Geological setting and petrochemistry of early Middle Devonian volcanic and gabbroic rocks in the Guysborough area, Nova Scotia

Thick conglomerate-dominated sedimentary successions of the Horton and lower Windsor groups in the southern Isle Madame area show provenance variations with stratigraphic position, based on pebble counts, petrographic observations, and facies trends throughout the conglomeratic units. These coarse clastic sediments were deposited in a transtensional basin that formed south of a splay of the Minas Fault Zone, now repeated by younger faults in the study area. A stratigraphic section 1300 m thick that includes the base of the Horton Group was derived mostly, if not entirely, from units in the Avalonian Mira terrane to the east. Similar provenance indications continue stratigraphically upward in this section and elsewhere on Isle Madame through the thick lower and central parts of the Horton Group. In the upper part of the Horton Group, an influx of high-grade metamorphic and deformed plutonic clasts is recorded in the conglomerates, and the percentage of this material continues to increase above a dark fine-grained interval and into the overlying Windsor Group. The metamorphic clasts strongly resemble local basement rocks exposed as belts between conglomeratic domains in Isle Madame, indicating that these deeper crustal rocks were unroofed within the former basin in the late Tournaisian, resulting in redirected drainage patterns. Paleocurrent and facies information suggest that the Mira terrane sources were located to the northwest at the time of deposition. Hence, paleogeographic reconstruction for the area involves not only unroofing of the deeper crustal rocks, but also dextral transcurrent movement to place the appropriate parts of the Mira terrane at the northwestern corner of exposed parts of the basin. This movement was along a subsequently deformed part of the Minas Fault Zone. RÉSUMÉDes successions sédimentaires épaisses dominées par le conglomérat du Groupe de Horton et de la partie inférieure du Groupe de Windsor dans le secteur sud de l'Isle Madame montrent des variations de provenance avec la position stratigraphique, selon le compte de galets, les observations pétrographiques et les tendances des faciès dans l' ensemble des unités conglomératiques. Ces sédiments clastiques grossiers ont été déposés dans un bassin transtensionnel qui s' est formé au sud du point de divergence de la zone de faille de Minas, maintenant répétés par des failles plus récentes dans la zone d' étude. Une section stratigraphique de 1 300 m d' épaisseur comprenant la base du Groupe de Horton provenait majoritairement, si ce n' est pas entièrement, des unités dans le terrane de Mira de l' Avalonien à l' est. Des indications de provenance similaire se poursuivent stratigraphiquement vers le haut dans cette section et ailleurs sur l'Isle Madame dans les parties épaisses inférieures et centrales du Groupe de Horton. Dans la partie supérieure du Groupe de Horton, un afflux de clastes plutoniques déformés et hautement métamorphiques est noté dans les conglomérats, et le pourcentage de ce matériel continue d'augmenter au-dessu...

Section: Paleogeographic Evolutionmentioning

confidence: 80%

Section: Provenance Indicationsmentioning

confidence: 99%

Section: Other Stratigraphic Successions Of the Study Areamentioning

confidence: 99%

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Stratigraphic evolution of provenance in a thick conglomerate-dominated Carboniferous succession in the southern Isle Madame area, Nova Scotia, and paleogeographic implications

Force¹

2014

“…These include the ~ 340 Ma basalts of Cape Breton Island (Blanchard et al 1984;Barr et al 1994), Carboniferous basalts of New Brunswick (Fyffe and Barr 1986;Park et al 2014), 385 Ma rocks of the Guysborough area, Nova Scotia (Cormier et al 1995), 355-362 Ma basalts of the Magdalen Basin (Barr et al 1985;PePiper andPiper 1998, La Flèche et al 1998), 330 to 375 Ma Fountain Lake Group basalts of Nova Scotia (Dessureau et al 2000), and ~ 370 Ma Wamsutta Formation in the Narragansett Basin of southern New England (Thompson and Hermes 2003).…”

Section: Discussionmentioning

confidence: 99%

The Appledore Island pluton of the Rye Complex, coastal New Hampshire and Maine, USA: geochronological and chemical evidence for the affinity of an enigmatic terrane

Dorais

Bothner

Buchwaldt

2014

The Rye Complex of coastal New Hampshire and Maine is a peri-Gondwanan terrrane that up to now had an uncertain origin. An offshore portion of the complex, Appledore Island of the Isles of Shoals, hosts a mainly dioritic intrusion that yielded an U-Pb zircon age of 361.09 ± 0.14 Ma, allowing comparison of its geochemical characteristics with mafic rocks of similar age across the northern Appalachian orogen. The Appledore Island diorite has similar major, trace, and isotopic compositions as continental rift tholeiite in the Narragansett Basin in southern New England and in the Maritimes Basin of Canada. These intraplate volcanic rocks range from 375 to 330 Ma, bracketing the age of the Appledore Island diorite. Their intraplate tectonic setting reflects regional extension during the Late Devonian to Early Carboniferous which produced successor basins after the Acadian orogeny. The geochemical and age similarities of the Appledore Island diorite and the mafic rocks of the successor basins suggest that the Rye Complex is a basement fragment of a successor basin block. Further evidence of the identity of the Rye Complex is provided by the isotopic composition of intermingled, comagmatic granitic rocks associated with the Appledore Island diorite. The granite has a Ganderian isotopic signature, suggesting that the Rye Complex is a Ganderian basement block that was transposed by movement along the Norumbega Fault System to its position adjacent to the Merrimack Trough of New Hampshire and Maine.

“…2) are in faulted contact with volcanicsedimentary units of the Late Devonian Guysborough Group to the south (Cormier et al 1995;White and Barr 1999), the Silurian -Early Devonian Arisaig Group to the west (Murphy et al 1991), and younger Carboniferous rocks on the north and east. Locally, along the northwestern margin, the sequence is disconformably overlain by the Macumber Formation of the Visean Windsor Group (Boehner and Giles 1993).…”

Section: Geological Settingmentioning

confidence: 99%

Stratigraphy and structure of the Horton Group, Lochaber-Mulgrave area, northern mainland Nova Scotia

Ténière

Barr

White³

2005

The Lochaber-Mulgrave area of northern mainland Nova Scotia is underlain by rocks of the Late Devonian -Early Carboniferous Horton Group, in faulted contact with older Devonian and Silurian rocks to the south and west, and younger Carboniferous rocks to the north and east. The Horton Group is divided into (from oldest to youngest) the Clam Harbour River, Tracadie Road, Caledonia Mills, and Steep Creek formations, with a total thickness of at least 4000 m. These units were deposited in a variety of braided fl uvial and shallow to deep lacustrine environments, and show lithological and stratigraphic similarities to the Horton Group elsewhere in Nova Scotia. Sparse palaeontological data from macrofossils and spores indicate an age range from Famennian to late Tournaisian. Compared to elsewhere in Nova Scotia, the Horton Group in the Lochaber-Mulgrave area is more deformed and metamorphosed, especially in the southern part of the area near the Roman Valley Fault. The time of regional deformation and metamorphism is constrained to ca. 340-335 Ma by whole-rock 40 40 Ar/ 39 39 Ar dating of slate in the Clam Harbour River and Tracadie Road formations. Regional deformation and metamorphism may have resulted from burial by older rocks of the Guysborough block, thrust over the Horton Group in the Lochaber-Mulgrave area from the south as a result of transpression at a restraining bend along the Chedabucto-Roman Valley fault system during juxtaposition of the Avalon and Meguma terranes.