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- Title
High-level emplacement of the Cape Chignecto pluton, Cobequid Highlands, Nova Scotia, Canada.
- Authors
PIPER, DAVID J. W.; GRANT, CALEB; PE-PIPER, GEORGIA
- Abstract
New field work at Refugee Cove in the southern Cape Chignecto Pluton shows evidence for inflation of the granite pluton by multiple sub-horizontal gabbro sills. These sills show igneous intrusive relationships with the granites and include xenoliths and rotated blocks of granite, with local evidence of digestion of granite. East of Refugee Cove, the stacked gabbro sills are cut by a 60 m-wide zone of mixed lithologies bounded by sub-vertical faults. This zone includes 60% granite, 35% gabbro, a metre-scale block of faintly layered feldspathic rhyolite, and polymictic breccia of irregular cm-scale fragments of rhyolite and bedded tuff in a mafic matrix. At the margins of the zone, clasts in the undeformed breccia are aligned parallel to the bounding fault. The zone is interpreted as a small high-level volcanic pipe or diatreme where eruptive products have fallen back into a volcanic vent. There, solidified granite and fragments of rhyolite and tuff were intruded by irregular bodies of gabbro. The cross-cutting untectonized relationship between the vent zone and the gabbro sills demonstrates that both are related to the latest Devonian-earliest Carboniferous plutonism. There is no evidence for co-existence of immiscible mafic and felsic magmas, which is demonstrated in the coeval Wentworth Pluton by lobate, mutually chilled contacts at the margins of gabbro sills. Explosive rhyolite eruptions in modern volcanoes result from emplacement of hot mafic magma into partly crystallized fractionating magma chambers. The Wentworth Pluton outcrops record such processes in an active magma chamber. At Refugee Cove, the rising volcanic products of such a magma chamber cut through the fully crystallized host granite to form a volcano at the surface. The Geopark would welcome further field and lab research on these remarkable rocks.
- Subjects
NOVA Scotia; IGNEOUS intrusions; RHYOLITE; GABBRO; BRECCIA; SILLS (Geology); MAGMAS; DEVONIAN Period
- Publication
Atlantic Geoscience, 2023, Vol 59, p61
- ISSN
2564-2987
- Publication type
Article
- DOI
10.4138/atlgeo.2023.002