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 are a of the southeastern Cape Breton Highlands. They are divided into seven ma p units based on field relations, texture, and mineralogy. Although sharp l ithological contacts have been mapped in the field, the plutons are chemica lly gradational, and are inferred to be a comagmatic suite, related by crys tal fractionation processes and/or variable amounts of melting of similar s ource rocks. Composition in the largest pluton, the ca. 100 km(2) Indian Br ook Granodiorite varies from more mafic in the northwest to more felsic in the southeast, consistent with pressures estimated from the Al-in-hornblend e geobarometer which suggest that the western part represents the deeper pa rt of the pluton. Volcanic rocks of the Price Point Formation and the chemi cally similar Murray Mountain Quartz Monzodiorite occur in the southeastern part of the area, and are inferred to represent the highest level of empla cement and accompanying extrusion of magma. The granitoid and volcanic rock s have petrochemical features consistent with origin in a continental margi n subduction zone, like other units of similar age in the Bras d'Or terrane .