Relation between the Deep Crustal Structure and Fluid Escape Structures at the Lesser Antilles Island arc.
Abstract
Analysis of combined geophysical data sets in subduction zones can provide insights on the seismic hazard. For example, the study of the deep structure gives information about the crustal geometry, and based on these results, modelling of heat-flow data can locate the temperature range consistent with the seismogenic behaviour along the interplate contact. On another scale mapping of fluid pathways in high resolution seismic and bathymetric data allows a first estimation of the quantity of fluids entering the subduction and determining their influence on mass wasting processes. Such a data set consisting of seismic, bathymetric and heat-flow data was acquired during the ANTITHESIS cruises (2013-2016) along the Lesser Antilles subduction zone. Forward modelling of the wide-angle seismic data reveals that the subducting Atlantic oceanic plate is about 5-7 km thick and the Caribbean crust at the arc is 18-km-thick. It is overlain by a 2-to-4-km-thick layer with seismic velocities that could represent volcanic products or to a carbonate platform. The velocities in the lower crustal layer reach 7.4 km/s corresponding to mafic rocks and plutons. The velocities in the upper mantle are 8.00-8.20 km/s, thereby excluding the existence of extensive serpentinisation. The heat-flow is 30% lower than expected for an incoming 80-myr-old oceanic plate. The anomalously low thermal gradient is possibly due to 1/ a depressed thermal structure of the oceanic crust related to the slow-spreading at the medio-Atlantic ridge or 2/ hydrothermal cooling in the trench by fluids percolation within the upper crust. Modelling both scenarii results in cold temperatures along the interplate contact, that, compared with the thermal structure of the central Lesser Antilles segment, shift landward the 60-150°C isotherms, commonly associated with the onset of the seismogenic behavior along the interplate contact. Analysis of the high resolution seismic data allows mapping of fluid migration paths and reveals the existence of several discrete morphologies such as a wedge shaped sedimentary masses and faults. The bathymetry shows rugged seafloor morphologies. Several types of pockmarks were mapped and slope maps reveal regions prone to mass wasting. Multibeam water column data indicate the presence of fluids or gas escaping into the seawater
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.T31C2918K
- Keywords:
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- 1031 Subduction zone processes;
- GEOCHEMISTRYDE: 7240 Subduction zones;
- SEISMOLOGYDE: 8104 Continental margins: convergent;
- TECTONOPHYSICSDE: 8413 Subduction zone processes;
- VOLCANOLOGY