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The proximal and upper crustal parts of VPMs are exposed along the coast of central W- and E-Greenland, giving access to the extrusive section and the underlying sheeted dyke complexes intruded through the continental basement 18, 19. Lithosphere extension leading to break-up is coeval with focusing of mantle melting, giving rise to VPMs 6, 7, 8. During this early stage, massive crustal dilatation occurs through dyking in the upper crust 16 and magma underplating at the Moho 17.
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Early melt produces volcanic traps that cover large areas including continental cratons and/or craton edge (up to 10 7 km 2 or more) 6, 7. As exemplified in the Afar area, significant lithosphere extension does not appear to be a prerequisite for initial mantle melting and consecutive syn-magmatic break-up 8, 9. VPMs characterize continental break-up in Large Igneous Provinces (LIPs) 6, 7, 8, 9. An alternative model invoking the exhumation of a mechanically weak lower crust has also been proposed for SPMs 15. Asthenospheric mantle melting and generation of MORB-type magmas would finally occur through impingement of the main detachment fault 13, 14. A major trans-lithospheric detachment developing seaward would finally exhume the upper lithospheric mantle through a rolling-hinge deformation of the footwall 5, 12 ( Fig. Lithosphere necking is accommodated by an early system of upward-concave conjugate detachment faults dipping “oceanward” 5, 13 ( Fig. In such settings, sub-crustal mantle can be exhumed and serpentinized in association with extreme crustal stretching and thinning ( Fig. SPMs show no record of significant mantle melting in their upper crustal section immediately before and throughout lithosphere extension 10. The distinction between between the volcanic (VPMs) and non-volcanic (in this case, sedimentary) passive margins (SPMs) is basically drawn on the basis of timing and degree of mantle melting in relation to lithosphere extension, break-up and plate separation 6, 7, 8, 9. The role of magma intrusion in favoring and focusing extension may be important as the lithosphere can be both thermally weakened by hypothetical lithospheric-scale dykes 4 or compositionally strengthened in lower crustal section by cooled mafic intrusions 5. However, passive margins record events that end with continental break-up, when the integrated strength of rifted lithosphere drops to zero 1, 3. In general terms, if we consider frictional and non-linear ductile behavior of rocks and extension rates of the order of a few cm/yr, the extension of “normal” continental lithosphere requires high levels of differential stresses 1, 2, 3. 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. Crustal-scale faults dipping continentward are rooted over this flowing material, thus isolating micro-continents within the future oceanic domain. 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.
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This lower crust is exhumed up to the bottom of the syn-extension extrusives at the outer parts of the margin. These faults root on a two-layer deformed ductile crust that appears to be partly of igneous nature. In contrast with non-volcanic margins, continentward-dipping detachment faults accommodate crustal necking at both conjugate volcanic margins. 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. volcanic and non-volcanic, without proposing distinctive mechanisms for their formation. Two major types of passive margins are recognized, i.e.