Abstract
AbstractThe combined effects of post‐rift magma emplacement and tectonic inversion on the hyper‐extended West Iberian Margin are unravelled in detail using multichannel 2D/3D seismic data. The Estremadura Spur, acting as an uplifted crustal block bounded by two first‐order transfer zones, shows evidence of four post‐rift tectonic events each with a distinctive seismic‐stratigraphic response that can be used to demonstrate the tectono‐magmatic interplay, namely: (a) the Campanian onset of magmatism (including the Fontanelas Volcano, the widespread evidence of multiple sill complexes and the detailed description of a >20 km long laccolith, the Estremadura Spur Intrusion; (b) the Campanian‐Maastrichtian NE‐SW event pervasively affecting the area, resulting in regional uplift, reverse faulting and folding; (c) the Paleocene‐mid Eocene inversion that resulted in widespread erosion and; (d) the Oligocene‐mid Miocene evidence of rejuvenated NW‐SE inversion marked by crestal faulting and forced‐fault folding establishing the final geometry of the area. The distinct deformation styles within each tectonic phase document a case of decoupled deformation between Late Cretaceous and Tertiary units, in response to the predominant stress field evolution, revealing that the magnitude of Late Cretaceous inversion is far more significant than the one affecting the latter units. A detailed analysis of the laccolith and its overburden demonstrate the distinct deformation patterns associated both with magma ascent (including extensional faulting, forced‐folding and concentric reverse faulting) and its interference as a rigid intrusive body during subsequent transpressive inversion. This reinforces the role that the combined tectono‐magmatic events played on the margin. Also analysed is the wider impact of post‐rift magmatism and the associate emplacement of sub‐lithospheric magma on the rheology of a thinned continental crust. This takes into account the simultaneous tectonic inversion of the margin, the implied alternative views on characteristic heat flow, and on how these can be incorporated in source rock organic maturity modelling.
Highlights
The West Iberian Margin (WIM; Figure 1), is a typical example of a magma-poor hyper-extended margin (e.g. Manatschal & Bernoulli, 1999; Tucholke et al, 2007)
The present study provides new insights regarding other key questions for the evolution of the WIM, namely: (a) What are the new age constraints for the magmatic occurrences on the submerged continental margin? (b) Are there any preferential pathways controlling the ascent of magma during the Late Cretaceous cycle? and, (c) What are the implications of this tectono-magmatic inheritance for the subsequent tectonic inversion of the margin? an overall discussion on the causes for the predominance of magmatic manifestations at specific segments of the margin is presented, taking into account the previously proposed presence of a deep seated heat source and its repercussions on the maturation of regional prospective source rocks, and on how deformable plate paleogeographic models for hyper-extended margins evolve after breakup
Based on high resolution 2D/3D multichannel seismic surveys from central West Iberian Margin (Estremadura Spur), this work documents the combined effects of sub-lithospheric post-rift magma plumbing system and tectonic inversion from Late Cretaceous onwards, showing the evidence of four major post-lithospheric breakup tectono-stratigraphic events largely controlled by the rotation of Iberia during the Alpine cycle
Summary
The West Iberian Margin (WIM; Figure 1), is a typical example of a magma-poor hyper-extended margin (e.g. Manatschal & Bernoulli, 1999; Tucholke et al, 2007). Evidence of an important pre-Tertiary (below BTU) magmatic plumbing system, is preserved throughout the study area, mainly underneath and around the region of the Fontanelas Volcano, and associated with the ESI Evidence of such system is composed of multiple seismic features mainly observed dominantly within sequence 5b (Figures 4-6), suggesting an interpreted age for the emplacement of these features to have occurred during the Turonian-mid Campanian period Associated with ESI, multiple high amplitude reflections are observed either underlying or overlying this laccolith-shape feature that are interpreted as sills (Figures 4-6) These are similar to those described by McLean et al (2017) in the Faroe-Shetland Basin, and to the general setting of the outcropping Sintra intrusion in the WIM onshore associated with a complex of numerous radial and concentric dykes (Kullberg & Kullberg, 2000; Terrinha et al, 2017). This aspect suggests that during this period tectonic activity is significantly decreased and that the controlling mechanisms would likely be associated with some minor tilting of the margin as a whole, as evidenced by the westwards inclined character of seismic horizons
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