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Nastapoka arc
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 was long suspected as the remnant of an ancient impact crater.〔Beals, C.S. (1968) ''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.〕 However, studies have cast doubt on this. In August 1972, Robert S. Dietz and J. Paul Barringer conducted an extensive search of much of the Nastapoka arc with First Nations and Inuit canoes and fishing boats 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.〔Dietz, R.S., and J.P. Barringer (1973) ''Hudson Bay Arc as an Astrobleme: a Negative Search. Meteoritics.'' 8:28–29.〕
Given the lack of evidence for an impact crater, the arc is now commonly regarded to be an arcuate boundary created during the Trans-Hudson orogeny, of tectonic origin between the Belcher Fold Belt and granitic rocks of the Superior Craton.〔Eaton, D.W., and F. Darbyshire (2010) ''Lithospheric architecture and tectonic evolution of the Hudson Bay region.'' Tectonophysics. v. 480, pp. 1–22.〕〔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.〕
==References==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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