The Formation and Morphology of Discordant Zones
Abstract
Oceanic fracture zones, which are produced by transform faults (i.e., first order discontinuities), are well mapped globally and provide a record of the paleo-spreading direction between tectonic plates. Here we investigate smaller-offset, non-rigid (higher order) discontinuities, known as tectonic discordant zones. Discordant zones are produced by transform-like offsets that migrate along the ridges, resulting in wavy symmetrical discontinuities on the ridge flanks (e.g., Matthews et al., 2011). They are analogous to propagating rifts but are concentrated along slow- to intermediate-spreading ridges. Globally, the total length of discordant zones is about one quarter that of fracture zones. However, less than 1% of discordant zones have been mapped in high resolution (e.g., Grindlay et al., 1991). Given this data gap, many questions regarding the nature of discordant zones remain, including: What is the cause of the migration of higher order discontinuities, and are their motions coordinated? What length offsets are typical of second-order discontinuities, and how does the variation affect the morphology of the discordant zone? What are the different isostatic compensation mechanisms of discordant zones, and what governs this?
In this study, we use newly complied global satellite-derived gravity and multibeam bathymetry data to investigate these features in detail. We find, of active higher-order discontinuities producing discordant zones in the Atlantic and Indian basins, that the average offset length is about 30 km, but the distribution is non-Gaussian. Preliminary isostatic compensation models, using high resolution bathymetric data from the MH370 search (among others), show that the discordant zones have low elastic thickness of 7-10 km, consistent with their formation on very young seafloor adjacent to spreading ridges.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMEP51D1863H
- Keywords:
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- 1105 Quaternary geochronology;
- GEOCHRONOLOGYDE: 1130 Geomorphological geochronology;
- GEOCHRONOLOGYDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICSDE: 8177 Tectonics and climatic interactions;
- TECTONOPHYSICS