scholarly journals Deep seated density anomalies across the Iberia-Africa plate boundary and its topographic response

2020 ◽  
Author(s):  
Ivone Jiménez-Munt ◽  
Montserrat Torne ◽  
Manel Fernàndez ◽  
Jaume Vergés ◽  
Ajay Kumar ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Lithospheric Mantle ◽  
Plate Boundary ◽  
Continental Collision ◽  
Potential Fields ◽  
Seismic Velocities ◽  
S Wave ◽  
Bouguer Anomalies ◽  
Compositional Structure ◽  
Lateral Variations

<p>The modes in which the lithosphere deforms during continental collision and the mechanisms involved are not well understood. While continental subduction and mantle delamination are often invoked in tectonophysical studies, these processes are difficult to be confirmed in more complex tectonic regions such as the Gibraltar Arc. We study the present-day density and compositional structure of the lithosphere along a transect running from S Iberia to N Africa crossing the western Gibraltar Arc. This region is located in the westernmost continental segment of the African-Eurasian plates, characterized by a diffuse transpressive plate boundary. An integrated and self-consistent geophysical-petrological methodology is used to model the lithosphere structure variations and the thermophysical properties of the upper mantle. The crustal structure is mainly constrained by seismic experiments and geological data, whereas the composition of the lithospheric mantle is constrained by xenolith data. The results show large lateral variations in the topography of the lithosphere-asthenosphere boundary (LAB). We distinguish different chemical lithospheric mantle domains that reproduce the main trends of the geophysical observables and the modelled P- and S-wave seismic velocities. A sublithospheric body colder than the surrounding mantle is needed beneath the Betics-Rif to adjust the measured potential fields. We link this body to the Iberian slab localized just to the east of the profile and having some effect on the geoid and Bouguer anomalies. Local isostasy allows explaining most of the topography, but an elastic thickness higher than 10 km is needed to explain local misfits between the Atlas and the Rif Mountains. This work has been supported by Spanish Ministry by the projects MITE (CGL2014-59516) and GeoCAM (PGC2018-095154-B-100).</p>

Quaternary sodic and potassic intraplate volcanism in northeast China controlled by the underlying heterogeneous lithospheric structures

Geology ◽  
2021 ◽  
Author(s):  
Xingli Fan ◽  
Qi-Fu Chen ◽  
Yinshuang Ai ◽  
Ling Chen ◽  
Mingming Jiang ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Lithospheric Mantle ◽  
Northeast China ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Subcontinental Lithospheric Mantle ◽  
Seismic Velocities ◽  
S Wave ◽  
Crust And Upper Mantle ◽  
Potassic Volcanism

The origin and mantle dynamics of the Quaternary intraplate sodic and potassic volcanism in northeast China have long been intensely debated. We present a high-resolution, three-dimensional (3-D) crust and upper-mantle S-wave velocity (Vs) model of northeast China by combining ambient noise and earthquake two-plane wave tomography based on unprecedented regional dense seismic arrays. Our seismic images highlight a strong correlation between the basalt geochemistry and upper-mantle seismic velocity structure: Sodic volcanoes are all characterized by prominent low seismic velocities in the uppermost mantle, while potassic volcanoes still possess a normal but thin upper-mantle “lid” depicted by high seismic velocities. Combined with previous petrological and geochemical research findings, we propose that the rarely erupted Quaternary potassic volcanism in northeast China results from the interaction between asthenospheric low-degree melts and the overlying subcontinental lithospheric mantle. In contrast, the more widespread Quaternary sodic volcanism in this region is predominantly sourced from the upwelling asthenosphere without significant overprinting from the subcontinental lithospheric mantle.

scholarly journals An integrated geophysical-petrological view of the lithosphere of the northern Apennines, Dinarides and Pannonian Basin.

2021 ◽  
Author(s):  
Montserrat Torne ◽  
Wentao Zhang ◽  
Ivone Jimenez-Munt ◽  
Ana Negredo ◽  
Estefania Bravo ◽  
...  
Keyword(s):  
Lithospheric Mantle ◽  
Pannonian Basin ◽  
Gravity Anomalies ◽  
Northern Apennines ◽  
Tyrrhenian Sea ◽  
Seismic Velocities ◽  
S Wave ◽  
Uppermost Mantle ◽  
Back Arc ◽  
Lateral Variations

<p>The present-day structure of the lithosphere and uppermost mantle of Northern Apennines and Dinarides region results from a complex tectonic scenario mainly driven by subduction of Tethyan oceanic domains. The study area and surrounding regions have been the goal of a large number of geophysical studies that have provided information on the velocity, density and temperature distribution in the lithosphere and uppermost mantle. However, the majority of them do not consider the contribution of the chemical composition and phase transitions on the physical properties in the lithospheric mantle. By applying and integrated petrological-geophysical approach -LitMod2D_2.0- we aim at constraining and characterizing the present-day lithosphere and mantle structure along a NE-SW trending 730 km long geo-transect crossing the Northern Tyrrhenian Sea, the Northern Apennines, the Adriatic Sea, the Dinarides fold belt and the Pannonian back-arc basin. Along the modelled geotransect, we infer the spatial distribution of density, thermal conductivity and seismic velocities based on the variations of gravity, geoid, elevation and heat flow consistently with the thermochemical conditions and with isostatic equilibrium. Our results show significant lateral variations in the lithospheric structure, affecting crustal and lithospheric mantle thickness, temperature, density distribution, and mantle composition that reveals the imprint of the complex geodynamic evolution of the area. This is a GeoCAM contribution (PGC2018-095154-B-I00)</p><p><strong>Keywords: </strong>Alpine Mediterranean orogeny, geoid and gravity anomalies, elevation, integrated petrological-geophysical modelling, mantle seismic P and S-wave velocity.</p>

Tectonic accretion and recycling of the continental lithosphere during the Alpine orogeny along the Pyrenees

2014 ◽  
Vol 185 (4) ◽  
pp. 257-277 ◽  
Author(s):  
Olivier Vanderhaeghe ◽  
Alexia Grabkowiak
Keyword(s):  
Lithospheric Mantle ◽  
Plate Boundary ◽  
Thermal Relaxation ◽  
Continental Collision ◽  
Orogenic Belt ◽  
Mountain Range ◽  
Continental Lithosphere ◽  
Calculated Volume ◽  
Ductile Flow ◽  
The Difference

Abstract The goal of this paper is to identify the fate of the continental lithosphere along the Iberia-Eurasia convergent plate boundary marked by the formation of the Pyrenean orogenic belt. The present-day volumes of crust and lithosphere beneath the Pyrenees and the volume of eroded crust redistributed in neighbo ring basins are evaluated based on a synthesis of available geological and geophysical data. The volumes that are expected to have transited across the former plate boundary are modeled taking into account Iberia-Eurasia convergence and making assumptions regarding the initial lithospheric and crustal structure of the Iberia-Eurasia plate boundary at the onset of continental collision (~83 Ma). Despite large uncertainties, the difference between the initial and present-day lithospheric structures suggests that at 83 Ma, either the Iberia-Eurasia plate boundary was marked by a zone of thinned lithosphere (oceanic and/or continental), or the lithosphere having transited across the plate boundary has for the most part been recycled into the mantle. At the crustal-scale, the volume of tectonically accreted crust is estimated by adding the volume of crust currently present in the Pyrenean orogenic belt to the volume of sediments deposited in neighboring basins, and by subtracting the initial volume of crust at the onset of continental collision considering two end-members, namely (i) a continental rift or (ii) a 35 km wide oceanic basin. In both cases, this tectonically accreted crustal volume is not enough to match the calculated volume of crust that has potentially transited across the plate boundary as a consequence of convergence since 83 Ma. As a result, our computation suggests that at least 30% (and as much as 63%) of the continental crust has subducted with the Iberian lithospheric slab and has been recycled into the mantle. In addition, the synthesis of topographic and geophysical (gravity and seismic tomography) reveals a peculiar crustal and lithospheric scale structure for the current day Pyrenees characterized by (i) an elliptical-cone-shape Pyrenean mountain range underlain by an elliptical-cone-shaped crustal root pointing down, and (ii) two tongues of lithospheric mantle in the central part of the belt. These features are interpreted as reflecting redistribution of the lithospheric mantle and of the orogenic crust by ductile flow after subduction and tectonic accretion. We propose that following a period of subduction/collision from 83 to 35 Ma, the decrease in the convergence rate between Iberia-Eurasia favored thermal relaxation of the Iberian slab promoting ductile flow and the development of gravitational instabilities. We suggest that the orogenic root has been dragged down by the dense lithospheric root and that part of it has been recycled into the mantle. In this view, the current-day lithospheric tongues represent the remnants of the lithospheric root after thermal relaxation and recycling by convective removal.

Gaussian beam migration

Geophysics ◽  
1990 ◽  
Vol 55 (11) ◽  
pp. 1416-1428 ◽  
Author(s):  
N. Ross Hill
Keyword(s):  
Gaussian Beam ◽  
Wave Field ◽  
Seismic Source ◽  
Velocity Model ◽  
Downward Continuation ◽  
Gaussian Beams ◽  
Seismic Velocities ◽  
Migration Method ◽  
Gaussian Beam Migration ◽  
Lateral Variations

Just as synthetic seismic data can be created by expressing the wave field radiating from a seismic source as a set of Gaussian beams, recorded data can be downward continued by expressing the recorded wave field as a set of Gaussian beams emerging at the earth’s surface. In both cases, the Gaussian beam description of the seismic‐wave propagation can be advantageous when there are lateral variations in the seismic velocities. Gaussian‐beam downward continuation enables wave‐equation calculation of seismic propagation, while it retains the interpretive raypath description of this propagation. This paper describes a zero‐offset depth migration method that employs Gaussian beam downward continuation of the recorded wave field. The Gaussian‐beam migration method has advantages for imaging complex structures. Like finite‐difference migration, it is especially compatible with lateral variations in velocity, but Gaussian beam migration can image steeply dipping reflectors and will not produce unwanted reflections from structure in the velocity model. Unlike other raypath methods, Gaussian beam migration has guaranteed regular behavior at caustics and shadows. In addition, the method determines the beam spacing that ensures efficient, accurate calculations. The images produced by Gaussian beam migration are usually stable with respect to changes in beam parameters.

scholarly journals An automatically updated S ‐wave model of the upper mantle and the depth extent of azimuthal anisotropy

2016 ◽  
Vol 43 (2) ◽  
pp. 674-682 ◽  
Author(s):  
Eric Debayle ◽  
Fabien Dubuffet ◽  
Stéphanie Durand
Keyword(s):  
Upper Mantle ◽  
Wave Model ◽  
Azimuthal Anisotropy ◽  
S Wave ◽  
Depth Extent

Structure of S-Wave Velocity in the Crust-Upper Mantle and Tectonic Setting of Strong Earthquakes Beneath Yunnan

2011 ◽  
Vol 54 (3) ◽  
pp. 286-298 ◽  
Author(s):  
Xiao-Man ZHANG ◽  
Jia-Fu HU ◽  
Yi-Li HU ◽  
Hai-Yan YANG ◽  
Jia CHEN ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Upper Mantle ◽  
Tectonic Setting ◽  
S Wave ◽  
Strong Earthquakes

Constraints on the composition of the crust and uppermost mantle in northwestern Canada: Vp/Vs variations along Lithoprobe's SNorCLE transect

2005 ◽  
Vol 42 (6) ◽  
pp. 1205-1222 ◽  
Author(s):  
Gabriela Fernández-Viejo ◽  
Ron M Clowes ◽  
J Kim Welford
Keyword(s):  
Wave Velocity ◽  
Upper Mantle ◽  
Laboratory Data ◽  
High Ratio ◽  
P Wave ◽  
S Wave ◽  
Uppermost Mantle ◽  
Crust And Upper Mantle ◽  
Slave Craton ◽  
Crustal Composition

Shear-wave seismic data recorded along four profiles during the SNoRE 97 (1997 Slave – Northern Cordillera Refraction Experiment) refraction – wide-angle reflection experiment in northwestern Canada are analyzed to provide S-wave velocity (Vs) models. These are combined with previous P-wave velocity (Vp) models to produce cross sections of the ratio Vp/Vs for the crust and upper mantle. The Vp/Vs values are related to rock types through comparisons with published laboratory data. The Slave craton has low Vp/Vs values of 1.68–1.72, indicating a predominantly silicic crustal composition. Higher values (1.78) for the Great Bear and eastern Hottah domains of the Wopmay orogen imply a more mafic than average crustal composition. In the western Hottah and Fort Simpson arc, values of Vp/Vs drop to ∼1.69. These low values continue westward for 700 km into the Foreland and Omineca belts of the Cordillera, providing support for the interpretation from coincident seismic reflection studies that much of the crust from east of the Cordilleran deformation front to the Stikinia terrane of the Intermontane Belt consists of quartzose metasedimentary rocks. Stikinia shows values of 1.78–1.73, consistent with its derivation as a volcanic arc terrane. Upper mantle velocity and ratio values beneath the Slave craton indicate an ultramafic peridotitic composition. In the Wopmay orogen, the presence of low Vp/Vs ratios beneath the Hottah – Fort Simpson transition indicates the presence of pyroxenite in the upper mantle. Across the northern Cordillera, low Vp values and a moderate-to-high ratio in the uppermost mantle are consistent with the region's high heat flow and the possible presence of partial melt.

Upper mantle thermal variations beneath the Transantarctic Mountains inferred from teleseismic S-wave attenuation

2006 ◽  
Vol 33 (3) ◽  
Author(s):  
Jesse F. Lawrence ◽  
Douglas A. Wiens ◽  
Andrew A. Nyblade ◽  
Sridhar Anandakrishan ◽  
Patrick J. Shore ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Wave Attenuation ◽  
S Wave ◽  
Transantarctic Mountains

scholarly journals Fault Zone Guided Wave generation on the locked, late interseismic Alpine Fault, New Zealand

2021 ◽  
Author(s):  
JD Eccles ◽  
AK Gulley ◽  
PE Malin ◽  
CM Boese ◽  
John Townend ◽  
...  
Keyword(s):  
Fault Zone ◽  
Plate Boundary ◽  
Guided Wave ◽  
S Wave ◽  
Low Velocity ◽  
Catchment Scale ◽  
Near Surface ◽  
Low Velocity Zone ◽  
Alpine Fault ◽  
Velocity Zone

© 2015. American Geophysical Union. All Rights Reserved. Fault Zone Guided Waves (FZGWs) have been observed for the first time within New Zealand's transpressional continental plate boundary, the Alpine Fault, which is late in its typical seismic cycle. Ongoing study of these phases provides the opportunity to monitor interseismic conditions in the fault zone. Distinctive dispersive seismic codas (~7-35Hz) have been recorded on shallow borehole seismometers installed within 20m of the principal slip zone. Near the central Alpine Fault, known for low background seismicity, FZGW-generating microseismic events are located beyond the catchment-scale partitioning of the fault indicating lateral connectivity of the low-velocity zone immediately below the near-surface segmentation. Initial modeling of the low-velocity zone indicates a waveguide width of 60-200m with a 10-40% reduction in S wave velocity, similar to that inferred for the fault core of other mature plate boundary faults such as the San Andreas and North Anatolian Faults.

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