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Distribution of and hydrographic controls on ferromanganese crusts: Tropic Seamount, Atlantic

Distribution of and hydrographic controls on ferromanganese crusts: Tropic Seamount, Atlantic
Distribution of and hydrographic controls on ferromanganese crusts: Tropic Seamount, Atlantic

Hydrogenetic ferromanganese crusts are likely to be exploited as resources for critical metals in the near future, yet the processes controlling where and how they grow are poorly understood. Using detailed mapping of seafloor outcrop and well constrained hydrographic modelling alongside scanning electron microscope imagery of samples from the Tropic Seamount, a star-shaped guyot located in the Tropical East Atlantic, we investigate the relationship between currents, ferromanganese crustal texture and the locations and intensity of crustal erosion. Here, we report the distribution of FeMn crusts and explore factors controlling their growth and erosion. We find that just over 35% of the summit plateau of the guyot exposes some form of ferromanganese crust mineralisation, with the rest variably covered by plains of mobile sediment and slim cliff exposures of carbonate. The steep flanks of the guyot largely expose ferromanganese crust both in situ and as debris flows. The strongest currents are located on the upper flanks of the guyot, the central part of its eastern limb, and across the summit plateau. Three categories of surface morphologies are identified; from pristine botryoidal surfaces to flat areas that have been completely polished by the erosive action of currents and sediment. The relationship between the outcrop of crusts, their erosional states and the hydrographic current regime to which they are exposed is complicated. There is a general correlation between the degree of erosion and location across the seamount, with the least eroded being found on the flanks below 2000 m water depth and the most heavily eroded crusts largely restricted to the summit area. Furthermore, the pristine samples all reside in areas that rarely experience current magnitudes over 0.2 m/s, suggesting that above this the currents have the ability to erode ferromanganese crust. However, there is a strong overlap between the measured current magnitudes at the locations of partially and completely eroded crusts, as well as partial overlap with the current magnitudes measured at pristine crust locations. This complexity is likely due to the presence of cliffs and plateaus increasing current magnitudes and turbidity at a scale smaller than the model resolution.

Atlantic, Critical elements, Ferromanganese crusts, Ferromanganese nodules, Seafloor mapping, Tropic Seamount
0169-1368
Yeo, I. A.
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Howarth, S. A.
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Spearman, J.
42cc3306-d7ce-4884-ad69-7291cc3eb812
Cooper, A.
92046e5e-bdc8-4a07-bf0e-0851e926d915
Crossouard, N.
a1d61696-3902-45b0-ae02-1e028538c834
Taylor, J.
fe1400d8-ad8e-4584-971a-102389b1b59e
Turnbull, M.
d0cc7296-a1e3-4ab9-b97c-2b785cf12361
Murton, B. J.
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Yeo, I. A.
62d8f65e-f259-44ee-9a02-77b54ee27a95
Howarth, S. A.
dd6533a2-a4bb-4cdc-b8b2-64a4303ee819
Spearman, J.
42cc3306-d7ce-4884-ad69-7291cc3eb812
Cooper, A.
92046e5e-bdc8-4a07-bf0e-0851e926d915
Crossouard, N.
a1d61696-3902-45b0-ae02-1e028538c834
Taylor, J.
fe1400d8-ad8e-4584-971a-102389b1b59e
Turnbull, M.
d0cc7296-a1e3-4ab9-b97c-2b785cf12361
Murton, B. J.
9076d07f-a3c1-4f90-a5d5-99b27fe2cb12

Yeo, I. A., Howarth, S. A., Spearman, J., Cooper, A., Crossouard, N., Taylor, J., Turnbull, M. and Murton, B. J. (2019) Distribution of and hydrographic controls on ferromanganese crusts: Tropic Seamount, Atlantic. Ore Geology Reviews, 114. (doi:10.1016/j.oregeorev.2019.103131).

Record type: Article

Abstract

Hydrogenetic ferromanganese crusts are likely to be exploited as resources for critical metals in the near future, yet the processes controlling where and how they grow are poorly understood. Using detailed mapping of seafloor outcrop and well constrained hydrographic modelling alongside scanning electron microscope imagery of samples from the Tropic Seamount, a star-shaped guyot located in the Tropical East Atlantic, we investigate the relationship between currents, ferromanganese crustal texture and the locations and intensity of crustal erosion. Here, we report the distribution of FeMn crusts and explore factors controlling their growth and erosion. We find that just over 35% of the summit plateau of the guyot exposes some form of ferromanganese crust mineralisation, with the rest variably covered by plains of mobile sediment and slim cliff exposures of carbonate. The steep flanks of the guyot largely expose ferromanganese crust both in situ and as debris flows. The strongest currents are located on the upper flanks of the guyot, the central part of its eastern limb, and across the summit plateau. Three categories of surface morphologies are identified; from pristine botryoidal surfaces to flat areas that have been completely polished by the erosive action of currents and sediment. The relationship between the outcrop of crusts, their erosional states and the hydrographic current regime to which they are exposed is complicated. There is a general correlation between the degree of erosion and location across the seamount, with the least eroded being found on the flanks below 2000 m water depth and the most heavily eroded crusts largely restricted to the summit area. Furthermore, the pristine samples all reside in areas that rarely experience current magnitudes over 0.2 m/s, suggesting that above this the currents have the ability to erode ferromanganese crust. However, there is a strong overlap between the measured current magnitudes at the locations of partially and completely eroded crusts, as well as partial overlap with the current magnitudes measured at pristine crust locations. This complexity is likely due to the presence of cliffs and plateaus increasing current magnitudes and turbidity at a scale smaller than the model resolution.

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Accepted/In Press date: 16 September 2019
e-pub ahead of print date: 27 September 2019
Published date: 1 November 2019
Keywords: Atlantic, Critical elements, Ferromanganese crusts, Ferromanganese nodules, Seafloor mapping, Tropic Seamount

Identifiers

Local EPrints ID: 435111
URI: https://eprints.soton.ac.uk/id/eprint/435111
ISSN: 0169-1368
PURE UUID: 27259f3f-34fc-4032-987d-13a1c0da4ffe
ORCID for S. A. Howarth: ORCID iD orcid.org/0000-0002-8017-8954

Catalogue record

Date deposited: 23 Oct 2019 16:30
Last modified: 02 Nov 2019 01:27

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