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  • 1
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    Episodic magmatism and serpentinized mantle exhumation at an ultraslow-spreading centre (2018)
    Nature Research
    In:  Nature Geoscience, 11 (6). pp. 444-448.
    Details
    Publication Date: 2021-02-08
    Description: Mid-ocean ridges spreading at ultraslow rates of less than 20 mm yr−1 can exhume serpentinized mantle to the seafloor, or they can produce magmatic crust. However, seismic imaging of ultraslow-spreading centres has not been able to resolve the abundance of serpentinized mantle exhumation, and instead supports 2 to 5 km of crust. Most seismic crustal thickness estimates reflect the depth at which the 7.1 km s−1 P-wave velocity is exceeded. Yet, the true nature of the oceanic lithosphere is more reliably deduced using the P- to S-wave velocity (Vp/Vs) ratio. Here we report on seismic data acquired along off-axis profiles of older oceanic lithosphere at the ultraslow-spreading Mid-Cayman Spreading Centre. We suggest that high Vp/Vs ratios greater than 1.9 and continuously increasing P-wave velocity, changing from 4 km s−1 at the seafloor to greater than 7.4 km s−1 at 2 to 4 km depth, indicate highly serpentinized peridotite exhumed to the seafloor. Elsewhere, either magmatic crust or serpentinized mantle deformed and uplifted at oceanic core complexes underlies areas of high bathymetry. The Cayman Trough therefore provides a window into mid-ocean ridge dynamics that switch between magma-rich and magma-poor oceanic crustal accretion, including exhumation of serpentinized mantle covering about 25% of the seafloor in this region.
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  • 2
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    Heat-flux off coast Chile measured during RV Sonne cruise SO181-1b (2005)
    GeoForschungsZentrum
    In:  [Talk] In: Sonderkolloquium "Geotechnologien", GeoForschungsZentrum Potsdam, 09.-10.06.2005, Potsdam . Continental margins - Earth's focal points of usage and hazard potential ; pp. 40-43 .
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    Publication Date: 2012-07-06
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 3
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    Seafloor, sediments, seismicity and shallow structures offshore southern Chile - selected preliminary results from TIPTEQ Cruise SO181 (2005)
    GeoForschungsZentrum
    In:  [Talk] In: Sonderkolloquium "Geotechnologien", GeoForschungsZentrum Potsdam, 09.-10.06.2005, Potsdam . Continental margins - earth's focal points of usage and hazard potential ; pp. 100-105 .
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    Publication Date: 2012-07-06
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 4
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    Impact of the lateral variability of the incoming ocean plate in South Chile on the structure of the marine forearc and the generation of mega thrust earthquakes (2005)
    GeoForschungsZentrum
    In:  [Talk] In: Sonderkolloquium "Geotechnologien", GeoForschungszentrum Potsdam, 09.06.-10.06.2005, Potsdam . Continental margins - earth's focal points of usage and hazard potential ; pp. 18-23 .
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    Publication Date: 2012-07-06
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 5
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    The Alboran volcanic-arc modulated the Messinian faunal exchange and salinity crisis (2018)
    Nature Research
    In:  Scientific Reports, 8 (13015).
    Details
    Publication Date: 2021-02-08
    Description: What process triggered the Mediterranean Sea restriction remains debated since the discovery of the Messinian Salinity Crisis (MSC). Recent hypotheses infer that the MSC initiated after the closure of the Atlantic-Mediterranean Betic and Rifean corridors, being modulated through restriction at the Gibraltar Strait. These hypotheses however, do not integrate contemporaneous speciation patterns of the faunal exchange between Iberia and Africa and geological features like the evaporite distribution. Exchange of terrestrial biota occurred before, during and after the MSC, and speciation models support an exchange path across the East Alborán basin (EAB) located a few hundreds of km east of the Gibraltar Strait. Yet, a structure explaining jointly geological and biological observations has remained undiscovered. We present new seismic data showing the velocity structure of a well-differentiated 14-17-km thick volcanic arc in the EAB. Isostatic considerations support that the arc-crust buoyancy created an archipelago and filter bridge across the EAB. Sub-aerial erosional unconformities and onlap relationships support that the arc was active between ~10-6 Ma. Progressive arc build-up leading to an archipelago and its later subsidence can explain the extended exchange of terrestrial biota between Iberia and Africa (~7-3 Ma), and agrees with patterns of biota speciation and terrestrial fossil distribution before the MSC (10-6.2 Ma). In this scenario, the West Alboran Basin (WAB) could then be the long-postulated open-marine refuge for the Mediterranean taxa that repopulated the Mediterranean after the MSC, connected to the deep restricted Mediterranean basin through a sill at the Alboran volcanic arc archipelago.
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  • 6
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    Earthquake crisis unveils the growth of an incipient continental fault system (2019)
    Nature Research
    In:  Nature Communications, 10 (Article number 3482).
    Details
    Publication Date: 2022-01-31
    Description: Large continental faults extend for thousands of kilometres to form boundaries between rigid tectonic blocks. These faults are associated with prominent topographic features and can produce large earthquakes. Here we show the first evidence of a major tectonic structure in its initial-stage, the Al-Idrissi Fault System (AIFS), in the Alboran Sea. Combining bathymetric and seismic reflection data, together with seismological analyses of the 2016 Mw 6.4 earthquake offshore Morocco – the largest event ever recorded in the area – we unveil a 3D geometry for the AIFS. We report evidence of left-lateral strike-slip displacement, characterise the fault segmentation and demonstrate that AIFS is the source of the 2016 events. The occurrence of the Mw 6.4 earthquake together with historical and instrumental events supports that the AIFS is currently growing through propagation and linkage of its segments. Thus, the AIFS provides a unique model of the inception and growth of a young plate boundary fault system.
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  • 7
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    Discovery of flat seismic reflections in the mantle beneath the young Juan de Fuca Plate (2020)
    Nature Research
    Details
    Publication Date: 2023-02-08
    Description: Crustal properties of young oceanic lithosphere have been examined extensively, but the nature of the mantle lithosphere underneath remains elusive. Using a novel wide-angle seismic imaging technique, here we show the presence of two sub-horizontal reflections at ∼11 and ∼14.5 km below the seafloor over the 0.51–2.67 Ma old Juan de Fuca Plate. We find that the observed reflectors originate from 300–600-m-thick layers, with an ∼7–8% drop in P-wave velocity. They could be explained either by the presence of partially molten sills or frozen gabbroic sills. If partially molten, the shallower sill would define the base of a thin lithosphere with the constant thickness (11 km), requiring the presence of a mantle thermal anomaly extending up to 2.67 Ma. In contrast, if these reflections were frozen melt sills, they would imply the presence of thick young oceanic lithosphere (20–25 km), and extremely heterogeneous upper mantle.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 8
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    Lower oceanic crust formed by in situ melt crystallization revealed by seismic layering (2022)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Oceanic crust forms at mid-ocean spreading centres through a combination of magmatic and tectonic processes, with the magmatic processes creating two distinct layers: the upper and the lower crust. While the upper crust is known to form from lava flows and basaltic dykes based on geophysical and drilling results, the formation of the gabbroic lower crust is still debated. Here we perform a full waveform inversion of wide-angle seismic data from relatively young (7–12-Myr-old) crust formed at the slow-spreading Mid-Atlantic Ridge. The seismic velocity model reveals alternating, 400–500 m thick, high- and low-velocity layers with ±200 m s−1 velocity variations, below ~2 km from the oceanic basement. The uppermost low-velocity layer is consistent with hydrothermal alteration, defining the base of extensive hydrothermal circulation near the ridge axis. The underlying layering supports that the lower crust is formed through the intrusion of melt as sills at different depths, which cool and crystallize in situ. The layering extends up to 5–15 km distance along the seismic profile, covering 300,000–800,000 years, suggesting that this form of lower crustal accretion is a stable process.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 9
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    Extensional tectonics and two-stage crustal accretion at oceanic transform faults (2021)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Oceanic transform faults are seismically and tectonically active plate boundaries1 that leave scars—known as fracture zones—on oceanic plates that can cross entire ocean basins2. Current descriptions of plate tectonics assume transform faults to be conservative two-dimensional strike–slip boundaries1,3, at which lithosphere is neither created nor destroyed and along which the lithosphere cools and deepens as a function of the age of the plate4. However, a recent compilation of high-resolution multibeam bathymetric data from 41 oceanic transform faults and their associated fracture zones that covers all possible spreading rates shows that this assumption is incorrect. Here we show that the seafloor along transform faults is systemically deeper (by up to 1.6 kilometres) than their associated fracture zones, in contrast to expectations based on plate-cooling arguments. Accretion at intersections between oceanic ridges and transform faults seems to be strongly asymmetric: the outside corners of the intersections show shallower relief and more extensive magmatism, whereas the inside corners have deep nodal basins and seem to be magmatically starved. Three-dimensional viscoplastic numerical models show that plastic-shear failure within the deformation zone around the transform fault results in the plate boundary experiencing increasingly oblique shear at increasing depths below the seafloor. This results in extension around the inside corner, which thins the crust and lithosphere at the transform fault and is linked to deepening of the seafloor along the transform fault. Bathymetric data suggest that the thinned transform-fault crust is augmented by a second stage of magmatism as the transform fault intersects the opposing ridge axis. This makes accretion at transform-fault systems a two-stage process, fundamentally different from accretion elsewhere along mid-ocean ridges.
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  • 10
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    Broad fault zones enable deep fluid transport and limit earthquake magnitudes (2023)
    Nature Research
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    Publication Date: 2024-03-22
    Description: Constraining the controlling factors of fault rupture is fundamentally important. Fluids influence earthquake locations and magnitudes, although the exact pathways through the lithosphere are not well-known. Ocean transform faults are ideal for studying faults and fluid pathways given their relative simplicity. We analyse seismicity recorded by the Passive Imaging of the Lithosphere-Asthenosphere Boundary (PI-LAB) experiment, centred around the Chain Fracture Zone. We find earthquakes beneath morphological transpressional features occur deeper than the brittle-ductile transition predicted by simple thermal models, but elsewhere occur shallower. These features are characterised by multiple parallel fault segments and step overs, higher proportions of smaller events, gaps in large historical earthquakes, and seismic velocity structures consistent with hydrothermal alteration. Therefore, broader fault damage zones preferentially facilitate fluid transport. This cools the mantle and reduces the potential for large earthquakes at localized barriers that divide the transform into shorter asperity regions, limiting earthquake magnitudes on the transform.
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