| 1. |
- Simancas, J.F., et al.
(författare)
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The seismic crustal structure of the Ossa-Morena Zone and its geological interpretation
- 2004
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Ingår i: Journal of Iberian Geology. - 1698-6180 .- 1886-7995. ; 30, s. 133-142
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Tidskriftsartikel (refereegranskat)abstract
- The IBERSEIS deep reflection seismic experiment has provided a crustal image of the Variscan orogen of southwest Iberia. A brief presentation of the entire seismic profile is given, and then the Ossa-Morena Zone (OMZ) and its boundaries are considered. The crust of the OMZ is shown to be divided into an upper crust, characterized by dominantly NE-dipping reflectivity, and a poorly reflective lower crust. The reflectivity of the upper crust has good correlation with the geological cross-section constructed from surface mapping. In the seismic image, the upper crustal geological structures are seen to merge in the middle crust. Nevertheless, the OMZ middle crust is not a mere detachment level, as it shows very unusual features: it appears as a band of strong reflectivity and irregular thickness (the Iberian Reflective Body, IRB) that we interpret as a great sill-like intrusion of basic rocks. The boundaries of the OMZ are considered sutures of the orogen, and their geometrical features, as deduced from geological mapping and the seismic image, are in accordance with the transpressional character of the Variscan collision recorded in SW Iberia. The present Moho is flat, obliterating the root of the orogen.
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| 2. |
- Alcalde, J., et al.
(författare)
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3-D reflection seismic imaging of the Hontomin structure in the Basque-Cantabrian Basin (Spain)
- 2013
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Ingår i: Solid Earth. - : Copernicus GmbH. - 1869-9510 .- 1869-9529. ; 4:2, s. 481-496
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Tidskriftsartikel (refereegranskat)abstract
- The Basque-Cantabrian Basin of the northern Iberia Peninsula constitutes a unique example of a major deformation system, featuring a dome structure developed by extensional tectonics followed by compressional reactivation. The occurrence of natural resources in the area and the possibility of establishing a geological storage site for carbon dioxide motivated the acquisition of a 3-D seismic reflection survey in 2010, centered on the Jurassic Hontomin dome. The objectives of this survey were to obtain a geological model of the overall structure and to establish a baseline model for a possible geological CO2 storage site. The 36 km(2) survey included approximately 5000 mixed (Vibroseis and explosives) source points recorded with a 25 m inline source and receiver spacing. The target reservoir is a saline aquifer, at approximately 1450 m depth, encased and sealed by carbonate formations. Acquisition and processing parameters were influenced by the rough topography and relatively complex geology. A strong near-surface velocity inversion is evident in the data, affecting the quality of the data. The resulting 3-D image provides constraints on the key features of the geologic model. The Hontom n structure is interpreted to consist of an approximately 10(7) m(2) large elongated dome with two major (W-E and NW-SE) striking faults bounding it. Preliminary capacity estimates indicate that about 1.2 Gt of CO2 can be stored in the target reservoir.
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| 3. |
- Alcalde, J., et al.
(författare)
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Active seismic characterization experiments of the Hontomin research facility for geological storage of CO2, Spain
- 2013
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836 .- 1878-0148. ; 19:0, s. 785-795
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Tidskriftsartikel (refereegranskat)abstract
- An active source seismic experiment was carried out as part of the subsurface characterization study of the first Spanish Underground Research Facility for Geological Storage of CO2 in Hontomín (Burgos, Spain). The characterization experiment included a 36 km2 3D seismic reflection survey and two three-component seismic profiles. The target reservoir is a saline aquifer located at 1450 m depth within Lower Jurassic carbonates (Lias). The main seal is formed by interlayered marlstones and marly limestones of Early to Middle Jurassic age (Dogger and Lias). The seismic images obtained allow defining the 3D underground architecture of the reservoir site. The structure consists of an asymmetric dome crosscut by a relatively complex fault system. The detailed characterization of the fracture system is currently under study to unravel the geometric distribution of the faults and their extent within the different formations that form the structure. The constrained model has guided the design of the injection and monitoring boreholes and provided the data for the baseline study. The resultant high resolution seismic model will be used as a reference in future monitoring stages.
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| 4. |
- Ayarza, P, et al.
(författare)
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Contrasting tectonic history of the are-continent suture in the Southern and Middle Urals: implications for the evolution of the orogen
- 2000
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Ingår i: Journal of the Geological Society. - : Geological Society of London. - 0016-7649 .- 2041-479X. ; 157, s. 1065-1076
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Tidskriftsartikel (refereegranskat)abstract
- The Main Uralian Fault has been considered the original arc–continent suture for 2000 km along the Uralide orogen. The symmetry of the tectonic units across it suggested a consistent east-dipping polarity for the palaeosubduction zone, which, together with its topographic and aeromagnetic signature, supported the idea of a single suture. However, several characteristics vary at different latitudes. In the Middle Urals, it is a strike-slip fault zone with moderately deformed and metamorphosed volcanic arc fragments in its hanging wall, and low-grade metamorphic rocks of the East European Craton in its footwall. Here, it has a prominent NNW-trending magnetic signature which cross-cuts north-trending anomalies in its hanging wall, and a pronounced reflection seismic signature that can be traced to the top of the middle crust at c. 5 s. TWT. In the Southern Urals, it is a serpentinite mélange zone of ambiguous kinematics, with a weakly deformed and metamorphosed volcanic arc in its hanging wall, and moderately metamorphosed to high pressure rocks of the East European Craton in its footwall. In this part of the orogen, it has a weak reflection seismic character, and a magnetic signature that parallels that of its hanging wall. On the basis of an integrated analysis of these different data sets, we suggest that the Main Uralian Fault, as it is currently defined, is not a single entity, but rather the original arc–continent suture in the south, and the western strand of a strike-slip fault system that reworked the original suture in the Middle Urals.
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| 5. |
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| 6. |
- Ayarza, P., et al.
(författare)
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Geophysical constraints on the structure of a limited ocean-continent subduction zone at the north Iberian margin
- 2004
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Ingår i: Tectonics. ; 23, s. 1010-
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Tidskriftsartikel (refereegranskat)abstract
- Late Cretaceous to Cenozoic convergence between Iberia and Europe led to the partial closure of the Bay of Biscay with limited southward subduction of oceanic crust below the North Iberian Margin. Inclined sub-Moho reflections and diffractions observed in deep seismic reflection profiles shot across the margin are especially well represented in two reflection profiles: ESCIN-3.2 and ESCIN-3.3. These two profiles have been chosen to test if the sub-Moho reflections correspond to true primary deep events and, provided that they are reflecting off the subduction zone, to investigate its deep structure. Spectral analysis together with travel time estimation and migration allow us to characterize a number of these sub-Moho events as deep-source, low-frequency (∼19 Hz), reflections and diffractions. Synthetic seismograms were generated by three-dimensional seismic modeling of a sub-Moho southward dipping surface, interpreted to correspond to the top of subducted oceanic crust. Comparison between the real and synthetic data show that inclined, low-frequency sub-Moho reflections in both, ESCIN-3.2 and ESCIN-3.3 profiles may correspond to reflections from southward subducted Bay of Biscay oceanic crust. Geoid, free-air gravity, and absolute topography modeling provides additional constraints on the lithospheric-scale structure of this limited ocean-continent subduction zone beneath the North Iberian Margin.
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| 7. |
- Ayarza, P, et al.
(författare)
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Integrated geological and geophysical studies in the SG4 borehole area, Tagil Volcanic Arc, Middle Urals: Location of seismic reflectors and source of the reflectivity
- 2000
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Ingår i: Journal of Geophysical Research. - : AMER GEOPHYSICAL UNION. - 0148-0227 .- 2156-2202. ; 105:B9, s. 21333-21352
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Tidskriftsartikel (refereegranskat)abstract
- Near-vertical incidence reflection seismic data acquired in the Tagil Volcanic Arc (Middle Urals) show the upper crust to be highly reflective. Two intersecting seismic lines located near the ongoing ∼5400 m deep SG4 borehole show that the main reflectivity strikes approximately N-S and dips ∼35°–55° to the east. Prominent reflections intercept the borehole at ∼1000, ∼1500, 2800–2900, ∼3400, and between ∼4000 and 5400 m, which correspond to intervals of low velocity/low density/low resistivity. The surface projections of these reflections lie parallel to the strike of magnetic anomaly trends. Multioffset vertical seismic profile (VSP) data acquired in the SG4 borehole show a seismic response dominated by P to S reflected converted waves from the moderately east dipping reflectivity and from a set of very steep east dipping reflectors not imaged by the surface data. Modeling of the VSP data constrains the depth at which reflectors intercept the borehole and suggests that the P to S conversions are best explained by low-velocity porous intervals rather than higher-velocity mafic material. The most prominent east dipping reflection on the surface seismic data is only imaged on VSP shots that sample the crust closer to the E-W seismic line. This discrepancy between the VSP and the surface seismic data is attributed to rapid lateral changes in the physical properties of the reflector. Surface and borehole data suggest that the low-velocity/low-density/low-resistivity intervals are the most important source of reflectivity in the SG4 borehole area, although lithological contrasts may also play a role. Drill cores from the these zones contain hydrothermal alteration minerals indicating interaction with fluids. Tectonic criteria suggest that they might represent imbricated fracture zones often bounding different lithologies and/or intrusions. Some of them might also represent high-porosity lava flows or pyroclastic units, common in island arc environments.
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| 8. |
- Brown D., Juhlin C., Tryggvason A., Steer D., Ayarza P., Beckholmen M., Rybalka A. and Bliznetsov M.
(författare)
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The Crustal Architecture of the Southern and Middle Urals from the URSEIS, ESRU, and Alapaev Reflection Seismic Profiles, in Orogenic Processes in the Paleozoic Uralides
- 2002
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Ingår i: Geophysical Monograph Series, AGU. ; , s. 33-48
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Tidskriftsartikel (refereegranskat)
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| 9. |
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| 10. |
- Carbonell, R., et al.
(författare)
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Geophysical Evidence of a Mantle Plume Derived Intrusion Complex
- 2004
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 31, s. L11601-
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Deep seismic reflection data acquired as part of the SW-Iberia EUROPROBE project across the transpressional Variscan orogen sample three tectonic terranes: the South Portuguese Zone, the Ossa-Morena Zone, and the Central Iberian Zone. The seismic data reveal the existence of a mid-crustal reflective body 140 km long and of variable thickness (up to 5 km), the Iberian Reflective body. The conductivity image provided by coincident MT soundings, the amplitude characteristics of the seismics, mineralization studies related to magmatic ore deposits, and the surface geology suggest that the IRB is a mantle-derived mafic intrusion. The geophysical, geological and petrological data suggest that the IRB is most probably an Early Carboniferous (approximately at 350–340 Ma) mantle-derived intrusion possibly linked to plume activity that took place in Europe in the Carboniferous and Permian.
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