiorites) were intruded in the mid-Miocene into pelitic and psammitic Jurassic sediments and Tertiary andesites and dacites forming a contact aureole. Progressive mineral zonations in the aureoles, determined from metamorphosed andesites and lithic-volcanic sediments recrystallised to give hypersthene-, hornblende-, and albite-epidote-actinolite-bearing assemblages, correspond to assemblages of the pyroxene hornfels, hornblende hornfels, and albite-epidote hornfels facies. Chemical analyses of nine hornfelses and the retention of chemical integrity of Iithic fragments in Paritu hornfelses indicate isochemical metamorphism. Electron-probe analyses are listed for three pyroxenes, six amphiboles, six biotites, and two garnets. A regular elemental distribution between similar co-existing mineral pairs suggests equilibrium crystallisation. An estimate of the physicochemical conditions of crystallisation of the Paritu hornfelses would be P(load) and P(water) <250 bars with temperatures of <450°C for albite-epidote hornfelses, 450 650°C for hornblende hornfelses, and 650–800°C for pyroxene hornfelses.