Hydrothermal activity involving ultramafics along the Mid-Atlantic Ridge

Author(s): Bougault, Henri; Barriga, F.; Fouquet, Y.
Author Affiliation(s): Primary:
IFREMER, Plouzane, France
Universidade de Lisboa, Portugal
Volume Title: Brazil 2000; 31st international geological congress; abstracts volume
Source: International Geological Congress [International Geological Congress, Abstracts = Congrès Géologique International, Résumés, Vol.31; Brazil 2000; 31st international geological congress, Rio de Janeiro, Brazil, Aug. 6-17, 2000. Publisher:], [location varies], International CODEN: IGABBY
Note: In English. File G0401009.PDF
Summary: Outcropping of ultramafics on the Ocean floor was thought to exist only along Fracture Zones (FZ). Sampling these rocks away from FZ during Leg 37 (1974) and 45 (1976) of DSDP on the Mid- Atlantic Ridge (MAR) remained unexplained. Further occurrence of these rocks was documented by off axis drilling during Leg 82 (1980). Ultramafic rocks were then sampled at many locations along the rift valley walls of the MAR. Consequently, direct exchange between the ocean and mantle rocks through fluid circulation is a major process associated to the construction of slow spreading ridges. Lowering the rock density, serpentinization is part of axial constructional processes. The reaction involves large production of hydrogen transported by fluid circulation to the ocean. The two hydrothermal sites developing on ultramafics discovered on the MAR, the Logachev site at 14°43'N and the Rainbow site at 36°13'N, confirm this type of direct exchange between the Ocean and the Mantle on a slow spreading ridge. The knowledge of this type of exchange at zero age on the MAR allows to consider likely processes to take place on sedimented ridges, including the early opening of an ocean and associated sedimentary basins. These processes involve interactions of hydrothermal fluids between the oceanic substratum and the above sedimentary layers: -Hydrogen reaction with sediment, either hydrocracking of the organic matter or (and) developing the Fisher Tropsch reaction to produce hydrocarbons from carbonates. -Precipitation of sulfides within sedimentary layers as already observed on a sedimented zero age ridge crest (Leg 169 of ODP).
Year of Publication: 2000
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 18 Geophysics, Solid-Earth; Atlantic Ocean; Deep Sea Drilling Project; Fracture zones; Hydrothermal vents; IPOD; Igneous rocks; Leg 169; Leg 37; Leg 45; Leg 82; Lithosphere; Mantle; Metasomatism; Mid-Atlantic Ridge; Mid-ocean ridges; Ocean Drilling Program; Ocean floors; Oceanic lithosphere; Plate tectonics; Plutonic rocks; Sea-floor spreading; Serpentinization; Spreading centers; Ultramafics
Coordinates: N405600 N482800 W1270000 W1284500
N360000 N380000 W0330000 W0360000
N220000 N230000 W0430000 W0470000
N330829 N385623 W0323334 W0434603
Record ID: 2003053869
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