He, Ne and Ar isotope signatures of mid-ocean ridge basalts and their implications for upper mantle structure: A case study from the Mid-Atlantic Ridge at 4–12°S

2016 ◽  
Vol 183 ◽  
pp. 94-105 ◽  
Author(s):  
Nicole A. Stroncik ◽  
Samuel Niedermann
Keyword(s):  
Upper Mantle ◽  
Mantle Structure ◽  
Upper Mantle Structure ◽  
Mid Ocean Ridge ◽  
Mid Atlantic Ridge ◽  
Ocean 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 A subduction influence on ocean ridge basalts outside the Pacific subduction shield

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
A. Y. Yang ◽  
C. H. Langmuir ◽  
Y. Cai ◽  
P. Michael ◽  
S. L. Goldstein ◽  
...  
Keyword(s):  
Upper Mantle ◽  
The Arctic ◽  
Mantle Flow ◽  
Mantle Heterogeneity ◽  
Gakkel Ridge ◽  
The Pacific ◽  
Mid Ocean Ridge ◽  
The Pacific Ocean ◽  
Back Arc ◽  
Ocean Ridge

AbstractThe plate tectonic cycle produces chemically distinct mid-ocean ridge basalts and arc volcanics, with the latter enriched in elements such as Ba, Rb, Th, Sr and Pb and depleted in Nb owing to the water-rich flux from the subducted slab. Basalts from back-arc basins, with intermediate compositions, show that such a slab flux can be transported behind the volcanic front of the arc and incorporated into mantle flow. Hence it is puzzling why melts of subduction-modified mantle have rarely been recognized in mid-ocean ridge basalts. Here we report the first mid-ocean ridge basalt samples with distinct arc signatures, akin to back-arc basin basalts, from the Arctic Gakkel Ridge. A new high precision dataset for 576 Gakkel samples suggests a pervasive subduction influence in this region. This influence can also be identified in Atlantic and Indian mid-ocean ridge basalts but is nearly absent in Pacific mid-ocean ridge basalts. Such a hemispheric-scale upper mantle heterogeneity reflects subduction modification of the asthenospheric mantle which is incorporated into mantle flow, and whose geographical distribution is controlled dominantly by a “subduction shield” that has surrounded the Pacific Ocean for 180 Myr. Simple modeling suggests that a slab flux equivalent to ~13% of the output at arcs is incorporated into the convecting upper mantle.

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