Ancient melt extraction from the oceanic upper mantle revealed by Re–Os isotopes in abyssal peridotites from the Mid-Atlantic ridge

2006 ◽  
Vol 244 (3-4) ◽  
pp. 606-621 ◽  
Author(s):  
Jason Harvey ◽  
Abdelmouhcine Gannoun ◽  
Kevin W. Burton ◽  
Nick W. Rogers ◽  
Olivier Alard ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Melt Extraction ◽  
Os Isotopes ◽  
Mid Atlantic Ridge

Serpentinization at the Rainbow and Saldanha sites, Mid-Atlantic Ridge: Mineralogical, geochemical, and isotopic features

2019 ◽  
Vol 57 (5) ◽  
pp. 677-706
Author(s):  
Isabel Ribeiro da Costa ◽  
Frederick Joseph Wicks ◽  
Fernando J.A.S. Barriga
Keyword(s):  
Upper Mantle ◽  
Hydrothermal Activity ◽  
Isotopic Data ◽  
Geochemical Characterization ◽  
Textural Evolution ◽  
Mantle Peridotites ◽  
Carbonate Deposition ◽  
Mid Atlantic Ridge ◽  
Ree Patterns

Abstract The Rainbow hydrothermal field (36°14′N) and the Saldanha seamount (36°34′N), in the Mid-Atlantic Ridge (MAR), are tectonic exposures of serpentinized upper mantle peridotites, both associated with significant hydrothermal activity. On the basis of detailed mineralogical and geochemical characterization of serpentinites from both sites, several serpentinization-related issues are discussed in the present work. As expected in oceanic environments, most of the sampled rocks are lizardite-chrysotile serpentinites exhibiting a variety of pseudomorphic through non-pseudomorphic textures, such textural evolution probably being related to changing water/rock ratios during this retrograde process. Oxygen isotope temperatures indicate that the serpentinization took place at 300–200 °C; on the other hand, isotopic data suggest that replacement of early pseudomorphic lizardite by lizardite ± chrysotile non-pseudomorphic textures requires that temperatures and/or water/rock ratios are high enough to promote the necessary dissolution–recrystallization processes. Mass-balance calculations for olivine-serpentine and orthopyroxene-serpentine pairs provided a basis for establishing serpentinization reactions likely to have produced the present rocks. Moreover, these calculations also showed that, notwithstanding some noticeable loss of MgO from olivine and of SiO2 from orthopyroxene, serpentinization of both minerals implies volume increases on the order of 26–27%, therefore potentially promoting the overall expansion of the rock. The geochemical and isotopic features of the studied rocks indicate that unmodified seawater was responsible for the serpentinization of the MAR peridotites. However, the mineralogy and REE patterns of some of these serpentinites indicate occasional subsequent interaction of the serpentinized rocks with seawater at much lower temperatures (seafloor alteration, characterized by carbonate deposition and negative Ce anomalies), or with high-temperature ore-forming hydrothermal fluids (ore-forming alteration, characterized by sulfide precipitation and steep positive Eu anomalies).

scholarly journals Noble gas systematics in new popping rocks from the Mid-Atlantic Ridge (14°N): Evidence for small-scale upper mantle heterogeneities

2019 ◽  
Vol 519 ◽  
pp. 70-82 ◽  
Author(s):  
Sandrine Péron ◽  
Manuel A. Moreira ◽  
Mark D. Kurz ◽  
Joshua Curtice ◽  
Jerzy S. Blusztajn ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Noble Gas ◽  
Small Scale ◽  
Mantle Heterogeneities ◽  
Mid Atlantic Ridge

Upper mantle heterogeneity below the Mid-Atlantic Ridge, 0°–15°N

1992 ◽  
Vol 97 (B4) ◽  
pp. 4461 ◽  
Author(s):  
E. Bonatti ◽  
A. Peyve ◽  
P. Kepezhinskas ◽  
N. Kurentsova ◽  
M. Seyler ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Mantle Heterogeneity ◽  
Mid Atlantic Ridge

Upper Mantle Structure beneath the Mid-Atlantic Ridge from Regional Waveform Modeling

2020 ◽  
Vol 110 (1) ◽  
pp. 18-25 ◽  
Author(s):  
Ingo Grevemeyer
Keyword(s):  
Upper Mantle ◽  
Velocity Structure ◽  
Vertical Component ◽  
Depth Interval ◽  
Mantle Structure ◽  
Waveform Modeling ◽  
Spreading Ridges ◽  
The Pacific ◽  
Upper Mantle Structure ◽  
Mid Atlantic Ridge

ABSTRACT The lithosphere is the outermost rigid layer of the Earth and includes the crust and brittle uppermost mantle. Because the poor seismic coverage of the ocean basins is the mantle structure of young lithosphere below midocean spreading centers poorly constrained, especially along slow spreading ridges. Surface waves radiated by midocean ridge earthquakes are excellent agents to study young lithosphere when being recorded in the vicinity of the ridge crest. Here, we use body and Rayleigh waves from six central Atlantic transform fault earthquakes with magnitude Mw>6 to constrain upper mantle structure away from ocean islands. Earthquakes were recorded by a network of broadband ocean-bottom seismometers deployed at the Mid-Atlantic Ridge (MAR) near 14°45′ N. Waveform modeling of vertical-component data at periods of 10–60 s yielded the velocity structure of the uppermost ∼100  km of the mantle and hence of the depth interval where lithospheric cooling is most evident. The data support that both S-wave velocity of the lithospheric lid and its thickness increases with age; velocities increase from 4.35 to 4.75  km/s and thickness from 30–50 to 70 km, sampling mantle with an average path age of ∼7 and 18 My, respectively. With respect to constraints found previously in the Pacific, lid velocities beneath the MAR are faster than beneath fast-spreading ridges, whereas asthenospheric velocities are similar to the Pacific. The fast velocity of the lid and slow velocity of the inversion zone may indicate effective hydrothermal cooling of the lithosphere.

scholarly journals Gabbroic rocks trapped in the upper mantle at the Mid-Atlantic Ridge

1997 ◽  
Author(s):  
M. Cannat ◽  
F. Chatin ◽  
H. Whitechurch ◽  
G. Ceuleneer
Keyword(s):  
Upper Mantle ◽  
Mid Atlantic Ridge
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