Limits...
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

Proposed model of conjugate VPM formation.Note that asymmetry in the width and/or crustal thickness of conjugate VPMs often exists20. (a) Initial stage associated with minor tectonic extension but with intense dilatation of the crust by mafic magmas (sills and dyke swarms in the lower and upper crust, respectively). Flat-lying basaltic traps (typically, ~2 km thick679) are extruded at this time. (b) Extreme crustal thinning and stretching during the necking stage with individualization of inner SDRs and a central continental block (C-Block, see also Fig. 4), to be compared with the SPMs-related H-Block (Fig. 1a). (c) Continental spreading through fragmentation of the C-block owing to bulk pure-shear deformation with formation of the outer SDRs. Author: L.G., using CorelDraw11.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4595843&req=5

f5: Proposed model of conjugate VPM formation.Note that asymmetry in the width and/or crustal thickness of conjugate VPMs often exists20. (a) Initial stage associated with minor tectonic extension but with intense dilatation of the crust by mafic magmas (sills and dyke swarms in the lower and upper crust, respectively). Flat-lying basaltic traps (typically, ~2 km thick679) are extruded at this time. (b) Extreme crustal thinning and stretching during the necking stage with individualization of inner SDRs and a central continental block (C-Block, see also Fig. 4), to be compared with the SPMs-related H-Block (Fig. 1a). (c) Continental spreading through fragmentation of the C-block owing to bulk pure-shear deformation with formation of the outer SDRs. Author: L.G., using CorelDraw11.

Mentions: Figure 5 takes into account the onshore, offshore and modelling data to summarize the main stages in the evolution and final structure of VPMs, as compared to SPMs (Fig. 1). Extreme crustal thinning and stretching leads to break-up (i.e. oceanization) in the case of both SPMs (Fig. 1b) and VPMs (Fig. 5c), but lithospheric pure shear (associated with continent-ward dipping shear-zones at both margins) dominate over simple shear at VPMs. Cold lithospheric mantle may be exhumed (and serpentinized) in SPMs, whereas the geodynamic evolution of VPMs involves a hot active and melting mix of sub-Moho and asthenospheric mantle, which never appears to reach the ocean floor (Fig. 5b,c).


Volcanic passive margins: another way to break up continents.

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

Proposed model of conjugate VPM formation.Note that asymmetry in the width and/or crustal thickness of conjugate VPMs often exists20. (a) Initial stage associated with minor tectonic extension but with intense dilatation of the crust by mafic magmas (sills and dyke swarms in the lower and upper crust, respectively). Flat-lying basaltic traps (typically, ~2 km thick679) are extruded at this time. (b) Extreme crustal thinning and stretching during the necking stage with individualization of inner SDRs and a central continental block (C-Block, see also Fig. 4), to be compared with the SPMs-related H-Block (Fig. 1a). (c) Continental spreading through fragmentation of the C-block owing to bulk pure-shear deformation with formation of the outer SDRs. Author: L.G., using CorelDraw11.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: Proposed model of conjugate VPM formation.Note that asymmetry in the width and/or crustal thickness of conjugate VPMs often exists20. (a) Initial stage associated with minor tectonic extension but with intense dilatation of the crust by mafic magmas (sills and dyke swarms in the lower and upper crust, respectively). Flat-lying basaltic traps (typically, ~2 km thick679) are extruded at this time. (b) Extreme crustal thinning and stretching during the necking stage with individualization of inner SDRs and a central continental block (C-Block, see also Fig. 4), to be compared with the SPMs-related H-Block (Fig. 1a). (c) Continental spreading through fragmentation of the C-block owing to bulk pure-shear deformation with formation of the outer SDRs. Author: L.G., using CorelDraw11.
Mentions: Figure 5 takes into account the onshore, offshore and modelling data to summarize the main stages in the evolution and final structure of VPMs, as compared to SPMs (Fig. 1). Extreme crustal thinning and stretching leads to break-up (i.e. oceanization) in the case of both SPMs (Fig. 1b) and VPMs (Fig. 5c), but lithospheric pure shear (associated with continent-ward dipping shear-zones at both margins) dominate over simple shear at VPMs. Cold lithospheric mantle may be exhumed (and serpentinized) in SPMs, whereas the geodynamic evolution of VPMs involves a hot active and melting mix of sub-Moho and asthenospheric mantle, which never appears to reach the ocean floor (Fig. 5b,c).

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