Magnetic anomalies south of the Murray Fracture Zone: New evidence for a secondary sea-floor spreading center and strike-slip movement

1971 ◽  
Vol 76 (26) ◽  
pp. 6265-6275 ◽  
Author(s):  
Alexander Malahoff ◽  
David W. Handschumacher
Keyword(s):  
Fracture Zone ◽  
Magnetic Anomalies ◽  
Strike Slip ◽  
Spreading Center ◽  
Sea Floor ◽  
Sea Floor Spreading ◽  
New Evidence ◽  
Strike Slip Movement

Comoros – New Evidence and Arguments for Continental Crust

2016 ◽  
Author(s):  
John Milsom ◽  
Phil Roach ◽  
Chris Toland ◽  
Don Riaroh ◽  
Chris Budden ◽  
...  
Keyword(s):  
Continental Crust ◽  
Fracture Zone ◽  
Seismic Data ◽  
Gravity Anomalies ◽  
Magnetic Anomalies ◽  
Magnetic Data ◽  
The West ◽  
Sea Floor ◽  
Inappropriate Use ◽  
Sea Floor Spreading

ABSTRACT As part of an ongoing exploration effort, approximately 4000 line-km of seismic data have recently been acquired and interpreted within the Comoros Exclusive Economic Zone (EEZ). Magnetic and gravity values were recorded along the seismic lines and have been integrated with pre-existing regional data. The combined data sets provide new constraints on the nature of the crust beneath the West Somali Basin (WSB), which was created when Africa broke away from Gondwanaland and began to move north. Despite the absence of clear sea-floor spreading magnetic anomalies or gravity anomalies defining a fracture zone pattern, the crust beneath the WSB has been generally assumed to be oceanic, based largely on regional reconstructions. However, inappropriate use of regional magnetic data has led to conclusions being drawn that are not supported by evidence. The identification of the exact location of the continent-ocean boundary (COB) is less simple than would at first sight appear and, in particular, recent studies have cast doubt on a direct correlation between the COB and the Davie Fracture Zone (DFZ). The new high-quality reflection seismic data have imaged fault patterns east of the DFZ more consistent with extended continental crust, and the accompanying gravity and magnetic surveys have shown that the crust in this area is considerably thicker than normal oceanic and that linear magnetic anomalies typical of sea-floor spreading are absent. Rifting in the basin was probably initiated in Karoo times but the generation of new oceanic crust may have been delayed until about 154 Ma, when there was a switch in extension direction from NW-SE to N-S. From then until about 120 Ma relative movement between Africa and Madagascar was accommodated by extension in the West Somali and Mozambique basins and transform motion along the DFZ that linked them. A new understanding of the WSB can be achieved by taking note of newly-emerging concepts and new data from adjacent areas. The better-studied Mozambique Basin, where comprehensive recent surveys have revealed an unexpectedly complex spreading history, may provide important analogues for some stages in WSB evolution. At the same time the importance of wide continent-ocean transition zones marked by the presence of hyper-extended continental crust has become widely recognised. We make use of these new insights in explaining the anomalous results from the southern WSB and in assessing the prospectivity of the Comoros EEZ.

New Evidence of the Dextral Strike-Slip Movement in the Liaohe Basin, China: Results from Sem Experiments

2001 ◽  
Vol 44 (6) ◽  
pp. 779-784
Author(s):  
Jia-Zeng SHAN ◽  
Hong-Jun SUN ◽  
Qian-Hua XIAO ◽  
Dao-Jing WANG ◽  
Kun XU ◽  
...  
Keyword(s):  
Strike Slip ◽  
Liaohe Basin ◽  
New Evidence ◽  
Dextral Strike Slip ◽  
Strike Slip Movement

Geology of the Northern End of Juan de Fuca Ridge and Sea-Floor Spreading

1974 ◽  
Vol 11 (10) ◽  
pp. 1384-1406 ◽  
Author(s):  
Sandra M. Barr ◽  
R. L. Chase
Keyword(s):  
Magnetic Anomaly ◽  
Fracture Zone ◽  
Juan De Fuca Ridge ◽  
Transform Fault ◽  
Sea Floor ◽  
Fuca Ridge ◽  
Juan De Fuca ◽  
Low Potassium ◽  
Sea Floor Spreading ◽  
Ocean Ridge

The northern end of Juan de Fuca Ridge consists of a series of basement ridges and valleys, inundated with sediment except for the axis of most recent sea-floor spreading. This axis is associated with the western of two branches of the Brunhes magnetic anomaly. The eastern branch of the magnetic anomaly is associated with a largely sediment-covered ridge, apparently produced by spreading early in the Brunhes Epoch. The intervening negative anomaly is probably caused by reversely magnetized rocks older than 0.7 m.y. Basalts dredged from the region of the northern end of Juan de Fuca Ridge have compositions typical of low-potassium ocean ridge basalts. They differ from basalts reported from the southern part of Juan de Fuca Ridge which have higher K2O, TiO2, FeOT, and FeOT/MgO. This difference is compatible with the hypothesis that a mantle plume exists under the southern part of the ridge. Distribution of earthquake epicenters suggests that the Queen Charlotte Fault Zone presently extends south of Explorer Ridge to intersect Juan de Fuca Ridge at 49°N and that the Sovanco Fracture Zone no longer functions as a transform fault.

Amplitudes of oceanic magnetic anomalies and the chemistry of oceanic crust: Synthesis and review of 'magnetic telechemistry'

1979 ◽  
Vol 16 (12) ◽  
pp. 2236-2262 ◽  
Author(s):  
P. R. Vogt
Keyword(s):  
Oceanic Crust ◽  
Fracture Zone ◽  
Hot Spots ◽  
Hot Spot ◽  
Magnetic Anomalies ◽  
High Amplitude ◽  
Fracture Zones ◽  
Juan De Fuca ◽  
Sea Floor Spreading ◽  
Ocean Ridge

A growing body of evidence suggests that certain areas of high-amplitude (H) sea-floor spreading-type magnetic anomalies reflect FeTi-enriched basalts of high remanent magnetization. A worldwide tabulation of these 'H-zones' is presented, together with a review of pertinent geochemical, rock magnetic, and deep-tow data relevant to the hypothesis of magnetic telechemistry.' H-zones are found in two tectonic settings: (1) along 102–103 km long sections of spreading axis close to hot spots; and (2) in narrow bands extending a few hundred kilometres along the edges of some fracture zones. Amplitudes in both provinces are 1.5 to 5, typically 2 to 3 times normal, and the hot spot H-zones are known from spreading half-rates of 0.6 to 3.7 cm yr−1 The highest amplitudes, magnetizations, and FeTi enrichment (up to 15–18% FeOT and 2–3% TiO2) seem to occur where both provinces overlap, i.e., where fracture zones occur near hot spots, for example along the Blanco Fracture Zone south of the Juan de Fuca hot spot and along the Inca Fracture Zone east of the Galapagos hot spot. The FeTi enrichment appears to reflect shallow-depth crystal fractionation (plagioclase, augite, and olivine), which is more extensive near hot spots, and more generally for fast-spreading ridges. H-zones presently affect at least 2.6 × 103 km, or 6.5% of the Mid-Ocean Ridge axis. However, the total known H-area of 8.5 × 105 km2 represents only 0.3% of oceanic crust. This suggests that older H-zones remain to be discovered, or/and that conditions favoring the formation of FeTi basalt and H-anomalies are more prevalent now than they have been on the average for the last 108 years. Evidence for the latter is provided by the known expansion of the magnetically well surveyed Juan de Fuca, Galapagos, and Yermak (Arctic) H-zones in the last 5 million years.

New estimates of rapid sea-floor spreading rates and the identification of young magnetic anomalies on the East Pacific rise, 6° and 11° S

1973 ◽  
Vol 19 (2) ◽  
pp. 225-229 ◽  
Author(s):  
David K. Rea ◽  
Jack Dymond ◽  
G. Ross Heath ◽  
Donald F. Heinrichs ◽  
Stephen H. Johnson ◽  
...  
Keyword(s):  
East Pacific Rise ◽  
Magnetic Anomalies ◽  
Sea Floor ◽  
East Pacific ◽  
Spreading Rates ◽  
Sea Floor Spreading

A discussion concerning the floor of the northwest Indian Ocean - A reconnaissance survey of the Murray Ridge

1966 ◽  
Vol 259 (1099) ◽  
pp. 187-197 ◽  
Keyword(s):  
Indian Ocean ◽  
Fracture Zone ◽  
Magnetic Measurements ◽  
Strike Slip ◽  
Substantial Contribution ◽  
Gulf Of Oman ◽  
Reconnaissance Survey ◽  
Line Spacing ◽  
Fault Scarps ◽  
Strike Slip Movement

Bathymetric and magnetic measurements at a 10-mile line spacing across the mouth of the Gulf of Oman have made a substantial contribution to knowledge of the area. A northeast-southwest alinement of bathymetric features, the presence of many fault scarps and the occurrence of elongated weakly magnetized seamounts similar to others farther south suggest that the Murray Ridge is continuous with the Owen fracture zone and support the idea that both are loci of strike-slip movement.

Origin of complex upper mantle structures in the southern Lewis Hills (Bay of Islands Ophiolite, Newfoundland)

1991 ◽  
Vol 28 (5) ◽  
pp. 774-787 ◽  
Author(s):  
Günter Suhr ◽  
Tom Calon ◽  
Sherry M. Dunsworth
Keyword(s):  
Fracture Zone ◽  
Upper Mantle ◽  
Oceanic Lithosphere ◽  
Strike Slip ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Small Scale ◽  
Spreading Ridge ◽  
Hill Area ◽  
Strike Slip Movement

The Springers Hill area (Lewis Hills, Bay of Islands Ophiolite) may represent oceanic lithosphere created in close proximity to the nontransform segment of an oceanic fracture zone. Upper mantle rocks exposed on Springers Hill were investigated to establish whether their development was affected by the thermal and rheological changes associated with oceanic fracture zones. Harzburgites of the Springers Hill area reveal complex structural patterns. On a small scale, foliations defined by orthopyroxene grains intersect foliations defined by spinel grains at various angles. Olivine petrofabric work demonstrates that only the spinel foliation is related to the preserved flow plane. The orthopyroxene foliation appears to be the result of pull-apart of formerly larger grains during high-temperature deformation. On the larger scale, orientation patterns of foliation, lineation, and dykes suggest that strike-slip movement occurred parallel and at high angle to the fracture- zone contact at various stages of a complex flow history. Given its location adjacent to a nontransform segment of oceanic lithosphere, the origin of the strike-slip movement parallel to the fracture zone must be clarified. It can be accounted for by movement of the older lithosphere past asthenosphere of the young spreading ridge during plate-driven flow.

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