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Carslberg ridge and mid-atlantic ridge: slow-spreading apparent analogs
Rutgers University.
NOC, European Way, Southampton.
Stockholm University.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
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2005 (English)In: AGU, Fall Meeting: 5-9 December 2005, San Francisco, California, American Geophysical Union (AGU), 2005Conference paper, Meeting abstract (Other academic)
Abstract [en]

We compare morphology, tectonics, petrology, and hydrothermal activity of a known section of the Mid-Atlantic Ridge (MAR) between the Kane and Atlantis fracture zones (full multi-beam coverage 21N to 31N) to the lesser known Carlsberg Ridge (CR; limited multi-beam coverage plus satellite altimetry). The CR extends from the Owen Fracture Zone (10N) to the Vityaz Fracture Zone (5S) and spreads at half-rates (~1.2-1.8 cm/yr) similar to the MAR: 1) Morphology: Both ridges exhibit distinct segmentation (primarily sinistral) and axial valleys with high floor to crest relief (range 1122-1771 m). Average lengths of segments (CR: 70 km; MAR: 50 km) and crest-to crest width of the axial valley are greater on the CR (40 km) than MAR (23 km). Axial volcanic ridges form the neovolcanic zone on both ridges, typically 2.6 km wide and 213 m high on the CR. Average water depth near segment centers is greater on the MAR (3933 m) than the CR (3564 m). V-shaped patterns oblique to the spreading axis are present on both ridges. 2) Tectonics: Segments on each ridge are predominantly separated by short-offset (<30 km) non-transform discontinuities with longer transform faults generally spaced hundreds of kilometers apart. Bulls-eye Mantle Bouguer Lows (-30 to -50 mgal) are present at centers of spreading segments on both ridges. Metamorphic core complexes of lower crust and upper mantle are present on the MAR section (at fracture zones) and at least at one locality at 58.33E on the CR. 3) Petrology: MORB composition from our 20 stations along the CR fall into the MORB family, with no evidence of hotspot inputs (no excess K or Nb), or extreme fractionation, similar to the MAR section. REE and trace element patterns between 57E and 61E on the CR indicate increasing melt depletion to the northwest, while glasses exhibit a striking systematic increase in MgO (decrease in fractionation) to the northwest and attain among the most primitive composition of any ocean ridge adjacent to the Owen fracture zone (9.93wt percent). Sr, Nd, and Pb isotopic compositions of Indian Ocean MORB are distinct from those of other oceans. They exhibit relatively higher 87Sr/86Sr, and lower 143Nd/144Nd, 207Pb/204Pb and 208Pb/204Pb for a given 206Pb/204Pb invoking mixing and regional-scale contamination of a depleted mantle with a variously designated enriched reservoir (EM1, EM2, DUPAL, etc.). 4) Hydrothermal activity: The MAR section encompasses a low-T hydrothermal field driven by the serpentinization at the Atlantis fracture zone (Lost City at 30N), and three high-temperature fields driven by magmatic heat in the axial valley (Broken Spur 29N, TAG 26N, and Snake Pit 23N). A 70 km-long, 1000 m-thick megaplume was detected in the water column up to 1400 m above the CR axial valley centered at 6.05N, 60.95E in August 2003, the first clear evidence of high-temperature hydrothermal activity on the CR. Further CR hydrothermal evidence includes relict sulfide chimneys at 58E; Mn-oxide coatings on basalts in the axial valley with Fe/Mn ratios at the boundary between hydrogenous and hydrothermal composition with thickness at two stations (1.67S, 67.77E; 5.35S, 68.62E) suggestive of hydrothermal input; and a d3He anomaly (166 per mil) in the water column at one of our stations in April 1979 (5.35S, 68.62E).

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2005.
Research subject
Ore Geology
URN: urn:nbn:se:ltu:diva-40385Local ID: f7a12970-146c-11dc-b9f0-000ea68e967bOAI: diva2:1013907
American Geophysical Union. 2005 Fall meeting : 05/12/2005 - 09/12/2005
Godkänd; 2005; 20070606 (ysko)Available from: 2016-10-03 Created: 2016-10-03Bibliographically approved

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Widenfalk, Lennart
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Department of Civil, Environmental and Natural Resources Engineering

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