Thermal and mechanical behaviour of the oceanic lithosphere constrained by geoid and gravity anomalies over the Mid-Atlantic Ridge axial valley

1987 ◽  
Vol 49 (1-2) ◽  
pp. 6-23 ◽  
Author(s):  
B. Lago
Keyword(s):  
Mechanical Behaviour ◽  
Gravity Anomalies ◽  
Oceanic Lithosphere ◽  
Mid Atlantic Ridge

Mantle thermal structure at northern Mid–Atlantic ridge from improved numerical methods and boundary conditions

2019 ◽  
Author(s):  
Marco Cuffaro ◽  
Edie Miglio ◽  
Mattia Penati ◽  
Marco Viganò
Keyword(s):  
Boundary Conditions ◽  
Thermal Structure ◽  
Oceanic Lithosphere ◽  
Geophysical Data ◽  
Mantle Flow ◽  
Viscous Forces ◽  
Versus Domain ◽  
Mid Atlantic Ridge ◽  
Velocity Constraints ◽  
New Formulation

Summary We computed mantle flow and thermal structure beneath a segment of the northern Mid-Atlantic ridge using numerical simulations adopting asymmetric spreading and ridge migration as boundary conditions. The objective is to obtain new insights on mantle processes acting at this ridge segment. We explored different lateral boundary conditions based on velocity, stress and stress-velocity constraints highlighting differences in the depth of the thermal base of the lithosphere versus domain width. Here, we propose a new formulation of lateral and bottom boundary conditions based on the choice of a proper tangential stress at the bottom and on lateral boundaries of the domain accounting for ridge migration. Moreover, dimensional analysis of governing equations suggests that heat generation due to work of the viscous forces cannot be neglected in the computations. Therefore, we included this thermal contribution into the numerical experiments providing an application to the northern Mid-Atlantic ridge at the reference latitude of 43 ○N. Results are compared with available geophysical data in the area, including also mantle tomography models. Asymmetric spreading and ridge migration in numerical modelling account for an asymmetric accretion of the oceanic lithosphere, supporting the evidence of the asymmetries described by geophysical data across the northern Mid-Atlantic ridge segments.

Distribution and evolution of uranium in the oceanic lithosphere

1979 ◽  
Vol 291 (1381) ◽  
pp. 423-431 ◽  
Keyword(s):  
Sea Water ◽  
Oceanic Lithosphere ◽  
Uranium Content ◽  
Major And Trace Elements ◽  
Ultramafic Rocks ◽  
Layer 2 ◽  
Secondary Enrichment ◽  
Layer 4 ◽  
Mid Atlantic Ridge ◽  
Fractionation Trend

Induced fission track techniques permit us to determine quantitatively the microscopic distribution of uranium in rocks, in their constituent minerals, and in percolating fluids. Both primary magmatic variations and secondary mobilization of uranium can be discerned. Concentrations of uranium in phenocrysts and fresh glasses of oceanic basalts and gabbros are very low (2-80 parts/10 9 ) and are comparable to concentrations in the same minerals of the associated ultramafic rocks. Variations with depth in D.S.D.P. holes show several distinct cyclic variations of uranium, accompanied by parallel trends in some major and trace elements. In Hole 332B (mid-Atlantic ridge, 36 °N), uranium and other elements can be shown to fall into two distinct groupings, each group following its own characteristic fractionation trend, suggesting that two distinct magmas differentiated independently beneath the median valley, the two magmas alternating in their contribution to the formation of oceanic layer 2. Earlier investigations of the uranium distribution in surface pillows and other dredged rocks exposed to sea water had shown that, owing to halmyrolysis, the uranium concentration increases systematically with distance from the axis of a midoceanic ridge. Subsequent investigations on rocks drilled from horizons deeper into oceanic layer 2 indicate that secondary enrichment or redistribution of uranium is confined to specific zones of altered basalt, near fractures, pillow and flow margins, and especially along horizontal planes of breccias and sediments in between massive flow where convective water circulation is thought to occur. Ultramafic rocks from the base of layer 3 and top of layer 4 are also enriched in uranium when hydrated by sea water during the process of serpentinization. A combination of these processes may double the uranium content of an oceanic lithospheric plate between the time of its formation and its eventual subduction.

CONDITIONS FOR CONJUGATED STRUCTURES OF DIAMANTINE AND LABUAN IN THE SOUTHEASTERN PARTOF THE INDIAN OCEAN (PHYSICAL MODELING)

2021 ◽  
Vol 43 (1) ◽  
pp. 20-28
Author(s):  
G. AGRANOV ◽  
E. DUBININ ◽  
A. GROKHOLSKII
Keyword(s):  
Indian Ocean ◽  
Physical Modeling ◽  
Experimental Studies ◽  
Gravity Anomalies ◽  
Oceanic Lithosphere ◽  
High Amplitude ◽  
Spreading Ridge ◽  
Southeastern Part ◽  
Antarctic Continent ◽  
The Indian Ocean

Conjugated Diamantin and Labuan structures located in the southeastern part of the Indian Ocean were formed as a result of the split of a single Australian-Antarctic continent and the continental rift movement towards the oceanic lithosphere of the Indian Ocean. The old oceanic lithosphere rift-induced destruction resulted in the formation of a new Southeast Indian spreading ridge. Areas of its initial formation on the old oceanic lithosphere record the Diamantin and Labuan suture zones separating blocks of the young and old lithosphere that in turn are expressed in an abruptly dissected topography and high-amplitude gravity anomalies. Experimental studies showed the formation of the conjugated zones of Diamantin and Labuan had occurred during the destruction of a powerful lithosphere under very slow stretching and spreading conditions.

Gravity anomalies of the Mid-Atlantic Ridge north of the Kane Fracture Zone

1996 ◽  
Vol 23 (23) ◽  
pp. 3431-3434 ◽  
Author(s):  
H. Fujimoto ◽  
N. Seama ◽  
J. Lin ◽  
T. Matsumoto ◽  
T. Tanaka ◽  
...  
Keyword(s):  
Fracture Zone ◽  
Gravity Anomalies ◽  
Mid Atlantic Ridge

The Mid-Atlantic Ridge Near 45 °N. XX. The Gravity Field

1972 ◽  
Vol 9 (8) ◽  
pp. 942-959 ◽  
Author(s):  
J. M. Woodside
Keyword(s):  
Gravity Data ◽  
Bouguer Anomaly ◽  
Gravity Anomalies ◽  
Spreading Rate ◽  
Survey Area ◽  
Free Air ◽  
Mid Atlantic Ridge ◽  
Sea Floor Spreading ◽  
Relationship Of ◽  
East West

Detailed maps of free-air, Bouguer, and residual gravity anomalies for a survey area 250 km wide across the Mid-Atlantic Ridge between 45° and 46 °N have been compiled. The Bouguer anomaly was terrain-corrected to a radius of 40 km. The residual anomaly was computed from the terrain-corrected Bouguer anomaly using an empirical linear relationship between the Bouguer anomaly and the bathymetry to predict a 'regional' Bouguer anomaly from the depth data. North–south and east–west trends in the gravity data are enhanced in the residual anomaly; and it is suggested that at least one short east–west transform fault may offset the ridge in a right-lateral sense. The offset is presumably a response to a change in sea-floor spreading direction from west–northwest/east–southeast to west/east about 10 m.y. ago. A change in spreading rate may have occurred at the same time. A difference in accretion rate on either side of the ridge axis is indicated by asymmetry in the gravity data and by differences in the topographic compensation across the axis. Variations in the relationship of terrain-corrected Bouguer anomaly to bathymetry within the survey area suggest that a density deficiency or buoyant forces in the upper mantle are responsible for the overall elevation of the crestal mountain region but that the topography of the high-fractured plateau may be partially compensated by undulations of the crust–mantle interface.

scholarly journals Global variation of seismic energy release with oceanic lithosphere age

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Nicolás Pinzón ◽  
Carlos A. Vargas
Keyword(s):  
Cross Sections ◽  
Thermal Evolution ◽  
Seismic Energy ◽  
Oceanic Lithosphere ◽  
Physical Factors ◽  
Additional Tool ◽  
Mid Ocean Ridge ◽  
Mid Atlantic Ridge ◽  
Spreading Rates ◽  
Ocean Ridge

AbstractVariations in Mid Ocean Ridge seismicity with age provide a new tool to understand the thermal evolution of the oceanic lithosphere. The sum of seismic energy released by earthquakes during a time, and for an area, is proportional to its lithospheric age. Asthenospheric temperatures emerge on ridge centers with new crust resulting in high seismic activity; thus, the energy released sum is highest on the young lithosphere and decreases with age. We propose a general model that relates the systematic variation of seismic energy released with the lithospheric age. Our analysis evaluates the main physical factors involved in the changes of energy released sum with the oceanic lithosphere age in MOR systems of different spreading rates. These observations are substantiated based on three cross-sections of the East Pacific Rise, six sections in the Mid Atlantic Ridge, and three profiles in the Central Indian Ridge. Our global model provides an additional tool for understanding tectonic processes, including the effects of seismicity and mid-plate volcanism, and a better understanding of the thermal evolution for the young oceanic lithosphere.

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