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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.


Related in: MedlinePlus

(a) Map of the first horizontal derivative of the Bouguer gravity field in the South Atlantic and location of the referred seismic profiles. PT, ET: Parana and Etendeka traps, respectively. WR, RGR: Walvis and Rio Grande Rises, respectively. APsB: Aptian Salt Basin. RGF not FTF: Rio Grande Transform. Author, P.W. using a software created by TOTAL. (b) Interpretation of PelotasSPAN line PS1-0090 (ION Geophysical). For original lines PS1-0040 and PS1-0090 along with interpretations, see Additional Data. Authors, P.W. and L.G., using CorelDraw11. (c) Crustal-scale profile of conjugate Pelotas and Namibia VPMs, during break-up. Figure is to scale. The arrow indicates the location of the earliest ocean-floor accretion. The Namibian profile22 is located in (a). Crustal structure and seismic velocities of Namibian margin are found in ref. 22. Authors L.G. and P.W, using CorelDraw11.
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f2: (a) Map of the first horizontal derivative of the Bouguer gravity field in the South Atlantic and location of the referred seismic profiles. PT, ET: Parana and Etendeka traps, respectively. WR, RGR: Walvis and Rio Grande Rises, respectively. APsB: Aptian Salt Basin. RGF not FTF: Rio Grande Transform. Author, P.W. using a software created by TOTAL. (b) Interpretation of PelotasSPAN line PS1-0090 (ION Geophysical). For original lines PS1-0040 and PS1-0090 along with interpretations, see Additional Data. Authors, P.W. and L.G., using CorelDraw11. (c) Crustal-scale profile of conjugate Pelotas and Namibia VPMs, during break-up. Figure is to scale. The arrow indicates the location of the earliest ocean-floor accretion. The Namibian profile22 is located in (a). Crustal structure and seismic velocities of Namibian margin are found in ref. 22. Authors L.G. and P.W, using CorelDraw11.

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) Map of the first horizontal derivative of the Bouguer gravity field in the South Atlantic and location of the referred seismic profiles. PT, ET: Parana and Etendeka traps, respectively. WR, RGR: Walvis and Rio Grande Rises, respectively. APsB: Aptian Salt Basin. RGF not FTF: Rio Grande Transform. Author, P.W. using a software created by TOTAL. (b) Interpretation of PelotasSPAN line PS1-0090 (ION Geophysical). For original lines PS1-0040 and PS1-0090 along with interpretations, see Additional Data. Authors, P.W. and L.G., using CorelDraw11. (c) Crustal-scale profile of conjugate Pelotas and Namibia VPMs, during break-up. Figure is to scale. The arrow indicates the location of the earliest ocean-floor accretion. The Namibian profile22 is located in (a). Crustal structure and seismic velocities of Namibian margin are found in ref. 22. Authors L.G. and P.W, using CorelDraw11.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: (a) Map of the first horizontal derivative of the Bouguer gravity field in the South Atlantic and location of the referred seismic profiles. PT, ET: Parana and Etendeka traps, respectively. WR, RGR: Walvis and Rio Grande Rises, respectively. APsB: Aptian Salt Basin. RGF not FTF: Rio Grande Transform. Author, P.W. using a software created by TOTAL. (b) Interpretation of PelotasSPAN line PS1-0090 (ION Geophysical). For original lines PS1-0040 and PS1-0090 along with interpretations, see Additional Data. Authors, P.W. and L.G., using CorelDraw11. (c) Crustal-scale profile of conjugate Pelotas and Namibia VPMs, during break-up. Figure is to scale. The arrow indicates the location of the earliest ocean-floor accretion. The Namibian profile22 is located in (a). Crustal structure and seismic velocities of Namibian margin are found in ref. 22. Authors L.G. and P.W, using CorelDraw11.
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