Volcanic passive margins: another way to break up continents

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.

The T‐Reflection and the Deep Crustal Structure of the Vøring Margin, Offshore mid‐Norway

“…The petrology and geochemistry results of the lava flows from ODP Hole 642E also show evidence of continental contamination (Abdelmalak, Meyer, et al, ; Meyer et al, ) that cannot easily be explained by the presence of a shallow serpentinized mantle lying just underneath the subaerial lava flows. In a similar tectonic setting (Uruguay volcanic margin), Clerc et al () showed evidence that the continental lower crust is most likely preserved underneath the SDR and adjacent basins and also confirm that volcanic margin and magma‐poor margins show striking differences (e.g., Clerc et al, ; Franke, ; Geoffroy et al, ).…”

Polyphase Magmatism During the Formation of the Northern East Greenland Continental Margin

“…This SDR wedge broadens southward up to 40 km at 75.2°N, where it is subdivided into two wedges. The individual wedges may be bounded by landward dipping faults (Figure ), as proposed in the general concept by Geoffroy et al (). The SDRs correspond widely to a negative magnetic polarization (Figures and ) and are clearly located landward of magnetic chron C24n.3n (C24B; cf.…”

Characterization of Seaward‐Dipping Reflectors Along the South American Atlantic Margin and Implications for Continental Breakup

“…Pálmason () then showed that the geometries of the Iceland Tertiary lava pile could be predicted by a kinematic model of plate crustal accretion, using lava production rate and extrusion geometries. However, recent fault‐controlled models have suggested that SDRs form during the tectonic thinning of heavily intruded continental crust and within oceanward‐dipping half grabens (Figure a; Geoffroy, ; Geoffroy et al, ). Quirk et al () propose a different fault‐based model where planar SDRs form in the hanging wall of a large‐offset normal fault in continental crust and younger convex‐upward SDRs are extruded above sheared gabbros and terminate against an axial horst composed of heavily intruded continental crust (Figure b).…”