A wide-angle upper mantle reflector in SW Iberia: Some constraints on its nature.

[EN]Deep and fast wide-angle reflection arrivals observed at offsets over 180 km, and over a reduced time interval of 1–1.5 s, have been observed in a seismic experiment shot across SW Iberia as part of the IBERSEIS project. Using different modelling approaches, these reflections have been found to...

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Autores: Ayarza Arribas, María Puy, Palomeras Torres, Inmaculada, Carbonell, R., Afonso, J.C., Simancas, F.
Tipo de recurso: artículo
Estado:Versión publicada
Fecha de publicación:2010
País:España
Institución:Universidad de Salamanca (USAL)
Repositorio:GREDOS. Repositorio Institucional de la Universidad de Salamanca
OAI Identifier:oai:gredos.usal.es:10366/155469
Acceso en línea:http://hdl.handle.net/10366/155469
Access Level:acceso abierto
Palabra clave:Wide-angle seismic experiment IBERSEIS
SW Iberia Variscan belt
Upper mantle
Spinel-lherzolite Garnet-lherzolite
Hales gradient zone
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spelling A wide-angle upper mantle reflector in SW Iberia: Some constraints on its nature.Ayarza Arribas, María PuyPalomeras Torres, InmaculadaCarbonell, R.Afonso, J.C.Simancas, F.Wide-angle seismic experiment IBERSEISSW Iberia Variscan beltUpper mantleSpinel-lherzolite Garnet-lherzoliteHales gradient zone[EN]Deep and fast wide-angle reflection arrivals observed at offsets over 180 km, and over a reduced time interval of 1–1.5 s, have been observed in a seismic experiment shot across SW Iberia as part of the IBERSEIS project. Using different modelling approaches, these reflections have been found to be consistent with a heterogeneous gradient zone located at 61–72 km depth that features an absolute P-wave velocity contrast from 8.2 to 8.3 km/s. Paradoxically, this interface has not been observed in coincident vertical incidence data, probably due to the change in the reflection coefficient with decreasing incidence angles, the lack of energy at high recording times for the near-vertical (vibroseis) data, and/or the different location of the CDPs in both experiments. Although the mantle is acknowledged to be highly heterogeneous and mantle lithologies are capable of giving impedance contrasts high enough as to be observed in seismic data, it is often seen as transparent from a seismic point of view. The short wavelength of mantle compositional heterogeneities is probably what hinders their identification with active source seismic data and only big and sharp discontinuities are imaged in vertical incidence experiments whereas regional transitional boundaries may be also observed at high incidence angles. Accordingly, we propose that deep reflectivity observed in SW Iberia must correspond to a regional–continental scale feature, not sharp enough as to be seen with vertical incidence energy. This feature, already identified in previous DSS experiments carried out in Iberia, has a depth, a P-wave velocity contrast and a transitional nature that match the characteristics proposed for the spinel-lherzolite to garnet-lherzolite phase transition, i.e. the Hales interface or gradient zone. This boundary is relatively narrow (at least 2–3 kb) in enriched mantle and appears deeper and along wider intervals when the mantle is depleted. In addition, it is a worldwide scale boundary already identified over large areas with different types of datasets. The variability in depth and sharpness of this interface, which is related to mantle chemistry, constrains the type of seismic techniques that should be used to identify it.Elsevier202420242010info:eu-repo/semantics/articleinfo:eu-repo/semantics/publishedVersionapplication/pdfhttp://hdl.handle.net/10366/155469reponame:GREDOS. Repositorio Institucional de la Universidad de Salamancainstname:Universidad de Salamanca (USAL)Inglésinfo:eu-repo/semantics/openAccessoai:gredos.usal.es:10366/1554692026-06-07T06:28:51Z
dc.title.none.fl_str_mv A wide-angle upper mantle reflector in SW Iberia: Some constraints on its nature.
title A wide-angle upper mantle reflector in SW Iberia: Some constraints on its nature.
spellingShingle A wide-angle upper mantle reflector in SW Iberia: Some constraints on its nature.
Ayarza Arribas, María Puy
Wide-angle seismic experiment IBERSEIS
SW Iberia Variscan belt
Upper mantle
Spinel-lherzolite Garnet-lherzolite
Hales gradient zone
title_short A wide-angle upper mantle reflector in SW Iberia: Some constraints on its nature.
title_full A wide-angle upper mantle reflector in SW Iberia: Some constraints on its nature.
title_fullStr A wide-angle upper mantle reflector in SW Iberia: Some constraints on its nature.
title_full_unstemmed A wide-angle upper mantle reflector in SW Iberia: Some constraints on its nature.
title_sort A wide-angle upper mantle reflector in SW Iberia: Some constraints on its nature.
dc.creator.none.fl_str_mv Ayarza Arribas, María Puy
Palomeras Torres, Inmaculada
Carbonell, R.
Afonso, J.C.
Simancas, F.
author Ayarza Arribas, María Puy
author_facet Ayarza Arribas, María Puy
Palomeras Torres, Inmaculada
Carbonell, R.
Afonso, J.C.
Simancas, F.
author_role author
author2 Palomeras Torres, Inmaculada
Carbonell, R.
Afonso, J.C.
Simancas, F.
author2_role author
author
author
author
dc.subject.none.fl_str_mv Wide-angle seismic experiment IBERSEIS
SW Iberia Variscan belt
Upper mantle
Spinel-lherzolite Garnet-lherzolite
Hales gradient zone
topic Wide-angle seismic experiment IBERSEIS
SW Iberia Variscan belt
Upper mantle
Spinel-lherzolite Garnet-lherzolite
Hales gradient zone
description [EN]Deep and fast wide-angle reflection arrivals observed at offsets over 180 km, and over a reduced time interval of 1–1.5 s, have been observed in a seismic experiment shot across SW Iberia as part of the IBERSEIS project. Using different modelling approaches, these reflections have been found to be consistent with a heterogeneous gradient zone located at 61–72 km depth that features an absolute P-wave velocity contrast from 8.2 to 8.3 km/s. Paradoxically, this interface has not been observed in coincident vertical incidence data, probably due to the change in the reflection coefficient with decreasing incidence angles, the lack of energy at high recording times for the near-vertical (vibroseis) data, and/or the different location of the CDPs in both experiments. Although the mantle is acknowledged to be highly heterogeneous and mantle lithologies are capable of giving impedance contrasts high enough as to be observed in seismic data, it is often seen as transparent from a seismic point of view. The short wavelength of mantle compositional heterogeneities is probably what hinders their identification with active source seismic data and only big and sharp discontinuities are imaged in vertical incidence experiments whereas regional transitional boundaries may be also observed at high incidence angles. Accordingly, we propose that deep reflectivity observed in SW Iberia must correspond to a regional–continental scale feature, not sharp enough as to be seen with vertical incidence energy. This feature, already identified in previous DSS experiments carried out in Iberia, has a depth, a P-wave velocity contrast and a transitional nature that match the characteristics proposed for the spinel-lherzolite to garnet-lherzolite phase transition, i.e. the Hales interface or gradient zone. This boundary is relatively narrow (at least 2–3 kb) in enriched mantle and appears deeper and along wider intervals when the mantle is depleted. In addition, it is a worldwide scale boundary already identified over large areas with different types of datasets. The variability in depth and sharpness of this interface, which is related to mantle chemistry, constrains the type of seismic techniques that should be used to identify it.
publishDate 2010
dc.date.none.fl_str_mv 2010
2024
2024
dc.type.none.fl_str_mv info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
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status_str publishedVersion
dc.identifier.none.fl_str_mv http://hdl.handle.net/10366/155469
url http://hdl.handle.net/10366/155469
dc.language.none.fl_str_mv Inglés
language_invalid_str_mv Inglés
dc.rights.none.fl_str_mv info:eu-repo/semantics/openAccess
eu_rights_str_mv openAccess
dc.format.none.fl_str_mv application/pdf
dc.publisher.none.fl_str_mv Elsevier
publisher.none.fl_str_mv Elsevier
dc.source.none.fl_str_mv reponame:GREDOS. Repositorio Institucional de la Universidad de Salamanca
instname:Universidad de Salamanca (USAL)
instname_str Universidad de Salamanca (USAL)
reponame_str GREDOS. Repositorio Institucional de la Universidad de Salamanca
collection GREDOS. Repositorio Institucional de la Universidad de Salamanca
repository.name.fl_str_mv
repository.mail.fl_str_mv
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