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Volcanic passive margins: another way to break up continents.

Geoffroy L, Burov EB, Werner P - Sci Rep (2015)

Bottom Line: Volcanic passive margins are associated with the extrusion and intrusion of large volumes of magma, predominantly mafic, and represent distinctive features of Larges Igneous Provinces, in which regional fissural volcanism predates localized syn-magmatic break-up of the lithosphere.Crustal-scale faults dipping continentward are rooted over this flowing material, thus isolating micro-continents within the future oceanic domain.Pure-shear type deformation affects the bulk lithosphere at VPMs until continental breakup, and the geometry of the margin is closely related to the dynamics of an active and melting mantle.

View Article: PubMed Central - PubMed

Affiliation: Université de Bretagne Occidentale, Brest, 29238 Brest.

ABSTRACT
Two major types of passive margins are recognized, i.e. volcanic and non-volcanic, without proposing distinctive mechanisms for their formation. Volcanic passive margins are associated with the extrusion and intrusion of large volumes of magma, predominantly mafic, and represent distinctive features of Larges Igneous Provinces, in which regional fissural volcanism predates localized syn-magmatic break-up of the lithosphere. In contrast with non-volcanic margins, continentward-dipping detachment faults accommodate crustal necking at both conjugate volcanic margins. These faults root on a two-layer deformed ductile crust that appears to be partly of igneous nature. This lower crust is exhumed up to the bottom of the syn-extension extrusives at the outer parts of the margin. Our numerical modelling suggests that strengthening of deep continental crust during early magmatic stages provokes a divergent flow of the ductile lithosphere away from a central continental block, which becomes thinner with time due to the flow-induced mechanical erosion acting at its base. Crustal-scale faults dipping continentward are rooted over this flowing material, thus isolating micro-continents within the future oceanic domain. Pure-shear type deformation affects the bulk lithosphere at VPMs until continental breakup, and the geometry of the margin is closely related to the dynamics of an active and melting mantle.

No MeSH data available.


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(a) Numerical model setup (see Methods). Red colour in the upper panel corresponds to magmatic underplating (viscosity is ~1024 to 1025 Pa.s and 1021 Pa.s for the ambient lower crust). An initial, negligibly small thermal anomaly (50 °C) is used to initialize rifting in the middle of the model, which dissipates soon afterwards. The bottom right panel shows a typical viscous-elastic-plastic lithospheric strength profile used in the numerical experiments. (b) 4.5 Ma after imposing a 1.5 cm/yr displacement on each side of the model. From top to bottom are shown: the material phase field, the effective viscosity field (in Pa.s) and the finite strain field. Note that the rheology used is viscous-elastic-plastic, so effective viscosity is defined as the ratio of deviatoric stress to strain rate, for illustrative purposes only. (c) Tectonic/dynamic sketch related to the left part of the enlarged finite strain panel in (b). Authors: E.B (modelling) and L.G. (interpretation). Images created from modelling results using Adobe Photoshop CS6 (results) and CorelDraw11 (interpretation).
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f3: (a) Numerical model setup (see Methods). Red colour in the upper panel corresponds to magmatic underplating (viscosity is ~1024 to 1025 Pa.s and 1021 Pa.s for the ambient lower crust). An initial, negligibly small thermal anomaly (50 °C) is used to initialize rifting in the middle of the model, which dissipates soon afterwards. The bottom right panel shows a typical viscous-elastic-plastic lithospheric strength profile used in the numerical experiments. (b) 4.5 Ma after imposing a 1.5 cm/yr displacement on each side of the model. From top to bottom are shown: the material phase field, the effective viscosity field (in Pa.s) and the finite strain field. Note that the rheology used is viscous-elastic-plastic, so effective viscosity is defined as the ratio of deviatoric stress to strain rate, for illustrative purposes only. (c) Tectonic/dynamic sketch related to the left part of the enlarged finite strain panel in (b). Authors: E.B (modelling) and L.G. (interpretation). Images created from modelling results using Adobe Photoshop CS6 (results) and CorelDraw11 (interpretation).

Mentions: In the present study we investigate the mechanisms of stretching and thinning of the continental lithosphere in magma-rich settings, based on new observational data and the results of physically consistent thermo-mechanical numerical modelling. We use a new set of long-offset commercial seismic reflection data from VPMs worldwide to study their deep structure down to ~40 km. For that we have selected two ION Geophysical dip-lines across the Pelotas volcanic margin in the southern Atlantic (Fig. 2a). The Pelotas and Namibia conjugate VPMs formed within the Gondwana-related Mantiqueira Province after the onset of eruption of the Parana-Etendeka volcanic traps during the Hauterivian20212223. The time-span of syn-magmatic continental lithosphere stretching/thinning is bracketed between ~130 Ma (end of traps emplacement) and ~115 Ma21. The magma budget of the Pelotas margin varies along-strike depending on its location with respect to the Rio Grande Rise (Fig. 2a,b)21: Line PS1-0090 (Fig. 2b) lies across a particularly magma-rich segment compared to Line PS1-0040 (see Fig. 1 in Extended Data). Although the ION Geophysical PelotasSPAN data set has recently been analysed21, we present here a different profile (PS1-0040; Fig. 1 in Extended Data) along with different interpretations. We also use seismic refraction and potential data from the conjugate margin of Namibia south of Walvis Rise2223, which are further constrained by a set of recent seismic reflection profiles (down to ~8–9 sec two-way travel time) as shown in Extended Data Fig. 3.


Volcanic passive margins: another way to break up continents.

Geoffroy L, Burov EB, Werner P - Sci Rep (2015)

(a) Numerical model setup (see Methods). Red colour in the upper panel corresponds to magmatic underplating (viscosity is ~1024 to 1025 Pa.s and 1021 Pa.s for the ambient lower crust). An initial, negligibly small thermal anomaly (50 °C) is used to initialize rifting in the middle of the model, which dissipates soon afterwards. The bottom right panel shows a typical viscous-elastic-plastic lithospheric strength profile used in the numerical experiments. (b) 4.5 Ma after imposing a 1.5 cm/yr displacement on each side of the model. From top to bottom are shown: the material phase field, the effective viscosity field (in Pa.s) and the finite strain field. Note that the rheology used is viscous-elastic-plastic, so effective viscosity is defined as the ratio of deviatoric stress to strain rate, for illustrative purposes only. (c) Tectonic/dynamic sketch related to the left part of the enlarged finite strain panel in (b). Authors: E.B (modelling) and L.G. (interpretation). Images created from modelling results using Adobe Photoshop CS6 (results) and CorelDraw11 (interpretation).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4595843&req=5

f3: (a) Numerical model setup (see Methods). Red colour in the upper panel corresponds to magmatic underplating (viscosity is ~1024 to 1025 Pa.s and 1021 Pa.s for the ambient lower crust). An initial, negligibly small thermal anomaly (50 °C) is used to initialize rifting in the middle of the model, which dissipates soon afterwards. The bottom right panel shows a typical viscous-elastic-plastic lithospheric strength profile used in the numerical experiments. (b) 4.5 Ma after imposing a 1.5 cm/yr displacement on each side of the model. From top to bottom are shown: the material phase field, the effective viscosity field (in Pa.s) and the finite strain field. Note that the rheology used is viscous-elastic-plastic, so effective viscosity is defined as the ratio of deviatoric stress to strain rate, for illustrative purposes only. (c) Tectonic/dynamic sketch related to the left part of the enlarged finite strain panel in (b). Authors: E.B (modelling) and L.G. (interpretation). Images created from modelling results using Adobe Photoshop CS6 (results) and CorelDraw11 (interpretation).
Mentions: In the present study we investigate the mechanisms of stretching and thinning of the continental lithosphere in magma-rich settings, based on new observational data and the results of physically consistent thermo-mechanical numerical modelling. We use a new set of long-offset commercial seismic reflection data from VPMs worldwide to study their deep structure down to ~40 km. For that we have selected two ION Geophysical dip-lines across the Pelotas volcanic margin in the southern Atlantic (Fig. 2a). The Pelotas and Namibia conjugate VPMs formed within the Gondwana-related Mantiqueira Province after the onset of eruption of the Parana-Etendeka volcanic traps during the Hauterivian20212223. The time-span of syn-magmatic continental lithosphere stretching/thinning is bracketed between ~130 Ma (end of traps emplacement) and ~115 Ma21. The magma budget of the Pelotas margin varies along-strike depending on its location with respect to the Rio Grande Rise (Fig. 2a,b)21: Line PS1-0090 (Fig. 2b) lies across a particularly magma-rich segment compared to Line PS1-0040 (see Fig. 1 in Extended Data). Although the ION Geophysical PelotasSPAN data set has recently been analysed21, we present here a different profile (PS1-0040; Fig. 1 in Extended Data) along with different interpretations. We also use seismic refraction and potential data from the conjugate margin of Namibia south of Walvis Rise2223, which are further constrained by a set of recent seismic reflection profiles (down to ~8–9 sec two-way travel time) as shown in Extended Data Fig. 3.

Bottom Line: Volcanic passive margins are associated with the extrusion and intrusion of large volumes of magma, predominantly mafic, and represent distinctive features of Larges Igneous Provinces, in which regional fissural volcanism predates localized syn-magmatic break-up of the lithosphere.Crustal-scale faults dipping continentward are rooted over this flowing material, thus isolating micro-continents within the future oceanic domain.Pure-shear type deformation affects the bulk lithosphere at VPMs until continental breakup, and the geometry of the margin is closely related to the dynamics of an active and melting mantle.

View Article: PubMed Central - PubMed

Affiliation: Université de Bretagne Occidentale, Brest, 29238 Brest.

ABSTRACT
Two major types of passive margins are recognized, i.e. volcanic and non-volcanic, without proposing distinctive mechanisms for their formation. Volcanic passive margins are associated with the extrusion and intrusion of large volumes of magma, predominantly mafic, and represent distinctive features of Larges Igneous Provinces, in which regional fissural volcanism predates localized syn-magmatic break-up of the lithosphere. In contrast with non-volcanic margins, continentward-dipping detachment faults accommodate crustal necking at both conjugate volcanic margins. These faults root on a two-layer deformed ductile crust that appears to be partly of igneous nature. This lower crust is exhumed up to the bottom of the syn-extension extrusives at the outer parts of the margin. Our numerical modelling suggests that strengthening of deep continental crust during early magmatic stages provokes a divergent flow of the ductile lithosphere away from a central continental block, which becomes thinner with time due to the flow-induced mechanical erosion acting at its base. Crustal-scale faults dipping continentward are rooted over this flowing material, thus isolating micro-continents within the future oceanic domain. Pure-shear type deformation affects the bulk lithosphere at VPMs until continental breakup, and the geometry of the margin is closely related to the dynamics of an active and melting mantle.

No MeSH data available.


Related in: MedlinePlus