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  • AGU (American Geophysical Union)  (3)
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  • 1
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    Compositional variation and 226Ra-230Th model ages of axial lavas from the southern Mid-Atlantic Ridge, 8°48′S (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Geochemistry, Geophysics, Geosystems, 17 (1). pp. 199-218.
    Details
    Publication Date: 2019-09-23
    Description: We present geological observations and geochemical data for the youngest volcanic features on the slow-spreading Mid-Atlantic Ridge at 8°48'S that shows seismic evidence for a thickened crust and excess magma formation. Young lava flows with high sonar reflectivity cover about 14 km2 in the axial rift and were probably erupted from two axial volcanic ridges each of about 3 km in length. Three different lava units occur along an about 11 km long portion of the ridge, and lavas from the northern axial volcanic ridge differ from those of the southern axial volcanic ridge and surrounding lava flows. Basalts from the axial rift flanks and from a pillow mound within the young flows are more incompatible element depleted than those from the young volcanic field. Lavas from this volcanic area have 226Ra-230Th disequilibria model ages of 1,000 and 4,000 years whereas the older lavas from the rift flank and the pillow mound, but also some of the lava field, are older than 8,000 years. Glasses from the northern and southern ends of the southern lava unit indicate up to 100°C cooler magma temperatures than in the center and increased assimilation of hydrothermally altered material. The compositional heterogeneity on a scale of 3 km suggests small magma batches rising vertically from the mantle to the surface without significant lateral flow and mixing. The observations on the 8°48'S lava field support the model of low frequency eruptions from single ascending magma batches that has been developed for slow-spreading ridges.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2015GC006016
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Young volcanism and related hydrothermal activity at 5°S on the slow-spreading southern Mid-Atlantic Ridge (2007)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 8 (Q11002).
    Details
    Publication Date: 2019-09-24
    Description: The effect of volcanic activity on submarine hydrothermal systems has been well documented along fast- and intermediate-spreading centers but not from slow-spreading ridges. Indeed, volcanic eruptions are expected to be rare on slow-spreading axes. Here we report the presence of hydrothermal venting associated with extremely fresh lava flows at an elevated, apparently magmatically robust segment center on the slow-spreading southern Mid-Atlantic Ridge near 5°S. Three high-temperature vent fields have been recognized so far over a strike length of less than 2 km with two fields venting phase-separated, vapor-type fluids. Exit temperatures at one of the fields reach up to 407°C, at conditions of the critical point of seawater, the highest temperatures ever recorded from the seafloor. Fluid and vent field characteristics show a large variability between the vent fields, a variation that is not expected within such a limited area. We conclude from mineralogical investigations of hydrothermal precipitates that vent-fluid compositions have evolved recently from relatively oxidizing to more reducing conditions, a shift that could also be related to renewed magmatic activity in the area. Current high exit temperatures, reducing conditions, low silica contents, and high hydrogen contents in the fluids of two vent sites are consistent with a shallow magmatic source, probably related to a young volcanic eruption event nearby, in which basaltic magma is actively crystallizing. This is the first reported evidence for direct magmatic-hydrothermal interaction on a slow-spreading mid-ocean ridge.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2006GC001509
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    The Relationships Between Volcanism, Tectonism, and Hydrothermal Activity on the Southern Equatorial Mid-Atlantic Ridge (2010)
    AGU (American Geophysical Union)
    In:  In: Diversity of Hydrothermal Systems on Slow Spreading Ocean Ridges. , ed. by Rona, P. A. and Devey, C. W. Geophysical Monograph Series, 188 . AGU (American Geophysical Union), Washington, DC, pp. 133-152. ISBN 978-0-87390-478-8
    Details
    Publication Date: 2013-07-18
    Description: The Mid-Atlantic Ridge south of the equator is a key region for many aspects of spreading axis studies, from biogeography to ridge-hotspot interaction. Despite this, the ridge axis had, until 2004, seen little systematic study. Repeated trips to the area since then have mapped and explored some 900 km of ridge length, from 2° to 14°S. The result is complete bathymetric and side-scan coverage of the axial region and the discovery and characterization of the first hydrothermal vents south of the equator. Such multisegment detailed and interdisciplinary coverage allows us to formulate a general model for the interplay between volcanism, tectonics, and hydrothermalism on a slow spreading ridge. The model defines three basic types of ridge morphology with specific hydrothermal characteristics: (a) a deep, tectonically dominated rift valley where hydrothermalism is seldom associated with volcanism and much more likely confined to long-lived bounding faults; (b) a shallower, segment-center bulge where a combination of repeated magmatic activity and tectonism results in repeated, possibly temporally overlapping periods of hydrothermal activity on the ridge axis; and (c) a very shallow axis beneath which temperatures in all but the uppermost crust are so high that deformation is ductile, inhibiting the formation of high-porosity deep fractures and severely depressing hydrothermal circulation. This model is used together with satellitederived predicted bathymetry to provide forecasts of the best places to look for hydrothermal sites in the remaining unexplored regions of the South Atlantic.
    Type: Book chapter , NonPeerReviewed
    Format: text
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    OceanRep: Book chapter
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