scholarly journals Reconstruction of the flanks of the Mid-Atlantic Ridge, 28° to 29°N: Implications for evolution of young oceanic lithosphere at slow-spreading centers

2004 ◽  
Vol 5 (9) ◽  
pp. n/a-n/a ◽  
Author(s):  
Heather Sloan ◽  
Philippe Patriat
Keyword(s):  
Oceanic Lithosphere ◽  
Mid Atlantic Ridge ◽  
Slow Spreading ◽  
Spreading Centers

The Heterogeneous Tethyan Oceanic Lithosphere of the Alpine Ophiolites

Elements ◽  
2021 ◽  
Vol 17 (1) ◽  
pp. 23-28 ◽  
Author(s):  
Elisabetta Rampone ◽  
Alessio Sanfilippo
Keyword(s):  
Oceanic Lithosphere ◽  
Passive Margin ◽  
Crustal Material ◽  
Crustal Accretion ◽  
Mantle Dynamics ◽  
Western Tethys ◽  
Mantle Peridotites ◽  
Slow Spreading ◽  
Tethys Ocean ◽  
Basaltic Crust

The Alpine–Apennine ophiolites are lithospheric remnants of the Jurassic Alpine Tethys Ocean. They predominantly consist of exhumed mantle peridotites with lesser gabbroic and basaltic crust and are locally associated with continental crustal material, indicating formation in an environment transitional from an ultra-slow-spreading seafloor to a hyperextended passive margin. These ophiolites represent a unique window into mantle dynamics and crustal accretion in an ultra-slow-spreading extensional environment. Old, pre-Alpine, lithosphere is locally preserved within the mantle sequences: these have been largely modified by reaction with migrating asthenospheric melts. These reactions were active in both the mantle and the crust and have played a key role in creating the heterogeneous oceanic lithosphere in this branch of the Mesozoic Western Tethys.

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.

scholarly journals Quantifying tectonic strain and magmatic accretion at a slow spreading ridge segment, Mid-Atlantic Ridge, 29°N

1999 ◽  
Vol 104 (B5) ◽  
pp. 10421-10437 ◽  
Author(s):  
J. Escartín ◽  
P. A. Cowie ◽  
R. C. Searle ◽  
S. Allerton ◽  
N. C. Mitchell ◽  
...  
Keyword(s):  
Spreading Ridge ◽  
Mid Atlantic Ridge ◽  
Slow Spreading

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.

The ophiolites of the Tibetan Geotraverses, Lhasa to Golmud (1985) and Lhasa to Kathmandu (1986)

1988 ◽  
Vol 327 (1594) ◽  
pp. 215-238 ◽  
Keyword(s):  
Subduction Zone ◽  
Oceanic Lithosphere ◽  
Island Arc ◽  
Passive Margin ◽  
Jinsha River ◽  
Geochemical Composition ◽  
The North ◽  
Kunlun Mountains ◽  
Slow Spreading ◽  
Back Arc

Ophiolite belts are found in Tibet along the Zangbo, Banggong and Jinsha River Sutures and in the Anyemaqen mountains, the eastern extension of the Kunlun mountains. Where studied, the Zangbo Suture ophiolites are characterized by: apparently thin crustal sequences (3-3.5 k m ); an abundance of sills and dykes throughout the crustal and uppermost mantle sequences; common intraoceanic melanges and unconformities; and an N-MORB petrological and geochemical composition. The ophiolites probably formed within the main neo-Tethyan ocean and the unusual features may be due to proximity to ridge-transform intersections, rather than to genesis at very slow -spreading ridges as the current consensus suggests. The Banggong Suture ophiolites have a supra-subduction zone petrological and geochemical composition — although at least one locality in the Ado Massif shows MORB characteristics. However, it is also apparent that the dykes and lavas show a regional chemical zonation, from boninites and primitive island arc tholeiites in the south of the ophiolite belt, through normal island arc tholeiites in the central belt to island arc tholeiites transitional to N-MORB in the north. The ophiolites could represent fragments of a fore-arc, island arc, back-arc complex developed above a Jurassic, northward-dipping subduction zone and emplaced in several stages during convergence of the Lhasa and Qiangtang terranes. The ophiolites of the Jinsha River Suture have a N-MORB composition where analysed, but more information is needed for a proper characterization. The Anyemaqen ophiolites, where studied, have a within-plate tholeiite composition and may have originated at a passive margin: it is not, however, certain whether true oceanic lithosphere, as opposed to strongly attenuated continental lithosphere, existed in this region.

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