Pop-Up Field in Lake Ontario Southeast of Toronto, Canada: Indicators of Late Glacial and Post-Glacial Strain
Abstract
A field of pop-ups in the Upper Ordovician Georgian Bay Formation is located in Lake Ontario south of Toronto Canada. A 1 km x 5 km area of these pop-ups (79o18'W to 79o26' W, 43o33'N to 43o36'N) has been surveyed extensively by high resolution boomer, side scan sonar, multibeam, and submersible. The pop-ups strike primarily NNW, WNW, ENE, NS and EW. The most prominent pop-ups have straight axes 1+ km long. The bathymetric relief across the axial zones is generally about 1-2m, although the structural relief at depth can be 5m+. Many of the narrow axial zones of the surficial pop-ups are located on deeper structural fractures at edges of structural blocks where the bedrock has undergone rigid body rotations. These blocks form much wider structures than the surficial pop-up, and include open anticlines, monoclines, thrusts and high angle faults. Pop-ups are generally younger than the last ice age, but post-glacial sediment onlaps the flanks of many of the pop-ups and larger structures, suggesting that some motion on these structures is not recent, and glacial till may be involved with a few of the pop-up structures. However, several pop-ups do not have a sediment veneer thick enough to be observed seismically. Submersible observations showed that bedrock pop-ups were covered by only a thin veneer of sediment. The pop-ups display master-abutting relationships similar to joint sets mapped onshore, suggesting that preexisting joint sets were utilized. That the sediment onlaps the flanks, but the axial zone appears relatively free of sediment, may indicate multiple motions on some of the pop-up structures, culminating with relatively recent strain. Other pop-ups are apparently relict (those with thick sediment across both the flanks and axial zone). The pop-ups appear to document ongoing deformation beginning with the end of the last ice age and continuing to relatively recently.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSM.S21A..03J
- Keywords:
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- 7205 Continental crust (1242);
- 7223 Seismic hazard assessment and prediction