1,721,001 research outputs found
Gridded multibeam bathymetry data (netCDF grid format) of the Lesser Antilles region from VOILA cruise JC149 (2017)
No full textThe bathymetry was mapped with a Simrad EM120 multibeam system in April-June 2017 during Lesser Antilles VOILA cruise JC149 (chief scientist Jenny Collier). The bathymetry was edited and gridded at a resolution of about 100m. The data file is in GMT-compatible netCDF grid format suitable for import to GMT scripts. The data file was generated as part of a NERC multidisciplinary consortium project called Volatiles in the Lesser Antilles - VoiLA, funded under NERC award NE/K010743/1.</span
Short-period ocean bottom seismometer (SPOBS) active-source data, Lesser Antilles arc, acquired during James Cook cruise JC149 - Leg 3 (2017) as part of the UK NERC VOILA experiment
No full textIn this active-source part of the VOILA (Volatiles in the Lesser Antilles) experiment, during James Cook cruise JC149 Leg 3, short-period ocean bottom seismometers (SPOBS) were deployed on the incoming plate and airguns from the James Cook vessel were fired to them. The OBS instruments were deployed in a roughly north-south orientation along strike, approximately 300-400km east of the trench and their positions were calculated by acoustic ranging. The data files presented here contain the vertical geophone components in standard SEG-Y format. Corrected airgun source-receiver distances have been added to the trace headers. The goal of this active-source portion of the VOILA experiment was to assess the geological structure and state of hydration of the subducting plate. The cruise report and other details may be accessed here https://www.bodc.ac.uk/resources/inventories/cruise_inventory/report/16390/. The chief scientist on Jame Cook cruise JC149 Leg 3 was Jenny Collier, and funding for the VOILA experiment was provided through a NERC multidisciplinary consortium project called Volatiles in the Lesser Antilles - VoiLA, supported by NERC award NE/K010743/1.</span
Downward continued ocean bottom seismometer data show continued hydrothermal evolution of mature oceanic upper crust
No full textHeat flow measurements indicate hydrothermal activity in oceanic crust continues at least for 65 m.y. after formation. Hydrothermal activity progressively fills cracks and pores with alteration products, which is expected to lead to a trend of increasing seismic velocities with age. Compilations of seismic-P-wave velocity models inverted from ocean bottom seismometer (OBS) data have failed to detect such an aging trend beyond crustal ages of ca. 10 Ma. However, in these models, the velocities of the uppermost crust, where fluid flow would be most concentrated, are poorly resolved. This is because as the oceanic crust matures, the first crustal arrivals on OBS records (which best resolve upper crustal velocities using tomographic inversion), become hidden in the coda of the water wave. This may lead to the masking of any aging trend in the seismic velocities. For the first time, we show how including downward continuation (DC) in the analysis of OBS data collected across 65 Ma seafloor significantly improves measurements of the P-wave velocities of the upper crust. Our new analysis reveals a highly heterogeneous upper crust, with ridge-parallel P-wave velocity variations of 25%, implying local porosity values that are up to double that of global averages. Our new results, combined with other most recent advanced seismic analyses, reveal that seismic velocities indeed evolve with age up to at least 70 Ma, confirming that hydrothermal activity continues in mature oceanic crust.</p
Estimating excess bound water content due to serpentinisation in mature slow-spreading oceanic crust using Vp/Vs
No full textMature oceanic crust carries chemically bound water which may be released in subduction zones or delivered to the deep mantle. Estimating water content in slow-spreading crust is challenging due to its complex lithology, requiring both P- and S-wave seismic velocity (Vp and Vs), the latter of which has been limited. Here we show 2D high-resolution Vp, Vs and excess bound water models due to serpentinisation of mature Atlantic crust near the Lesser Antilles. The ridge-parallel line crosses eight seafloor-spreading segments with equal numbers of magma-robust and magma-poor. Hydration is highly variable and mainly accommodated in strongly serpentinised peridotites, dominantly in magma-poor segments, which are not preferentially located near fracture zones. Serpentinised peridotites (17% of the crust) host four times more water than normal magmatic crust, increasing Atlantic subduction bound water budget by ~ 50%. This has implications back in geological time such as during supercontinent breakups when slow-spreading crust subduction was more common
Volatile recycling at the Lesser Antilles Arc: Processes and consequences
No full textSubduction zones are the prime regions where water is exchanged between the solid Earth, oceans and atmosphere. Yet, water transport through subduction is only partially understood. In this project, we target the Lesser Antilles Arc, one of only two zones that subducts lithosphere formed at the slowly spreading Mid-Atlantic Ridge. Atlantic lithosphere is more hydrated, especially in the mantle part, than lithosphere consumed at Pacific and Indian Ocean trenches, making it a key endmember to advance understanding.</span
Seafloor sediment thickness beneath the VoiLA broadband ocean-bottom seismometer deployment in the Lesser Antilles from P-to-S delay times
Full text linkBroad-band ocean-bottom seismometer (OBS) deployments present an opportunity to investigate the seafloor sediment thickness, which is important for constraining sediment deposition, and is also useful for subsequent seismological analyses. The Volatile Recycling in the Lesser Antilles (VoiLA) project deployed 34 OBSs over the island arc, fore- and backarc of the Lesser Antilles subduction zone for 15 months from 2016 to 2017. Using the amplitudes and delay times of P-to-S (Ps) scattered waves from the conversion of teleseismic earthquake Pwaves at the crust–sediment boundary and pre-existing relationships developed for Cascadia, we estimate sediment thickness beneath each OBS. The delay times of the Ps phases vary from 0.20 ± 0.06 to 3.55 ± 0.70 s, generally increasing from north to south. Using a single-sediment and single-crystalline crust earth model in each case, we satisfactorily model the observations of eight OBSs. At these stations we find sediment thicknesses range from 0.43 ± 0.45 to 5.49 ± 3.23 km. To match the observations of nine other OBSs, layered sediment and variable thickness crust is required in the earth model to account for wave interference effects on the observed arrivals. We perform an inversion with a two-layer sediment and a single-layer crystalline crust in these locations finding overall sediment thicknesses of 1.75 km (confidence region: 1.45–2.02 km) to 7.93 km (confidence region: 6.32–11.05 km), generally thinner than the initial estimates based on the pre-existing relationships. We find agreement between our modelled velocity structure and the velocity structure determined from the VoiLA active-source seismic refraction experiment at the three common locations. Using the Ps values and estimates from the VoiLA refraction experiment, we provide an adjusted relationship between delay time and sediment equations for the Lesser Antilles. Our new relationship is H=1.42dt , where H is sediment thickness in kilometres and dt is mean observed Ps delay time in seconds, which may be of use in other subduction zone settings with thick seafloor sediments
Bathymetric mapping of the coastal and offshore geology and structure of the Jurassic Coast, Weymouth Bay, UK
Full text linkFour hundred square kilometres of 1 m binned, full coverage swath bathymetry data, integrated with similar resolution onshore topography, have been used to generate a seamless onshore to offshore bedrock map covering an extensive area adjacent to the ‘Jurassic Coast’ World Heritage site. Analysis of these data provides new insights into the structural development of the Purbeck Monocline Cenozoic inversion structure; in particular, variations in the expression of strain between the hanging-wall block and the fault inversion zone. The footwall to the basin-bounding faults compartmentalized deformation and uplift, and acted as a buttress to compression. The data also show a limited thickness changes within the major lithostratigraphical divisions, and a notable absence of basin-related extensional faulting in the offshore area that is in marked contrast to the more extensively studied onshore region. This indicates that prior to inversion, the basin evolved by intermittent activity on a few major extensional faults. This improved understanding of the development of the basin and inversion structures results from our ability to integrate and quantitatively manipulate these high-resolution and spatially extensive offshore and onshore datasets
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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