3D modeling of the deep structures of distal rifted margins | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS

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  3D modeling of the deep structures of distal rifted margins

Mercredi 21 Juin 2017
Séminaires Géosciences Marines
Julia Autin
(IPG Strasbourg)
Extrait: 

The observation of anomalously high seismic velocities (with Vp > 7.1 km/s) under rifted margins is associated with the presence of deep Lower Crustal Bodies (LCBs) or Low Velocity Bodies (LVBs) (Eldholm et al., 2000). In addition, the observed gravity field and combined seismic and gravity modelling studies (Hirsch et al., 2010; Maystrenko et al., 2013) along volcanic margins indicate that these LCBs also represent high-density domains. Several hypotheses can explain their lithology and emplacement: (1) mafic intrusions emplaced during the rifting and often related to Seaward Dipping Reflectors (SDRs) at the surface (Eldholm et al., 2000), (2) serpentinised mantle exhumed during the final extreme thinning of the crust, and (3) high degree metamorphic rocks inherited from a previous orogenic phase (Ebbing et al., 2006). It is a difficult task to determine the lithology and geometry of the lower crustal bodies but it is of first importance to understand their role in the development of rifted margins.
The study of both the geometry and lithology of the LCBs and LVBs is a prerequisite in order to assess the complexity of the processes related to the margin evolution. In this study, we combine 3D gravity modelling with 3D calculations of the conductive thermal field. The 3D structural model, including sedimentary and crustal layers, is complemented by (1) the top of the high density lower crust and (2) the lithosphere-asthenosphere boundary. We investigate the possible geometry and lithology of LCBs. To do so, we assess which geometry, densities and thermal properties are consistent with the observed gravity and thermal fields. The results of this analysis provide insights on the possible lithology and origin of the LCBs and may also explain the role of LCBs in rifted margins evolution, especially during subsidence and vertical movements.