Crude quantitative estimates of the original northwest–southeast dimension of the Sudbury Structure, south-central Canadian Shield

Shanks, W. S.; Schwerdtner, W. M.

doi:10.1139/e91-149

Cited by 37 publications

(14 citation statements)

References 8 publications

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“…The cooling of this typical vertical section, modeled in the one-dimensional approximation, gives a solidification time for the SIC on the order of several hundred kiloyears which depends mostly on the initial thickness of the melt layer. Due to this prolonged cooling, the observed tectonic deformation of the impact structure (e.g., Shanks and Schwerdtner, 1991) can occur well before the final solidification of the impact melt. Such a deformation, which acted during the cooling, could explain several well-known features of the SIC.…”

Section: Discussionmentioning

confidence: 99%

“…Within the frame of this impact model, the Sudbury Igneous Complex (SIC), together with the clast-rich sequences on top (Basal Member of the Onaping Formation) and bottom (Sublayer) are interpreted as solidified impact melt body (Brockmeyer, 1990;Grieve et al, 1991;Deutsch et al, 1995). Postimpact tectonism resulted in deformation of the impact structure, and hence this melt body, causing overthrusting in the South Range (e.g., Shanks and Schwerdtner, 1991;Milkereit et al, 1994) and finally yielding an elliptically shaped bowl, the SIC. According to Lithoprobe investigations, the maximum depth of this bowl is 6 km below the present surface (e.g., Milkereit et al, 1994;Deutsch and Grieve, 1994).…”

Section: Introductionmentioning

confidence: 99%

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Sudbury impact event: Cratering mechanics and thermal history

Ivanov¹,

Deutsch²

1999

Large Meteorite Impacts and Planetary Evolution; II

129

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The Sudbury Igneous Complex (SIC) is interpreted as the solidified impact melt body of the 1.850-g.y.-old Sudbury impact structure. First results of cratering and thermal modeling for this ~250-km sized multi-ring structure are presented. The numerical calculations were done for the vertical impact of a stony (granite) body (cylindrical projectile, 12.5 km in diameter and height) impacting at a granite target with a velocity of 20 km s -1 . These simulations yield estimates of the transient cavity dimensions and the temperature field below the impact structure just after the modification stage. One-dimensional heat transfer modeling sets constraints for the thermal history of the impact melt. Cooling of the melt sheet, the present SIC, from the initial temperature of 2,000°K to the liquidus at 1,450°K lasted several 100 k.y, and below the solidus at 1,270°K, about 300 k.y. to 2 m.y., depending on the initial melt thickness H(SIC). The cooling sequence was modeled for H(SIC) of 2.5, 4, and 6 km. Given this long duration of cooling, postimpact tectonic processes during the Penokean orogeny may well have deformed the melt sheet prior to its final solidification. Prolonged cooling as well as this large-scale deformation may explain the present structural position and the composition of the Offset Dikes, consisting of differentiated impact melt.Ivanov, B. A.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sudbury impact event: Cratering mechanics and thermal history

Ivanov¹,

Deutsch²

1999

Large Meteorite Impacts and Planetary Evolution; II

129

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“…Based on the empirical relationship between the two (SU:D is about 1:10, Melosh and Ivanov 1999), Grieve and Therriault (2000) may have overestimated the size of this impact structure (D: minimum of 250-280 km assuming a SU of 26-38 km) as the component of orogenic deformation of rock uplift is not considered in their analysis. Partial exhumation of the Levack Gneiss Complex prior to impact explains also the presence of higher-grade metamorphic rocks underlying the North Range, despite the fact that rocks underlying the South Range were uplifted on the South Range Shear Zone, with respect to the North Range by about 10 to 15 km (Shanks and Schwerdtner 1991b).…”

Section: Pre-impact Tectonismmentioning

confidence: 99%

Structural characteristics of the Sudbury impact structure, Canada: Impact-induced versus orogenic deformation-A review

Riller

2005

Meteoritics &Amp; Planetary Science

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Abstract-Orogenic deformation, both preceding and following the impact event at Sudbury, strongly hinders a straightforward assessment of impact-induced geological processes that generated the Sudbury impact structure. Central to understanding these processes is the state of strain of the Sudbury Igneous Complex, the solidified impact melt sheet, its underlying target rocks, overlying impact breccias and post-impact sedimentary rocks. This review addresses (1) major structural, metamorphic and magmatic characteristics of the impact melt sheet and associated dikes, (2) attempts that have been made to constrain the primary geometry of the igneous complex, (3) modes of impactinduced deformation as well as (4) mechanisms of pre-and post-impact orogenic deformation. The latter have important consequences for estimating parameters such as magnitude of structural uplift, tilting of pre-impact (Huronian) strata and displacement on major discontinuities which, collectively,have not yet been considered in impact models. In this regard, a mechanism for the emplacement of Offset Dikes is suggested, that accounts for the geometry of the dikes and magmatic characteristics, as well as the occurrence of sulfides in the dikes. Moreover, re-interpretation of published paleomagnetic data suggests that orogenic folding of the solidified melt sheet commenced shortly after the impact. Uncertainties still exist as to whether the Sudbury impact structure was a peak-ring or a multi-ring basin and the deformation mechanisms of rock flow during transient cavity formation and crater modification.

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“…Neodymium isotope data (Faggart et ai., 1985) indicated for the first time that the SIC consists of remelted Archean crustal material and is compatible with an impact melt origin. Detailed mineralogical-geochemical studies and field work (e.g., Avennann, 1994;Avermann and Brockmeyer, 1992;Brockmeyer, 1990;MUller-Mohr, 1992; as well as new structural and geophysical data (e.g., Butler, 1994;Cowan and Schwerdtner, 1994;McGrath and Broome, 1994;Milkereit et ai., 1992;Roest and Pilkington, 1994;Shanks and Schwerdtner, 1991) have resulted in a consistent model, in which the Sudbury Structure is plausibly interpreted as the teetonised and deeply eroded remnant of an -250 km large multi-ring impact basin, with the SIC as a coherent but complex impact melt sheet within the inner ring (e.g., Brockmeyer, 1990;Grieve et ai., 1991;Masaitis, 1993;Deutsch and Grieve, 1994;Stoffler et al, 1994;Deutsch et ai., 1995). The geochemical complexity observed for the various lithologies, which were generated by impact melting,…”

Section: Geological Settingmentioning

confidence: 99%

Impact melt dikes in the Sudbury multi‐ring basin (Canada): Implications from uranium‐lead geochronology on the Foy Offset Dike

Osterman

Schärer

Deutsch

1996

Meteorit & Planetary Scien

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Abstract-To investigate the origin of Offset Dikes and their age relationships to major impact generated lithologies in the Sudbury multi-ring impact structure, such as the Main Mass of the Sudbury "Igneous" Complex, zircon and baddeleyite were dated by the V-Pb chronometer. The rocks analysed are one diorite and two quartz diorites from inside the Foy Offset, one quartz diorite from the contact zone, and two country rock samples collected at 10 and 30 m distances from the contact within the Levack Gneiss Complex. The 21 analysed zircon and baddeleyite fractions yield a crystallization age of 1852 +4/-3 (20-) Ma for the accessory minerals in the Foy Offset Dike and an age of2635 ± 5 Ma for the shocked Levack country rock, in which zircons show significant shock effects (multiple sets of planar fractures), in contrast to the totally unshocked zircons of the Offset Dike. Within given errors, the new age of 1852 Ma is identical to the pooled 1850 ± I Ma V-Pb age determined by Krogh et al. (1984) as the crystallization age of accessory phases in different lithologies of the Sudbury "Igneous" Complex, which has been interpreted to represent the coherent impact melt sheet of the Sudbury Structure. This excellent agreement of the ages substantiates that emplacement of the Offset Dikes occurred coevally with the formation of the impact melt sheet. Total absence of inherited zircons in the central part of the Foy Offset indicates melting of the precursor material at temperatures well above 1700 DC, which emphasizes the origin of the dike lithologies by impact melting.

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Crude quantitative estimates of the original northwest–southeast dimension of the Sudbury Structure, south-central Canadian Shield

Cited by 37 publications

References 8 publications

Sudbury impact event: Cratering mechanics and thermal history

Sudbury impact event: Cratering mechanics and thermal history

Structural characteristics of the Sudbury impact structure, Canada: Impact-induced versus orogenic deformation-A review

Impact melt dikes in the Sudbury multi‐ring basin (Canada): Implications from uranium‐lead geochronology on the Foy Offset Dike

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