scholarly journals RELIEF-FORMING FACTORS OF ATLANTIC OCEAN TRANSFORM FAULTS

2021 ◽  
pp. 41-57
Author(s):  
V.A. Bogolyubsky ◽  
◽  
E.P. Dubinin ◽  
S.Yu. Sokolov ◽  
◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Deep Structure ◽  
Morphometric Parameters ◽  
Active Part ◽  
Transform Fault ◽  
Transform Faults ◽  
Bathymetric Data ◽  
Analogue Modeling ◽  
Mid Atlantic Ridge ◽  
Axis Offset

Transform faults are widespread within the Atlantic Ocean. Their relief is determined by a variety of factors related mainly to the peculiarities of the deep structure of the lithosphere and regional geodynamics. The degree of their influence changes when passing from one morphotectonic province of the Atlantic Ocean to another. The differences are manifested in the morphology of the main elements of the transform fault and the correlation of their morphometric parameters with the length of the active part, which was shown earlier by analogue modeling. The dependence between the depth of the transform valley and the axis offset of the Mid-Atlantic Ridge along the transform fault has been revealed. Variations in the values of morphometric parameters are interpreted as a consequence of different duration of fault development, as well as different degrees of influence of secondary factors within each of the provinces. Based on the analysis of the bathymetric data on the Atlantic transform faults, five main groups of relief-forming factors are identified, and the relative degree of importance of the factors is determined for each of them. It is assumed that the identified dependences are preserved for the transform faults in other oceans.

The Southwell Topple – reassessment of a very large coastal toppling failure on the Isle of Portland, UK

2021 ◽  
pp. qjegh2020-146
Author(s):  
Alan P. Dykes ◽  
Edward N. Bromhead
Keyword(s):  
South Coast ◽  
Mass Movements ◽  
Transform Fault ◽  
The South ◽  
Transform Faults ◽  
Bathymetric Data ◽  
Central Depression ◽  
Toppling Failure

The Southwell Topple is a spectacular example of a toppling failure on the southeastern coastline of the Isle of Portland, on the south coast of England. Types of mass movements, which occur around almost the entire coastline of Portland and include some other much smaller but well-known topples, vary depending on local geological and topographic contexts. The ‘Southwell Landslide’ of 1734 (i.e. the Southwell Topple), differs in most respects from all the others, not least in its size. We examine the historical and geological contexts of the Southwell Topple in order to explain its origins and characteristics. The recently published bathymetric data from the DORIS project reveals the tectonic context for the landslide, particularly the frequent transform faults parallel to the southeastern coastline of Portland and the axis of the Shambles Syncline forming Portland's ‘central depression’. It appears that the Southwell Topple resulted from coast-parallel tectonic discontinuities – probably a single joint and/or transform fault – through the Portland Stone combined with preferential marine erosion of the underlying weaker Portland Sand.

scholarly journals Uppermost Mantle Velocity beneath the Mid-Atlantic Ridge and Transform Faults in the Equatorial Atlantic Ocean

2020 ◽  
Author(s):  
Guilherme W. S. de Melo ◽  
Ross Parnell-Turner ◽  
Robert P. Dziak ◽  
Deborah K. Smith ◽  
Marcia Maia ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Upper Mantle ◽  
Equatorial Atlantic ◽  
Uppermost Mantle ◽  
Transform Faults ◽  
Equatorial Atlantic Ocean ◽  
Mid Atlantic Ridge ◽  
Mantle Velocity ◽  
Ray Paths

ABSTRACT Seismic rays traveling just below the Moho provide insights into the thermal and compositional properties of the upper mantle and can be detected as Pn phases from regional earthquakes. Such phases are routinely identified in the continents, but in the oceans, detection of Pn phases is limited by a lack of long-term instrument deployments. We present estimates of upper-mantle velocity in the equatorial Atlantic Ocean from Pn arrivals beneath, and flanking, the Mid-Atlantic Ridge and across several transform faults. We analyzed waveforms from 50 earthquakes with magnitude Mw>3.5, recorded over 12 months in 2012–2013 by five autonomous hydrophones and a broadband seismograph located on the St. Peter and St. Paul archipelago. The resulting catalog of 152 ray paths allows us to resolve spatial variations in upper-mantle velocities, which are consistent with estimates from nearby wide-angle seismic experiments. We find relatively high velocities near the St. Paul transform system (∼8.4  km s−1), compared with lower ridge-parallel velocities (∼7.7  km s−1). Hence, this method is able to resolve ridge-transform scale velocity variations. Ray paths in the lithosphere younger than 10 Ma have mean velocities of 7.9±0.5  km s−1, which is slightly lower than those sampled in the lithosphere older than 20 Ma (8.1  km±0.3  s−1). There is no apparent systematic relationship between velocity and ray azimuth, which could be due to a thickened lithosphere or complex mantle upwelling, although uncertainties in our velocity estimates may obscure such patterns. We also do not find any correlation between Pn velocity and shear-wave speeds from the global SL2013sv model at depths <150  km. Our results demonstrate that data from long-term deployments of autonomous hydrophones can be used to obtain rare and insightful estimates of uppermost mantle velocities over hundreds of kilometers in otherwise inaccessible parts of the deep oceans.

PRELIMINARY FORESHOCK ANALYSIS OF SUBMARINE TRANSFORM FAULT EARTHQUAKES ALONG THE EQUATORIAL MID-ATLANTIC RIDGE

2016 ◽  
Author(s):  
Ross P. Meyer ◽  
◽  
Joe H. Haxel ◽  
Robert P. Dziak ◽  
Deborah K. Smith
Keyword(s):  
Transform Fault ◽  
Mid Atlantic Ridge

Evolution of migrating transform faults in anisotropic oceanic crust: examples from Iceland

2019 ◽  
Vol 56 (12) ◽  
pp. 1297-1308 ◽  
Author(s):  
Jeffrey A. Karson ◽  
Bryndís Brandsdóttir ◽  
Páll Einarsson ◽  
Kristján Sæmundsson ◽  
James A. Farrell ◽  
...  
Keyword(s):  
Plate Boundary ◽  
Fault Zones ◽  
Plate Boundaries ◽  
Transform Fault ◽  
Eurasian Plate ◽  
Transform Faults ◽  
The North ◽  
Rift Propagation ◽  
Oriented Parallel ◽  
Ocean Ridge

Major transform fault zones link extensional segments of the North American – Eurasian plate boundary as it transects the Iceland Hotspot. Changes in plate boundary geometry, involving ridge jumps, rift propagation, and related transform fault zone migration, have occurred as the boundary has moved relative to the hotspot. Reconfiguration of transform fault zones occurred at about 6 Ma in northern Iceland and began about 3 Ma in southern Iceland. These systems show a range of different types of transform fault zones, ranging from diffuse, oblique rift zones to narrower, well-defined, transform faults oriented parallel to current plate motions. Crustal deformation structures correlate with the inferred duration and magnitude of strike-slip displacements. Collectively, the different expressions of transform zones may represent different stages of development in an evolutionary sequence that may be relevant for understanding the tectonic history of plate boundaries in Iceland as well as the structure of transform fault zones on more typical parts of the mid-ocean ridge system.

A new approach to the opening of the eastern Mediterranean Sea and the origin of the Hellenic Subduction Zone. Part 1: The eastern Mediterranean Sea

2019 ◽  
Vol 56 (11) ◽  
pp. 1119-1143 ◽  
Author(s):  
Xavier Le Pichon ◽  
A.M. Celâl Şengör ◽  
Caner İmren
Keyword(s):  
Mediterranean Sea ◽  
Eastern Mediterranean ◽  
Transform Fault ◽  
Northern Boundary ◽  
Transform Faults ◽  
Southern Boundary ◽  
New Approach ◽  
Eastern Mediterranean Sea ◽  
Lateral Shearing ◽  
Central Atlantic

We identify long transform faults that frame the eastern Mediterranean Sea and that were active during Jurassic and probably the Early Cretaceous, during the opening of the central Atlantic Ocean. We show that the African margin of the eastern Mediterranean Sea is an 1800 km long transform fault that absorbed the Africa/Eurasia Jurassic left-lateral motion during the opening of the central Atlantic. We call this transform fault the Eastern Mediterranean South Transform fault (EMST). We identify two other transform faults that were active simultaneously and framed the eastern Mediterranean Sea during its formation. These are the Apulia Transform fault (AT) and the Eastern Mediterranean North Transform fault (EMNT). The AT, three hundred km north of the EMST, followed the southern boundary of the Apulia block. Still 300 km farther north, the EMNT formed the northern boundary of this eastern Mediterranean shear zone. This last fault has been destroyed over a large portion by the Hellenic subduction. We relate these transform faults to the kinematics of the Jurassic Africa/Eurasia motion. We conclude that the eastern Mediterranean Sea is a long pull-apart created by left-lateral shearing of the Adria block as it was structurally linked to Africa.

Deep-tow studies of the Vema Fracture Zone: 1. Tectonics of a major slow slipping transform fault and its intersection with the Mid-Atlantic Ridge

1986 ◽  
Vol 91 (B3) ◽  
pp. 3334-3354 ◽  
Author(s):  
Ken. C. Macdonald ◽  
David A. Castillo ◽  
Stephen P. Miller ◽  
Paul J. Fox ◽  
Kim A. Kastens ◽  
...  
Keyword(s):  
Fracture Zone ◽  
Transform Fault ◽  
Mid Atlantic Ridge

Surveying the flanks of the Mid-Atlantic Ridge: the Atlantis Basin, North Atlantic Ocean (36°N)

2004 ◽  
Vol 209 (1-4) ◽  
pp. 199-222 ◽  
Author(s):  
T.M. Alves ◽  
T. Cunha ◽  
S. Bouriak ◽  
A. Volkonskaya ◽  
J.H. Monteiro ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Mid Atlantic Ridge

Petrology of a transform fault zone and adjacent ridge segments

1971 ◽  
Vol 268 (1192) ◽  
pp. 423-441 ◽  
Keyword(s):  
Oceanic Crust ◽  
Fault Zone ◽  
Fracture Zone ◽  
Volcanic Eruptions ◽  
Spreading Ridge ◽  
Transform Fault ◽  
Transform Faults ◽  
Near Surface ◽  
The North ◽  
Transform Fault Zone

The Verna Fracture Zone in the North Atlantic (9 to 11° N), which has been identified as a transform fault zone, contains exposures of serpentinized peridotites, while its adjacent ridge segments are floored mainly by typical abyssal ocean ridge basalts. This petrologic contrast correlates with the greater frequency of volcanic eruptions along the actively spreading ridge segments compared to the transform fault zone. Where rifting components occur across transform faults, exposures of the deeper zone of oceanic crust may result. The bathymetry of the Verna Fracture Zone suggests that some uplift parallel to the fracture zone as well as rifting led to exposures of deeper rocks. The basalts from the adjacent ridge axes contain ‘xenocrysts’ of plagioclase and olivine and more rarely of chromite. These appear to have a cognate origin, perhaps related to cooling and convection in near surface magma chambers. The basalts from the ridge axes, offset and on opposite sides of the transform fault, have similar features and compositions. The plagioclase peridotites have mineralogical features which indicate equilibration in the plagioclase pyrolite facies, suggesting maximum equilibration depths of around 30 km for a temperature of around 1200 °C. The chemical characteristics of the Vema F.Z. peridotites suggest that they may be undifferentiated mantle, emplaced as a subsolidus hot plastic intrusion or as a crystal mush. The abundance of peridotites and serpentinized peridotites is believed to reflect their abundance in seismic layer three of the oceanic crust.

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