Backstripping the Briançonnais (Western Alps) to test Alpine rifting models

2020 ◽  
Author(s):  
Martina Forzese ◽  
Robert W. H. Butler ◽  
Randell Stephenson ◽  
Rosanna Maniscalco
Keyword(s):  
Shallow Water ◽  
Numerical Models ◽  
Western Alps ◽  
Stratigraphic Sequence ◽  
Vertical Movements ◽  
Starting Point ◽  
Stretching Factor ◽  
Tethys Ocean ◽  
Differential Uplift ◽  
Uplift And Erosion

<p>During the Mesozoic, the relative movement of African and Eurasian plates caused the opening of the Tethys Ocean. The rifting phase is well charted by the stratigraphic sequence of Western Alps, which provide an exceptional record of continental margin evolution. The Briançonnais domain occupies a pivotal place for testing various rifting models. This domain contains a remarkably uniform succession of very shallow-water carbonates of Triassic age, capped by Middle-Jurassic shallow-water carbonates or by non-deposition before passing abruptly up into deep-water facies. Here we show that the back-stripped Mesozoic tectonic evolution of the Briançonnais block can be applied to investigate models of lithospheric stretching. Applying the Airy correction, we found that the Triassic is characterised by a constant tectonic subsidence rate of 17 m/Ma. If this is the result of “post-rift” thermal re-equilibration of upper mantle after late Palaeozoic rifting, this rift phase occurred with a stretching factor of c 1.4. That this thermal subsidence was modulated by differential uplift and erosion of the Briançonnais in the early Jurassic implies significant mantle thinning, reducing net density of the Briançonnais lithosphere. The subsidence of more than 3000m during Bathonian-Callovian stages are too rapid to be explained by thermal re-equilibration: it suggests substantial crustal thinning. Our results demonstrate that a uniform stretching model is not able to explain the Jurassic isostatic movement of the Briançonnais domain. It is consistent with two-stage, depth-variable stretching of the Briançonnais lithosphere during the Jurassic. Our study represents a starting point for more sophisticated and developed numerical models, to explain rapid vertical movements in hyper-extended continental margins.</p>

scholarly journals Metasediments Covering Ophiolites in the HP Internal Belt of the Western Alps: Review of Tectono-Stratigraphic Successions and Constraints for the Alpine Evolution

Minerals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 411
Author(s):  
Paola Tartarotti ◽  
Silvana Martin ◽  
Andrea Festa ◽  
Gianni Balestro
Keyword(s):  
High Pressure ◽  
Western Alps ◽  
Metamorphic Evolution ◽  
Alpine Orogeny ◽  
Sedimentary Evolution ◽  
Hp Metamorphism ◽  
Tethys Ocean ◽  
Depositional Setting ◽  
Oceanic Rocks ◽  
Outer Band

Ophiolites of the Alpine belt derive from the closure of the Mesozoic Tethys Ocean that was interposed between the palaeo-Europe and palaeo-Adria continental plates. The Alpine orogeny has intensely reworked the oceanic rocks into metaophiolites with various metamorphic imprints. In the Western Alps, metaophiolites and continental-derived units are distributed within two paired bands: An inner band where Alpine subduction-related high-pressure (HP) metamorphism is preserved, and an outer band where blueschist to greenschist facies recrystallisation due to the decompression path prevails. The metaophiolites of the inner band are hugely important not just because they provide records of the prograde tectonic and metamorphic evolution of the Western Alps, but also because they retain the signature of the intra-oceanic tectono-sedimentary evolution. Lithostratigraphic and petrographic criteria applied to metasediments associated with HP metaophiolites reveal the occurrence of distinct tectono-stratigraphic successions including quartzites with marbles, chaotic rock units, and layered calc schists. These successions, although sliced, deformed, and superposed in complex ways during the orogenic stage, preserve remnants of their primary depositional setting constraining the pre-orogenic evolution of the Jurassic Tethys Ocean.

scholarly journals Kelvin wave hydraulic control induced by interactions between vortices and topography

2011 ◽  
Vol 687 ◽  
pp. 194-208 ◽  
Author(s):  
Andrew McC. Hogg ◽  
William K. Dewar ◽  
Pavel Berloff ◽  
Marshall L. Ward
Keyword(s):  
Shallow Water ◽  
Analytical Solutions ◽  
Critical Condition ◽  
Numerical Models ◽  
Kelvin Waves ◽  
Water Model ◽  
Hydraulic Jumps ◽  
Hydraulic Control ◽  
Kelvin Wave ◽  
Shallow Water Model

AbstractThe interaction of a dipolar vortex with topography is examined using a combination of analytical solutions and idealized numerical models. It is shown that an anticyclonic vortex may generate along-topography flow with sufficient speeds to excite hydraulic control with respect to local Kelvin waves. A critical condition for Kelvin wave hydraulic control is found for the simplest case of a 1.5-layer shallow water model. It is proposed that in the continuously stratified case this mechanism may allow an interaction between low mode vortices and higher mode Kelvin waves, thereby generating rapidly converging isopycnals and hydraulic jumps. Thus, Kelvin wave hydraulic control may contribute to the flux of energy from mesoscale to smaller, unbalanced, scales of motion in the ocean.

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

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

<p>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.</p><p> </p><p>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 mélanges. 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.</p><p> </p><p>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.</p><p> </p><p>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.</p>

Flow Fields Inside Stocked Fish Cages and the Near Environment

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Lars C. Gansel ◽  
Siri Rackebrandt ◽  
Frode Oppedal ◽  
Thomas A. McClimans
Keyword(s):  
Atlantic Salmon ◽  
Water Flow ◽  
Laboratory Tests ◽  
Numerical Models ◽  
Field Measurements ◽  
Flow Patterns ◽  
Fish Swimming ◽  
Swimming Depth ◽  
Starting Point ◽  
Fish Cages

This study explores the average flow field inside and around stocked Atlantic salmon (Salmo salar L.) fish cages. Laboratory tests and field measurements were conducted to study flow patterns around and through fish cages and the effect of fish on the water flow. Currents were measured around an empty and a stocked fish cage in a fjord to verify the results obtained from laboratory tests without fish and to study the effects of fish swimming in the cage. Fluorescein, a nontoxic, fluorescent dye, was released inside a stocked fish cage for visualization of three-dimensional flow patterns inside the cage. Atlantic salmon tend to form a torus shaped school and swim in a circular path, following the net during the daytime. Current measurements around an empty and a stocked fish cage show a strong influence of fish swimming in this circular pattern: while most of the oncoming water mass passes through the empty cage, significantly more water is pushed around the stocked fish cage. Dye experiments show that surface water inside stocked fish cages converges toward the center, where it sinks and spreads out of the cage at the depth of maximum biomass. In order to achieve a circular motion, fish must accelerate toward the center of the cage. This inward-directed force must be balanced by an outward force that pushes the water out of the cage, resulting in a low pressure area in the center of the rotational motion of the fish. Thus, water is pulled from above and below the fish swimming depth. Laboratory tests with empty cages agree well with field measurements around empty fish cages, and give a good starting point for further laboratory tests including the effect of fish-induced currents inside the cage to document the details of the flow patterns inside and adjacent to stocked fish cages. The results of such experiments can be used as benchmarks for numerical models to simulate the water flow in and around net pens, and model the oxygen supply and the spreading of wastes in the near wake of stocked fish farms.

scholarly journals Generalized Z-Grid Model for Numerical Weather Prediction

Atmosphere ◽  
2019 ◽  
Vol 10 (4) ◽  
pp. 179 ◽  
Author(s):  
Yuanfu Xie
Keyword(s):  
Shallow Water ◽  
Finite Volume ◽  
Numerical Models ◽  
Weather Prediction ◽  
Shallow Water Equation ◽  
Computing Time ◽  
Time Integration ◽  
Grid Model ◽  
Rotating Shallow Water ◽  
Volume Models

Z-grid finite volume models conserve all-scalar quantities as well as energy and potential enstrophy and yield better dispersion relations for shallow water equations than other finite volume models, such as C-grid and C-D grid models; however, they are more expensive to implement. During each time integration, a Z-grid model must solve Poisson equations to convert its vorticity and divergence to a stream function and velocity potential, respectively. To optimally utilize these conversions, we propose a model in which the stability and possibly accuracy on the sphere are improved by introducing more stencils, such that a generalized Z-grid model can utilize longer time-integration steps and reduce computing time. Further, we analyzed the proposed model’s dispersion relation and compared it to that of the original Z-grid model for a linearly rotating shallow water equation, an important property for numerical models solving primitive equations. The analysis results suggest a means of balancing stability and dispersion. Our numerical results also show that the proposed Z-grid model for a shallow water equation is more stable and efficient than the original Z-grid model, increasing the time steps by more than 1.4 times.

scholarly journals Wave Climate at Shallow Waters along the Abu Dhabi Coast

Water ◽  
2018 ◽  
Vol 10 (8) ◽  
pp. 985 ◽  
Author(s):  
Waleed Hamza ◽  
Letizia Lusito ◽  
Francesco Ligorio ◽  
Giuseppe Tomasicchio ◽  
Felice D’Alessandro
Keyword(s):  
Shallow Water ◽  
Numerical Models ◽  
Grid Point ◽  
Arabian Gulf ◽  
Acoustic Doppler Current Profiler ◽  
Wave Climate ◽  
Abu Dhabi ◽  
Water Conditions ◽  
Key Factor ◽  
Offshore Wave

High-resolution, reliable global atmospheric and oceanic numerical models can represent a key factor in designing a coastal intervention. At the present, two main centers have the capabilities to produce them: the National Oceanic and Atmospheric Administration (NOAA) in the U.S.A. and the European Centre for Medium-Range Weather Forecasts (ECMWF). The NOAA and ECMWF wave models are developed, in particular, for different water regions: deep, intermediate, and shallow water regions using different types of spatial and temporal grids. Recently, in the Arabian Gulf (also named Persian Gulf), the Abu Dhabi Municipality (ADM) installed an ADCP (Acoustic Doppler Current Profiler) to observe the atmospheric and oceanographic conditions (water level, significant wave height, peak wave period, water temperature, and wind speed and direction) at 6 m water depth, in the vicinity of the shoreline of the Saadiyat beach. Courtesy of Abu Dhabi Municipality, this observations dataset is available; the recorded data span the period from June 2015 to January 2018 (included), with a time resolution of 10 min and 30 min for the atmospheric and oceanographic variables, respectively. At the ADCP deployment location (ADMins), the wave climate has been determined using wave propagation of the NOAA offshore wave dataset by means of the Simulating WAves Nearshore (SWAN) numerical model, the NOAA and ECMWF wave datasets at the closest grid point in shallow water conditions, and the SPM ’84 hindcasting method with the NOAA wind dataset used as input. It is shown that the best agreement with the observed wave climate is obtained using the SPM ’84 hindcasting method for the shallow water conditions.

scholarly journals A Potential Enstrophy and Energy Conserving Scheme for the Shallow-Water Equations Extended to Generalized Curvilinear Coordinates

2017 ◽  
Vol 145 (3) ◽  
pp. 751-772 ◽  
Author(s):  
Michael D. Toy ◽  
Ramachandran D. Nair
Keyword(s):  
Shallow Water ◽  
Shallow Water Equations ◽  
Empirical Test ◽  
Normal Mode Analysis ◽  
Second Order ◽  
Curvilinear Coordinates ◽  
Mode Analysis ◽  
Convergence Error ◽  
Starting Point ◽  
Potential Enstrophy

An energy and potential enstrophy conserving finite-difference scheme for the shallow-water equations is derived in generalized curvilinear coordinates. This is an extension of a scheme formulated by Arakawa and Lamb for orthogonal coordinate systems. The starting point for the present scheme is the shallow-water equations cast in generalized curvilinear coordinates, and tensor analysis is used to derive the invariant conservation properties. Preliminary tests on a flat plane with doubly periodic boundary conditions are presented. The scheme is shown to possess similar order-of-convergence error characteristics using a nonorthogonal coordinate compared to Cartesian coordinates for a nonlinear test of flow over an isolated mountain. A linear normal mode analysis shows that the discrete form of the Coriolis term provides stationary geostrophically balanced modes for the nonorthogonal coordinate and no unphysical computational modes are introduced. The scheme uses centered differences and averages, which are formally second-order accurate. An empirical test with a steady geostrophically balanced flow shows that the convergence rate of the truncation errors of the discrete operators is second order. The next step will be to adapt the scheme for use on the cubed sphere, which will involve modification at the lateral boundaries of the cube faces.

Experimental Validation of a New Shallow Water CALM Buoy Design

2013 ◽  
Author(s):  
A. Neil Williams ◽  
Williams G. McDougal
Keyword(s):  
Shallow Water ◽  
Experimental Validation ◽  
Numerical Models ◽  
Water Environment ◽  
Model Testing ◽  
Model Tests ◽  
Hydrodynamic Efficiency ◽  
Shallow Water Environment

This paper presents an overview of the model testing of a new turret-type CALM buoy concept developed by WISON for shallow water (20m–80m) applications. In the WISON design the outer body of the buoy is hexagonal, a geometry that allows for ease of fabrication while retaining hydrodynamic efficiency. The overall objective of the model tests was to demonstrate the performance of this new design for a typical shallow water environment under both operating and survival conditions. Additionally, the model tests were intended to provide data to calibrate the numerical models for buoy motions and line tensions used in the design, and to give guidance regarding the suitability of the buoy freeboard and deckhouse arrangement.

The Yorkshire Dogger: III. Upper Eskdale

1943 ◽  
Vol 80 (6) ◽  
pp. 209-230 ◽  
Author(s):  
R. H. Rastall ◽  
J. E. Hemingway
Keyword(s):  
Shallow Water ◽  
Sea Level ◽  
Marine Sediments ◽  
Sea Water ◽  
Second Phase ◽  
Faunal Assemblage ◽  
Chemical Changes ◽  
Main Series ◽  
Uplift And Erosion ◽  
Shallow Water Sediments

1. A sequence of strata is determined in the Dogger of Upper Eskdale and its tributary valleys. The rocks fall into three main series, which are subdivided into groups.2. The underlying Yeovilian sediments, originally included with the Dogger, are mapped and briefly described. The unconformity between them and the Dogger is emphasized.3. The Dogger is marine throughout but only the oldest yields an adequate faunal assemblage, similar to that of the Glaisdale Oolite Series (upper opalinum). The greater part of the Dogger of this area is therefore younger than that of the Yorkshire Coast.4. Chemical changes in the sea-water caused the deposition of siderite to characterize the earliest phase (Glaisdale Oolite Series). This was succeeded by a phase of dominantly chamosite deposition (the Chamositic Series) followed by a reversion to siderite deposition (the Ajalon Series).5. Earth-movement controlled sedimentation over the area. During the first phase an eastern tilt to the region held the centre and west above or near sea-level, where it received no sediment. The second phase saw general depression with the accumulation of shallow water sediments. This was followed by uplift and erosion when a broad shallow valley was cut. Partial depression then flooded the valley with derived marine sediments.

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