scholarly journals What can seismic noise tell us about the Alpine reactivation of the Iberian Massif? An example in the Iberian Central System

2020 ◽  
Author(s):  
Juvenal Andrés ◽  
Puy Ayarza ◽  
Martin Schimmel ◽  
Imma Palomeras ◽  
Mario Ruiz ◽  
...  
Keyword(s):  
Seismic Data ◽  
Seismic Noise ◽  
Mountain Range ◽  
Upper Crust ◽  
Foreland Basins ◽  
Iberian Massif ◽  
Central System ◽  
Deep Crustal Structure ◽  
Southern Central ◽  
Lower Crustal

Abstract. The Iberian Central System, formed after the Alpine reactivation of the Variscan Iberian Massif, features maximum altitudes of 2500 m. It is surrounded by two foreland basins with contrasting elevation: The Duero Basin to the N, located at 750–800 m and the Tajo Basin to the S, lying at 450–500 m. The deep crustal structure of this mountain range seems to be characterized by the existence of a moderate crustal root that provides isostatic support for its topography. New seismic data is able to constrain the geometry of this crustal root, which appears to be defined by a northward lower crustal imbrication of the southern Central Iberian crust underneath this range. Contrarily to what was expected, this imbrication also affects the upper crust, as the existing orogen-scale mid-crustal Variscan detachment was probably assimilated during the Carboniferous crustal melting that gave rise to the Central System batholith. This implies that the reactivated upper crustal fractures can reach lower crustal depths, thus allowing the entire crust to sink. This new model can explain the differences in topography between the Central System foreland basins. Also, it provides further constrains on the crustal geometry of this mountain range, as it seems to be that of an asymmetric Alpine-type orogen, thus hindering the existence of buckling processes as the sole origin of the deformation. Results presented here have been achieved after autocorrelation of seismic noise along the CIMDEF profile. Although the resolution of the dataset features limited resolution (0.5–4 Hz, stations placed at ~ 5 km), this methodology has allowed us to pinpoint some key structures that helped to constraint the deformation mechanisms that affected Central Iberia during the Alpine orogeny.

scholarly journals What can seismic noise tell us about the Alpine reactivation of the Iberian Massif? An example in the Iberian Central System

Solid Earth ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 2499-2513
Author(s):  
Juvenal Andrés ◽  
Puy Ayarza ◽  
Martin Schimmel ◽  
Imma Palomeras ◽  
Mario Ruiz ◽  
...  
Keyword(s):  
Seismic Noise ◽  
Deformation Mechanisms ◽  
Mountain Range ◽  
Foreland Basins ◽  
Iberian Massif ◽  
Central System ◽  
The North ◽  
Deep Crustal Structure ◽  
Southern Central ◽  
Lower Crustal

Abstract. The Iberian Central System, formed after the Alpine reactivation of the Variscan Iberian Massif, features maximum altitudes of 2500 m. It is surrounded by two foreland basins with contrasting elevation: the Duero Basin to the north, located at 750–800 m, and the Tajo Basin to the south, lying at 450–500 m. The deep crustal structure of this mountain range seems to be characterized by the existence of a moderate crustal root that provides isostatic support for its topography. New seismic data are able to constrain the geometry of this crustal root, which appears to be defined by a northward lower-crustal imbrication of the southern Central Iberian crust underneath this range. Contrarily to what was expected, this imbrication also affects the upper crust, as the existing orogen-scale mid-crustal Variscan detachment was probably assimilated during the Carboniferous crustal melting that gave rise to the Central System batholith. In addition, the lower crust might have thinned, allowing coupled deformation at both crustal levels. This implies that the reactivated upper-crustal fractures can reach lower-crustal depths, thus allowing the entire crust to sink. This new model can explain the differences in topography between the Central System foreland basins. Also, it provides further constraints on the crustal geometry of this mountain range, as it seems to be that of an asymmetric Alpine-type orogen, thus hindering the existence of buckling processes as the sole origin of the deformation. The results presented here have been achieved after autocorrelation of seismic noise along the CIMDEF (Central Iberian Massif DEFormation Mechanisms) profile. Although the resolution of the dataset features limited resolution (0.5–4 Hz, stations placed at ∼ 5 km), this methodology has allowed us to pinpoint some key structures that helped to constraint the deformation mechanisms that affected Central Iberia during the Alpine orogeny.

scholarly journals Lithospheric structure of the Iberian Central System (Iberian Massif) imaged by the wide-angle seismic reflection/refraction CIMDEF experiment 

2021 ◽  
Author(s):  
Irene DeFelipe ◽  
Puy Ayarza ◽  
Imma Palomeras ◽  
Juvenal Andrés ◽  
Mario Ruiz ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Seismic Reflection ◽  
P Wave ◽  
Lithospheric Structure ◽  
Mountain Range ◽  
Wide Angle ◽  
Topographic Feature ◽  
Iberian Massif ◽  
Central System ◽  
P Wave Velocity

<p>The Iberian Central System represents an outstanding topographic feature in the central Iberian Peninsula. It is an intraplate mountain range formed by igneous and metasedimentary rocks of the Variscan Iberian Massif that has been exhumed since the Eocene in the context of the Alpine orogeny. The Iberian Central System has been conventionally interpreted as a thick-skinned pop-up mountain range thrust over the Duero and Tajo foreland basins. However, its lithospheric structure and the P-wave velocity distribution are not yet fully resolved. In order to place geophysical constraints on this relevant topographic feature, to identify lithospheric discontinuities, and to unravel the crustal deformation mechanisms, a wide-angle seismic reflection and refraction experiment, CIMDEF (Central Iberian Mechanism of DEFormation), was acquired in 2017 and 2019. It is a NNW-SSE oriented 360-km long profile that runs through the Duero basin, the Iberian Central System and the Tajo basin. First results based on forward modeling by raytracing show an irregularly layered lithosphere and allow to infer the depth extent of the northern Iberian Central System batholith. The crust is ~ 31 km thick under the Duero and Tajo basins and thickens to ~ 39 km under the Iberian Central System. A conspicuous thinning of the lower crust towards the south of the Iberian Central System is also modeled. Along this transect, a continuous and high amplitude upper mantle feature is observed and modeled as the reflection of an interface dipping from 58 to 62 km depth featuring a P-wave velocity contrast of 8.2 to 8.3 km/s. Our preliminary results complement previous models based on global-phase seismic and noise interferometry and gravity data, provide new constraints to validate the accuracy of passive seismic methods at lithospheric scale, and contribute with a resolute P-wave velocity model of the study area to unravel the effect of the Alpine reactivation on the central Iberian Massif.<br>This project has been funded by the EIT-RawMaterials 17024 (SIT4ME) and the MINECO projects: CGL2016-81964-REDE, CGL2014-56548-P.</p>

scholarly journals Lithospheric image of the Central Iberian Zone (Iberian Massif) using Global-Phase Seismic Interferometry

2019 ◽  
Author(s):  
Juvenal Andrés ◽  
Deyan Draganov ◽  
Martin Schimmel ◽  
Puy Ayarza ◽  
Imma Palomeras ◽  
...  
Keyword(s):  
Lower Crust ◽  
Scale Model ◽  
Seismic Interferometry ◽  
Mountain Range ◽  
Iberian Massif ◽  
Central System ◽  
Duero Basin ◽  
Short Period ◽  
Single Station ◽  
Spanish Central System

Abstract. 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 while the Duero Basin presents 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 also identified by 1) the geometry of the Moho discontinuity 2) an imbricated crustal architecture and/or 3) the rheological properties of the lithosphere. Shedding some light about these features are the main targets 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 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 (> 120º 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 relative 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. The upper crust has a very distinctive signature depending on the region. Reflectivity at upper-mantle depths is scattered throughout the profile, located between 13–18 s, and probably related with the Hales discontinuity.

scholarly journals Deep Crustal Structure of the Capricorn Orogen from Gravity and Seismic Data

2015 ◽  
Vol 2015 (1) ◽  
pp. 1-3
Author(s):  
Abdulrhman H. Alghamdi ◽  
Alan R.A. Aitken ◽  
Michael C. Dentith
Keyword(s):  
Crustal Structure ◽  
Seismic Data ◽  
Deep Crustal Structure

Crustal structure of the Valhalla complex, British Columbia, from Lithoprobe seismic-reflection and potential-field data

1990 ◽  
Vol 27 (8) ◽  
pp. 1048-1060 ◽  
Author(s):  
David W. S. Eaton ◽  
Frederick A. Cook
Keyword(s):  
Heat Flux ◽  
North American ◽  
Seismic Reflection ◽  
Surface Heat Flux ◽  
Field Data ◽  
High Surface ◽  
Surface Heat ◽  
Upper Crust ◽  
Potential Field Data ◽  
Lower Crustal

The Valhalla complex, situated in the Omineca crystalline belt in southeastern British Columbia, is a Cordilleran metamorphic core complex bordering the suture zone between Quesnellia and North American rocks. The region is tectonically interposed between a convergent plate margin along Canada's west coast and the stable North American craton, and is characterized by a crustal thickness of ~ 35 km, high surface heat flux, and elevated lower crustal electrical conductivity. In this study, Lithoprobe deep-crustal seismic-reflection data, potential-field data, and geological constraints have been used to gain a better understanding of crustal structure in the vicinity of the Valhalla complex. Analysis of Bouguer gravity and total-field aeromagnetic data indicates that mafic oceanic rocks and various syn- and post-accretionary granitoid plutonic rocks are not major constituents of the upper crust underlying the complex. The seismic data reveal a moderately reflective upper crust and image several fault zones, including a very high amplitude, west-dipping reflection that is interpreted as a significant Late Cretaceous or Paleocene thrust fault. The fault-zone reflectivity may be related to compositional heterogeneity and (or) seismic anisotropy associated with mylonites. The lower crust appears to be nonreflective, in contrast with other areas of high surface heat flux and elevated lower crustal conductivity. Taken together, the various data show that the Valhalla complex is likely cored by North American metasedimentary rocks and reveal features related to the Jurassic to Paleocene compressional fabric, which has been largely overprinted at the surface by subsequent Eocene extension.

Thermodynamic constraints on assimilation of silicic crust by primitive magmas

2021 ◽  
Author(s):  
Jussi S Heinonen ◽  
Frank J Spera ◽  
Wendy A Bohrson
Keyword(s):  
Phase Equilibria ◽  
Lower Crust ◽  
Primitive Mantle ◽  
Upper Crust ◽  
Basaltic Composition ◽  
Primitive Magma ◽  
Partial Melts ◽  
Thermodynamic Limits ◽  
Melt Composition ◽  
Lower Crustal

<p>Some studies on basaltic and more primitive rocks suggest that their parental magmas have assimilated more than 50 wt.% (relative to the initial uncontaminated magma) of crustal silicate wallrock. But what are the thermodynamic limits for assimilation by primitive magmas? This question has been considered for over a century, first by N.L. Bowen and many others since then. Here we pursue this question quantitatively using a freely available thermodynamic tool for phase equilibria modeling of open magmatic systems — the Magma Chamber Simulator (MCS; https://mcs.geol.ucsb.edu).</p><p>In the models, komatiitic, picritic, and basaltic magmas of various ages and from different tectonic settings assimilate progressive partial melts of average lower, middle, and upper crust. In order to pursue the maximum limits of assimilation constrained by phase equilibria and energetics, the mass of wallrock in the simulations was set at twice that of the initially pristine primitive magmas. In addition, the initial temperature of wallrock was set close to its solidus at a given pressure. Such conditions would approximate a rift setting with tabular chambers and high magma input causing concomitant crustal heating and steep geotherms.</p><p>Our results indicate that it is difficult for any primitive magma to assimilate more than 20−30 wt.% of upper crust before evolving to intermediate/felsic compositions. However, if assimilant is lower crust, typical komatiitic magmas can assimilate more than their own weight (range of 59−102 wt.%) and retain a basaltic composition. Even picritic magmas, more relevant to modern intraplate settings, have a thermodynamic potential to assimilate 28−49 wt.% of lower crust before evolving into intermediate/felsic compositions.</p><p>These findings have important implications for petrogenesis of magmas. The parental melt composition and the assimilant heavily influence both how much assimilation is energetically possible in primitive magmas and the final magma composition. The fact that primitive mantle melts have potential to partially melt and assimilate significant fractions of (lower) crust may have fundamental importance for how trans-Moho magmatic systems evolve and how crustal growth is accomplished. Examples include generation of siliceous high-magnesium basalts in the Precambrian and anorogenic anorthosite-mangerite-charnockite-granite complexes with geochemical evidence of considerable geochemical overprint from (lower) crustal sources.</p>

scholarly journals A U‐Pb Study of Zircons from a Lower Crustal Granulite Xenolith of the Spanish Central System: A Record of Iberian Lithospheric Evolution from the Neoproterozoic to the Triassic

2006 ◽  
Vol 114 (4) ◽  
pp. 471-483 ◽  
Author(s):  
Javier Fernández‐Suárez ◽  
Ricardo Arenas ◽  
Teresa E. Jeffries ◽  
Martin J. Whitehouse ◽  
Carlos Villaseca
Keyword(s):  
Central System ◽  
Granulite Xenolith ◽  
System A ◽  
Spanish Central System ◽  
Lower Crustal ◽  
Lithospheric Evolution

scholarly journals Elevated magma fluxes deliver high-Cu magmas to the upper crust

Geology ◽  
2020 ◽  
Vol 48 (10) ◽  
pp. 957-960
Author(s):  
Daniel Cox ◽  
Sebastian F.L. Watt ◽  
Frances E. Jenner ◽  
Alan R. Hastie ◽  
Samantha J. Hammond ◽  
...  
Keyword(s):  
Small Proportion ◽  
Ore Deposits ◽  
Crustal Evolution ◽  
Upper Crust ◽  
Convergent Margins ◽  
Ore Genesis ◽  
Porphyry Cu ◽  
Show Evidence ◽  
Lower Crustal ◽  
Garnet Fractionation

Abstract Porphyry Cu-Au ore deposits are globally associated with convergent margins. However, controls on the processing and distribution of the chalcophile elements (e.g., Cu) during convergent margin magmatism remain disputed. Here, we show that magmas feeding many Chilean stratovolcanoes fractionate sulfides with a high-Cu/Ag ratio early in their crustal evolution. These magmas show evidence of lower-crustal garnet and amphibole crystallization, and their degree of sulfide fractionation and Cu depletion increase with both crustal thickness and the extent of garnet fractionation. However, samples from a small proportion of volcanoes with elevated eruptive fluxes depart from this Cu-depleting trend, instead erupting Cu-rich magmas. This implies that at these atypical sites, elevated magma productivity and crustal throughput, potentially facilitated by “pathways” exploiting major crustal fault systems, enable rapid magma transit, avoiding lower-crustal Cu-depleting sulfide fractionation and potentially playing an important role in porphyry ore genesis.

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