Segmentation and morphotectonic variations along a slow-spreading center: The Mid-Atlantic Ridge (24�00? N? 30�40? N)

1993 ◽  
Vol 15 (3) ◽  
pp. 153-200 ◽  
Author(s):  
Jean-Christophe Semp�r� ◽  
Jian Lin ◽  
Holly S. Brown ◽  
Hans Schouten ◽  
G. M. Purdy
2021 ◽  
Author(s):  
Sofia Panasiuk ◽  
Melissa O. Anderson ◽  
Ármann Höskuldsson ◽  
Fernando Martinez ◽  
Dominik Pałgan

<p>The Reykjanes Ridge is a spreading center that presents an opportunity to track the dynamic formation of structural and volcanic features at an asymmetric slow-spreading plate boundary. The ridge spans the northern ~1000 km of the Mid Atlantic Ridge and has been spreading at a full spreading rate of ~20 mm/year [1]. The characteristic along-ridge basement depth, crustal thickness, and chemical gradient have been variably attributed to an active mantle plume beneath Iceland, or a passive mantle anomaly pre-dating the rifting [1]. A unique feature of the ridge is that it spreads obliquely to the spreading axis: a consequence of the change in spreading direction from ~125<sup>o </sup>to ~100<sup>o</sup> due to the failure of the triple junction between the Greenland, Eurasian, and North American plates 37 Mya [2]. Along with the sudden change in orientation, disjunct ridge segments were formed and separated by transform faults which have been continuously eliminating from north to south, thereby re-establishing the original linear geometry of the ridge [1]. The Bight Transform Zone is the final remaining transform fault and constitutes the boundary between the southern Reykjanes Ridge and the northern Mid-Atlantic Ridge. Despite the termination of strike-slip transform fault motion, the ridge remains in a state of active tectonic deformation as demonstrated by the time-dependant orientations of linear structures, lengths of spreading segments, and deviation from the previously asserted linear continuity of the ridge. Investigating the relationship between structures, volcanism, and regional geodynamics is possible with the application of a novel remote-predictive geological mapping method based on interpretations from newly acquired bathymetric and acoustic backscatter data. Notably, the bathymetric data provides significant high-resolution coverage of both on-axis and off-axis regions, allowing us to track the evolution of the ridge for up to 13 Mya. The acoustic backscatter data aids in the interpretation of geologic features and terrains whose distribution and morphology reflect both present-day and historic ridge dynamics. This analysis will produce new insight into the on-going first and second-order deformation of the Reykjanes Ridge, its controls, and its effects on diffuse low-temperature vs. focused high-temperature hydrothermal venting.</p><p>[1] Martinez et al., 2020. Reykjanes Ridge evolution: Effects of plate kinematics, small-scale upper mantle convection, and a regional mantle gradient. Earth-Science Reviews.</p><p>[2] Jones, Stephen M., 2003. Test of a ridge–plume interaction model using oceanic crustal structure around Iceland. Earth and Planetary Science Letters.</p>


Geology ◽  
2020 ◽  
Author(s):  
Clément de Sagazan ◽  
Jean-Arthur Olive

The stabilizing effect of surface processes on strain localization, albeit predicted by several decades of geodynamic modeling, remains difficult to document in real tectonic settings. Here we assess whether intense sedimentation can explain the longevity of the normal faults bounding the Andaman Sea spreading center (ASSC). The structure of the ASSC is analogous to a slow-spreading mid-ocean ridge (MOR), with symmetric, evenly spaced axis-facing faults. The average spacing of faults with throws ≥100 m (8.8 km) is however large compared to unsedimented MORs of commensurate spreading rate, suggesting that sedimentation helps focus tectonic strain onto a smaller number of longer-lived faults. We test this idea by simulating a MOR with a specified fraction of magmatic plate separation (M), subjected to a sedimentation rate (s) ranging from 0 to 1 mm/yr. We find that for a given M ≥ 0.7, increasing s increases fault lifespan by ~50%, and the effect plateaus for s > 0.5 mm/yr. Sedimentation prolongs slip on active faults by leveling seafloor relief and raising the threshold for breaking new faults. The effect is more pronounced for faults with a slower throw rate, which is favored by a greater M. These results suggest that sedimentation-enhanced fault lifespan is a viable explanation for the large spacing of ASSC faults if magmatic input is sufficiently robust. By contrast, longer-lived faults that form under low M are not strongly influenced by sedimentation.


1999 ◽  
Vol 104 (B5) ◽  
pp. 10421-10437 ◽  
Author(s):  
J. Escartín ◽  
P. A. Cowie ◽  
R. C. Searle ◽  
S. Allerton ◽  
N. C. Mitchell ◽  
...  

1978 ◽  
Vol 15 (12) ◽  
pp. 1930-1940 ◽  
Author(s):  
M. J. Clark ◽  
J. M. Hall ◽  
J. W. Peirce

Rock and paleomagnetic measurements have been made on a set of 54 basalts dredged from 17 stations located within the central valley of the Cayman Trough. Seventeen of the samples could be oriented with respect to the in situ vertical by the use of lava cooling ledges and stalactites.Peak remanent intensities in the Cayman Trough are lower than peak Mid-Atlantic Ridge values by a factor of 2 or 3 even after allowance is made for the latitudinal variation in geomagnetic field intensity. This difference is likely to be the result of the combined effects of relatively low saturation magnetization and more advanced low temperature oxidation of titanomagnetite in the Cayman Trough basalts.Five young, reversely magnetized basalts, similar to those found on the Mid-Atlantic Ridge, occur in the Cayman Trough sample set.Plots of the magnetic parameters of the pillow basalts with distance from the axis of the trough show broad highs or lows associated with the axis. Our interpretation is that crustal formation in the central valley has occurred recently, but it has either been rather diffuse or is now much disturbed tectonically on a small scale in comparison with the Mid-Atlantic Ridge. Analysis of the distribution of Curie temperatures suggests that crustal accretion has been slow (0.1–0.4 cm year−1 half-rate) and may have ceased in the area studied at about 0.6 Ma BP.


1994 ◽  
Vol 121 (3-4) ◽  
pp. 451-468 ◽  
Author(s):  
Peter J. Michael ◽  
Donald W. Forsyth ◽  
Donna K. Blackman ◽  
Paul J. Fox ◽  
Barry B. Hanan ◽  
...  

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