The Mid-Atlantic Ridge Near 45°N. XXIII. Analysis of Bathymetric and Magnetic Data

1975 ◽  
Vol 12 (3) ◽  
pp. 337-346 ◽  
Author(s):  
P. J. Bhattacharyya ◽  
R. D. Hyndman ◽  
M. J. Keen

Bathymetric and magnetic data obtained from the Mid-Atlantic Ridge near 45°N have been analyzed numerically to determine trends, offsets and local structure. The estimates of regional trends in the data reveal that the average structural trend in this area is 17°E of north, made up of nearly north–south segments periodically offset by small right lateral displacements. The east–west offsets, not always visually manifest in contour maps of the data have been located by a cross-correlation scheme. Frequent small offsets may be the way a ridge crest accommodates to a spreading direction not perpendicular to the general trend of the crest. There is evidence for an old, now dead spreading center to the west of the median valley. This old center with an orientation of about 15°W, terminating in a right lateral transform fault has been abandoned in favor of frequent small offsets which provide smaller resistance to spreading.

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>


2016 ◽  
Author(s):  
Ross P. Meyer ◽  
◽  
Joe H. Haxel ◽  
Robert P. Dziak ◽  
Deborah K. Smith

Geology ◽  
2021 ◽  
Author(s):  
Toru Yamasaki ◽  
Gen Shimoda ◽  
Kenichiro Tani ◽  
Jinichiro Maeda ◽  
Futoshi Nanayama

Recent reconstructions of global plate motions suggest that the Izanagi-Pacific Ridge was subducted along the eastern margin of Eurasia at ca. 50 Ma. In the Hidaka magmatic zone (HMZ), which was located at the northeastern end of the Eurasian plate, three magmatic pulses occurred (46–45, 40–36, and 19–18 Ma). We report whole-rock geochemical and Sr-Nd-Pb isotopic data for 36 Ma high-Sr/Y (adakitic) rocks from the HMZ and show that these rocks formed by partial melting of oceanic crust and were emplaced as near-trench intrusions during ridge subduction. We reevaluate the nature of plutonic rocks in the HMZ and show that both the 46–45 and 40–36 Ma granitoids have essentially identical geochemical features. The distribution of plutons and magmatic cessation between 45 and 40 Ma are best explained by subduction of a ridge-transform intersection with a large offset of the ridge axis. The boundary between the Eocene granitoids corresponds to the position of a paleo–transform fault, and adakitic magmatism was caused by partial melting triggered by slab tearing at an overlapping spreading center. The paleoridge-transform configuration coincides with the locations of later large faults and a peridotite body.


Displacements along strike slip faults in the ocean floor are measured by fitting magnetic anomaly patterns. In the northeastern Pacific Ocean the combined left lateral displacement of 1400 km across the Mendocino and the Pioneer faults can now be followed with a few interruptions from 140 to 165° W, or a distance of 2200 km. The western end of the correlatable pattern has not yet been reached. In latitude the pattern stretches between 28 and 41° N, or a distance of 1450 km. Right lateral displacements of 150 and 680 km separated by a disturbed zone have been measured on the Murray fault between 125 and 152° W. The disturbed zone occurs on the south side of the Murray fault. It is characterized by more rugged topography and is bordered by groups of volcanoes at its eastern and western boundaries. Across the faults the bathymetric contours are displaced in the same direction and roughly by the same amount as the magnetic intensity pattern. Fourteen magnetic profiles across the Mid-Atlantic Ridge between 30 and 6° S show a persistent magnetic anomaly on the crest of the ridge which can be followed from one profile to the next, whereas topographic features lack this continuity. Mapping the position of the crest anomaly suggests that if the ridge was originally continuous, it has now been cut into sections by strike slip faults.


1986 ◽  
Vol 91 (B3) ◽  
pp. 3334-3354 ◽  
Author(s):  
Ken. C. Macdonald ◽  
David A. Castillo ◽  
Stephen P. Miller ◽  
Paul J. Fox ◽  
Kim A. Kastens ◽  
...  

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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