Journal Of Geophysical Research: Solid Earth, Apr 1, 2021
Observations from field sampling (i.e., mantle xenoliths and outcrops of exhumed mantle) and indi... more Observations from field sampling (i.e., mantle xenoliths and outcrops of exhumed mantle) and indirect methods (e.g., the range of measured seismic velocities) suggest that the continental upper mantle is mainly peridotitic in composition. However, the mantle's composition is not uniform (e.g., Stracke, 2012), and the significant lithological and structural heterogeneities can produce impedance contrasts high enough to be observed in seismic data (Fumagalli & Klemme, 2015). The birth and evolution of new seismic techniques and the densification of seismic arrays have confirmed the presence of layering within the continental lithosphere, with numerous positive and negative velocity change at the discontinuities (e.g., Clowes et al., 2010; Thybo & Anderson, 2006, and references therein).
The size, frequency, and intensity of volcanic eruptions are strongly controlled by the volume an... more The size, frequency, and intensity of volcanic eruptions are strongly controlled by the volume and connectivity of magma within the crust. Several geophysical and geochemical studies have produced a comprehensive model of the magmatic system to depths near 7 km beneath Mount St. Helens (Washington State, USA), currently the most active volcano in the Cascade Range. Data limitations have precluded imaging below this depth to observe the entire primary shallow magma reservoir, as well as its connection to deeper zones of magma accumulation in the crust. The inversion of P and S wave traveltime data collected during the active-source component of the iMUSH (Imaging Magma Under St. Helens) project reveals a high P-wave (Vp)/S-wave (Vs) velocity anomaly beneath Mount St. Helens between depths of 4 and 13 km, which we interpret as the primary upper-middle crustal magma reservoir. Beneath and southeast of this shallow reservoir, a low Vp velocity column extends from 15 km depth to the Moho. Deep long-period events near the boundary of this column indicate that this anomaly is associated with the injection of magmatic fluids. Southeast of Mount St. Helens, an upper-middle crustal high Vp/Vs body beneath the Indian Heaven Volcanic Field may also have a magmatic origin. Both of these high Vp/Vs bodies are at the boundaries of the low Vp middle-lower crustal column and both are directly above high Vp middle-lower crustal regions that may represent cumulates associated with recent Quaternary or Paleogene-Neogene Cascade magmatism. Seismicity immediately following the 18 May 1980 eruption terminates near the top of the inferred middle-lower crustal cumulates and directly adjacent to the inferred middle-lower crustal magma reservoir. These spatial relationships suggest that the boundaries of these high-density cumulates play an important role in both vertical and lateral transport of magma through the crust.
The Spanish Central System is an intraplate mountain range that divides the Iberian Inner Plateau... more The Spanish Central System is an intraplate mountain range that divides the Iberian Inner Plateau in two sectors-the northern Duero Basin and the Tajo Basin to the south. The topography of the area is highly variable with the Tajo Basin having an average altitude of 450-500 m and the Duero Basin having a higher average altitude of 750-800 m. The Spanish Central System is characterized by a thick-skin pop-up and pop-down configuration formed by the reactivation of Variscan structures during the Alpine orogeny. The high topography is, most probably, the response of a tectonically thickened crust that should be the response to (1) the geometry of the Moho discontinuity, (2) an imbricated crustal architecture, and/or (3) the rheological properties of the lithosphere. Shedding some light on these features is the main target of the current investigation. In this work, we present the lithospheric-scale model across this part of the Iberian Massif. We have used data from the Central Iberian Massif Deformation (CIMDEF) project, which consists of recordings of an almost-linear array of 69 short-period seismic stations, which define a 320 km long transect. We have applied the so-called global-phase seismic interferometry. The technique uses continuous recordings of global earthquakes (> 120 • epicentral distance) to extract global phases and their reverberations within the lithosphere. The processing provides an approximation of the zero-offset reflection response of a single station to a vertical source, sending (near)-vertical seismic energy. Results indeed reveal a clear thickening of the crust below the Central System, resulting, most probably, from an imbrication of the lower crust. Accordingly, the crust-mantle boundary is mapped as a relatively flat interface at approximately 10 s two-way travel time except in the Central System, where this feature deepens towards the NW reaching more than 12 s. The boundary between the upper and lower crust is well defined and is found at 5 s two-way travel time. The upper crust has a very distinctive signature depending on the region. Reflectivity at upper-mantle depths is scattered throughout the profile, located between 13 and 18 s, and probably related to the Hales discontinuity.
The Iberian Massif presents a geometry characterized by two oroclines: the conspicuous and tight ... more The Iberian Massif presents a geometry characterized by two oroclines: the conspicuous and tight Ibero-armorican arc to the north and the older and less pronounced Central Iberian Arc (CIA) to the south. The latter is clearly depicted by low amplitude, short wavelength magnetic anomalies in its external part and long wavelength, higher amplitude magnetic anomalies in its internal part. The origin of these is under study as they seem to be indicators of the deep evolution of this orogen in the Iberian Peninsula.Three magnetic anomalies stand out in the internal part of the CIA. To the north, the Eastern Galicia Magnetic Anomaly overlaps the Lugo Gneiss Dome, a structure delineated by extensional detachments. Here, the exhumation at high temperatures during late Variscan gravitational collapse triggered the formation of magnetite in metasediments, migmatites and S-type syn-orogenic granites, thus stablishing a clear relationship between tectonics and magnetization. To the west, the Porto-Viseu-Guarda Magnetic Anomaly has still an unclear origin, but it also overlaps an area characterized by extensional tectonics, gneiss domes development and granite intrusion. However, the most magnetic outcropping rocks are late Variscan I-type granites (Lavadores granite) and the Mindelo Migmatitic Complex. None of them shows a relationship between magnetization and extension. Contrarily, magnetic minerals seem to be related to the composition of the resisters in migmatites and to the formation of the Lavadores granite itself. Finally, the Spanish Central System Magnetic Anomaly, at the core of the CIA, also overlaps the exhumed products of late Variscan extension (granites and migmatites). The magnetic anomaly associated to this part of the arc has been studied in the Castellanos Antiform, a discrete extensional dome located in its northern part, where the interaction between high degree metasediments, extension, and migmatization can be revised. New high resolution magnetic and gravity data indicate that the magnetic anomaly coincides with a high Bouguer gravity anomaly, and overlaps an outcrop of granitoids with tonalitic xenoliths and gabbros. The relationship between gravity and magnetic anomalies, together with the lack of outcropping magnetic granitoids and/or migmatites in the Central System, and the high amount of heterogeneous xenoliths, including basic rocks, suggest that in central Iberia, late Variscan extension might have involved deeper levels of the crust and maybe the mantle. Considering the location of this area, in the core of the CIA, and the simultaneity between late Variscan extension and the CIA formation, we suggest that the development of the latter might have played an important role in the supply of mantle material.Funding: grant PID2020-117332GB-C21 and projects SA084P20, MCIN/AEI/10.13039/501100011033 and TED2021-130440B-I
Since the late 80s, the Iberian Massif has been sampled by different controlled and natural sourc... more Since the late 80s, the Iberian Massif has been sampled by different controlled and natural source seismic experiments. The ILIHA-DSS, IBERSEIS-WA and ALCUDIA-WA wide-angle reflection/refraction surveys acquired in south and western Iberia have offsets and energy large enough to illuminate the uppermost mantle and reveal some deep reflected energy. Sub-Moho reflections can be also observed in vertical incidence (ALCUDIA-NI) and seismic interferometry (CIMDEF) transects beneath the Central Iberian Zone. All datasets indicate that the energy reflects off an interface with a positive velocity contrast at a depth that concurs with that assumed for the Hales discontinuity that is the phase transition from spinel to garnet lherzolite. The coda and amplitude of this event suggest that it can correspond to a ~10 km thick heterogeneous layer where the spinel and garnet ratio varies. To test this hypothesis we used a 2D second order finite-difference acoustic full wave-field scheme on a P-wave velocity model with a layer consisting of randomly distributed bodies, thinner than ¼ of the wavelength of the seismic waves featuring a ΔVp=±0.1 km/s at the considered depth range. Resulting synthetic shot gathers reproduce well the observed amplitudes and codas as the constructive interference caused by the layering produces a tuning effect in this gradient heterogeneous zone.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
The Spanish Central System is an intraplate mountain range dividing the Iberian Inner Plateau in ... more The Spanish Central System is an intraplate mountain range dividing the Iberian Inner Plateau in two sectors-the Duero Basin (N) and, the Tajo Basin (S). The latter has an average altitude of 450-500 m while the former presents a higher average altitude 750-800 m. This intraplate orogen features a thick-skin pop-up and pop-down configuration formed by the reactivation of Variscan structures. Its high topography is the response of a tectonically thickened crust evidenced by 1) the geometry of the Moho discontinuity 2) an imbricated crustal architecture and/or 3) the rheological properties of the lithosphere. Research has been carried out to build a lithospheric-scale model across the orogen. A 400 km long multi-seismic transect has been acquired using natural and controlled source seismic data. The earthquakes and seismic noise data was acquired over a period of one to two months of continuous recording along a linear array (69 short-period seismic stations). The controlled source data included over 1000 stations and a series of acoustic sources. This effort has delineated the geometry of the base of the crust by: Global-Phase Seismic and, conventional noise interferometry, and, wide-angle imaging. The Global Phase approach used PK, PKiKP and PKIKP phases of earthquakes (> 120° epicentral distance). Stacking of the autocorrelations of these phases contribute to a pseudo zero-offset X-section. The application of ambient noise seismic interferometry complements the zero-offset reflection image, defining the geometry of the Moho. Further details on the lithospheric structure is provided by seismic wide-angle reflection images, which reveal a clear thickening of the crust below the Central System resulting, most probably, from an imbrication of the lower crust. Accordingly, the crust-mantle boundary is mapped as a relative flat interface at approximately 10 s two-way travel time except under the Central System, where this feature deepens towards the NW reaching more than 12 s. An intra-crustal boundary is well defined at 5 s. Reflectivity within upper-mantle depths is scattered throughout the profile, located between 13-18 s, and probably related with the Hales discontinuity.
During the last 15 years, the IBERSEIS and ALCUDIA controlled source experiments have acquired ve... more During the last 15 years, the IBERSEIS and ALCUDIA controlled source experiments have acquired vertical incidence and wide angle seismic reflection data in southwest Spain. Apart from providing detailed information of the crust, these datasets have also imaged a conspicuous sub-crustal reflector. First identified on the IBERSEIS wide-angle reflection dataset, this interface seemed to feature a positive seismic impedance contrast. A boundary located between 62-71 km depth, with a Vp increase from 8.2 km/s to 8.3 km/s allowed us to model clear wide angle reflections found at 180 km offsets. The fact that this reflector was not identified in the coincident vertical incidence dataset led us interpret it as a gradient zone. A correlation with the ‘Hales gradient zone’, i.e. the boundary between spinel and garnet peridotites was our preferred interpretation. The ALCUDIA experiment, later acquired northwards of the IBERSEIS profiles, also shows prominent sub-crustal arrivals. However, these reflections also appear locally in the vertical incidence dataset at 19 s TWT, further constraining the depth at which this feature is located. In addition, the ALCUDIA wide-angle dataset shows refractions that become first arrivals above 180 km. This suggests that this boundary features a positive Vp contrast, varying its character from a transition zone to a sharper discontinuity. Integration of the information provided by the IBERSEIS and ALCUDIA datasets with older data from the ILIHA project, where a mantle feature was identified at similar depths, allows us to map a regional scale upper mantle discontinuity in southwest Iberia. Its Vp increase, sub-horizontal geometry and tectonic context indicate that it is probably related to a phase transition, likely the Hales discontinuity.Peer Reviewe
Journal of Geophysical Research: Solid Earth, 2018
In this work the thermal structure of the Iberian Peninsula is derived from magnetic data by calc... more In this work the thermal structure of the Iberian Peninsula is derived from magnetic data by calculating the bottom of the magnetization, assumed to be the Curie‐point depth (CPD) isotherm, which accounts for the depth at which magnetite becomes paramagnetic (580°C). Comparison of the CPD with crustal thickness maps along with a heat flow map derived from the CPD provides new insights on the lithospheric thermal regime. Within Iberia, the CPD isotherm has thickness in the range of 17 to 29 km. This isotherm is shallow (<18 km) offshore, where the lithosphere is thinner. In continental Iberia, the NW Variscan domain presents a magnetic response that is most probably linked to thickening and later extension processes during the late Variscan Orogeny, which resulted in widespread crustal melting and emplacement of granites (in the Central Iberian Arc). The signature of the CPD at the Gibraltar Arc reveals a geometry consistent with the slab roll‐back geodynamic model that shaped the...
Comprehensive set of seismic and potential field data from the whole European Variscan belt is us... more Comprehensive set of seismic and potential field data from the whole European Variscan belt is used to interpret the structure and evolution of the European Variscides as defined by Martínez Catalán et al. (2021). The gravity data show the presence of high amplitude, short-wavelength gravity anomalies correlated with the outcrops of eclogites, ultramafic rocks and ophiolites delineating the main body of the Mid-Variscan Allochthon (MVA) and the Devonian Mid-Variscan suture (MVS). The medium amplitude and elongated long-wavelength gravity highs, aligned parallel to the Variscan structural grain, correspond to the low-grade Proterozoic rocks of the MVA and Devonian arc – back-arc system. On the other hand, the short wavelength negative gravity anomalies developed in the central part of the belt coincide with Carboniferous (330–310 Ma) per- to meta-aluminous magmatic bodies. The magnetic data show two belts correlated with Carboniferous Rhenohercynian and Devonian Mid-Variscan magmatic...
The late Variscan gravitational collapse and coeval magmatism are getting the attention of the co... more The late Variscan gravitational collapse and coeval magmatism are getting the attention of the community due to their role in the generation of strategic mineral resources. In this regard, the GOLDFINGER project’s main scope is to study how the Variscan orogenic architecture controls the generation of strategic ore deposits (i.e. Sn, W, Nb, Ta, Sc, Au, Sb). With this goal, a 3D model of a gneissic dome with several mineral deposits will be constructed based on high-resolution geophysics (Seismic/Gravity/Magnetism), and regional geology. The study area encompasses the Martinamor gneiss dome which represents a Late-Variscan syn-collisional extensional system with a well-preserved architecture. This gneiss dome structure presents low topography, relatively flat structural geometry in-depth, and contrasting lithotypes regarding seismic, gravity, and magnetic properties. As part of the project, in spring 2022 the area was covered by 30 low-period seismic recorders with 2Hz sensors in a r...
Journal Of Geophysical Research: Solid Earth, Apr 1, 2021
Observations from field sampling (i.e., mantle xenoliths and outcrops of exhumed mantle) and indi... more Observations from field sampling (i.e., mantle xenoliths and outcrops of exhumed mantle) and indirect methods (e.g., the range of measured seismic velocities) suggest that the continental upper mantle is mainly peridotitic in composition. However, the mantle's composition is not uniform (e.g., Stracke, 2012), and the significant lithological and structural heterogeneities can produce impedance contrasts high enough to be observed in seismic data (Fumagalli & Klemme, 2015). The birth and evolution of new seismic techniques and the densification of seismic arrays have confirmed the presence of layering within the continental lithosphere, with numerous positive and negative velocity change at the discontinuities (e.g., Clowes et al., 2010; Thybo & Anderson, 2006, and references therein).
The size, frequency, and intensity of volcanic eruptions are strongly controlled by the volume an... more The size, frequency, and intensity of volcanic eruptions are strongly controlled by the volume and connectivity of magma within the crust. Several geophysical and geochemical studies have produced a comprehensive model of the magmatic system to depths near 7 km beneath Mount St. Helens (Washington State, USA), currently the most active volcano in the Cascade Range. Data limitations have precluded imaging below this depth to observe the entire primary shallow magma reservoir, as well as its connection to deeper zones of magma accumulation in the crust. The inversion of P and S wave traveltime data collected during the active-source component of the iMUSH (Imaging Magma Under St. Helens) project reveals a high P-wave (Vp)/S-wave (Vs) velocity anomaly beneath Mount St. Helens between depths of 4 and 13 km, which we interpret as the primary upper-middle crustal magma reservoir. Beneath and southeast of this shallow reservoir, a low Vp velocity column extends from 15 km depth to the Moho. Deep long-period events near the boundary of this column indicate that this anomaly is associated with the injection of magmatic fluids. Southeast of Mount St. Helens, an upper-middle crustal high Vp/Vs body beneath the Indian Heaven Volcanic Field may also have a magmatic origin. Both of these high Vp/Vs bodies are at the boundaries of the low Vp middle-lower crustal column and both are directly above high Vp middle-lower crustal regions that may represent cumulates associated with recent Quaternary or Paleogene-Neogene Cascade magmatism. Seismicity immediately following the 18 May 1980 eruption terminates near the top of the inferred middle-lower crustal cumulates and directly adjacent to the inferred middle-lower crustal magma reservoir. These spatial relationships suggest that the boundaries of these high-density cumulates play an important role in both vertical and lateral transport of magma through the crust.
The Spanish Central System is an intraplate mountain range that divides the Iberian Inner Plateau... more The Spanish Central System is an intraplate mountain range that divides the Iberian Inner Plateau in two sectors-the northern Duero Basin and the Tajo Basin to the south. The topography of the area is highly variable with the Tajo Basin having an average altitude of 450-500 m and the Duero Basin having a higher average altitude of 750-800 m. The Spanish Central System is characterized by a thick-skin pop-up and pop-down configuration formed by the reactivation of Variscan structures during the Alpine orogeny. The high topography is, most probably, the response of a tectonically thickened crust that should be the response to (1) the geometry of the Moho discontinuity, (2) an imbricated crustal architecture, and/or (3) the rheological properties of the lithosphere. Shedding some light on these features is the main target of the current investigation. In this work, we present the lithospheric-scale model across this part of the Iberian Massif. We have used data from the Central Iberian Massif Deformation (CIMDEF) project, which consists of recordings of an almost-linear array of 69 short-period seismic stations, which define a 320 km long transect. We have applied the so-called global-phase seismic interferometry. The technique uses continuous recordings of global earthquakes (> 120 • epicentral distance) to extract global phases and their reverberations within the lithosphere. The processing provides an approximation of the zero-offset reflection response of a single station to a vertical source, sending (near)-vertical seismic energy. Results indeed reveal a clear thickening of the crust below the Central System, resulting, most probably, from an imbrication of the lower crust. Accordingly, the crust-mantle boundary is mapped as a relatively flat interface at approximately 10 s two-way travel time except in the Central System, where this feature deepens towards the NW reaching more than 12 s. The boundary between the upper and lower crust is well defined and is found at 5 s two-way travel time. The upper crust has a very distinctive signature depending on the region. Reflectivity at upper-mantle depths is scattered throughout the profile, located between 13 and 18 s, and probably related to the Hales discontinuity.
The Iberian Massif presents a geometry characterized by two oroclines: the conspicuous and tight ... more The Iberian Massif presents a geometry characterized by two oroclines: the conspicuous and tight Ibero-armorican arc to the north and the older and less pronounced Central Iberian Arc (CIA) to the south. The latter is clearly depicted by low amplitude, short wavelength magnetic anomalies in its external part and long wavelength, higher amplitude magnetic anomalies in its internal part. The origin of these is under study as they seem to be indicators of the deep evolution of this orogen in the Iberian Peninsula.Three magnetic anomalies stand out in the internal part of the CIA. To the north, the Eastern Galicia Magnetic Anomaly overlaps the Lugo Gneiss Dome, a structure delineated by extensional detachments. Here, the exhumation at high temperatures during late Variscan gravitational collapse triggered the formation of magnetite in metasediments, migmatites and S-type syn-orogenic granites, thus stablishing a clear relationship between tectonics and magnetization. To the west, the Porto-Viseu-Guarda Magnetic Anomaly has still an unclear origin, but it also overlaps an area characterized by extensional tectonics, gneiss domes development and granite intrusion. However, the most magnetic outcropping rocks are late Variscan I-type granites (Lavadores granite) and the Mindelo Migmatitic Complex. None of them shows a relationship between magnetization and extension. Contrarily, magnetic minerals seem to be related to the composition of the resisters in migmatites and to the formation of the Lavadores granite itself. Finally, the Spanish Central System Magnetic Anomaly, at the core of the CIA, also overlaps the exhumed products of late Variscan extension (granites and migmatites). The magnetic anomaly associated to this part of the arc has been studied in the Castellanos Antiform, a discrete extensional dome located in its northern part, where the interaction between high degree metasediments, extension, and migmatization can be revised. New high resolution magnetic and gravity data indicate that the magnetic anomaly coincides with a high Bouguer gravity anomaly, and overlaps an outcrop of granitoids with tonalitic xenoliths and gabbros. The relationship between gravity and magnetic anomalies, together with the lack of outcropping magnetic granitoids and/or migmatites in the Central System, and the high amount of heterogeneous xenoliths, including basic rocks, suggest that in central Iberia, late Variscan extension might have involved deeper levels of the crust and maybe the mantle. Considering the location of this area, in the core of the CIA, and the simultaneity between late Variscan extension and the CIA formation, we suggest that the development of the latter might have played an important role in the supply of mantle material.Funding: grant PID2020-117332GB-C21 and projects SA084P20, MCIN/AEI/10.13039/501100011033 and TED2021-130440B-I
Since the late 80s, the Iberian Massif has been sampled by different controlled and natural sourc... more Since the late 80s, the Iberian Massif has been sampled by different controlled and natural source seismic experiments. The ILIHA-DSS, IBERSEIS-WA and ALCUDIA-WA wide-angle reflection/refraction surveys acquired in south and western Iberia have offsets and energy large enough to illuminate the uppermost mantle and reveal some deep reflected energy. Sub-Moho reflections can be also observed in vertical incidence (ALCUDIA-NI) and seismic interferometry (CIMDEF) transects beneath the Central Iberian Zone. All datasets indicate that the energy reflects off an interface with a positive velocity contrast at a depth that concurs with that assumed for the Hales discontinuity that is the phase transition from spinel to garnet lherzolite. The coda and amplitude of this event suggest that it can correspond to a ~10 km thick heterogeneous layer where the spinel and garnet ratio varies. To test this hypothesis we used a 2D second order finite-difference acoustic full wave-field scheme on a P-wave velocity model with a layer consisting of randomly distributed bodies, thinner than ¼ of the wavelength of the seismic waves featuring a ΔVp=±0.1 km/s at the considered depth range. Resulting synthetic shot gathers reproduce well the observed amplitudes and codas as the constructive interference caused by the layering produces a tuning effect in this gradient heterogeneous zone.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
The Spanish Central System is an intraplate mountain range dividing the Iberian Inner Plateau in ... more The Spanish Central System is an intraplate mountain range dividing the Iberian Inner Plateau in two sectors-the Duero Basin (N) and, the Tajo Basin (S). The latter has an average altitude of 450-500 m while the former presents a higher average altitude 750-800 m. This intraplate orogen features a thick-skin pop-up and pop-down configuration formed by the reactivation of Variscan structures. Its high topography is the response of a tectonically thickened crust evidenced by 1) the geometry of the Moho discontinuity 2) an imbricated crustal architecture and/or 3) the rheological properties of the lithosphere. Research has been carried out to build a lithospheric-scale model across the orogen. A 400 km long multi-seismic transect has been acquired using natural and controlled source seismic data. The earthquakes and seismic noise data was acquired over a period of one to two months of continuous recording along a linear array (69 short-period seismic stations). The controlled source data included over 1000 stations and a series of acoustic sources. This effort has delineated the geometry of the base of the crust by: Global-Phase Seismic and, conventional noise interferometry, and, wide-angle imaging. The Global Phase approach used PK, PKiKP and PKIKP phases of earthquakes (> 120° epicentral distance). Stacking of the autocorrelations of these phases contribute to a pseudo zero-offset X-section. The application of ambient noise seismic interferometry complements the zero-offset reflection image, defining the geometry of the Moho. Further details on the lithospheric structure is provided by seismic wide-angle reflection images, which reveal a clear thickening of the crust below the Central System resulting, most probably, from an imbrication of the lower crust. Accordingly, the crust-mantle boundary is mapped as a relative flat interface at approximately 10 s two-way travel time except under the Central System, where this feature deepens towards the NW reaching more than 12 s. An intra-crustal boundary is well defined at 5 s. Reflectivity within upper-mantle depths is scattered throughout the profile, located between 13-18 s, and probably related with the Hales discontinuity.
During the last 15 years, the IBERSEIS and ALCUDIA controlled source experiments have acquired ve... more During the last 15 years, the IBERSEIS and ALCUDIA controlled source experiments have acquired vertical incidence and wide angle seismic reflection data in southwest Spain. Apart from providing detailed information of the crust, these datasets have also imaged a conspicuous sub-crustal reflector. First identified on the IBERSEIS wide-angle reflection dataset, this interface seemed to feature a positive seismic impedance contrast. A boundary located between 62-71 km depth, with a Vp increase from 8.2 km/s to 8.3 km/s allowed us to model clear wide angle reflections found at 180 km offsets. The fact that this reflector was not identified in the coincident vertical incidence dataset led us interpret it as a gradient zone. A correlation with the ‘Hales gradient zone’, i.e. the boundary between spinel and garnet peridotites was our preferred interpretation. The ALCUDIA experiment, later acquired northwards of the IBERSEIS profiles, also shows prominent sub-crustal arrivals. However, these reflections also appear locally in the vertical incidence dataset at 19 s TWT, further constraining the depth at which this feature is located. In addition, the ALCUDIA wide-angle dataset shows refractions that become first arrivals above 180 km. This suggests that this boundary features a positive Vp contrast, varying its character from a transition zone to a sharper discontinuity. Integration of the information provided by the IBERSEIS and ALCUDIA datasets with older data from the ILIHA project, where a mantle feature was identified at similar depths, allows us to map a regional scale upper mantle discontinuity in southwest Iberia. Its Vp increase, sub-horizontal geometry and tectonic context indicate that it is probably related to a phase transition, likely the Hales discontinuity.Peer Reviewe
Journal of Geophysical Research: Solid Earth, 2018
In this work the thermal structure of the Iberian Peninsula is derived from magnetic data by calc... more In this work the thermal structure of the Iberian Peninsula is derived from magnetic data by calculating the bottom of the magnetization, assumed to be the Curie‐point depth (CPD) isotherm, which accounts for the depth at which magnetite becomes paramagnetic (580°C). Comparison of the CPD with crustal thickness maps along with a heat flow map derived from the CPD provides new insights on the lithospheric thermal regime. Within Iberia, the CPD isotherm has thickness in the range of 17 to 29 km. This isotherm is shallow (<18 km) offshore, where the lithosphere is thinner. In continental Iberia, the NW Variscan domain presents a magnetic response that is most probably linked to thickening and later extension processes during the late Variscan Orogeny, which resulted in widespread crustal melting and emplacement of granites (in the Central Iberian Arc). The signature of the CPD at the Gibraltar Arc reveals a geometry consistent with the slab roll‐back geodynamic model that shaped the...
Comprehensive set of seismic and potential field data from the whole European Variscan belt is us... more Comprehensive set of seismic and potential field data from the whole European Variscan belt is used to interpret the structure and evolution of the European Variscides as defined by Martínez Catalán et al. (2021). The gravity data show the presence of high amplitude, short-wavelength gravity anomalies correlated with the outcrops of eclogites, ultramafic rocks and ophiolites delineating the main body of the Mid-Variscan Allochthon (MVA) and the Devonian Mid-Variscan suture (MVS). The medium amplitude and elongated long-wavelength gravity highs, aligned parallel to the Variscan structural grain, correspond to the low-grade Proterozoic rocks of the MVA and Devonian arc – back-arc system. On the other hand, the short wavelength negative gravity anomalies developed in the central part of the belt coincide with Carboniferous (330–310 Ma) per- to meta-aluminous magmatic bodies. The magnetic data show two belts correlated with Carboniferous Rhenohercynian and Devonian Mid-Variscan magmatic...
The late Variscan gravitational collapse and coeval magmatism are getting the attention of the co... more The late Variscan gravitational collapse and coeval magmatism are getting the attention of the community due to their role in the generation of strategic mineral resources. In this regard, the GOLDFINGER project’s main scope is to study how the Variscan orogenic architecture controls the generation of strategic ore deposits (i.e. Sn, W, Nb, Ta, Sc, Au, Sb). With this goal, a 3D model of a gneissic dome with several mineral deposits will be constructed based on high-resolution geophysics (Seismic/Gravity/Magnetism), and regional geology. The study area encompasses the Martinamor gneiss dome which represents a Late-Variscan syn-collisional extensional system with a well-preserved architecture. This gneiss dome structure presents low topography, relatively flat structural geometry in-depth, and contrasting lithotypes regarding seismic, gravity, and magnetic properties. As part of the project, in spring 2022 the area was covered by 30 low-period seismic recorders with 2Hz sensors in a r...
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