Long-Term evolution of non-transform discontinuities at the Mid-Atlantic Ridge, 24°N - 27°30′N
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We studied long-term evolution of non-transform discontinuities (NTDs) on the Mid-Atlantic Ridge from 0 to ~20-25 Ma crust using plate reconstructions of multibeam bathymetry, long-range HMR1 sidescan sonar, residual mantle Bouguer gravity anomaly, and gravity-derived crustal thickness. NTDs have propagated north and south with respect to flowlines of relative plate motion and both rapidly and slowly compared to the half spreading rate, and at times they have been quasi-stable. Fast, short-term (<2 m.y.) propagation is driven by reduced magma supply (increased extension) in the propagating ridge tip when NTD ridge-axis offsets are small (<~ 5 km). Slow propagation can be much longer term. Some NTDs show classic structures of rift propagation including inner and outer pseudofaults and crustal blocks transferred between ridge flanks by discontinuous jumps of the propagating ridge tip. In all cases crustal transfer occurs within the NTD valley. Aside from ridge-axis offset, the evolution of NTDs appears to be controlled by three factors: (1) Gross volume and distribution of magma supplied to ridge segments as controlled by 3D heterogeneities in mantle fertility and/or dynamic upwelling; this controls fundamental ridge segmentation. (2) The lithospheric plumbing system through which magma is delivered to the crust. (3) The consequent focusing of tectonic extension in magma-poor parts of spreading segments, typically at segment ends, which can drive propagation. We also observe long-wavelength (5-10 m.y.) RMBA asymmetry between the conjugate ridge flanks, and we attribute this to asymmetric distribution of density anomalies in the upper mantle.
These datasets were used to interpret the evolution of non-transform discontinuities on the Mid-Atlantic Ridge (MAR). They include multibeam bathymetry, calculated non-isostatic topography, side-scan sonar data, free-air and residual mantle Bouguer gravity, and modeled crustal thickness on the MAR at 24 - 27°N.
Suggested CitationDataset: Zheng, Tingting, Tucholke, Brian E., Lin, Jian, "Long-Term evolution of non-transform discontinuities at the Mid-Atlantic Ridge, 24°N - 27°30′N", 2018-12, DOI:10.26025/z2z7-kd89, https://hdl.handle.net/1912/24315
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