Ottawa-Bonnechere Graben

Coordinates: 45°34′36″N 76°54′58″W / 45.5767°N 76.9162°W / 45.5767; -76.9162
Source: Wikipedia, the free encyclopedia.
Ottawa-Bonnechere Graben
Late Proterozoic to Early Paleozoic
GeologyGraben
Dimensions
 • Length700 km (435 mi)

The Ottawa-Bonnechere Graben (also known as the Ottawa Graben) is a geological structure that coincides with a 55 km (34 mi) wide topographic depression extending from near

Montréal through Ottawa. It is part of the Saint Lawrence rift system that also includes the seismically active Saguenay graben.[1] This rift valley was formed when the Earth's crust moved downward about a kilometre between two major fault zones known as the Mattawa and Petawawa faults.[2]

Geography

The Ottawa-Bonnechere Graben measures about 700 km (435 mi), running from the

Saint Lawrence River valley and links the Ottawa and Saguenay Graben.[3][4]

The 200 km (124 mi) segment of the Ottawa-Bonnechere Graben west of Ottawa was the first to be recognized as a

mya (million years ago); similar events formed the Temiskaming Graben ~449–451 mya.[5] These grabens were reactivated during the breakup of supercontinent Pangaea some 150 mya.[6]

Geology

Three of the central Monteregian Hills viewed from space (from left: Mont Saint-Hilaire, Mont Rougemont and Mont Yamaska).

Since the Late Proterozoic to Early Paleozoic, erosion has removed the volcanic peaks, exposing a number of relic volcanic pipes, such as Callander Bay and the Manitou Islands in Lake Nipissing.[7]

These features are

supersonic eruption of deep-origin volcanoes. Batholiths and dikes were also exposed by erosion, such as the Timber Lake, Mulock, West Arm, Powassan and Bonfield batholiths.[7] The expressions of a thick pile of dominantly mafic, bimodal volcanics and the Tibbit Hill volcanics in the Humber Zone of the Quebec Appalachians are believed to be related to the formation of the Ottawa-Bonnechere Graben.[2] The precise age of these volcanics is unknown but they are either early Cambrian and late Precambrian.[2] This volcanism was probably coeval with the emplacement of the Grenville dike swarm.[citation needed
]

Minor but significant igneous activity occurred during the Mesozoic era, including

intrusions along the Ottawa-Bonnechere Graben and elsewhere in Ontario. This second episode of alkalic volcanism occurred along the eastern part of the graben in the early Cretaceous
.

The products of this event are the Monteregian Hills in Montérégie, Quebec. These are thought to have formed as a result of the North American Plate sliding westward over a long-lived center of upwelling magma called the New England hotspot,[8] and is the eroded remnants of intrusive stocks.

These intrusive stocks have been variously interpreted as the feeder intrusions of long

extinct volcanoes, which would have been active about 125 million years ago,[2][9][10] or as intrusives that never breached the surface in volcanic activity.[11] Of all these features, Mont Saint-Hilaire
is the best known as a source of rare specimens.

View of the Ottawa Valley from the Gatineau Hills

Along the northern side of the Ottawa-Bonnechere Graben lies a dramatic escarpment that forms the southern edge of the Gatineau Hills. This escarpment, called the Eardley Escarpment, makes this part of the graben an attractive location for rock climbers and hikers, offering a beautiful view of the relatively flat fields below, which extend to the Ottawa River.

On or near a branch of the Ottawa-Bonnechere Graben lies the Brent impact crater.[7] It is 3.8 km (2.4 mi) in diameter and the age is estimated about 400 million years (Early Devonian). The impact crater, which was first recognized in 1951 from aerial photographs, formed in Precambrian gneisses.

TNT
and occurred when this area was probably covered by a shallow sea.

History

The depressions formed by the graben across the rugged Canadian Shield were a spillway for the Great Lakes after the last ice age.[13] Later they became a thoroughfare for exploration and trade. These depressions now contain the Ottawa River and its tributary the Mattawa, which rises at Trout Lake near Lake Nipissing. The latter is the source of the French River, which drains into Lake Huron. This water route, with few portages, connected Lake Huron and the Saint Lawrence River by a much shorter route than through the lower Great Lakes. It was the mainline of the French-Canadian voyageurs engaged in the fur trade; they took canoes on the waterways along this route from Montreal to the upper Great Lakes and the pays d'en haut—the "upper country" in the old Northwest.[13] [14] The valley of the Ottawa and Montreal Rivers and Lake Timiskaming was also part of a branch route to James Bay in the days of the fur brigades.[15] The valleys are now used by more modern forms of transportation, including the Canadian Pacific Railway and the Trans-Canada Highway.[16]

After the arrival of European settlers in North America, the

Canadian Heritage River
, and as such, its shores are now protected from further development and logging. Today, the river and lakes are mainly used for recreation.

See also

  • Midcontinent Rift System – Geological rift in the center of the North American continent
  • Ottawa Valley – Valley in Ontario and Quebec in Canada
  • Volcanology of Canada
     – Volcanic activity in Canada
  • Volcanology of Eastern Canada
     – volcanic areas and lava formations in Eastern Canada

References

  1. doi:10.1016/j.jog.2005.01.003
    .
  2. ^
    Bibcode:1981LPICo.457..114K., pages 114, 115, and 116
    .
  3. ^ a b Tremblay, Alain; Lemieux, Yvon (2001). "Supracrustal Faults of the St. Lawrence rift System between Cap Tourments and Baie-Saint-Paul, Quebec" (PDF). Current Research 2001-D15. Geological Survey of Canada. Retrieved 2007-06-20.
  4. ^ "Map". Archived from the original on 2008-04-10. Retrieved 2007-12-15.
  5. ^ Sajal, Sharma; Dix, George R.; Coniglio, Mario; Achad, Aicha; Riva, John F. V. (2005-09-27). "Records of Punctuated Tectonism in Platform-Interior Graben Systems (Ontario, Canada) Far-Flung from Contemporaneous Taconic Orogenesis in the Northern Appalachians" (PDF). Calgary, Alberta: searchanddiscovery.net. Archived from the original (PDF) on 2008-04-10. Retrieved 2007-12-16. Poster presentation at AAPG Annual Convention, Calgary, Alberta, June 19–22, 2005, and abstract.
  6. ^ The Ottawa Bonnechere Graben Retrieved on 2007-11-18
  7. ^ a b c "Background Geology of the North Bay area". Archived from the original on 2007-12-20. Retrieved 2007-12-15.
  8. PMID 17377580
    .
  9. ^ "A Hundred-Million Year History of the Corner Rise and New England Seamounts". Archived from the original on 2006-05-03. Retrieved 2007-11-16.
  10. ^ "The Monteregian Hills: Igneous Intrusions". Geoscape Montreal. Natural Resources Canada. Archived from the original on 2009-04-26. Retrieved 2006-11-16.
  11. ^ "Geology of Gault Nature Reserve, Mont St. Hilaire". McGill University. Archived from the original on 2007-12-20. Retrieved 2007-12-16.
  12. ^
    doi:10.1038/215725a0
    .
  13. ^ a b "Natural Areas Report: Mattawa River". National Heritage Information Center. Ontario Ministry of National Resources. 2005-06-05. Archived from the original on November 9, 2005. Retrieved 2007-12-15.
  14. ISBN 978-1-55971-045-9
    .
  15. ISBN 978-1-55971-045-9
    .
  16. Highway 17
    , and other routes.

External links

45°34′36″N 76°54′58″W / 45.5767°N 76.9162°W / 45.5767; -76.9162

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