Interplay of tectonics and magmatism during post-rift inversion on the central West Iberian Margin (Estremadura Spur)

ABSTRACT: The combined effects of post-rift magma emplacement and tectonic inversion on the hyper-extended West Iberian Margin are unravelled in detail using multichan nel 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 dem onstrate the tectono-magmatic interplay, namely: (a) the Campanian onset of mag matism (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 deforma tion styles within each tectonic phase document a case of decoupled deformation be tween Late Cretaceous and Tertiary units, in response to the predominant stress field evolution, revealing that the magnitude of Late Cretaceous inversion is far more sig nificant 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 transpres sive 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.info:eu-repo/semantics/publishedVersio

Limits of the seismogenic zone in the epicentral region of the 26 December 2004 great Sumatra-Andaman earthquake: Results from seismic refraction and wide-angle reflection surveys and thermal modeling

The 26 December 2004 Sumatra earthquake (Mw = 9.1) initiated around 30 km depth and ruptured 1300 km of the Indo-Australian Sunda plate boundary. During the Sumatra OBS (ocean bottom seismometer) survey, a wide angle seismic profile was acquired across the epicentral region. A seismic velocity model was obtained from combined travel time tomography and forward modeling. Together with reflection seismic data from the SeaCause II cruise, the deep structure of the source region of the great earthquake is revealed. Four to five kilometers of sediments overlie the oceanic crust at the trench, and the subducting slab can be imaged down to a depth of 35 km. We find a crystalline backstop 120 km from the trench axis, below the fore arc basin. A high velocity zone at the lower landward limit of the raycovered domain, at 22 km depth, marks a shallow continental Moho, 170 km from the trench. The deep structure obtained from the seismic data was used to construct a thermal model of the fore arc in order to predict the limits of the seismogenic zone along the plate boundary fault. Assuming 100C-150C as its updip limit, the seismogenic zone is predicted to begin 530 km from the trench. The downdip limit of the 2004 rupture as inferred from aftershocks is within the 350C 450C temperature range, but this limit is 210-250 km from the trench axis and is much deeper than the fore arc Moho. The deeper part of the rupture occurred along the contact between the mantle wedge and the downgoing plate

Use of 16S rRNA Gene Based Clone Libraries to Assess Microbial Communities Potentially Involved in Anaerobic Methane Oxidation in a Mediterranean Cold Seep

This study provides data on the diversities of bacterial and archaeal communities in an active methane seep at the Kazan mud volcano in the deep Eastern Mediterranean sea. Layers of varying depths in the Kazan sediments were investigated in terms of (1) chemical parameters and (2) DNA-based microbial population structures. The latter was accomplished by analyzing the sequences of directly amplified 16S rRNA genes, resulting in the phylogenetic analysis of the prokaryotic communities. Sequences of organisms potentially associated with processes such as anaerobic methane oxidation and sulfate reduction were thus identified. Overall, the sediment layers revealed the presence of sequences of quite diverse bacterial and archaeal communities, which varied considerably with depth. Dominant types revealed in these communities are known as key organisms involved in the following processes: (1) anaerobic methane oxidation and sulfate reduction, (2) sulfide oxidation, and (3) a range of (aerobic) heterotrophic processes. In the communities in the lowest sediment layer sampled (22–34 cm), sulfate-reducing bacteria and archaea of the ANME-2 cluster (likely involved in anaerobic methane oxidation) were prevalent, whereas heterotrophic organisms abounded in the top sediment layer (0–6 cm). Communities in the middle layer (6–22 cm) contained organisms that could be linked to either of the aforementioned processes. We discuss how these phylogeny (sequence)-based findings can support the ongoing molecular work aimed at unraveling both the functioning and the functional diversities of the communities under study

Phylogenetic Relationships among Deep-Sea and Chemosynthetic Sea Anemones: Actinoscyphiidae and Actinostolidae (Actiniaria: Mesomyaria)

Sea anemones (Cnidaria, Actiniaria) are present in all marine ecosystems, including chemosynthetic environments. The high level of endemicity of sea anemones in chemosynthetic environments and the taxonomic confusion in many of the groups to which these animals belong makes their systematic relationships obscure. We use five molecular markers to explore the phylogenetic relationships of the superfamily Mesomyaria, which includes most of the species that live in chemosynthetic, deep-sea, and polar sea habitats and to test the monophyly of the recently defined clades Actinostolina and Chemosynthina. We found that sea anemones of chemosynthetic environments derive from at least two different lineages: one lineage including acontiate deep-sea taxa and the other primarily encompassing shallow-water taxa

Phylogeny and Diversification Patterns among Vesicomyid Bivalves

Vesicomyid bivalves are among the most abundant and diverse symbiotic taxa in chemosynthetic-based ecosystems: more than 100 different vesicomyid species have been described so far. In the present study, we investigated the phylogenetic positioning of recently described vesicomyid species from the Gulf of Guinea and their western Atlantic and Pacific counterparts using mitochondrial DNA sequence data. The maximum-likelihood (ML) tree provided limited support for the recent taxonomic revision of vesicomyids based on morphological criteria; nevertheless, most of the newly sequenced specimens did not cluster with their morphological conspecifics. Moreover, the observed lack of geographic clustering suggests the occurrence of independent radiations followed by worldwide dispersal. Ancestral character state reconstruction showed a significant correlation between the characters “depth” and “habitat” and the reconstructed ML phylogeny suggesting possible recurrent events of ‘stepwise speciation’ from shallow to deep waters in different ocean basins. This is consistent with genus or species bathymetric segregation observed from recent taxonomic studies. Altogether, our results highlight the need for ongoing re-evaluation of the morphological characters used to identify vesicomyid bivalves