Description: The dataset contains the raw .segy files of the ocean bottom seismometers/hydrophones (OBS/H) that recorded wide-angle seismic data along 6 profiles in the Porcupine Basin. The active-source seismic survey was conducted by GEOMAR in 2004. The cruise report, navigation files for each profile, and geographical coordinates of each OBS/H are also included in this dataset.

Description: We provide seismic refraction and wide-angle data from two profile shot across the marine fore-arc of Nicaragua, Central Maerica. Profiles NIC20 and NIC50 were obtained aboard the US R/V Maurice Ewing cruise EW00–05 in 2000. All profile run across the condinantal margin and provide in total 26 digital record sections.

Description: We provide seismic refraction and wide-angle data from a profile shot across the marine fore-arc of Nicaragua, Central Maerica. Profile P1 was acquired with the German RV SONNE in 1996. The profile runs across the condinantal margin and provide in total 10 digital record sections.

Description: Highlights • Low upper mantle seismic velocity indicates mantle hydration in the Porcupine Basin. • Crustal stretching factors suggest crustal break up in the Porcupine Basin. • Fault-controlled mantle hydration explains across-axis mantle velocity variations. • Along-axis variations in mantle hydration control the development of low-angle faults. Abstract Mantle hydration (serpentinisation) at magma-poor rifted margins is thought to play a key role in controlling the kinematics of low-angle faults and thus, hyperextension and crustal breakup. However, because geophysical data principally provide observations of the final structure of a margin, little is known about the evolution of serpentinisation and how this governs tectonics during hyperextension. Here we present new observational evidence on how crustal strain-dependent serpentinisation influences hyperextension from rifting to possible crustal breakup along the axis of the Porcupine Basin, offshore Ireland. We present three new P-wave seismic velocity models that show the seismic structure of the uppermost lithosphere and the geometry of the Moho across and along the basin axis. We use neighbouring seismic reflection lines to our tomographic models to estimate crustal stretching ( ) of ∼2.5 in the north at 52.5° N and 〉10 in the south at 51.7° N. These values suggest that no crustal embrittlement occurred in the northernmost region, and that rifting may have progressed to crustal breakup in the southern part of the study area. We observed a decrease in mantle velocities across the basin axis from east to west. These variations occur in a region where is within the range at which crustal embrittlement and serpentinisation are possible ( 3–4). Across the basin axis, the lowest seismic velocity in the mantle spatially coincides with the maximum amount of crustal faulting, indicating fault-controlled mantle hydration. Mantle velocities also suggest that the degree of serpentinisation, together with the amount of crustal faulting, increases southwards along the basin axis. Seismic reflection lines show a major detachment fault surface that grows southwards along the basin axis and is only visible where the inferred degree of serpentinisation is 〉15%. This observation is consistent with laboratory measurements that show that at this degree of serpentinisation, mantle rocks are sufficiently weak to allow low-angle normal faulting. Based on these results, we propose two alternative formation models for the Porcupine Basin. The first involves a northward propagation of the hyperextension processes, while the second model suggests higher extension rates in the centre of the basin than in the north. Both scenarios postulate that the amount of crustal strain determines the extent and degree of serpentinisation, which eventually controls the development of detachments faults with advanced stretching.

Description: The Gorringe Bank is a gigantic seamount that separates the Horseshoe and Tagus abyssal plains offshore SW Iberia, in a zone that hosts the convergent boundary between the Africa and Eurasia plates. Although the region has been the focus of numerous investigations since the early 1970s, the lack of appropriate geophysical data makes the nature of the basement, and thus the origin of the structures, still debated. In this work, we present combined P-wave seismic velocity and gravity models along a transect that crosses the Gorringe Bank from the Tagus to the Horseshoe abyssal plains. The P-wave velocity structure of the basement is similar in the Tagus and Horseshoe plains. It shows a 2.5–3.0 km-thick top layer with a velocity gradient twice stronger than oceanic Layer 2 and an abrupt change to an underlying layer with a five-fold weaker gradient. Velocity and density is lower beneath the Gorringe Bank probably due to enhanced fracturing, that have led to rock disaggregation in the sediment-starved northern flank. In contrast to previous velocity models of this region, there is no evidence of a sharp crust–mantle boundary in any of the record sections. The modelling results indicate that the sediment overlays directly serpentinite rock, exhumed from the mantle with a degree of serpentinization decreasing from a maximum of 70–80% under the top of Gorringe Bank to less than 5% at a depth of ∼20 km. We propose that the three domains were originally part of a single serpentine rock band, of nature and possibly origin similar to the Iberia Abyssal Plain ocean–continent transition, which was probably generated during the earliest phase of the North Atlantic opening that followed continental crust breakup (Early Cretaceous). During the Miocene, the NW–SE trending Eurasia–Africa convergence resulted in thrusting of the southeastern segment of the exhumed serpentinite band over the northwestern one, forming the Gorringe Bank. The local deformation associated to plate convergence and uplift could have promoted pervasive rock fracturing of the overriding plate, leading eventually to rock disaggregation in the northern flank of the GB, which could be now a potential source of rock avalanches and tsunamis.

Description: The Porcupine Basin is a Mesozoic failed rift located in the North Atlantic margin (SW Ireland). Here, we present two sets of tomographic images obtained with travel-time tomography of two different active-source seismic data sets: ocean bottom seismic (OBS) data and long-streamer data. The study provides new insights into geological processes that occurred at different scales and geological stages during the formation of the Porcupine Basin. OBS-derived images show the Vp structure of the uppermost lithosphere and the geometry of the Moho across and along the basin axis, providing insights into formation processes that occurred during lithospheric extension in the Mesozoic. In particular, these tomographic results together with neighboring seismic reflection lines provide crustal stretching (βc) estimates of ∼2.5 in the north at 52.5N and 〉 10 in the south at 51.7N. These values suggest that no crustal embrittlement occurred in the northernmost region, and that rifting has potentially reached crustal breakup in the southern part of the study area. Tomographic images reveal that mantle velocities decrease across the basin axis from east to west. These variations occur in a region where βc is within the range at which crustal embrittlement and serpentinisation are possible (βc 3-4). Across the basin axis, the lowest seismic velocity in the mantle spatially coincides with the maximum amount of crustal faulting, indicating fault-controlled mantle hydration. Mantle velocities also suggest that the degree of serpentinisation, together with the amount of crustal faulting, increases southwards along the basin axis. Seismic reflection lines show a major detachment fault surface that grows southwards along the basin axis and is only visible where the inferred degree of serpentinisation is 〉 15 %. This is consistent with laboratory measurements that show that at this degree of serpentinisation, mantle rocks are sufficiently weak to allow low-angle normal faulting. In contrast, the long-streamer tomographic image shows the Vp structure of the post-rift section in much more detail than OBS-derived images providing insights into basin-scale processes that occurred after lithospheric extension during the Cenozoic. The tomographic image reveals faster vertical velocity gradient in the center of the basin than in the flanks. This variation together with a relatively thick sediment accumulation in the center of the basin suggests higher overburden pressure and compaction compared to the margins. This suggests fluid flow driven by differential compaction towards the margins of the basin. The model also reveals two prominent vertical velocity anomalies located at the western margin of the basin, coinciding with the location of a reactivated basin-bounding fault. Comparing the corresponding time-migrated seismic section with the tomographic model, we observe that the hanging wall of the basin-bounding fault is not significantly affected by major normal faulting and yet is associated with comparatively lower seismic velocities. This result together with exploration well data suggests high effective porosities within the hanging wall suggesting potential overpressured areas. Our results suggest that the western basin-bounding fault is acting as a barrier for fluid migration causing overpressured areas over the western flank.

Description: The Western Mediterranean region is represented by a system of backarc basins associated to slab rollback and retreat of subduction fronts. The onset of formation of these basins took place in the Oligocene with the opening of the Valencia Through, the Liguro-Provençal and the Algero-Balearic basins, and subsequently, by the formation of the Alboran and Tyrrhenian basins during the early Tortonian. The opening of these basins involved rifting that in some regions evolved until continental break up, that is the case of the Liguro-Provençal, Algero-Balearic, and Tyrrhenian basins. Previous geophysical works in the first two basins revealed a rifted continental crust that transitions to oceanic crust along a region where the basement nature is not clearly defined. In contrast, in the Tyrrhenian Basin, recent analysis of new geophysical and geological data shows a rifted continental crust that transitions along a magmatic-type crust to a region where the mantle is exhumed and locally intruded by basalts. This basement configuration is at odds with current knowledge of rift systems and implies rapid variations of strain and magma production.

Description: The Tyrrhenian Basin is a region created by Neogene extensional tectonics related to slab rollback of the east-southeast–migrating Apennine subduction system, commonly believed to be actively underthrusting the Calabrian arc. A compilation of 〉12,000 km of multichannel seismic profiles, much of them recently collected or reprocessed, provided closer scrutiny and the mapping of previously undetected large compressive structures along the Tyrrhenian margin. This new finding suggests that Tyrrhenian Basin extension recently ceased. The ongoing compressional reorganization of the basin indicates a change of the regional stress field in the area, confirming that slab rollback is no longer a driving mechanism for regional kinematics, now dominated by the Africa-Eurasia lithospheric collision.