scholarly journals Thermal conditions during deformation of partially molten crust from TitaniQ geothermometry: rheological implications for the anatectic domain of the Araçuaí belt, eastern Brazil

Solid Earth ◽  
2014 ◽  
Vol 5 (2) ◽  
pp. 1223-1242 ◽  
Author(s):  
G. C. G. Cavalcante ◽  
A. Vauchez ◽  
C. Merlet ◽  
M. Egydio-Silva ◽  
M. H. Bezerra de Holanda ◽  
...  
Keyword(s):  
Partial Melting ◽  
Flow Direction ◽  
Regional Scale ◽  
Thermal Conditions ◽  
Middle Crust ◽  
Low Viscosity ◽  
Lateral Extrusion ◽  
Eastern Brazil ◽  
Gravity Driven ◽  
Gravity Driven Flow

Abstract. During the Neoproterozoic orogeny, the middle crust of the Araçuaí belt underwent widespread partial melting. At the regional scale, this anatectic domain is characterized by a progressive rotation of the flow direction from south to north, suggesting a 3-D deformation of the anatectic middle crust. To better determine whether melt volumes present in the anatectic middle crust of the Araçuaí orogen were large enough to allow a combination of gravity-driven and convergence-driven deformation, we used the titanium-in-quartz (TitaniQ) geothermometer to estimate the crystallization temperatures of quartz grains in the anatectic rocks. When possible, we compared these estimates with thermobarometric estimates from traditional exchange geothermobarometers applied to neighboring migmatitic kinzigites. TitaniQ temperatures range from 750 to 900 °C, suggesting that quartz starts crystallizing at minimum temperatures of ≥ 800 °C. These results, combined with the bulk-rock chemical composition of diatexites, allows the estimation of a minimum of ~ 30% melt and a corresponding viscosity of ~ 109–1010 Pa s. Such a minimum melt content and low viscosity are in agreement with interconnected melt networks observed in the field. Considering that these characteristics are homogeneous over a wide area, this supports the finding that the strength of the middle crust was severely weakened by extensive partial melting, making it prone to gravity-driven flow and lateral extrusion.

scholarly journals Thermal conditions during deformation of partially molten crust from TitaniQ geothermometry: rheological implications for the anatectic domain of the Araçuaí belt, Eastern Brazil

2014 ◽  
Vol 6 (1) ◽  
pp. 1299-1333 ◽  
Author(s):  
G. C. G. Cavalcante ◽  
A. Vauchez ◽  
C. Merlet ◽  
M. Egydio-Silva ◽  
M. H. Bezerra de Holanda ◽  
...  
Keyword(s):  
Partial Melting ◽  
Flow Direction ◽  
Regional Scale ◽  
Thermal Conditions ◽  
Rock Composition ◽  
Middle Crust ◽  
Low Viscosity ◽  
Lateral Extrusion ◽  
Eastern Brazil ◽  
Gravity Driven

Abstract. During the Neoproterozoic orogeny, the middle crust of the Araçuaí belt underwent widespread partial melting. At the regional scale, this anatectic domain is characterized by a progressive rotation of the flow direction from South to North, suggesting a 3-D deformation of the anatectic middle crust. To better constrain whether melt volumes present in the anatectic middle crust of the Araçuaí orogen were large enough to allow a combination of gravity-driven and convergence-driven deformation, we used the titanium-in-quartz geothermometer (TitaniQ) to estimate the crystallization temperatures of quartz grains in the anatectic rocks. When possible, we compared these estimates with thermobarometric estimates from traditional exchange geothermobarometers applied to neighboring migmatitic kinzigites. TitaniQ temperatures range from 750 to 800 °C, suggesting that quartz start crystallizing at a minimum temperatures ≥800 °C. These results, combined with the bulk-rock composition of isolated leucosomes allow to estimate a minimum of ∼30% melt in the anatectic leucossomes and a corresponding viscosity of ∼109–110 Pa s. Such a minimum melt content and low viscosity are in agreement with interconnected melt networks observed in the field. Considering that these characteristics are homogeneous over a wide area, this supports that the strength of the middle crust was severely weaken by extensive partial melting turning it prone to gravity-driven channel flow and lateral extrusion.

Drainage of viscous gravity currents from the edge of a porous or fractured domain with variable properties

2021 ◽  
Author(s):  
Vittorio Di Federico ◽  
Alessandro Lenci ◽  
Valentina Ciriello
Keyword(s):  
Oil Recovery ◽  
Flow Direction ◽  
Gravity Currents ◽  
Fractured Media ◽  
Porous Media Flow ◽  
Finite Domain ◽  
Model Parameters ◽  
Late Time ◽  
Gravity Driven ◽  
Gravity Driven Flow

<p>Gravity-driven flow in porous and fractured media has been extensively investigated in recent years in connection with numerous environmental and industrial applications, including seawater intrusion, oil recovery, penetration of drilling fluids into reservoirs, contaminant migration such as NAPL spreading in shallow aquifers, and carbon dioxide sequestration in subsurface formations. The propagation of such currents is typically governed by the interplay between viscous and buoyancy forces, with negligible inertial effects. For long and thin currents, the spreading can be described by similarity solutions for a variety of geometries, with topographic controls often playing a crucial role. These solutions can be extended to gravity-driven flow in vertical narrow fractures or cracks via the well-known Hele-Shaw (HS) analogy between parallel plate and porous media flow, with the aperture <em>b</em> (distance between fracture walls) squared being the analogue of permeability <em>k</em> according to <em>k</em> = <em>b</em><sup>2</sup>/12.  </p><p>Buoyancy-driven spreading in porous and fractured media is also influenced by spatial heterogeneity of medium properties; permeability, porosity, and aperture gradients affect the propagation distance and shape of gravity currents, with practical implications for remediation and storage. In this paper we are interested in the coupled effect of heterogeneity and a fixed edge draining the current at one end of a finite domain. Simultaneous permeability and porosity gradients parallel to the flow are considered: this is equivalent to a wedge-shaped fracture, as the Hele-Shaw analogy necessarily accounts for both permeability and porosity gradients.</p><p>A current of density ρ+Δρ advances horizontally in a fluid of density ρ under the sharp interface approximation, and is drained by an edge at a distance <em>x</em> = <em>L</em> from the origin; a no-flow boundary condition is considered at <em>x</em> = 0. We neglect vertical velocities for an elongated current; this implies vertical equilibrium, and in turn an hydrostatic pressure distribution within the advancing current. The final assumption is of vanishing height of the current at the draining edge after a relatively short adjustment time, favoured by the increase in permeability/porosity or aperture along the flow direction.</p><p>Under these assumptions, a semi-analytical solution is derived for the height of the current <em>h</em>(<em>x</em>, <em>t</em>) in a self-similar form, valid as a late-time approximation modelling the drainage phenomenon after the influence of the initial condition has vanished. This allows transforming the nonlinear PDE governing the flow into a nonlinear ODE amenable to a numerical solution. Knowledge of the current profile then yields the residual mass in the fracture and the drainage flowrate at the edge. A full sensitivity analysis to model parameters is performed, and the conditions required to avoid an unphysical or asymptotically invalid result are discussed. An extension to non-Newtonian rheology is then presented.</p>

scholarly journals Topography-based flow-directional roughness: potential and challenges

2016 ◽  
Vol 4 (2) ◽  
pp. 343-358 ◽  
Author(s):  
Sebastiano Trevisani ◽  
Marco Cavalli
Keyword(s):  
Surface Roughness ◽  
Surface Texture ◽  
Flow Direction ◽  
Texture Modeling ◽  
Digital Terrain ◽  
Measuring Surface ◽  
Morphological Detail ◽  
Gravity Driven ◽  
Gravity Driven Flow ◽  
Landscape Morphology

Abstract. Surface texture analysis applied to high-resolution digital terrain models (HRDTMs) is a promising approach for extracting useful fine-scale morphological information. Surface roughness, considered here as a synonym of surface texture, can have a discriminant role in the detection of different geomorphic processes and factors. Very often, the local morphology presents, at different scales, anisotropic characteristics that could be taken into account when calculating or measuring surface roughness. The high morphological detail of HRDTMs permits the description of different aspects of surface roughness, beyond an evaluation limited to isotropic measures of surface roughness. The generalization of the concept of roughness implies the need to refer to a family of specific roughness indices capable of capturing specific multiscale and anisotropic aspects of surface morphology. An interesting set of roughness indices is represented by directional measures of roughness that can be meaningful in the context of analyzed and modeled flow processes. Accordingly, we test the application of a flow-oriented directional measure of roughness based on the geostatistical bivariate index MAD (median of absolute directional differences), which is computed considering surface gravity-driven flow direction. MAD is derived from a modification of a variogram and is specifically designed for the geomorphometric analysis of HRDTMs. The presented approach shows the potential impact of considering directionality in the calculation of roughness indices. The results demonstrate that the use of flow-directional roughness can improve geomorphometric modeling (e.g., sediment connectivity and surface texture modeling) and the interpretation of landscape morphology.

Tectonic relaxation and the development of cross fold in the Singhbhum Proterozoic mobile belt: Insights from physical and numerical model experiments

2020 ◽  
Author(s):  
Puspendu Saha ◽  
Atin Kumar Mitra ◽  
Nibir Mandal
Keyword(s):  
Shear Stress ◽  
Large Scale ◽  
Flow Direction ◽  
Regional Scale ◽  
Three Dimensional ◽  
Mobile Belt ◽  
Horizontal Shear ◽  
Eastern Flank ◽  
Analogue Models ◽  
Gravity Driven Flow

<p>Mobile belts are generally characterized by deformational structures of multiple generations, indicating complex spatial and temporal evolution of the strain fields. These deformed terrains show interference patterns indicating superposition of structures striking transverse to the orogenic trend which leads to the development of cross folds in mobile belts. Despite significant work on cross-folding, it is still not well understood how horizontal shortening can develop regionally along the trend of an orthogonal convergent belts. Our present work deals with the spectacular cross-folds in the eastern flank of the Singhbhum Proterozoic mobile belt.</p><p>This study uses three-dimensional continuum models to address the long-standing question: what is the tectonics of regional scale cross-folds with axial planes transecting the orogenic trend? Physical experiments were conducted with PDMS (Poly dimethyl siloxane), a Newtonian viscous material under lower strain rate of deformation. We propose that the belt underwent orogen-parallel flow during tectonic relaxation, developing orogen-parallel shortening, as observed in analogue models. This gravity-driven flow appears to be potential factor for cross folding in orogenic belts. In order to substantiate the deformation of analogue models, the horizontal shear stress was mapped in FE models. This reveals a distinct zone of shear stress localization in the eastern flank. Model results suggest that the arcuate belt is likely to show deformations by large horizontal shear at the flank of the model. This prediction agrees to the observations from analogue models. In order to study the large scale three-dimensional flow pattern, velocity vectors are plotted in the model. The vector diagram shows that the material flow does not take place orthogonally to the orogenic trend, while at the NE margin the flow direction is parallel to orogenic trend, resulting in the development of cross folds in Singhbhum mobile belts.</p>

scholarly journals Topography-based flow-directional roughness: potential and challenges

2015 ◽  
Vol 3 (4) ◽  
pp. 1399-1444
Author(s):  
S. Trevisani ◽  
M. Cavalli
Keyword(s):  
Surface Roughness ◽  
Surface Texture ◽  
Flow Direction ◽  
Texture Modeling ◽  
Digital Terrain ◽  
Measuring Surface ◽  
Morphological Detail ◽  
Gravity Driven ◽  
Gravity Driven Flow ◽  
Landscape Morphology

Abstract. Surface texture analysis applied to High Resolution Digital Terrain Models (HRDTMs) is a promising approach for extracting useful fine-scale morphological information. Surface roughness, considered here as a synonym of surface texture, can have a discriminant role in the detection of different geomorphic processes and factors. Very often, the local morphology presents, at different scales, anisotropic characteristics that could be taken into account when calculating or measuring surface roughness. The high morphological detail of HRDTMs permits the description of different aspects of surface roughness, beyond an evaluation limited to isotropic measures of surface roughness. The generalization of the concept of roughness implies the need to refer to a family of specific roughness indices capable of capturing specific multi-scale and anisotropic aspects of surface morphology. An interesting set of roughness indices is represented by directional measures of roughness that can be meaningful in the context of analyzed and modeled flow processes. Accordingly, we test the application of a flow-oriented directional measure of roughness based on the geostatistical bivariate index MAD (median of absolute directional differences), which is computed considering surface gravity-driven flow direction. MAD is derived from a modification of a variogram and is specifically designed for the geomorphometric analysis of HRDTMs. The presented approach shows the potential impact of considering directionality in the calculation of roughness indices. The results demonstrate that the use of flow directional roughness can improve geomorphometric modeling (e.g., sediment connectivity and surface texture modeling) and the interpretation of landscape morphology.

EFFECT OF FLOCCULATING AGENTS ON DRAG IN GRAVITY-DRIVEN FLOW SYSTEMS

2017 ◽  
Vol 44 (4) ◽  
pp. 339-347
Author(s):  
M. K. S. V. Raghav ◽  
Ravi Teja ◽  
Chirravuri Subbarao
Keyword(s):  
Flow Systems ◽  
Gravity Driven ◽  
Gravity Driven Flow

Drag reduction using mixed solutions of hydrotrope and surfactant in gravity driven flow systems

2013 ◽  
Vol 8 (3) ◽  
pp. 22-27
Author(s):  
M. Venkata Ramana ◽  
◽  
Ch. V. Subbarao ◽  
P. V. Gopal singh ◽  
Krishna Prasad K.M.M ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Mixed Solutions ◽  
Flow Systems ◽  
Gravity Driven ◽  
Gravity Driven Flow

scholarly journals Two-Dimensional Convection Induced by Gravity and Centrifugal Forces in a Rotating Porous Layer Far Away from the Axis of Rotation

1998 ◽  
Vol 4 (2) ◽  
pp. 73-90 ◽  
Author(s):  
Peter Vadasz ◽  
Saneshan Govender
Keyword(s):  
Rayleigh Number ◽  
Porous Layer ◽  
Temperature Fields ◽  
Wave Number ◽  
Marginal Stability ◽  
Two Dimensional ◽  
Wide Range ◽  
Gravity Driven ◽  
Gravity Driven Flow ◽  
The Stability

The stability and onset of two-dimensional convection in a rotating fluid saturated porous layer subject to gravity and centrifugal body forces is investigated analytically. The problem corresponding to a layer placed far away from the centre of rotation was identified as a distinct case and therefore justifying special attention. The stability of a basic gravity driven convection is analysed. The marginal stability criterion is established in terms of a critical centrifugal Rayleigh number and a critical wave number for different values of the gravity related Rayleigh number. For any given value of the gravity related Rayleigh number there is a transitional value of the wave number, beyond which the basic gravity driven flow is stable. The results provide the stability map for a wide range of values of the gravity related Rayleigh number, as well as the corresponding flow and temperature fields.

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