Geological setting and petrology of the Rocky Brook area, Western Cape Breton Island, Nova Scotia
LE3 .A278 2016
Barr, Sandra M.
Bachelor of Science
Earth & Environmental Sciences
The Rocky Brook area 15 km southeast of the town of Chéticamp in the Cape Breton Highlands was mapped and sampled for petrographic and chemical studies. The area is underlain mostly by the Cambrian (?) Jumping Brook Metamorphic Suite (JBMS), bounded on the west by the Devonian Fisset Brook Formation, which in places unconformably overlies the JBMS and in other places is faulted against it, and on the east by a faulted contact with the Devonian Margaree Pluton. The JBMS is divided into the Faribault Brook Formation, consisting mainly of metabasalt and minor metagreywacke, and the Barren Brook Formation, consisting of metagreywacke and minor metasiltstone. Geochemical data and petrographic analysis indicate that the protolith of the metabasalt is mid-ocean ridge basalt (MORB). The Barren Brook Formation is inferred to overlie conformably the Faribault Brook Formation, and the two units are interpreted to have been formed in a back-arc basin based on their chemical and lithological features. Petrographic study of clasts in an area of conglomerate inferred to overlie the Barren Brook Formation shows that it contains clasts of Fisset Brook Formation basalt, constraining its age to Devonian or younger. The Jumping Brook Metamorphic Suite is intruded by several younger igneous units, including mafic and quartz-feldspar porphyry dykes, monzogranite, and stockwork-style quartz-veined quartz-feldspar porphyry. The mafic dykes are interpreted to be related to the Devonian Fisset Brook Formation basalt based on petrographical and chemical similarities. The quartz-feldspar porphyry dykes and monzogranite are most likely related to the Devonian magmatism in the area based on chemistry, petrographic features, and lack of metamorphism. Relationship to other units and age of the stockwork-style quartz-veined quartz-feldspar porphyry remain enigmatic.
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