Mid-Atlantic Ridge

About: Mid-Atlantic Ridge is a research topic. Over the lifetime, 1466 publications have been published within this topic receiving 59291 citations. The topic is also known as: Atlantic-Indian-Ridge & MAR.

Spatial variability of turbulent mixing in the Abyssal Ocean

Abstract: Ocean microstructure data show that turbulent mixing in the deep Brazil Basin of the South Atlantic Ocean is weak at all depths above smooth abyssal plains and the South American Continental Rise. The diapycnal diffusivity there was estimated to be less than or approximately equal to 0.1 x 10(-4) meters squared per second. In contrast, mixing rates are large throughout the water column above the rough Mid-Atlantic Ridge, and the diffusivity deduced for the bottom-most 150 meters exceeds 5 x 10(-4) meters squared per second. Such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry.

An off-axis hydrothermal vent field near the Mid-Atlantic Ridge at 30° N

Abstract: Evidence is growing that hydrothermal venting occurs not only along mid-ocean ridges but also on old regions of the oceanic crust away from spreading centres Here we report the discovery of an extensive hydrothermal field at 30 degrees N near the eastern intersection of the Mid-Atlantic Ridge and the Atlantis fracture zone The vent field--named 'Lost City'--is distinctly different from all other known sea-floor hydrothermal fields in that it is located on 15-Myr-old crust, nearly 15 km from the spreading axis, and may be driven by the heat of exothermic serpentinization reactions between sea water and mantle rocks It is located on a dome-like massif and is dominated by steep-sided carbonate chimneys, rather than the sulphide structures typical of 'black smoker' hydrothermal fields We found that vent fluids are relatively cool (40-75 degrees C) and alkaline (pH 90-98), supporting dense microbial communities that include anaerobic thermophiles Because the geological characteristics of the Atlantis massif are similar to numerous areas of old crust along the Mid-Atlantic, Indian and Arctic ridges, these results indicate that a much larger portion of the oceanic crust may support hydrothermal activity and microbial life than previously thought

Thermal and chemical structure of the Iceland plume

Abstract: Basaltic lavas, forming thick offshore seaward-dipping reflector sequences (SDRS) and onshore igneous provinces around the North Atlantic margins, represent melting of anomalously hot mantle in the head of the ancestral Iceland plume. Some of these lavas are chemically and isotopically indistinguishable from recent Icelandic basalt, but others more closely resemble basalt erupted at normal segments of mid-ocean ridges (N-MORB). In this paper we show that Icelandic basalt and N-MORB define parallel tight arrays on a plot oflog(Nb/Y) against log(Zr/Y), with N-MORB relatively deficient in Nb. Deficiency or excess of Nb, relative to the lower bound of the Iceland array, may be expressed as ΔNb=1.74+log⁡(Nb/Y)−1.92log⁡(Zr/Y)such that Icelandic basalt has ΔNb > 0 and N-MORB has ΔNb < 0. ΔNb is a fundamental source characteristic and is insensitive to the effects of variable degrees of mantle melting, source depletion through melt extraction, crustal contamination of the magmas, or subsequent alteration. We use new and published Nb, Zr and Y data to identify the mantle sources for Palaeocene and Eocene basaltic lavas erupted around the Atlantic margins in order to deduce the thermal and compositional structure of the head of the ancestral Iceland plume. The results show that the head of the plume was zoned, with an axial zone of Icelandic mantle surrounded by a thick outer shell of anomalously hot but compositionally normal N-MORB-source mantle. The zoning is very similar in scale and character to that seen today along the Reykjanes Ridge and is difficult to reconcile with the initiation of rifting and SDRS formation through the impact of a large plume head originating solely from the lower mantle. The thick outer shell of hot, depleted upper mantle, which formed more than half the volume of the plume head, suggests that at least part of the plume originated in the thermal boundary layer at the base of the upper mantle.

Chemical Characteristics and Origin of Oceanic Ridge Volcanic Rocks

Abstract: Oceanic ridge volcanic rocks alkali metal, alkaline earth, rare earth, nickel and major element content, observing partial melting