Automated reconstruction of the Vøring volcanic margin incorporating non-extensional processes

<p>The Vøring Margin offshore Norway is a typical example of volcanic passive margin. The evolution of the inner Vøring Margin is well explained by standard models of lithosphere extension (McKenzie, 1978). Basin modelling tools based on the assumption of lithosphere extension then satisfactorily simulate the tectonic and thermal evolution of the inner margin.</p><p>However, models of extension fail to reproduce key observations at the outer (volcanic) domain of the Vøring Margin. These specific observations include uplift at time of breakup, the presence of SDRs and magma additions at the base of the lower crust usually referred as the lower crustal body and interpreted as magma underplating or highly intruded lower crust. Additional, non-extensional processes are required to satisfy these observations.</p><p>Excess magmatism and uplift of the outer margin during the breakup time has been explained by the arrival of the hot Icelandic mantle “plume” (Skogseid et al., 2000) or by other sublithospheric processes such as small-scale convection (van Wijk et al., 2001). Melt retention in the asthenosphere has also been proposed to explain uplift at passive margins (Quirk & Rüpke, 2018). At last, mantle phase transitions caused by pressure and temperature changes in the mantle during extension may contribute to uplift (Simon & Podladchikov, 2008).</p><p>These processes must be included in the basin modelling procedure to reliably simulate the evolution of the volcanic margin.</p><p>We use the Tecmod2d modelling suite (Rüpke et al., 2008) to simulate the tectono-thermal evolution along two crustal transects crossing the Vøring Margin. Tecmod uses an automated inversion scheme approach. Processes such as magmatic underplating, melt retention, mantle phase transitions, and differential thinning can be taken into account.</p><p>We test various tectono-thermal models of the margin evolution that incorporate or not these processes. Models incorporating a plume emplaced at Eocene time and taking into account magmatic processes (melt retention and magmatic underplate) satisfactorily reproduce the specific observations of the outer (volcanic) margin. This result backs the contribution of the hot Iceland plume on the evolution of the Vøring Margin.</p><p> </p><p><strong>References</strong></p><p>McKenzie, D. (1978) Some remarks on development of sedimentary basins. Earth Planet. Sci. Lett., 40, 25-32.</p><p>Quirk, D.G., Rüpke, L.H. Melt-induced buoyancy may explain the elevated rift-rapid sag paradox during breakup of continental plates. Sci Rep <strong>8, </strong>9985 (2018). https://doi.org/10.1038/s41598-018-27981-2</p><p>Rüpke, L.H., Schmalholz, S.M., Schmid, D.W. & Podladchikov, Y.Y. (2008) Automated Thermotectonostratigraphic basin reconstruction: Viking Graben case study. AAPG Bull., 92, 309^326.</p><p>Simon, N.S.C., Podladchikov, Y.Y., 2008. The effect of mantle composition on density in the extending lithosphere. Earth Planet. Sci. Lett.272, 148–157.</p><p>Skogseid, J., Planke, S., Faleide, J.I., Pedersen, T., Eldholm, O. & Neverdal, F. (2000)Ne Atlantic continental rifting and volcanic margin formation. In: Dynamics of the NorwegianMargin (Ed. by A.Nottvedt, B.T. Larsen, R.H.Gabrielsen, S. Olaussen, B.Torudbakken, J. Skogseid,H. Brekke & O. Birkeland), Geol. Soc. Spec. Publ., 167, 295^326.</p><p>van Wijk, J. W., Huismans, R. S., Ter Voorde, M., & Cloetingh, S. A. P. L. (2001). Melt generation at volcanic continental margins: No need for a mantle plume? Geophysical Research Letters, 28(20), 3995–3998. https://doi.org/10.1029/2000GL012848.</p>

Conjunction between diachronic volcanic processes and transform margin leads to the unusual structure of the Demerara transform marginal plateau and its three different margins.

<p><span>The Demerara plateau (offshore Suriname and French Guiana) is an original transform marginal plateau located at the junction between the central and the equatorial Atlantic domains. New results combining the interpretation of several datasets of high-penetration industrial MCS, academic MCS and wide-angle seismic data image a 30 km thick crust in the plateau, evolving towards three different margins to the two adjacent oceanic domains.</span></p><p><span>This work shows that this oceanic relief is a Jurassic volcanic margin located at the southern termination of the Central Atlantic rifting, and forming the divergent western margin of the Demerara plateau. New result from dredges also show the influence of a hotspot in this rifting phase. The resulting transitional domain is unusual, characterized by a progressive thinning of the margin toward the west and the presence of SDRs outer bodies on a reworked unit probably of continental origin. Unambiguous oceanic crust is identified at about 100 km from the slope break of the shelf. Toward the plateau, the outer SDR body let place to several thick superimposed inner SDR.</span></p><p><span>Then, this Jurassic domain was remarkably reworked during the Cretaceous rifting phase linked to the opening of the Equatorial Atlantic. This second event restructured this volcanic object, forming a transform northern margin and a divergent eastern margin, each with a specific transitional domain.</span></p><p><span>The presence of a volcanic margin which subsequently undergoes a non-coaxial opening with transform constraints is relatively unusual. Our data help to better constrain the transitional domains and the TOC of the Equatorial Atlantic Cretaceous margins. </span></p><p><span>The characterization of the northern and eastern extension limit of the SDRs formations and of the high velocity lower crust observed in the plateau is an important regional issue. This knowledge is necessary in particular to characterize the volumes and structures associated with the Jurassic volcanic episode, which control the thermo-structural Cretaceous evolution of the plateau and the adjacent domains.</span></p>

Demerara Rise, offshore Suriname: Magma-rich segment of the Central Atlantic Ocean, and conjugate to the Bahamas hot spot

The Demerara Rise is a prominent bathymetric feature that has been considered as a broad expression of shallow continental basement and used in conjunction with the Guinea Plateau as a pinning point for circum-Atlantic plate reconstructions. Previously, shallow-penetration, poorly imaged seismic data over the Demerara Rise were modeled with the lower sequences interpreted as continental crust at relatively shallow depths. However, new long-offset, deeply penetrating seismic data provide evidence that basement nearly or entirely comprises excessively thick volcanic strata (approximately 21 km). Seismic character and geometry, 2D gravity modeling, and volcanic margin analogs were used to identify unfaulted, convex-upward seaward dipping reflector (SDR) packages. These steeply dipping (approximately 20°) igneous successions are westwardly divergent, and occur as offlapping reflector sets in trains as long as 250 km. This rift-related volcanism now recognized at the Demerara Rise was probably conjugate to syn-rift volcanism in South Florida/Great Bahama Bank, and from this we have predicted a volcanic element for the Guinea Plateau. This volcanism could be linked to a Bahamas hot spot at the initial opening of the Central Atlantic. Six SDR packages have been interpreted below the Late Jurassic-Early Cretaceous carbonate section of the rise, indicating that the early volcanism produced a marine substrate upon which the subsequent carbonate bank section developed. We have inferred that this Early Cretaceous volcanic/carbonate margin continued into the Guinea Plateau of West Africa. The pre-Aptian section was inverted and peneplained with a strong angular unconformity prior to the Early Cretaceous opening of the Equatorial Atlantic seaway. The newly identified Central Atlantic volcanic margin of the Demerara Rise holds implications of a volcanic origin for its conjugate margins. We have confirmed a voluminous magma-rich opening of the southeastern Central Atlantic.