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Structure and development of an axial volcanic ridge: Mid-Atlantic Ridge, 45°N

Structure and development of an axial volcanic ridge: Mid-Atlantic Ridge, 45°N
Structure and development of an axial volcanic ridge: Mid-Atlantic Ridge, 45°N
We describe the most comprehensive and detailed high resolution survey of an axial volcanic ridge (AVR) ever conducted, at 45°N on the Mid-Atlantic Ridge. We use 3 m resolution sidescan sonar, deep-towed magnetic field measurements, video observations from eleven ROV dives, and two very-high-resolution bathymetry and magnetic surveys. The most recently active AVR has high topographic relief, high acoustic backscatter, high crustal magnetization and little faulting. It is sharp-crested, 25 × 4 km in extent and 500 m high, and is covered by approximately 8000 volcanic “hummocks” whose detailed nature is revealed for the first time. Each is an individual volcano ? 450 m in diameter and ? 200 m high, ranging from steep-sided (45°) cones to low domes. Many have suffered significant flank collapse. Hummocks tend to align in rows parallel to the AVR axis, parallel to its NE-trending spurs or, on its lower flanks, sub-normal to the AVR trend. These latter are spaced 1–2 km apart and comprise 1–2 km-long rows of single volcanoes. We infer that their emplacement is controlled by down-flank magma transport, possibly via lava tubes. The AVR contains only one large flat-topped seamount. The flanking median valley floor consists of either older hummocky volcanic terrain or flat-lying, mostly sediment-covered lavas. These typically have low-relief lobate surfaces, inflation and collapse structures, and occasional lava tubes and tumuli. The AVR displays open fissures, mostly along its crest. There is direct evidence for only a few small faults on the AVR, though steep, outward-facing slopes draped by elongate pillows may be small normal faults covered by lava. The surrounding median valley floor is heavily fissured. Normal faults cut it and an older AVR, the latter displaying significant outward facing faults. High crustal magnetization, an approximate proxy for crustal age within the Brunhes, is confined to the active AVR. Magnetic palaeointensity measurements are consistent with ages up to ~ 12 ka for several samples from the active AVR and ? 12 ka for one sample from the median valley floor. This is much less than the predicted spreading age, implying distribution of melt off-axis or episodic AVR growth.
0012-821X
228-241
Searle, R.C.
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Murton, B.J.
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Achenbach, K.
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LeBas, T.
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Tivey, M.
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Yeo, I.
bfacd80a-5ac8-46f8-bb04-978106147023
Cormier, M.H.
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Carlut, J.
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Ferreira, P.
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Mallows, C.
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Morris, K.
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Schroth, N.
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van Calsteren, P.
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Waters, C.
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Searle, R.C.
aacbd084-421e-4813-86b7-ac7d84da376f
Murton, B.J.
9076d07f-a3c1-4f90-a5d5-99b27fe2cb12
Achenbach, K.
76342682-de53-43c1-854c-a41765d4513e
LeBas, T.
f0dbad80-bb38-412c-be77-b8b9faef1854
Tivey, M.
05141f54-1b47-4df6-8da2-bd43c4a0a6ac
Yeo, I.
bfacd80a-5ac8-46f8-bb04-978106147023
Cormier, M.H.
92441920-1851-4417-be86-e9f87d121a95
Carlut, J.
cbb7a892-ac04-48e9-a136-40500675b40f
Ferreira, P.
9bcff512-d844-4c62-9f2a-f8431b0bf402
Mallows, C.
ff7ac505-9ee5-40d3-b6a7-ee442ed946db
Morris, K.
4df92a43-2e62-4371-a857-cd99f7eeec83
Schroth, N.
293778ba-fd1d-4090-bef4-6e7858fe8082
van Calsteren, P.
cef7436a-75e0-42a9-82e8-94d1b815886f
Waters, C.
fcb702d4-162d-4cae-a6c0-a7bbd73b8754

Searle, R.C., Murton, B.J., Achenbach, K., LeBas, T., Tivey, M., Yeo, I., Cormier, M.H., Carlut, J., Ferreira, P., Mallows, C., Morris, K., Schroth, N., van Calsteren, P. and Waters, C. (2010) Structure and development of an axial volcanic ridge: Mid-Atlantic Ridge, 45°N. Earth and Planetary Science Letters, 299 (1-2), 228-241. (doi:10.1016/j.epsl.2010.09.003).

Record type: Article

Abstract

We describe the most comprehensive and detailed high resolution survey of an axial volcanic ridge (AVR) ever conducted, at 45°N on the Mid-Atlantic Ridge. We use 3 m resolution sidescan sonar, deep-towed magnetic field measurements, video observations from eleven ROV dives, and two very-high-resolution bathymetry and magnetic surveys. The most recently active AVR has high topographic relief, high acoustic backscatter, high crustal magnetization and little faulting. It is sharp-crested, 25 × 4 km in extent and 500 m high, and is covered by approximately 8000 volcanic “hummocks” whose detailed nature is revealed for the first time. Each is an individual volcano ? 450 m in diameter and ? 200 m high, ranging from steep-sided (45°) cones to low domes. Many have suffered significant flank collapse. Hummocks tend to align in rows parallel to the AVR axis, parallel to its NE-trending spurs or, on its lower flanks, sub-normal to the AVR trend. These latter are spaced 1–2 km apart and comprise 1–2 km-long rows of single volcanoes. We infer that their emplacement is controlled by down-flank magma transport, possibly via lava tubes. The AVR contains only one large flat-topped seamount. The flanking median valley floor consists of either older hummocky volcanic terrain or flat-lying, mostly sediment-covered lavas. These typically have low-relief lobate surfaces, inflation and collapse structures, and occasional lava tubes and tumuli. The AVR displays open fissures, mostly along its crest. There is direct evidence for only a few small faults on the AVR, though steep, outward-facing slopes draped by elongate pillows may be small normal faults covered by lava. The surrounding median valley floor is heavily fissured. Normal faults cut it and an older AVR, the latter displaying significant outward facing faults. High crustal magnetization, an approximate proxy for crustal age within the Brunhes, is confined to the active AVR. Magnetic palaeointensity measurements are consistent with ages up to ~ 12 ka for several samples from the active AVR and ? 12 ka for one sample from the median valley floor. This is much less than the predicted spreading age, implying distribution of melt off-axis or episodic AVR growth.

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Published date: 15 October 2010
Organisations: Marine Geoscience

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Local EPrints ID: 167215
URI: http://eprints.soton.ac.uk/id/eprint/167215
ISSN: 0012-821X
PURE UUID: 26a98fa0-3ba5-4c9b-953a-3c28c83aa434

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Date deposited: 09 Nov 2010 14:26
Last modified: 14 Mar 2024 02:15

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Contributors

Author: R.C. Searle
Author: B.J. Murton
Author: K. Achenbach
Author: T. LeBas
Author: M. Tivey
Author: I. Yeo
Author: M.H. Cormier
Author: J. Carlut
Author: P. Ferreira
Author: C. Mallows
Author: K. Morris
Author: N. Schroth
Author: P. van Calsteren
Author: C. Waters

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