Montagnais: A submarine impact structure on the Scotian Shelf, eastern Canada

Abstract

Research Article| April 01, 1989 Montagnais: A submarine impact structure on the Scotian Shelf, eastern Canada LUBOMIR F. JANSA; LUBOMIR F. JANSA 1Geological Survey of Canada, Atlantic Geoscience Centre, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia, B2Y 4A2, Canada Search for other works by this author on: GSW Google Scholar GEORGIA PE-PIPER; GEORGIA PE-PIPER 2Department of Geology, St. Mary's University, Halifax, Nova Scotia, B3H 3C3, Canada Search for other works by this author on: GSW Google Scholar P. BLYTH ROBERTSON; P. BLYTH ROBERTSON 3Geological Survey of Canada 1 Observatory Crescent, Ottawa Ontario, K1A 0Y3, Canada Search for other works by this author on: GSW Google Scholar OTTO FRIEDENREICH OTTO FRIEDENREICH 4Shell Canada Limited P.O. Box 100, Station M, Calgary, Alberta T2P 2H5, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information LUBOMIR F. JANSA 1Geological Survey of Canada, Atlantic Geoscience Centre, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia, B2Y 4A2, Canada GEORGIA PE-PIPER 2Department of Geology, St. Mary's University, Halifax, Nova Scotia, B3H 3C3, Canada P. BLYTH ROBERTSON 3Geological Survey of Canada 1 Observatory Crescent, Ottawa Ontario, K1A 0Y3, Canada OTTO FRIEDENREICH 4Shell Canada Limited P.O. Box 100, Station M, Calgary, Alberta T2P 2H5, Canada Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1989) 101 (4): 450–463. https://doi.org/10.1130/0016-7606(1989)101<0450:MASISO>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation LUBOMIR F. JANSA, GEORGIA PE-PIPER, P. BLYTH ROBERTSON, OTTO FRIEDENREICH; Montagnais: A submarine impact structure on the Scotian Shelf, eastern Canada. GSA Bulletin 1989;; 101 (4): 450–463. doi: https://doi.org/10.1130/0016-7606(1989)101<0450:MASISO>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The first impact crater in the ocean has been identified on the outer continental shelf off Nova Scotia, Canada. The crater is well preserved and buried by 510 m of Tertiary and Quaternary marine sediments. The crater is a circular structure at least 45 km wide and 2.7 km deep, with a central structural uplift. The uplift is at least 1,250 m and possibly 2,900 m in height. Its upper surface is 11.5 km across, and it has a central pit 3.5 km wide in the center. An exploratory oil well located near the center of the structure encountered Cambro-Ordovician metamorphic rocks of the "basement," which are fractured with planar deformation features in quartz representative of pressures in the 8- to 12-GPa range. The uplifted basement is covered by 552 m of breccia. Shock-induced features are common; they include planar lamellae in quartz and feldspars; partial to total isotropization of silicates; and the occurrence of mixed tectosilicate glasses, some of which exhibit flow textures with total dissociation of the mafic components to ill-defined aggregates. These features are diagnostic of a 35-to 50-GPa shock level for parts of the breccia. The top of the breccia is covered by a 40.5-m-thick suevite zone. Two crystalline melt-rock horizons 72 and 34 m thick are enclosed in the breccia. Even though the feldspars in the melt are labradorite to bytownite in composition, the chemical composition of the rock is rhyolitic, with 70%-77% of SiO2, similar to the composition of the basement. There is no obvious enrichment in siderophile elements, except an increase in iridium (0.1-0.3 ppb). The occurrence of a thick section of impact melt rocks and breccia capping the central uplift is a feature not recognized in other complex impact craters and may be a function of impact into a marine environment.Dating by 39Ar/40Ar indicates that the impact occurred at about 51 Ma, late early Eocene, and this is confirmed by biostratigraphic data from immediately overlying sediments. The compositional and structural imprint left on the Montagnais structure by the colliding body points to the impactor being most probably the nucleus of a comet. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.