Genetic Relations Between the Aves Ridge and the Grenada Back-Arc Basin, East Caribbean Sea

The Grenada Basin separates the active Lesser Antilles Arc from the Aves Ridge, described as a Cretaceous‐Paleocene remnant of the “Great Arc of the Caribbean.” Although various tectonic models have been proposed for the opening of the Grenada Basin, the data on which they rely are insufficient to reach definitive conclusions. This study presents, a large set of deep‐penetrating multichannel seismic reflection data and dredge samples acquired during the GARANTI cruise in 2017. By combining them with published data including seismic reflection data, wide‐angle seismic data, well data and dredges, we refine the understanding of the basement structure, depositional history, tectonic deformation and vertical motions of the Grenada Basin and its margins as follows: (1) rifting occurred during the late Paleocene‐early Eocene in a NW‐SE direction and led to seafloor spreading during the middle Eocene; (2) this newly formed oceanic crust now extends across the eastern Grenada Basin between the latitude of Grenada and Martinique; (3) asymmetrical pre‐Miocene depocenters support the hypothesis that the southern Grenada Basin originally extended beneath the present‐day southern Lesser Antilles Arc and probably partly into the present‐day forearc before the late Oligocene‐Miocene rise of the Lesser Antilles Arc; and (4) the Aves Ridge has subsided along with the Grenada Basin since at least the middle Eocene, with a general subsidence slowdown or even an uplift during the late Oligocene, and a sharp acceleration on its southeastern flank during the late Miocene. Until this acceleration of subsidence, several bathymetric highs remained shallow enough to develop carbonate platforms

Seismic images and magnetic signature of the Late Jurassic to Early Cretaceous Africa-Eurasia plate boundary off SW Iberia

Over the last two decades numerous studies have investigated the structure of the west Iberia continental margin, a non-volcanic margin characterized by a broad continent–ocean transition (COT). However, the nature and structure of the crust of the segment of the margin off SW Iberia is still poorly understood, because of sparse geophysical and geological data coverage. Here we present a 275-km-long multichannel seismic reflection (MCS) profile, line AR01, acquired in E–W direction across the Horseshoe Abyssal Plain, to partially fill the gap of information along the SW Iberia margin. Line AR01 runs across the inferred plate boundary between the Iberian and the African plates during the opening of the Central Atlantic ocean. The boundary separates crust formed during or soon after continental rifting of the SW Iberian margin from normal seafloor spreading oceanic crust of the Central Atlantic ocean. Line AR01 has been processed and pre-stack depth migrated to show the tectonic structure of the crust across the palaeo plate boundary. This boundary is characterized by a 30–40-km-wide zone of large basements highs related to landward-dipping reflections, which penetrate to depths of 13–15 km, and it marks a change in the character of the basement structure and relief from east to west. In this study, we have used pre-stack depth migrated images, the velocity model of line AR01 and magnetic data available in the area to show that the change in basement structure occurs across the fossil plate boundary, separating African oceanic crust of the M series (M21–M16) to the west from the transitional crust of the Iberian margin to the east

Evolution and segmentation of oblique rift in a cold lithosphere: Insights from analogue modeling

International audienc

Ocean-continent transition and oceanic ridge structural evolution (eastern Gulf of Aden): Implications for rift to seafloor spreading processes

International audienc

How and when did a strong thinning occur in the Gulf of Aden? A discussion from field, geophysical data and analogue models

International audienc

Continental breakup history of poor magmatic margins from seismic reflection and analogue modeling (oriental Gulf of Aden)

International audienc

Structure and evolution of a passive margin in a compressive environment : example of the south-western Alps-Ligurian basin junction during the Cenozoic

We focus on the northern Ligurian margin, at the geological junction of the subalpine domain and the Ligurian oceanic basin, in order (1) to identify the location of the southern limit of the Alpine compressive domain during the Cenozoic, and (2) to study the influence of a compressive environment on the tectonic and sedimentary evolution of a passive margin. Based on published onshore and offshore data, we first propose a chronology of the main extensional and compressional regional tectonic events. High-resolution seismic data image the margin structure down to similar to 3 km below seafloor. These data support that past rifting processes control the present-day margin structure, and that 2800-4000 m of synrift sediment was deposited on this segment of the margin in two steps. First, sub-parallel reflectors indicate sediment deposition within a subsident basin showing a low amount of extension. Then, a fan-shaped sequence indicates block tilting and a higher amount of extension. We do not show any influence of the Miocene Alpine compression on the present-day margin structure at our scale of investigation, despite the southern subalpine relief formed in the close hinterland at that time. The southern front of the Miocene Alps was thus located upslope from the continental margin. Finally, a comparison with the Gulf of Lions margin suggests that the tectonic influence of the Alpine compression on the rifting processes is restrited to an increase of the subsidence related to flexure ahead of the Alpine front, explaining abnormally high synrift thicknesses in the study area. The Alpine environment, however, has probably controlled the sedimentary evolution of the margin since the rifting. Indeed, sediment supply and distribution would be mainly controlled by the permanent building of relief in the hinterland and by the steep basin morphology, rather than by sea-level fluctuations, even during the Messinian sea-level low-stand

Inversion of back-arc basins : example of the Ligurian Basin, Western Mediterranean

The Mediterranean back-arc basins, once opened, are often rapidly submitted to inversion along the complex Eurasian-African convergent border. Along their continental margins, these small basins consist of heterogeneous systems that juxtapose lithospheres with different nature, mechanical behavior and structural inheritance. In this study, we focus on the northern Ligurian margin to examine how such complex systems might deform when they are submitted to compressive stress. The northern Ligurian margin, of Oligo-Miocene age, has been undergoing contraction over at least the last 6 Ma. Below the margin, active thrust faults responsible for the regional uplift of the continental edge have been proposed in previous works, but have never been imaged. Seaward of the margin, no recent or active crustal compressional structure has been identified so far in the oceanic domain, although seismicity extends as far as midway through the basin. We use seismic reflection data, including 72- and 12-channel high-resolution acquisitions (MALISAR, 2006 and FABLES, 2012) and 96-channel deep-penetrating ones (MALIS, 1995), to image the Ligurian margin and the adjacent oceanic domain. In the seismic lines, the Messinian event, well dated over the Mediterranean (5.96-5.32 Ma) and well identified in the seismic stratigraphy, allows us to quantify the vertical deformation over the last 5.3 Ma. The seismic reflection data set is interpreted together with 3D-velocity-depth models deduced from wide-angle seismic data (GROSMARIN, 2008). Below the margin, the contraction is characterized by folds, south verging thrusts, tilted crustal blocks, and by a global margin uplift that exceeds 1500m. Within the adjacent oceanic domain, noticeable deformation is restricted to large, SW-NE elongated salt walls located 10 to 40 km from the margin toe, over a 70 km length. We interpret them as resulting from combined deep-seated crustal and thin-skinned deformations. However, although the salt walls are well expressed in the seafloor morphology, their seismic images do not reveal any significant vertical throw across their trace, and the amount of deformation gradually disappears toward the structure ends. This suggests that the post-Messinian deformation taken along these features is moderate, compared to the margin. The synchronicity of the crustal deformation in the oceanic and the continental domains supports the idea that the lower deformation amounts observed within the deep basin are related to different mechanical behaviours within the continental margin and the adjacent oceanic domain, rather than the result of a recent basinward propagation of the deformation. Thermo-mechanical models suggest that mainly two factors could control the focused deformation along the margin: (1) the locus of highest topographic gradient of the main crustal interfaces, (2) the thermal contrast between the subsiding cooling oceanic domain and the uplifting warming margin. According to these models, the continental versus oceanic nature of the lithospheres would be of second order in the localization of the deformation