Mid-ocean ridges are the Earth's most extensive and active volcanic chains. They are also, particularly at slow spreading rates, rift zones, where plate divergence is in part accommodated by faults. Large offset normal faults, also called detachments, are characteristic of slow-spreading ridges, where they account for the widespread emplacement of mantle-derived rocks at the seafloor. In most cases, these detachments occur together with ridge magmatism, with melt injection and faulting interacting to shape the newly formed oceanic lithosphere. Here, we seek to better understand these interactions and their effects on oceanic accretion by studying the end-member case of a ridge where magmatism is locally almost absent. The portion of the Southwest Indian ridge we are studying has an overal low melt supply, focused to discrete axial volcanoes, leaving almost zero melt to intervening sections of the axial valley. One of these nearly amagmatic section of the ridge, located at 64°E, has been the focus of several past cruises (sampling, mapping and seismic experiments). Here we report on the most recent cruise to the area (RV Pourquoi Pas? with ROV Victor; dec-jan 2017), during which we performed high resolution mapping, submersible exploration and sampling of the ultramafic seafloor and of sparse volcanic formations. Our findings are consistent with the flip-flop detachment hypothesis proposed for this area by Sauter et al. (Nature Geosciences, 2013; ultramafic seafloor forming in the footwall of successive detachment faults, each cutting into the footwall of the previous fault, with an opposite polarity). Our observations also document the extent and geometry of deformation in the footwall of a young axial detachment, the role of mass-wasting for the evolution of this detachment, and provide spectacular evidence for serpentinization-related hydrothermal circulation and for spatial links between faults and volcanic eruptions.

Mid Ocean Ridge Processes at Very Low Melt Supply : Submersible Exploration of Smooth Ultramafic Seafloor at the Southwest Indian Ridge, 64 degree E - T32C-01 / Cannat, Mathilde; Agrinier, Pierre; Bickert, Manon; Brunelli, Daniele; Hamelin, Cedric; Lecoeuvre, Aurélien; Lie Onstad, Solveig; Maia, Marcia; Prampolini, Mariacristina; Rouméjon, Stéphane; Vitale Brovarone, Alberto. - (2017). ((Intervento presentato al convegno AGU FALL MEETING tenutosi a NEW ORLEANS - USA nel 13/12/2017.

Mid Ocean Ridge Processes at Very Low Melt Supply : Submersible Exploration of Smooth Ultramafic Seafloor at the Southwest Indian Ridge, 64 degree E - T32C-01

Daniele Brunelli;Mariacristina Prampolini;
2017

Abstract

Mid-ocean ridges are the Earth's most extensive and active volcanic chains. They are also, particularly at slow spreading rates, rift zones, where plate divergence is in part accommodated by faults. Large offset normal faults, also called detachments, are characteristic of slow-spreading ridges, where they account for the widespread emplacement of mantle-derived rocks at the seafloor. In most cases, these detachments occur together with ridge magmatism, with melt injection and faulting interacting to shape the newly formed oceanic lithosphere. Here, we seek to better understand these interactions and their effects on oceanic accretion by studying the end-member case of a ridge where magmatism is locally almost absent. The portion of the Southwest Indian ridge we are studying has an overal low melt supply, focused to discrete axial volcanoes, leaving almost zero melt to intervening sections of the axial valley. One of these nearly amagmatic section of the ridge, located at 64°E, has been the focus of several past cruises (sampling, mapping and seismic experiments). Here we report on the most recent cruise to the area (RV Pourquoi Pas? with ROV Victor; dec-jan 2017), during which we performed high resolution mapping, submersible exploration and sampling of the ultramafic seafloor and of sparse volcanic formations. Our findings are consistent with the flip-flop detachment hypothesis proposed for this area by Sauter et al. (Nature Geosciences, 2013; ultramafic seafloor forming in the footwall of successive detachment faults, each cutting into the footwall of the previous fault, with an opposite polarity). Our observations also document the extent and geometry of deformation in the footwall of a young axial detachment, the role of mass-wasting for the evolution of this detachment, and provide spectacular evidence for serpentinization-related hydrothermal circulation and for spatial links between faults and volcanic eruptions.
AGU FALL MEETING
NEW ORLEANS - USA
13/12/2017
Cannat, Mathilde; Agrinier, Pierre; Bickert, Manon; Brunelli, Daniele; Hamelin, Cedric; Lecoeuvre, Aurélien; Lie Onstad, Solveig; Maia, Marcia; Prampolini, Mariacristina; Rouméjon, Stéphane; Vitale Brovarone, Alberto
Mid Ocean Ridge Processes at Very Low Melt Supply : Submersible Exploration of Smooth Ultramafic Seafloor at the Southwest Indian Ridge, 64 degree E - T32C-01 / Cannat, Mathilde; Agrinier, Pierre; Bickert, Manon; Brunelli, Daniele; Hamelin, Cedric; Lecoeuvre, Aurélien; Lie Onstad, Solveig; Maia, Marcia; Prampolini, Mariacristina; Rouméjon, Stéphane; Vitale Brovarone, Alberto. - (2017). ((Intervento presentato al convegno AGU FALL MEETING tenutosi a NEW ORLEANS - USA nel 13/12/2017.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11380/1167663
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