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Non-transform offsets along the Mid-Atlantic Ridge south of the Azores (38N-34N): ultramafic exposures and hosting of hydrothermal vents

Non-transform offsets along the Mid-Atlantic Ridge south of the Azores (38N-34N): ultramafic exposures and hosting of hydrothermal vents
Non-transform offsets along the Mid-Atlantic Ridge south of the Azores (38N-34N): ultramafic exposures and hosting of hydrothermal vents
Ten contiguous non-transform offsets (NTOs) along the Mid-Atlantic Ridge (MAR) south of the Azores (between 38°N and 35°40?N) have been studied in detail using swath bathymetric, acoustic backscatter and deep-tow high-resolution sidescan sonar (TOBI) data. In contrast with discontinuities studied elsewhere at slow-spreading ridges, these left-lateral NTOs are consistently broader and larger, with complex structural fabrics accommodating the offset. They are characterized by a range of elevated and faulted massifs detached from their segment flanks, with an irregular acoustic backscatter pattern. Some of these massifs have been explored and sampled recently during dive cruises revealing that they are composed of upper mantle peridotites and lower crustal rocks, and sometimes associated with high-temperature hydrothermal venting. Water column surveys adjacent to these massifs show high CH4 and low TDM (total dissolvable manganese) concentrations, possibly resulting from the process of serpentinization of ultramafic rocks. The correlation between the shallow dome-like shaped massifs and the high concentrations of CH4 (associated with low levels of Mn) is of particular interest to predict the outcrop of ultramafic rocks within the NTOs where no geological data are available. The exposure of the ultramafic massifs within the NTOs is favored by low magmatic supply and low-angle detachment faulting occurring at segment ends. The pervasive fracturing and faulting at these discontinuities favor circulation of hydrothermal fluids and occurrence of high-temperature vent sites.
MID ATLANTIC RIDGE, DISCONTINUITIES, HYDROTHERMAL ACTIVITY, BATHYMETRIC DATA, METHANE, SIDESCAN SONAR, TOBI, MANGANESE
0012-821X
89-103
Gracia, E.
f9e61943-c032-4be7-9c37-c5199fc8950e
Charlou, J.L.
9f7c1bf8-16e0-47a9-9ada-5e593b7c2953
Radford-Knoery, J.
9a3f1906-64ba-4b1c-ac18-47a21bd3c1b6
Parson, L.M.
8985a003-911e-402e-a858-3ecbd09d6771
Gracia, E.
f9e61943-c032-4be7-9c37-c5199fc8950e
Charlou, J.L.
9f7c1bf8-16e0-47a9-9ada-5e593b7c2953
Radford-Knoery, J.
9a3f1906-64ba-4b1c-ac18-47a21bd3c1b6
Parson, L.M.
8985a003-911e-402e-a858-3ecbd09d6771

Gracia, E., Charlou, J.L., Radford-Knoery, J. and Parson, L.M. (2000) Non-transform offsets along the Mid-Atlantic Ridge south of the Azores (38N-34N): ultramafic exposures and hosting of hydrothermal vents. Earth and Planetary Science Letters, 177 (1/2), 89-103. (doi:10.1016/S0012-821X(00)00034-0).

Record type: Article

Abstract

Ten contiguous non-transform offsets (NTOs) along the Mid-Atlantic Ridge (MAR) south of the Azores (between 38°N and 35°40?N) have been studied in detail using swath bathymetric, acoustic backscatter and deep-tow high-resolution sidescan sonar (TOBI) data. In contrast with discontinuities studied elsewhere at slow-spreading ridges, these left-lateral NTOs are consistently broader and larger, with complex structural fabrics accommodating the offset. They are characterized by a range of elevated and faulted massifs detached from their segment flanks, with an irregular acoustic backscatter pattern. Some of these massifs have been explored and sampled recently during dive cruises revealing that they are composed of upper mantle peridotites and lower crustal rocks, and sometimes associated with high-temperature hydrothermal venting. Water column surveys adjacent to these massifs show high CH4 and low TDM (total dissolvable manganese) concentrations, possibly resulting from the process of serpentinization of ultramafic rocks. The correlation between the shallow dome-like shaped massifs and the high concentrations of CH4 (associated with low levels of Mn) is of particular interest to predict the outcrop of ultramafic rocks within the NTOs where no geological data are available. The exposure of the ultramafic massifs within the NTOs is favored by low magmatic supply and low-angle detachment faulting occurring at segment ends. The pervasive fracturing and faulting at these discontinuities favor circulation of hydrothermal fluids and occurrence of high-temperature vent sites.

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More information

Published date: 2000
Keywords: MID ATLANTIC RIDGE, DISCONTINUITIES, HYDROTHERMAL ACTIVITY, BATHYMETRIC DATA, METHANE, SIDESCAN SONAR, TOBI, MANGANESE

Identifiers

Local EPrints ID: 8857
URI: http://eprints.soton.ac.uk/id/eprint/8857
ISSN: 0012-821X
PURE UUID: 46e464e7-93cb-4f28-96b4-d54591c128a7

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Date deposited: 13 Sep 2004
Last modified: 15 Jul 2019 19:38

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Contributors

Author: E. Gracia
Author: J.L. Charlou
Author: J. Radford-Knoery
Author: L.M. Parson

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