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

Abstract

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 km2 Indian Brook Granodioritc varies from more mafic in the northwest to more felsic in the southeast, consistent with pressures estimated from the Al-in-homblende 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 lerrane.La roche granitoïde Néoprotérozoique tardif constituent la majeure partie de la région d'Indian Brook au sud-est des hautes terres du Cap Breton. Elles sont divisées en sept unités de carte basées sur des observations sur le terrain, la texture, et la minéralogie. Bien que de forts contacts lithologiques aient été tracés dans sur le terrain, les plutons sont chimiquement graduels, et sont déduis pour être un groupe comagmatique, associée par les processus de cristallisation fractionnée et/ou des quantités variables de la fonte de roche similaire à la source. La composition dans le plus grand pluton, c. 100 km2 de granodiorite D'Indian Brook a une variation de mafique dans le nord-ouest à felsique dans le du sud-est, conformé à des pressions estimées à partir du géobaromètre d'Al-dans-homblende qui suggèrent que la partie occidentale représente une part plus profonde du pluton. Les roches volcaniques de la Formation Price Point et les roches chimiquement semblables de Murray Mountain Quartz Monzodiorite on lieu dans la partie sud-est de la zone, et sont impliquées pour représenter le niveau le plus élevé de la mise en place et l'accompagnement de l'extrusion de magma. Les roches granitoïdes et volcaniques ont les dispositifs pétrochimiques conformés à l'origine dans une zone continentale de subduction de marge, comme d'autres unités d'âge semblable dans le terrane de Bras d'Or.[Traduit par la rédaction] In t r o d u c t i o nLate Neoproterozoic granitoid plutons and minor metavolcanic rocks form most o f the southeastern Cape Breton Highlands (Fig. 1) (Fig. 1, inset). In contrast, Dostal et al. (1996) did not recognize these separate

Granitoid plutons in peri-Gondwanaan terranes of Cape Breton Island, Nova Scotia, Canada: new U-Pb (zircon) age constraints

“…This age supports the inferred co-magmatic relationship between the volcanic rocks and associated plutons (Grecco and Barr 1999), although it is somewhat older than the dated plutons which have ages between 570 Ma (Birch Plain granite -see below) and 555 Ma (Ingonish River tonalite; Dunning et al 1990). The Birch Plain granite is in the northern part of the eastern highlands plutonic belt, intruded by the Cape Smokey pluton dated at 493 ± 2 Ma (Dunning et al 1990).…”

“…The Birch Plain granite is in the northern part of the eastern highlands plutonic belt, intruded by the Cape Smokey pluton dated at 493 ± 2 Ma (Dunning et al 1990). Based on map distribution, the presence of variably weak to strong foliation, and the presence of xenoliths in the Indian Brook granodiorite that appear to have been derived from the Birch Plain granite, the Birch Plain granite has been assumed to be older than the Indian Brook unit ( Grecco and Barr 1999). It is cut by mafic dykes of unknown age with sharp contacts and well developed chilled margins; possible magma mingling relationships are developed in places.…”

Field relations, age, and tectonic setting of metamorphic and plutonic rocks in the Creignish Hills – North Mountain area, southwestern Cape Breton Island, Nova Scotia, Canada

“…8c). These characteristics are shared by Neoproterozoic plutons throughout the Bras d'Or terrane (e.g., Farrow and Barr 1992;Raeside and Barr 1990;Grecco and Barr 1999;Wasylik et al 2005;Swanton 2010). It is clear that a huge volume of plutonic rocks was emplaced in the Bras d'Or terrane mainly between about 565-550 Ma and that they formed in an Andeantype continental margin subduction zone.…”

Basement-cover relations in the southeastern Cape Breton Highlands, Nova Scotia, Canada

“…The Eastern Highlands Shear Zone has been recognized to display a protracted period of motion (Lin 1995), although the dominant phase of mylonite development ended in the Late Devonian. Late Neoproterozoic plutonic rocks in the southeastern highlands display telescoping of units (Farrow andBarr 1992, Grecco andBarr 1999), with increasingly greater amounts of uplift toward the northwest. Similarly, telescoping in the opposite direction has been recognized in the western highlands (Craw 1984) using metamorphic zonal assemblages.…”