Late Neoproterozoic granitoid and metavolcanic rocks of the Indian Brook Area, southeastern Cape Breton Highlands, Nova Scotia

Late Neoproterozoic granitoid rocks constitute most of the Indian Brook area of the southeastern Cape Breton Highlands. They are divided into seven map units based on field relations, texture, and mineralogy. Although sharp lithological contacts have been mapped in the field, the plutons are chemically gradational, and are inferred to be a comagmatic suite, related by crystal fractionation processes and/or variable amounts of melting of similar source rocks. Composition in the largest pluton, the ca. 100 km(2) Indian Brook Granodiorite varies from more mafic in the northwest to more felsic in the southeast, consistent with pressures estimated from the Al-in-hornblende geobarometer which suggest that the western part represents the deeper part of the pluton. Volcanic rocks of the Price Point Formation and the chemically similar Murray Mountain Quartz Monzodiorite occur in the southeastern part of the area, and are inferred to represent the highest level of emplacement and accompanying extrusion of magma. The granitoid and volcanic rocks have petrochemical features consistent with origin in a continental margin subduction zone, like other units of similar age in the Bras d'Or terrane.