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Accretionary processes in the axial valley of the Mid-Atlantic Ridge 27 degrees N - 30 degrees N from TOBI side-scan sonar images

Accretionary processes in the axial valley of the Mid-Atlantic Ridge 27 degrees N - 30 degrees N from TOBI side-scan sonar images
Accretionary processes in the axial valley of the Mid-Atlantic Ridge 27 degrees N - 30 degrees N from TOBI side-scan sonar images
We analyse TOBI side-scan sonar images collected during Charles Darwin cruise CD76 in the axial valley of the Mid-Atlantic Ridge (MAR) between 27° N and 30° N (Atlantis Transform Fault). Mosaics of the two side-scan sonar swaths provide a continuous image of the axial valley and the inner valley walls along more than six second-order segments of the MAR. Tectonic and volcanic analyses reveal a high-degree intra-segment and inter-segment variability. We distinguish three types of volcanic morphologies: hummocky volcanoes or volcanic ridges, smooth, flat-topped volcanoes, and lava flows. We observe that the variations in the tectonics from one segment to another are associated with variations in the distribution of the volcanic morphologies. Some segments have more smooth volcanoes near their ends and in the discontinuities than near their mid-point, and large, hummocky axial volcanic ridges. Their tectonic deformation is usually limited to the edges of the axial valley near the inner valley walls. Other segments have smooth volcanoes distributed along their length, small axial volcanic ridges, and their axial valley floor is affected by numerous faults and fissures. We propose a model of volcano-tectonic cycles in which smooth volcanoes and lava flows are built during phases of high magmatic flux. Hummocky volcanic ridges are constructed more progressively, by extraction of magma from pockets located preferentially beneath the centre of the segments, during phases of low magma input. These cycles might result from pulses in melt migration from the mantle. Melt arrival would lead to the rapid emplacement of smooth-textured volcanic terrains, and would leave magma pockets, mostly beneath the centre of the segments where most melt is produced. During the end of the volcanic cycle magma would be extracted from these reservoirs through dikes with a low magma pressure, building hummocky volcanic ridges at low effusion rates. In extreme cases, this volcanic phase would be followed by amagmatic extension until a new magma pulse arrives from the mantle.
TOBI, OCEAN CRUST, MID ATLANTIC RIDGE, "CHARLES DARWIN", CRUISE 76 1993, SIDE SCAN SONAR
0025-3235
87-119
Briais, A.
c6257edb-5ac5-4649-81a7-799ee77e2403
Sloan, H.
d7710359-1ff9-4d6e-9e64-b2b790b0dd19
Parson, L.M.
8985a003-911e-402e-a858-3ecbd09d6771
Murton, B.J.
9076d07f-a3c1-4f90-a5d5-99b27fe2cb12
Briais, A.
c6257edb-5ac5-4649-81a7-799ee77e2403
Sloan, H.
d7710359-1ff9-4d6e-9e64-b2b790b0dd19
Parson, L.M.
8985a003-911e-402e-a858-3ecbd09d6771
Murton, B.J.
9076d07f-a3c1-4f90-a5d5-99b27fe2cb12

Briais, A., Sloan, H., Parson, L.M. and Murton, B.J. (2000) Accretionary processes in the axial valley of the Mid-Atlantic Ridge 27 degrees N - 30 degrees N from TOBI side-scan sonar images. Marine Geophysical Researches, 21 (1/2), 87-119. (doi:10.1023/A:1004722213652).

Record type: Article

Abstract

We analyse TOBI side-scan sonar images collected during Charles Darwin cruise CD76 in the axial valley of the Mid-Atlantic Ridge (MAR) between 27° N and 30° N (Atlantis Transform Fault). Mosaics of the two side-scan sonar swaths provide a continuous image of the axial valley and the inner valley walls along more than six second-order segments of the MAR. Tectonic and volcanic analyses reveal a high-degree intra-segment and inter-segment variability. We distinguish three types of volcanic morphologies: hummocky volcanoes or volcanic ridges, smooth, flat-topped volcanoes, and lava flows. We observe that the variations in the tectonics from one segment to another are associated with variations in the distribution of the volcanic morphologies. Some segments have more smooth volcanoes near their ends and in the discontinuities than near their mid-point, and large, hummocky axial volcanic ridges. Their tectonic deformation is usually limited to the edges of the axial valley near the inner valley walls. Other segments have smooth volcanoes distributed along their length, small axial volcanic ridges, and their axial valley floor is affected by numerous faults and fissures. We propose a model of volcano-tectonic cycles in which smooth volcanoes and lava flows are built during phases of high magmatic flux. Hummocky volcanic ridges are constructed more progressively, by extraction of magma from pockets located preferentially beneath the centre of the segments, during phases of low magma input. These cycles might result from pulses in melt migration from the mantle. Melt arrival would lead to the rapid emplacement of smooth-textured volcanic terrains, and would leave magma pockets, mostly beneath the centre of the segments where most melt is produced. During the end of the volcanic cycle magma would be extracted from these reservoirs through dikes with a low magma pressure, building hummocky volcanic ridges at low effusion rates. In extreme cases, this volcanic phase would be followed by amagmatic extension until a new magma pulse arrives from the mantle.

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Published date: 2000
Keywords: TOBI, OCEAN CRUST, MID ATLANTIC RIDGE, "CHARLES DARWIN", CRUISE 76 1993, SIDE SCAN SONAR

Identifiers

Local EPrints ID: 8722
URI: http://eprints.soton.ac.uk/id/eprint/8722
ISSN: 0025-3235
PURE UUID: 73e2359d-16a5-4fd1-8b94-70db3c39ea78

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Date deposited: 25 Aug 2004
Last modified: 15 Jul 2019 19:38

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Contributors

Author: A. Briais
Author: H. Sloan
Author: L.M. Parson
Author: B.J. Murton

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