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.

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.

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.

Array of Thermoelectric Coolers for On-Chip Thermal Management

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
Owen Sullivan ◽  
Man Prakash Gupta ◽  
Saibal Mukhopadhyay ◽  
Satish Kumar
Keyword(s):  
Steady State ◽  
Current Pulse ◽  
Hot Spots ◽  
Hot Spot ◽  
High Amplitude ◽  
Peak Temperature ◽  
Thermoelectric Coolers ◽  
Electronic Package ◽  
Current Pulses ◽  
On Chip

Site-specific on-demand cooling of hot spots in microprocessors can reduce peak temperature and achieve a more uniform thermal profile on chip, thereby improve chip performance and increase the processor’s life time. An array of thermoelectric coolers (TECs) integrated inside an electronic package has the potential to provide such efficient cooling of hot spots on chip. This paper analyzes the potential of using multiple TECs for hot spot cooling to obtain favorable thermal profile on chip in an energy efficient way. Our computational analysis of an electronic package with multiple TECs shows a strong conductive coupling among active TECs during steady-state operation. Transient operation of TECs is capable of driving cold-side temperatures below steady-state values. Our analysis on TEC arrays using current pulses shows that the effect of TEC coupling on transient cooling is weak. Various pulse profiles have been studied to illustrate the effect of shape of current pulse on the operation of TECs considering crucial parameters such as total energy consumed in TECs peak temperature on the chip, temperature overshoot at the hot spot and settling time during pulsed cooling of hot spots. The square root pulse profile is found to be the most effective with maximum cooling and at half the energy expenditure in comparison to a constant current pulse. We analyze the operation of multiple TECs for cooling spatiotemporally varying hot spots. The analysis shows that the transient cooling using high amplitude current pulses is beneficial for short term infrequent hot spots, but high amplitude current pulse cannot be used for very frequent or long lasting hot spots.

scholarly journals Morphotectonics of the Mascarene Islands

1998 ◽  
Vol 41 (2) ◽  
Author(s):  
R. Hantke ◽  
A. E. Scheidegger
Keyword(s):  
Indian Ocean ◽  
Stress Field ◽  
Fracture Zone ◽  
Hot Spot ◽  
Ocean Bottom ◽  
Fracture Zones ◽  
Mascarene Islands ◽  
The Indian Ocean ◽  
Close Fit

A study is made of the orientations (strikes/trends) of joints, valleys, ridges and lineaments, i.e. of the (potentially) morphotectonic features, of the Mascarene Islands (Reunion, Mauritius and Rodrigues) in the Indian Ocean. It turns out that a connection exists between these features on all islands. For the joints alone, the results for Mauritius as a whole agree closely with those for Rodrigues as a whole, and also partially with those of Reunion. Inasmuch as the trends of the valleys, ridges and lineaments are related to the trends (strikes) of the joints, a common morphotectonic predesign seems to be present for all features studied. The morphotectonic orientations on the island also agree closely with the trends of fracture zones, ridges and trenches in the nearby ocean bottom; which has had a bearing on the theories of the origin of the Mascarene Islands. Generally, a hot-spot origin is preferred for Reunion, and may be for Mauritius as well, although differing opinions have also been voiced. The dynamics of a hot-spot is hard to reconcile with the close fit of the joint strikes in Réunion with the trends of the Madagascar and Rodrigues fracture zones. The closely agreeing joint maxima in Mauritius and Rodrigues í across the deep Mauritius trench í also agree with the trend of that trench and with the trend of the Rodrigues fracture zone. Thus, it would appear as most likely that the trends of joints and of fracture zones are all part of the same pattern and are due to the same cause: viz. to action of the neotectonic stress field.

scholarly journals Structure and evolution of the Jan Mayen Microcontinent

2020 ◽  
Author(s):  
Anke Dannowski ◽  
Michael Schnabel ◽  
Udo Barckhausen ◽  
Dieter Franke ◽  
Martin Thorwart ◽  
...  
Keyword(s):  
Continental Crust ◽  
Oceanic Crust ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
Magnetic Anomalies ◽  
High Amplitude ◽  
Total Width ◽  
Ocean Bottom ◽  
East Greenland ◽  
The North

<p>The Jan Mayen Ridge (JMR) is a 150-km-long and 10–30 km wide seafloor expression in N-S direction in the centre of the North Atlantic and part of the Jan Mayen Microcontinent (JMMC). Previous studies show that the eastern flank of the JMR was formed during the breakup of the Norway Basin along today’s Aegir Ridge, prior to magnetic anomaly C23 (~50 Ma). The western margin of the JMMC is conjugate to East Greenland. Rifting gradually propagated northward, likely from Chron C21 (~46 Ma) onward. Fan-shaped magnetic anomalies in the Norway Basin suggest that the JMMC must have rotated counter-clockwise. The JMR is likely underlain by continental crust. Volcanic flows have been observed within the sediments in the Jan Mayen Basin (JMB). While a relatively uniform upper crust was observed throughout the JMMC, the thickness of the lower continental crust varies significantly from up to 15 km below the JMR down to almost zero thickness towards the western part of the JMB. However, the character of the lower crust and the development of the conjugate East Greenland – JMMC margins during Oligocene are still disputed.</p><p>Here, we investigate the crustal structure of the JMMC using a new 265-km-long seismic refraction line crossing the JMMC at 69.7°N in E-W direction, which was acquired on board of RV Maria S. Merian during cruise MSM67. The profile consists of 30 ocean bottom seismometers (OBS) with a spacing of 9.5 km. The dataset was complemented by on-board gravity measurements and a magnetometer array towed behind the vessel during shooting. The line extends from oceanic crust in the Norway Basin, across the microcontinent and into oceanic crust that formed at the presently active mid-oceanic Kolbeinsey Ridge. The magnetic profile shows old seafloor spreading anomalies in the east (likely anomaly 24, ~52 Ma), then low amplitude magnetic anomalies in the central portion of the profile, which are typical for many plutonic continental rocks. On the western part of the profile, high amplitude anomalies of younger oceanic crust (likely anomalies C5C trough C6, ~19–16 Ma) are recognized near the western termination of the JMB. The seismic velocity distribution and crustal thickness vary strongly along the profile, with velocities typical for oceanic crust at either end of the profile and a thickened crust (12–13 km) underneath the JMR. This suggests that the JMMC consists of thinned continental crust with a total width of 100 km.</p>

scholarly journals Oceanic fracture zones do not provide deep sections in the crust

1976 ◽  
Vol 13 (9) ◽  
pp. 1223-1235 ◽  
Author(s):  
J. Francheteau ◽  
P. Choukroune ◽  
R. Hekinian ◽  
X. Le Pichon ◽  
H. D. Needham
Keyword(s):  
Oceanic Crust ◽  
Fracture Zone ◽  
Fault System ◽  
Published Data ◽  
Transform Domain ◽  
Average Thickness ◽  
Fracture Zones ◽  
Transform Fault ◽  
The Third ◽  
Layer 2

Data from rock-dredging have often been used to infer that oceanic fracture zones provide a 'window' into layers of the oceanic crust lying at a depth below the surface that is approximately equivalent to the vertical offset of the fracture zone, and thus permit the reconstruction of a crustal stratigraphy for the whole of acoustic layer 2 (commonly considered to have an average thickness of ~2 km) and, in some interpretations, for the upper part of layer 3. Alternatively, it has been suggested that fracture zones are preferential sites of serpentinite mega-dykes differing in composition from layer 3 but containing inclusions of the third layer. The published data indicate that basalts and basaltic rubble are abundant in fracture zones and, on analysis, do not justify the assumptions that have been made. The structure of fracture zones limits the possible extent of crustal sections exposed on their walls. Moreover, it is suggested that rocks of different layers of the lithosphere can be emplaced in the transform domain due to the dynamic of the transform fault system, itself.

Geophysical observations of the northern Juan de Fuca Ridge system: lessons in sea-floor spreading

1993 ◽  
Vol 30 (2) ◽  
pp. 278-300 ◽  
Author(s):  
E. E. Davis ◽  
R. G. Currie
Keyword(s):  
Oceanic Crust ◽  
Plate Tectonics ◽  
Hydrothermal Systems ◽  
Juan De Fuca Ridge ◽  
Plate Boundaries ◽  
Plate Motions ◽  
Sea Floor ◽  
Fuca Ridge ◽  
Juan De Fuca ◽  
Sea Floor Spreading

By virtue of its proximity to the coastline of North America and to numerous oceanographic institutions, the Juan de Fuca Ridge has been the focus of a large number of marine geological, geochemical, and geophysical investigations. Systematic studies began in the early 1960's with the geophysical survey of A. D. Raff and R. G. Mason, which provided much of the foundation for the development of the extraordinarily successful paradigms of sea-floor spreading and plate tectonics. Subsequent systematic and detailed studies of the plates and plate boundaries of the area by investigators from many academic, industrial, and government agencies, including the Geological Survey of Canada, have provided the basis for much of the fundamental understanding we now have of global plate motions and the processes that are involved in the creation of new oceanic crust at sea-floor spreading centres. Much of the success of these studies can be attributed to the geological diversity found along the Juan de Fuca Ridge. Clear examples are present of "normal" volcanically robust ridge segments, deep extensional rift valleys, stable and evolving transform faults, nontransform ridge offsets, propagating rifts, and off-axis seamount chains. Much has been learned about the nature of hydrothermal circulation through intensive studies of the many active hydrothermal systems and mature hydrothermal deposits that occur in both unsedimented and sedimented environments along the ridge. Better understanding of the way that oceanic crust chemically and physically "ages" is emerging from studies on the ridge and ridge flank. A clear history of the evolution of the ridge and of plate motions is provided by the magnetic anomalies mapped over the ridge and adjacent plates. From this history, lessons have been learned about the causes and consequences of plate motions, fragmentation, and internal deformation. Some of the success of these studies can be attributed to the rapidly evolving geophysical tools which provide ever increasing efficiency of operation and resolution. A new phase of study most recently begun involves the deployment of sea-floor geophysical "observatories" that provide a means by which temporal variations and events can be monitored over extended periods of time. These new studies are expected to yield yet another level of understanding of the processes that have produced two thirds of the Earth's surface as well as many important geologic formations in terrestrial settings.

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