The crustal structure of the north-eastern Gulf of Aden continental margin: insights from wide-angle seismic data

International audienceThe wide-angle seismic (WAS) and gravity data of the Encens survey allow us to determinethe deep crustal structure of the north-eastern Gulf of Aden non-volcanic passive margin.The Gulf of Aden is a young oceanic basin that began to open at least 17.6 Ma ago. Itscurrent geometry shows first- and second-order segmentation: our study focusses on theAshawq–Salalah second-order segment, between Alula–Fartak and Socotra–Hadbeen fracturezones. Modelling of theWAS and gravity data (three profiles across and three along the margin)gives insights into the first- and second-order structures. (1) Continental thinning is abrupt(15–20 km thinning across 50–100 km distance). It is accommodated by several tilted blocks.(2) The ocean–continent transition (OCT) is narrow (15 km wide). The velocity modellingprovides indications on its geometry: oceanic-type upper-crust (4.5 km s−1) and continentaltypelower crust (>6.5 km s−1). (3) The thickness of the oceanic crust decreases from West(10 km) to the East (5.5 km). This pattern is probably linked to a variation of magma supplyalong the nascent slow-spreading ridge axis. (4) A 5 km thick intermediate velocity body (7.6to 7.8 kms−1) exists at the crust-mantle interface below the thinned margin, the OCT and theoceanic crust. We interpret it as an underplated mafic body, or partly intruded mafic materialemplaced during a ‘post-rift’ event, according to the presence of a young volcano evidencedby heat-flow measurement (Encens-Flux survey) and multichannel seismic reflection (Encenssurvey). We propose that the non-volcanic passive margin is affected by post-rift volcanismsuggesting that post-rift melting anomalies may influence the late evolution of non-volcanicpassive margins

From Continental Hyperextension to Seafloor Spreading: New Insights on the Porcupine Basin from Wide-angle Seismic Data

Key Points: - New analysis of wide-angle seismic data from the southern Porcupine Basin. - Evidence for presence of oceanic crust in the southern Porcupine Basin. - Jurassic rifting propagated from south to north, resulting in non-uniform strain when rifting stopped. The deep structure and sedimentary record of rift basins provide an important insight into understanding the geological processes involved in lithospheric extension. We investigate the crustal structure and large‐scale sedimentary architecture of the southern Porcupine Basin, offshore Ireland along three wide‐angle seismic profiles, supplemented by thirteen selected seismic reflection profiles. The seismic velocity and crustal geometry models obtained by joint refraction and reflection travel‐time inversion clearly image the deep structure of the basin. Our results suggest the presence of three distinct crustal domains along the rifting axis: (a) continental crust becoming progressively hyperextended from north to south through the basin, (b) a transitional zone of uncertain nature and (c) a 7‐8 km thick zone of oceanic crust. The latter is overlain by a ~ 8 km compacted Upper Paleozoic‐Mesozoic succession and ~ 2 km of Cenozoic strata. Due to the lack of clear magnetic anomalies and in the absence of well control, the precise age of interpreted oceanic crust is unknown. However, we can determine an age range of Late Jurassic to Late Cretaceous from the regional context. We propose a northward‐propagating rifting process in the Porcupine Basin, resulting in variations in strain along the rift axis

Deep structure of the Porcupine Basin from wide-angle seismic data

The Porcupine Basin, part of the frontier petroleum exploration province west of Ireland, has an extended history that commenced prior to the opening of the North Atlantic Ocean. Lithospheric stretching factors have previously been estimated to increase from 6 in the south of the basin. Thus, it is an ideal location to study the processes leading to hyper-extension on continental margins. The Porcupine Median Ridge (PMR) is located in the south of the basin and has been alternatively interpreted as a volcanic feature, a serpentinite mud diapir or a tilted block of continental crust. Each of these interpretations has different implications for the thermal history of the basin. We present results from travel-time tomographic modelling of two approximately 300 km-long wide-angle seismic profiles across the northern and southern parts of the basin. Our results show: (1) the geometry of the crust, with maximum crustal stretching factors of up to 6 and 10 along the northern and southern profiles, respectively; (2) asymmetry of the basin structures, suggesting some simple shear during extension; (3) low velocities beneath the Moho that could represent either partially serpentinized mantle or mafic under-plating; and (4) a possible igneous composition of the PMR

Tectono-stratigraphic evolution and crustal architecture of the Orphan Basin during North Atlantic rifting

The Orphan Basin is located in the deep offshore of the Newfoundland margin, and it is bounded by the continental shelf to the west, the Grand Banks to the south, and the continental blocks of Orphan Knoll and Flemish Cap to the east. The Orphan Basin formed in Mesozoic time during the opening of the North Atlantic Ocean between eastern Canada and western Iberia–Europe. This work, based on well data and regional seismic reflection profiles across the basin, indicates that the continental crust was affected by several extensional episodes between the Jurassic and the Early Cretaceous, separated by events of uplift and erosion. The preserved tectono-stratigraphic sequences in the basin reveal that deformation initiated in the eastern part of the Orphan Basin in the Jurassic and spread towards the west in the Early Cretaceous, resulting in numerous rift structures filled with a Jurassic–Lower Cretaceous syn-rift succession and overlain by thick Upper Cretaceous to Cenozoic post-rift sediments. The seismic data show an extremely thinned crust (4–16 km thick) underneath the eastern and western parts of the Orphan Basin, forming two sub-basins separated by a wide structural high with a relatively thick crust (17 km thick). Quantifying the crustal architecture in the basin highlights the large discrepancy between brittle extension localized in the upper crust and the overall crustal thinning. This suggests that continental deformation in the Orphan Basin involved, in addition to the documented Jurassic and Early Cretaceous rifting, an earlier brittle rift phase which is unidentifiable in seismic data and a depth-dependent thinning of the crust driven by localized lower crust ductile flow

Prospective observational cohort study of the association between antiplatelet therapy, bleeding and thrombosis in patients with coronary stents undergoing noncardiac surgery

Background: The perioperative management of antiplatelet therapy in noncardiac surgery patients who have undergone previous percutaneous coronary intervention (PCI) remains a dilemma. Continuing dual antiplatelet therapy (DAPT) may carry a risk of bleeding, while stopping antiplatelet therapy may increase the risk of perioperative major adverse cardiovascular events (MACE). Methods: Occurrence of Bleeding and Thrombosis during Antiplatelet Therapy In Non-Cardiac Surgery (OBTAIN) was an international prospective multicentre cohort study of perioperative antiplatelet treatment, MACE, and serious bleeding in noncardiac surgery. The incidences of MACE and bleeding were compared in patients receiving DAPT, monotherapy, and no antiplatelet therapy before surgery. Unadjusted risk ratios were calculated taking monotherapy as the baseline. The adjusted risks of bleeding and MACE were compared in patients receiving monotherapy and DAPT using propensity score matching. Results: A total of 917 patients were recruited and 847 were eligible for inclusion. Ninety-six patients received no antiplatelet therapy, 526 received monotherapy with aspirin, and 225 received DAPT. Thirty-two patients suffered MACE and 22 had bleeding. The unadjusted risk ratio for MACE in patients receiving DAPT compared with monotherapy was 1.9 (0.93–3.88), P=0.08. There was no difference in MACE between no antiplatelet treatment and monotherapy 1.03 (0.31–3.46), P=0.96. Bleeding was more frequent with DAPT 6.55 (2.3–17.96) P=0.0002. In a propensity matched analysis of 177 patients who received DAPT and 177 monotherapy patients, the risk ratio for MACE with DAPT was 1.83 (0.69–4.85), P=0.32. The risk of bleeding was significantly greater in the DAPT group 4.00 (1.15–13.93), P=0.031. Conclusions: OBTAIN showed an increased risk of bleeding with DAPT and found no evidence for protective effects of DAPT from perioperative MACE in patients who have undergone previous PCI

A genetic link between transform and hyper-extended margins

The similarity between the geometry of the West African and South American coastlines is among one of the strongest natural observations supporting the plate tectonic paradigm. However, using classical plate tectonic approaches to model these conjugate transform margins results in a high degree of variability in palaeogeographic reconstructions. Using state-of-the-art 3D coupled thermo-mechanical numerical models, we simulate for the first time, crustal deformation at the onset of oceanisation along large offset oblique margins. Our models show that obliquity causes oceanic rift propagation to stall, resulting in an apparent polyphased tectonic evolution, and in some circumstances leads to the formation of hyper-extended margins. As a result, conjugate margins located at the edge of future fracture zones are highly asymmetric from rifting to spreading, with their lengths differing by a factor of 5 to 10, before the the final phase of break-up occurs. Accounting for this discrepancy should ameliorate future palaeogeographic reconstructions

Experimental disc heat flux identification on a reduced scale braking system using the inverse heat conduction method

International audienceThis work focuses on the local heat fluxes on a disc during braking conditions. The generated heat and the temperature field are identified using an inverse heat conduction method coupled to temperature measurements inside the disc. Function specification is used to estimate the boundary conditions in the model without any prior information on the flux intensity and the evolution regarding the time and the position on the sliding surface. Disc heat flux identifications are performed for different braking conditions (sliding speed and normal pressure) on a High-Speed Tribometer. The temperature values are obtained using a telemetry system that allows inductive data transfer. The influence of the braking conditions on the heat repartition and the surface temperature is discussed