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首页> 外文期刊>Journal of geophysical research. Solid earth: JGR >Long-Term Evolution of Nontransform Discontinuities at the Mid-Atlantic Ridge, 24°N-27°30'N
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Long-Term Evolution of Nontransform Discontinuities at the Mid-Atlantic Ridge, 24°N-27°30'N

机译：中大西洋脊的非转换不连续的长期演变，24°N-27°30'n

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摘要

We studied long-term evolution of nontransform discontinuities (NTDs) on the Mid-Atlantic Ridge from 0- to ~20- to 25-Ma crust using plate reconstructions of multibeam bathymetry, long-range HMR1 sidescan sonar, residual mantle Bouguer gravity anomaly (RMBA), 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; at times they have been quasi-stable. Fast, short-term (<2 Myr) propagation is driven by reduced magma supply (increased tectonic extension) in the propagating ridge tip when NTD ridge-axis offsets are small (?5 km). Propagation at larger offsets generally is slower and longer term. These NTDs can 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 3-D 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 Myr) RMBA asymmetry between the conjugate ridge flanks, and we attribute this to asymmetric distribution of density anomalies in the upper mantle.
机译：我们使用Multibeam Bathymetry的板重建，远程HMR1 SideScan Sonar，剩余地幔Bouguer重力异常（ RMBA）和重力衍生的地壳厚度。 NTDS在北方和南方传播到相对板运动的流动线，与半传播速率快速且缓慢地繁殖;有时他们已经准稳定了。当NTD脊轴偏移较小时，快速，短期（<2 myr）传播通过减少的岩浆电源（增加构造延伸）在传播的脊尖端中减少（增加的构造延伸）（？5公里）。在较大偏移处的传播通常较慢且长期较慢。这些NTD可以示出裂缝传播的经典结构，包括内部和外部伪轴和外部伪轴和在脊之间传递的地壳块，通过传播脊尖的不连续跳跃在脊侧面之间传递。在所有情况下，在NTD谷内发生地壳转移。除了脊轴偏移之外，NTD的演变似乎是由三个因素控制的：（1）岩石段提供给脊段的总成积和分布，如搭便物生育和/或动态上升的3D异质性;这控制了基本的山脊分割。 （2）岩白管道系统，岩浆通过该系统送到外壳。 （3）随后在岩浆差的岩石部分差的岩石部件部分的重点，通常在段端部，其可以驱动传播。我们还观察到共轭脊侧面之间的长波长（5-10 myr）RMBA不对称，并且我们将这种情况归因于上部地幔中的密度异常的不对称分布。

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