The Eastern Hudson Bay Arc (also known as the Nastapoka Arc)

by: Charles O’Dale

• Type: Probably NON IMPACT
• Location: N 56° 43’ W 80° 02’, Quebec, Canada
• Diameter: <450 Kilometres

From the beginning of the Observatory’s interest in craters this feature had been suspected of having a meteoritic origin and Beals had compiled the evidence, largely geological and topographical. The arc is closely circular, with a diameter of 300 miles. Its shoreline differs from other sections of Hudson Bay in that it consists of hills rising several hundred feet above the shore, considerably higher than the surrounding Shield. There is geological evidence that it embraces a basin nearly 30,000 feet deep filled with sedimentary and metamorphic rocks with interbedded volcanics. The strata around its boundary all dip toward its centre. In a companion paper Halliday supports the impact interpretation, by comparing the feature with ones of comparable size on the Moon and on Mars, and with established terrestrial craters. He shows the probable profile of a 300-mile crater; its depth is less than the 30,000 feet suggested for the Hudson Bay arc, which could be explained as due to depression of the earth under the weight of sediments. He makes an interesting estimate: to produce a crater 300 miles in diameter would require a meteorite, if iron, 21 miles in diameter, with a volume of 4,000 cubic miles.

A hole was drilled on Neilson Island, within the arc, in 1962. The core lacked any evidence of shock metamorphism, but one hole was not regarded as sufficient to settle the question of possible meteoric origin. [from John H. Hodgson A History of the Dominion Observatories Part 2, 1946-1970]

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Lithospheric architecture and tectonic evolution of the Hudson Bay region

David W. Eaton , Fiona Darbyshire

Abstract

Hudson Bay conceals several fundamental tectonic elements of the North American continent, including most of the ca. 1.9–1.8 Ga Trans-Hudson orogen (THO) and the Paleozoic Hudson Bay basin. Formed due to a collision between two cratons, the THO is similar in scale and tectonic style to the modern Himalayan–Karakorum orogen. During collision, the lobate shape of the indentor (Superior craton) formed an orogenic template that, along with the smaller Sask craton, exerted a persistent influence on the tectonic evolution of the region resulting in anomalous preservation of juvenile Proterozoic crust. Extensive products of 2.72–2.68 Ga and 1.9–1.8 Ga episodes of subduction are preserved, but the spatial scale of corresponding domains increases by roughly an order-of-magnitude (to 1000 km, comparable to modern subduction environments) from the Archean to the Proterozoic. Based on analysis of gravity and magnetic data and published field evidence, we propose a new tectonic model in which Proterozoic crust in the southeastern third of Hudson Bay formed within an oceanic or marginal-basin setting proximal to the Superior craton, whereas the northwestern third is underlain by Archean crust. An intervening central belt truncates the southeastern domains and is interpreted to be a continental magmatic arc.

Thick, cold and refractory lithosphere that underlies the Bay is well imaged by surface-wave studies and comprises a large component of the cratonic mantle keel beneath North America. The existence of an unusually thick mantle root indicates that subduction and plate collision during the Trans-Hudson orogeny were ‘root-preserving’ (if not ‘root-forming’) processes. Although the Hudson Bay basin is the largest by surface area of four major intracratonic basins in North America, it is also the shallowest. Available evidence suggests that basin subsidence may have been triggered by eclogitization of lower-crustal material. Compared to other basins of similar age in North America, the relatively stiff lithospheric root may have inhibited subsidence of the Hudson Bay basin.

The gravity field of eastern Hudson Bay: Evidence for a flextural origin for the Hudson Bay (Nastapoka) Arc? Authors Andrew Hynes TECTONICS Volume 10, Issue 4 August 1991

Abstract The Nastapoka Arc, on the east coast of Hudson Bay, is almost perfectly circular and closely follows the unconformable contact between Archean Superior province gneisses and shallowly seaward dipping early Proterozoic Nastapoka Group supracrustals. Its form may be explained by flexing of the lithosphere due to loading by thrust sheets from the Trans-Hudson orogen to the west. Such flexing produces a peripheral bulge east of the coast which should be reflected in a positive gravity anomaly there. Gravity data averaged around the arc show such a positive anomaly, although its precise amplitude is uncertain because of local variation in the gravity field. Lithospheric flexure of the arc due to loading can be modeled by superposition of discshaped loads centered on the arc. For a lithospheric Young’s modulus of 1.0 × 1011 N m−2 and Poisson’s ratio 0.25, the present geometry of the arc can be reproduced only by reducing the elastic thickness to 20±2 km. The peripheral bulge predicted for the model yields a gravity anomaly very similar to that observed if it is fully imaged at the Moho. The absence of a regional negative gravity anomaly over the arc, despite a great thickness of transported rocks present at its center, requires that the crust in the region was unusually thin before thrust emplacement. The unusually low elastic thickness required for the model may reflect highly fractured crust. Both features are consistent with the former presence of a rifted continental margin in the region, as predicted for many models of the Trans-Hudson orogen.

The present state of the studies of the Hudson Bay Arc is described here in M.E. Brookfield’s ABSTRACT:

Over 40 years ago, Beals (1968) proposed an impact origin for the great eastern arc of Hudson Bay, which extends for 650 kilometres through an angle of 155 degrees and has a coherent circular raised rim on its landward side. A rift extends at right angles outwards on the southeastern side and within the arc, the basin is filled with Proterozoic sediments.

The best fit circle has a radius of 230 kilometres and the arc deviates from this circle by less than 10 km along its entire length. More recently, Goodings and Brookfield (1992) noted that closing the James Bay rift aligns the Sutton ridge to form an arc of 240 degrees, or two-thirds of a circle. The remainder is cut by the younger circular northern Hudson Bay cratonic basin. Apart from impact, no other plausible explanation has been proposed for this great ring fracture (and another ring fracture may exist outside this one). But, because no definitive evidence of impact was found, little has been published on the Hudson Bay arc since 1968. Recent studies of multi-ringed basins on other planets, and of other old multi-ringed basin on Earth (e.g. Vredefort), provide criteria for re-investigation and re- interpretation of published reports. Along the Hudson Bay arc, bodies of pseudotachylite, monomict and exotic breccias are associated with faults, and overlying sediments may show evidence of re-worked impact melts. If investigations are positive, Hudson Bay arc would form part of the largest identified multi-ringed impact on Earth, with a minimum diameter of 450 kilometres. Beals, C. S., 1968. On the possibility of a catastrophic origin for the great arc of eastern Hudson Bay. In: Beals, C.S.(editor), Science, History and Hudson Bay, volume 2. Department of Energy Mines and Resources, Ottawa. p.985- 999. Goodings, C.R. & Brookfield, M.E., 1992. Proterozoic transcurrent movements along the Kapuskasing lineament (Superior Province, Canada) and their relationship to surrounding structures. Earth-Science Reviews, 32: 147-185. (M.E. Brookfield 2006)

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The Nastapoka arc is a geological feature located on the southeastern shore of Hudson Bay, Canada. It is a near-perfect circular arc, covering more than 160° of a 450 km diameter circle. Due to its shape, the arc has long been suspected as the remnant of an ancient impact crater.[1] In August 1972, Dr. Robert S. Deitz and J. Paul Barringer conducted extensive search of much of the Nastapoka arc by Indian and Eskimo canoes and fishing boat in an investigation of its impact origin. They examined the abundant and extensive rock exposures that occur within the region of the Nastapoka arc and found a complete lack of shatter cones, suevite-type or other unusual melt rocks, pseudotachylite or mylonite, radial faults or fractures, unusual injection breccias, or any other evidence of shock metamorphism.[2] More commonly, it is regarded to be an arcuate boundary, which was created during the Trans-Hudson orogeny, of tectonic origin between the Belcher Fold Belt and granitic rocks of the Superior Craton.[3][4]

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The Nastapoka Arc, on the east coast of Hudson Bay, is almost perfectly circular and closely follows the unconformable contact between Archean Superior province gneisses and shallowly seaward dipping early Proterozoic Nastapoka Group supracrustals. Its form may be explained by flexing of the lithosphere due to loading by thrust sheets from the Trans-Hudson orogen to the west. Such flexing produces a peripheral bulge east of the coast which should be reflected in a positive gravity anomaly there. Gravity data averaged around the arc show such a positive anomaly, although its precise amplitude is uncertain because of local variation in the gravity field. Lithospheric flexure of the arc due to loading can be modeled by superposition of discshaped loads centered on the arc. For a lithospheric Young’s modulus of 1.0 × 1011 N m−2 and Poisson’s ratio 0.25, the present geometry of the arc can be reproduced only by reducing the elastic thickness to 20±2 km. The peripheral bulge predicted for the model yields a gravity anomaly very similar to that observed if it is fully imaged at the Moho. The absence of a regional negative gravity anomaly over the arc, despite a great thickness of transported rocks present at its center, requires that the crust in the region was unusually thin before thrust emplacement. The unusually low elastic thickness required for the model may reflect highly fractured crust. Both features are consistent with the former presence of a rifted continental margin in the region, as predicted for many models of the Trans-Hudson orogen (Hynes 1991).

2016 DISCOVERY

Evidence for early life in Earth’s oldest hydrothermal vent precipitates

Abstract

Although it is not known when or where life on Earth began, some of the earliest habitable environments may have been submarine-hydrothermal vents. Here we describe putative fossilized microorganisms that are at least 3,770 million and possibly 4,280 million years old in ferruginous sedimentary rocks, interpreted as seafloor-hydrothermal vent-related precipitates, from the Nuvvuagittuq belt in Quebec, Canada. These structures occur as micrometre-scale haematite tubes and filaments with morphologies and mineral assemblages similar to those of filamentous microorganisms from modern hydrothermal vent precipitates and analogous microfossils in younger rocks. The Nuvvuagittuq rocks contain isotopically light carbon in carbonate and carbonaceous material, which occurs as graphitic inclusions in diagenetic carbonate rosettes, apatite blades intergrown among carbonate rosettes and magnetite–haematite granules, and is associated with carbonate in direct contact with the putative microfossils. Collectively, these observations are consistent with an oxidized biomass and provide evidence for biological activity in submarine-hydrothermal environments more than 3,770 million years ago. (Matthew S. Dodd, ET AL; 09 January 2017 )

Haematite tubes from the NSB hydrothermal vent deposits that represent the oldest microfossils and evidence for life on Earth. Credit: Matthew Dodd

Haematite filament attached to a clump of iron in the lower right, from hydrothermal vent deposits in the Nuvvuagittuq Supracrustal Belt in Québec, Canada. These clumps of iron and filaments were microbial cells and are similar to modern microbes found in vent environments. Credit: M.Dodd

Read more at: https://phys.org/news/2017-03-world-oldest-fossils-unearthed.html#jCp

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References

[see – METEORITE]

Beals, C.S. On the possibility of a catastrophic origin for the great arc of eastern Hudson Bay. in C.S. Beals, ed., pp. 985-999, Science, history and Hudson Bay, vol. 2. Ottawa, Ontario, Canada Department of Energy, Mines and Resources. 1968.

Brookfield M.E. 2006, THE GREAT ARC OF EASTERN HUDSON BAY, CANADA: PART OF THE LARGEST MULTIRINGED IMPACT BASIN ON EARTH? Geological Society of America. 2006.

Brent Dalrymple, Radiometric Dating Does Work! Reports of the National Center for Science Education

Dietz, R.S., and J.P. Barringer (1973) Hudson Bay Arc as an Astrobleme: a Negative Search. Meteoritics. 8:28–29.

Eaton, D.W., and F. Darbyshire (2010) Lithospheric architecture and tectonic evolution of the Hudson Bay region. Tectonophysics. v. 480, pp. 1–22.

Grieve R.A.F., Robertson P.B., IMPACT STRUCTURES IN CANADA, the Journal of the Royal Astronomical Society of Canada, February 1975

Hynes, A.J. (1991) The gravity field of eastern Hudson Bay: Evidence for a flexural origin for the Hudson Bay (Nastapoka) arc? Tectonics. 10:722–728.

Innes M., Recent Advances in Meteorite Crater Research, Meteoritics 1964.