Anisotropy of the zone of exhumed continental mantle and the structure of the earliest-formed oceanic crust west of Iberia
Anisotropy of the zone of exhumed continental mantle and the structure of the earliest-formed oceanic crust west of Iberia
Wide-angle seismic data recorded on 13 ocean bottom instruments in the Southern Iberia Abyssal Plain have been analysed for the presence of P-wave azimuthal anisotropy. Small anisotropy (< 7 %) was identifed at depths of 3-7 km below the top of the basement, with a fast velocity direction oriented at N142°E. Similar studies over oceanic crust have found that the fast velocity direction corresponds with the plate spreading direction. It is difficult to reconcile the direction found here with other observations, and rotation of the upper mantle by motion along low-angle normal faults is proposed to account for the discrepancy. Margin parallel extension is identified in MCS profiles collected over crust formed within 20 m.y. of the onset of seafloor spreading and is related to the uphft of the region west of Gahcia Bank. Small amounts of extension are identified in margin normal profiles. Sub-horizontal reflections identified in all the profiles result from out-of-plane energy, compositional and hydrothermal layering and previous shot multiples. Modelling of the satellite free-air gravity anomalies along the I AM-10 profile revealed crust of 5 - 6 ±l km thickness with up to 10% variations of the lower crustal density. These variations are consistent with the presence of a previously unmapped fracture zone which affects 125±5-110±5 Ma crust. The density models and crustal reflectivity of the profiles collected over the early-formed oceanic crust are similar to those of profiles collected away from margins. Regions of enhanced reflectivity of the basement surface are attributed to the emplacement of lava flows as a result of additional magma supply during the propagation of the paleo-ridge. The conformable sediment sequence, consistent with the seismic stratigraphy identi- fled in the Southern Iberia Abyssal Plain, indicates changes in the sedimentation pattern during the Eocene as a result of the subduction of the southern margin of the Bay of Bis- cay. Anomalous packages and contourite deposits in the sediment column are attributed to deep-water currents at about 4.6-4.7 km depth.
University of Southampton
Cole, Philip Bruce
01dc97b4-6285-4ace-bc1e-527d17d4e634
2003
Cole, Philip Bruce
01dc97b4-6285-4ace-bc1e-527d17d4e634
Cole, Philip Bruce
(2003)
Anisotropy of the zone of exhumed continental mantle and the structure of the earliest-formed oceanic crust west of Iberia.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Wide-angle seismic data recorded on 13 ocean bottom instruments in the Southern Iberia Abyssal Plain have been analysed for the presence of P-wave azimuthal anisotropy. Small anisotropy (< 7 %) was identifed at depths of 3-7 km below the top of the basement, with a fast velocity direction oriented at N142°E. Similar studies over oceanic crust have found that the fast velocity direction corresponds with the plate spreading direction. It is difficult to reconcile the direction found here with other observations, and rotation of the upper mantle by motion along low-angle normal faults is proposed to account for the discrepancy. Margin parallel extension is identified in MCS profiles collected over crust formed within 20 m.y. of the onset of seafloor spreading and is related to the uphft of the region west of Gahcia Bank. Small amounts of extension are identified in margin normal profiles. Sub-horizontal reflections identified in all the profiles result from out-of-plane energy, compositional and hydrothermal layering and previous shot multiples. Modelling of the satellite free-air gravity anomalies along the I AM-10 profile revealed crust of 5 - 6 ±l km thickness with up to 10% variations of the lower crustal density. These variations are consistent with the presence of a previously unmapped fracture zone which affects 125±5-110±5 Ma crust. The density models and crustal reflectivity of the profiles collected over the early-formed oceanic crust are similar to those of profiles collected away from margins. Regions of enhanced reflectivity of the basement surface are attributed to the emplacement of lava flows as a result of additional magma supply during the propagation of the paleo-ridge. The conformable sediment sequence, consistent with the seismic stratigraphy identi- fled in the Southern Iberia Abyssal Plain, indicates changes in the sedimentation pattern during the Eocene as a result of the subduction of the southern margin of the Bay of Bis- cay. Anomalous packages and contourite deposits in the sediment column are attributed to deep-water currents at about 4.6-4.7 km depth.
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Published date: 2003
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Local EPrints ID: 465081
URI: http://eprints.soton.ac.uk/id/eprint/465081
PURE UUID: 691811a7-5d7c-4973-8836-743b895062b9
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Last modified: 16 Mar 2024 19:56
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Philip Bruce Cole
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