Processes and deformation rates generating seismicity in metropolitan France and conterminous Western Europe

Most of metropolitan France and conterminous Western Europe is currently located within the Eurasia intraplate domain, far from major plate boundaries (the Atlantic ridge and Nubia – Eurasia convergence zone). As in other intraplate regions, present-day deformation and seismicity rates are very slow, resulting in limited data and strong uncertainties on the ongoing seismotectonics and seismic hazards. In the last two decades, new geological, seismological and geodetic data and research have brought to light unexpected deformation patterns in metropolitan France, such as orogen-normal extension ca. 0.5 mm yr−1 in the Pyrenees and Western Alps that cannot be associated with their mountain-building history. Elsewhere, present-day deformation and seismicity data provide a partial picture that points to mostly extensive to strike-slip deformation regimes (except in the Western Alps foreland). A review of the numerous studies and observations shows that plate tectonics (plate motion, mantle convection) are not the sole, nor likely the primary driver of present-day deformation and seismicity and that additional processes must be considered, such as topography potential energy, erosion or glacial isostatic adjustment since the last glaciation. The exact role of each process probably varies from one region to another and remains to be characterized. In addition, structural inheritance (crust or mantle weakening from past tectonic events) can play a strong role in deformation localization and amplification up to factors of 5–20, which could explain some of the spatial variability in seismicity. On the basis of this review, we identify three research directions that should be developed to better characterize the seismicity, deformation rates and related processes in metropolitan France: macroseismic and historical seismicity, especially regarding moment magnitude estimations; geodetic deformation, including in regions of low seismicity where the ratio of seismic to aseismic deformation remains a key unknown; an integrated and consistent seismotectonic framework comprising numerical models, geological, seismological and geodetic data. The latter has the potential for significant improvements in the characterization of seismicity and seismic hazard in metropolitan France but also Western Europe.

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Synconvergent and coherent (ultra)high-pressure crustal rock exhumation

10.5194/egusphere-egu21-11119 ◽

2021 ◽

Author(s):

Lorenzo G. Candioti ◽

Joshua D. Vaughan-Hammon ◽

Thibault Duretz ◽

Stefan M. Schmalholz

Keyword(s):

Numerical Models ◽

A Priori ◽

Western Alps ◽

Ultrahigh Pressure ◽

Plate Motion ◽

Crustal Rock ◽

Plate Boundaries ◽

Crustal Rocks ◽

Natural Data ◽

The Alps

Ultrahigh-pressure (UHP) continental crustal rocks were first discovered in the Western Alps in 1984 and have since then been observed at many convergent plate boundaries worldwide. Unveiling the processes leading to the formation and exhumation of (U)HP metamorphic crustal rocks is key to understand the geodynamic evolution of orogens such as the Alps.&#160;Previous numerical studies investigating (U)HP rock exhumation in the Alps predicted deep (>80 km) subduction of crustal rocks and rapid buoyancy-driven exhumation of mainly incoherent (U)HP units, involving significant tectonic mixing forming so-called m&#233;langes. Furthermore, these predictions often rely on excessive erosion or periods of divergent plate motion as important exhumation mechanism. Inconsistent with field observations and natural data, application of these models to the Western Alps was recently criticised.&#160;Here, we present models with continuous plate convergence, which exhibit local tectonic-driven upper plate extension enabling compressive- and buoyancy-driven exhumation of coherent (U)HP units along the subduction interface, involving feasible erosion.&#160;The two-dimensional petrological-thermo-mechanical numerical models presented here predict both subduction initiation and serpentinite channel formation without any a priori prescription of these two features. The (U)HP units are exhumed coherently, without significant internal deformation. Modelled pressure and temperature trajectories and exhumation velocities of selected crustal units agree with estimates for the Western Alps. The presented models support previous hypotheses of synconvergent exhumation, but do not rely on excessive erosion or divergent plate motion. Thus, our predictions provide new insights into processes leading to the exhumation of coherent (U)HP crustal units consistent with observations and natural data from the Western Alps.

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Geodetic deformation rates and driving processes in metropolitan France and neighboring Western Europe

10.5194/egusphere-egu2020-7327 ◽

2020 ◽

Author(s):

Stephane Mazzotti ◽

Juliette Grosset ◽

Christine Masson ◽

Philippe Vernant

Keyword(s):

Plate Tectonics ◽

Western Europe ◽

Western Alps ◽

Joint Analysis ◽

Normal Extension ◽

Isostatic Adjustment ◽

Definition Of ◽

A Minor ◽

Aquitaine Basin ◽

Rhone Valley

We constrain present-day deformation rates and styles in metropolitan France and neighboring Western Europe using a dataset of ca. 1200 GNSS horizontal and vertical velocities from continuous and semi-continuous stations. The characterization and correction of network-scale common-mode noise, combined with two independent network analysis technics allow the resolution of very small horizontal velocities (resp. strain rates) with a 95% confidence ca. 0.1&#8211;0.2 mm/yr (resp. ca. 1 x 10-9 yr-9) on a spatial scale of 100&#8211;200 km. The resulting velocity and strain rate fields show regional coherent patterns that can be associated with features that have been previously identified (e.g., orogen-normal extension in the Pyrenees and Western Alps), but also with new deformation patterns such as North-South shortening in northeastern France - southwestern Germany north of the Alpine Front (Vosges - Rhine Graben - Black Forest). A joint analysis of these new geodetic data with seismicity and focal mechanism catalogs allows the definition of regional seismo-tectonic models that can be compared with the numerous models of deformation processes proposed for Western Europe, from plate tectonics to erosion or Glacial Isostatic Adjustment. We show that plate and micro-plate tectonics play a minor (probably negligible) role in present-day deformation in metropolitan France and that alternative non-tectonic processes must be considered to better understand the origin of recent moderate earthquakes such as the March 2019 Ml=4.9 Montendre earthquake in the Aquitaine Basin or the Nov. 2019 Mw=4.8 Teil earthquake in the Rhone Valley.

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Towards community-driven paleogeographic reconstructions: integrating open-access paleogeographic and paleobiology data with plate tectonics

Biogeosciences ◽

10.5194/bg-10-1529-2013 ◽

2013 ◽

Vol 10 (3) ◽

pp. 1529-1541 ◽

Cited By ~ 42

Author(s):

N. Wright ◽

S. Zahirovic ◽

R. D. Müller ◽

M. Seton

Keyword(s):

Ocean Circulation ◽

Plate Tectonics ◽

Numerical Models ◽

Plate Motion ◽

Temporal Data Mining ◽

Dynamic Topography ◽

Southeastern Australia ◽

Eastern Australia ◽

Spatio Temporal ◽

Fossil Data

Abstract. A variety of paleogeographic reconstructions have been published, with applications ranging from paleoclimate, ocean circulation and faunal radiation models to resource exploration; yet their uncertainties remain difficult to assess as they are generally presented as low-resolution static maps. We present a methodology for ground-truthing the digital Palaeogeographic Atlas of Australia by linking the GPlates plate reconstruction tool to the global Paleobiology Database and a Phanerozoic plate motion model. We develop a spatio-temporal data mining workflow to validate the Phanerozoic Palaeogeographic Atlas of Australia with paleoenvironments derived from fossil data. While there is general agreement between fossil data and the paleogeographic model, the methodology highlights key inconsistencies. The Early Devonian paleogeographic model of southeastern Australia insufficiently describes the Emsian inundation that may be refined using biofacies distributions. Additionally, the paleogeographic model and fossil data can be used to strengthen numerical models, such as the dynamic topography and the associated inundation of eastern Australia during the Cretaceous. Although paleobiology data provide constraints only for paleoenvironments with high preservation potential of organisms, our approach enables the use of additional proxy data to generate improved paleogeographic reconstructions.

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Some Geodetic Aspects of the Plate Tectonics Hypothesis

International Astronomical Union Colloquium ◽

10.1017/s0252921100081136 ◽

1980 ◽

Vol 56 ◽

pp. 87-101

Author(s):

Kurt Lambeck

Keyword(s):

Plate Tectonics ◽

Geodetic Data ◽

Geophysical Data ◽

Plate Boundaries ◽

Frequency Range ◽

Crustal Motion ◽

Intraplate Tectonics ◽

The Earth ◽

Seismic Frequencies ◽

Body Tides

AbstractGeodetic observations of gravity, body tides, the Earth’s rotation and crustal motion and deformation potentially provide important constraints in the general inversion of geophysical data for determining the structure and evolution of the Earth. More specifically, the geodetic data provide constraints on the rheology of the planet in the frequency range intermediate between geological and seismic frequencies, on the geologically instantaneous kinematics of the Earth and on the mechanisms responsible for the motions within the Earth, results that are intimately related to the plate tectonics hypothesis. The discussion is limited here to only a few aspects of these “geodetic” aspects of this hypothesis, including deformation along plate boundaries, intraplate tectonics and vertical motions.

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Deciphering paleogeography from orogenic architecture: constructing orogens by a future closure of the Indian Ocean as thought experiment

10.5194/egusphere-egu21-7270 ◽

2021 ◽

Author(s):

Thomas Schouten ◽

Douwe van Hinsbergen

Keyword(s):

Indian Ocean ◽

Plate Tectonics ◽

Thought Experiment ◽

Continental Drift ◽

Plate Motion ◽

Plate Boundaries ◽

Diagnostic Features ◽

Independent Basis ◽

Plate Deformation ◽

The Indian Ocean

Orogens that form at convergent plate boundaries typically consist of accreted rock units that form an incomplete archive of subducted oceanic and continental lithosphere, as well as of deformed crust of the former upper plate. Reading the construction of orogenic architecture forms the key to decipher the paleogeographic distribution of oceans and continents, as well as bathymetric and topographic features that existed thereon such as igneous plateaus, seamounts, microcontinents, or magmatic arcs. Owing to its complicated opening history, the Indian Ocean comprises a mosaic of such features that is an excellent illustration of the degree of geographic complexity that must have occurred in now-subducted oceanic realms of the geologic past and provides the ideal natural laboratory to validate interpretations of present-day orogenic architecture in terms of paleogeography. Current classification schemes of orogens divide between settings associated with termination of subduction (continent-continent collision, continent-ocean collision (obduction)) and with ongoing subduction (accretionary orogenesis), alongside intraplate orogens. Perceived diagnostic features for such classifications, particularly of collisional orogenesis, hinge on dynamic interpretations linking downgoing plate paleogeography to upper plate deformation, plate motion changes, or magmatism. Here, we show, however, that Mesozoic-Cenozoic orogens that undergo collision almost all defy these proposed diagnostic features and behave like accretionary orogens instead. To reconstruct paleogeography of subducted and upper plates, we therefore propose an alternative approach to navigating through orogenic architecture: subducted plate units comprise nappes (or m&#233;langes) with Ocean Plate Stratigraphy (OPS) and Continental Plate Stratigraphy (CPS) stripped from their now-subducted or otherwise underthrust lower crustal and mantle lithospheric underpinnings. Upper plate deformation and paleogeography respond to the competition between absolute motion of the upper plate and the subducting slab. Our navigation approach through orogenic architecture aims to avoid a priori dynamic interpretations that link downgoing plate paleogeography to deformation or magmatic responses in the upper plate, to provide an independent basis for geodynamic analysis. From our analysis we identify &#8216;rules of orogenesis&#8217; that link the rules of rigid plate tectonics with the reality of plate deformation. We illustrate the use of these rules with a thought experiment, in which we predict two contrasting orogenic architectures that may result from the closure of the Indian Ocean and subsequent collision of the Somali, Malagasy and Indian Margins in a global continental drift scenario for a future supercontinent. We illustrate that our inferred rules (of thumb) generate orogenic architecture that is analogous to elements of modern orogens, unlocking the well-known modern geography as inspiration for developing testable hypotheses that aid interpreting paleogeography from orogens that formed since the birth of plate tectonics.

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Effect of grid resolution on tectonic regimes in global-scale convection models

10.5194/egusphere-egu2020-4483 ◽

2020 ◽

Author(s):

Enrico Marzotto ◽

Marcel Thielmann ◽

Gregor Golabek

Keyword(s):

Plate Tectonics ◽

Numerical Models ◽

Global Scale ◽

Grid Resolution ◽

Physical Parameters ◽

Plate Boundaries ◽

Temperature Dependent ◽

Tectonic Regime ◽

Radiogenic Heating ◽

Spherical Annulus

A key ingredient to reproduce plate-tectonics in numerical models is a viscoplastic rheology. Strongly temperature-dependent rheology generates a rigid lid at the surface, whereas plastic rheology allows for the formation of plate boundaries. The yield stress limiter &#160;controls the strength of the lithosphere.Depending on the value used for &#160;different tectonics regimes can be observed: (i) dripping behaviour (low , (ii) plate-like behaviour (intermediate-low ), (iii) Episodic behaviour (intermediate-high ) and (iv) Stagnant lid behaviour (high ).Each lid behaviour can be distinguished by comparing the evolution profile of several parameters: temperature, viscosity, surface Nusselt number and mobility (Tackley, 2000a.).Despite the great importance of physical parameters, the outcome of geodynamical models is also affected by the grid resolution as it has been shown that the critical that separates each lid behavior is resolution dependent (Tosi et al., 2015).Here we use the code StagYY (Tackley, 2008) in a 2D spherical annulus geometry (Hernlund & Tackley, 2008) to determine the resolution-dependent tectonic regime in a global-scale convection setting. We tested 12 grid resolutions (ranging from 128x32 to 1024x128 nodal points) and 9 different &#160;(ranging from 10 to 90 MPa), keeping all the remaining physical parameters unchanged.For these simplified models we assume isothermal free slip boundaries, constant radiogenic heating, no melting, endothermic (410) and exothermic (660) phase transitions. Each simulation was run for 15 Gyrs with a Rayleigh number of &#8776;8*10^7 to make sure that steady-state conditions were reached.Our resolution tests show that the observed tectonic regime is affected by grid resolution as this parameter controls how well the lithosphere is resolved. Low radial resolutions favour weak lid regimes (dripping and plate-like) as the lithosphere is defined by few thick cells, that propagate basal stress to shallower depths. On the other hand low azimuthal resolutions favour strong lid regimes (episodic and stagnant) since plate boundaries remain unresolved. In conclusion, only at high grid resolutions (512x128 and higher) the numerical influence on the observed tectonic regime is low.

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Looking beyond kinematics: 3D thermo-mechanical modelling reveals the dynamics of transform margins

Solid Earth ◽

10.5194/se-12-1211-2021 ◽

2021 ◽

Vol 12 (5) ◽

pp. 1211-1232

Author(s):

Anthony Jourdon ◽

Charlie Kergaravat ◽

Guillaume Duclaux ◽

Caroline Huguen

Keyword(s):

Boundary Conditions ◽

Strain Localization ◽

Numerical Models ◽

Motion Vector ◽

Shear Zones ◽

Strike Slip ◽

Plate Motion ◽

Plate Boundaries ◽

Mechanical Modelling ◽

Extension Direction

Abstract. Transform margins represent ∼ 30 % of non-convergent margins worldwide. Their formation and evolution have traditionally been addressed through kinematic models that do not account for the mechanical behaviour of the lithosphere. In this study, we use high-resolution 3D numerical thermo-mechanical modelling to simulate and investigate the evolution of intra-continental strain localization under oblique extension. The obliquity is set through velocity boundary conditions that range from 15∘ (high obliquity) to 75∘ (low obliquity) every 15∘ for rheologies of strong and weak lower continental crust. Numerical models show that the formation of localized strike-slip shear zones leading to transform continental margins always follows a thinning phase during which the lithosphere is thermally and mechanically weakened. For low- (75∘) to intermediate-obliquity (45∘) cases, the strike-slip faults are not parallel to the extension direction but form an angle of 20∘ to 40∘ with the plate motion vector, while for higher obliquities (30∘ to 15∘) the strike-slip faults develop parallel to the extension direction. Numerical models also show that during the thinning of the lithosphere, the stress and strain re-orient while boundary conditions are kept constant. This evolution, due to the weakening of the lithosphere, leads to a strain localization process in three major phases: (1) initiation of strain in a rigid plate where structures are sub-perpendicular to the extension direction; (2) distributed deformation with local stress field variations and formation of transtensional and strike-slip structures; (3) formation of highly localized plate boundaries stopping the intra-continental deformation. Our results call for a thorough re-evaluation of the kinematic approach to studying transform margins.

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Beyond Plate Tectonics: Looking at Plate Deformation with Space Geodesy

Symposium - International Astronomical Union ◽

10.1017/s0074180900134941 ◽

1988 ◽

Vol 129 ◽

pp. 341-350

Author(s):

Thomas H. Jordan ◽

J. Bernard Minster

Keyword(s):

Plate Tectonics ◽

Plate Boundary ◽

Point Of View ◽

Space Geodesy ◽

Plate Motion ◽

Plate Boundaries ◽

Measurement Systems ◽

Motion Models ◽

Plate Deformation ◽

Continental Plate

We address the requirements that must be met by space-geodetic systems to place useful, new constraints on horizontal secular motions associated with the geological deformation of the earth's surface. Plate motions with characteristic speeds of about 50 mm/yr give rise to displacements that are easily observed by space geodesy. However, in order to improve the existing plate-motion models, the tangential components of relative velocities on interplate baselines must be resolved to an accuracy of < 3 mm/yr. Because motions considered small from a geodetic point of view have rather dramatic geological effects, especially when taken up as compression or extension of continental crust, detecting plate deformation by space-geodetic methods at a level that is geologically unresolvable places rather stringent requirements on the precision of the measurement systems: the tangential components on intraplate baselines must be observed with an accuracy of < 1 mm/yr. Among the measurements of horizontal secular motions that can be made by space geodesy, those pertaining to the rates within the broad zones of deformation characterizing the active continental plate boundaries are the most difficult to obtain by conventional ground-based geodetic and geological techniques. Measuring the velocities between crustal blocks to ± 5 mm/yr on 100-km to 1000-km length scales can yield geologically significant constraints on the integrated deformation rates across continental plate-boundary zones such as the western United States. However, baseline measurements in geologically complicated zones of deformation are useful only to the extent that the endpoints can be fixed in a local kinematical frame that includes major crustal blocks. For this purpose, the establishment of local geodetic networks around major VLBI and SLR sites in active areas should receive high priority.

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Vertically Driven Dynamics and Magmatism of Rapid Subduction Initiation in the Western Pacific

10.5194/egusphere-egu2020-19611 ◽

2020 ◽

Author(s):

Ben Maunder ◽

Saskia Goes ◽

Julie Prytulak ◽

Mark Reagan

Keyword(s):

Plate Tectonics ◽

Numerical Models ◽

Plate Boundaries ◽

Temporal And Spatial Distribution ◽

Subduction Initiation ◽

Primary Driver ◽

International Ocean Discovery Program ◽

Subduction System ◽

The Western Pacific

Plate tectonics requires the formation of plate boundaries. Particularly important is the enigmatic initiation of subduction: the sliding of one plate below the other, and the primary driver of plate tectonics. A continuous, in situ record of subduction initiation was recovered by the International Ocean Discovery Program Expedition 352, which drilled a segment of the fore-arc of the Izu-Bonin-Mariana subduction system, revealing a distinct magmatic progression with a rapid timescale (approximately 1 million years). Here, using numerical models, we demonstrate that these observations cannot be produced by previously proposed horizontal external forcing. Instead a geodynamic evolution that is dominated by internal, vertical forces produces both the temporal and spatial distribution of magmatic products, and progresses to self-sustained subduction. Such a primarily internally driven initiation event is necessarily whole-plate scale and the rock sequence generated (also found along the Tethyan margin) may be considered as a smoking gun for this type of event.

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Plate tectonics and Earth System Science

10.5194/egusphere-egu21-9351 ◽

2021 ◽

Author(s):

Dietmar Müller

Keyword(s):

Plate Tectonics ◽

Plate Boundary ◽

Plate Motion ◽

Plate Boundaries ◽

Earth System ◽

Dynamic Topography ◽

Lithospheric Deformation ◽

The Earth ◽

Plate Models ◽

Reconstruction Software

Over the last 25 years the theory of plate tectonics and a growing set of geo-databases have been used to develop global plate models with increasing sophistication, enabled by open-source plate reconstruction software, particularly GPlates. Today&#8217;s editable open-access community models include networks of evolving plate boundaries and deforming regions, reflecting the fact that tectonic plates are not always rigid. The theory of plate tectonics was originally developed primarily based on magnetic anomaly and fracture zone data from the ocean basins. As a consequence there has been a focus on applying plate tectonics to modelling the Jurassic to present-day evolution of the Earth based on the record of preserved seafloor, or only modelling the motions of continents at earlier times. Modern plate models are addressing this shortcoming with recently developed technologies built upon the pyGPlates python library, utilising evolving plate boundary topologies to reconstruct entirely destroyed seafloor for the entire Phanerozoic. Uncertainties in these reconstructions are large and can represented with end-member scenarios. These models are paving the way for a multitude of applications aimed at better understanding Earth system evolution, connecting surface processes with the Earth&#8217;s mantle via plate tectonics. These models allow us to address questions such as: What are the causes of major perturbations in the interplay between tectonic plate motion and Earth&#8217;s deep interior? How do lithospheric deformation, mantle convection driven dynamic topography and climate change together drive regional changes in erosion and sedimentation? How are major perturbations of the plate-mantle system connected to environmental change, biological extinctions and species radiation?

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