FN Archimer Export Format
PT J
TI On spreading modes and magma supply at slow and ultraslow mid-ocean ridges
BT 
AF CANNAT, Mathilde
   SAUTER, Daniel
   LAVIER, Luc
   BICKERT, Manon
   MOMOH, Ekeabino
   LEROY, Sylvie
AS 1:1;2:2;3:3;4:1;5:1;6:4;
FF 1:;2:;3:;4:;5:;6:;
C1 Marine Geosciences, Institut de Physique du Globe de Paris, UMR 7154 - CNRS, Université de Paris, France
   Institut de Physique du Globe de Strasbourg, UMR 7516 - CNRS, Université de Strasbourg, France
   Department of Geological Sciences, Institute for Geophysics, Jackson School of Geosciences, The University of Texas at Austin, United States
   Sorbonne Université, CNRS-INSU, Institut des Sciences de la Terre de Paris, ISTeP, France
C2 UNIV PARIS, FRANCE
   UNIV STRASBOURG, FRANCE
   UNIV TEXAS AUSTIN, USA
   UNIV PARIS 06, FRANCE
IF 4.823
TC 61
UR https://archimer.ifremer.fr/doc/00767/87880/93480.pdf
LA English
DT Article
CR MD 199 / SISMO-SMOOTH
BO Marion Dufresne
DE ;slow and ultraslow mid-ocean ridges;divergent plate boundaries;detachment faults;melt supply;axial lithosphere;tectonic and magmatic seafloor spreading processes
AB The ultraslow eastern Southwest Indian Ridge (SWIR) offers an opportunity to study the effect of magma supply on an ultraslow mid-ocean ridge starting from quasi-melt-free detachment-dominated spreading, and transitioning to volcanic spreading as one nears prominent axial volcanos. Detachments in the quasi melt-free mode extend along-axis 60 to 95 km and have a lifetime of 0.6 to 1.5 myrs. They cut into their predecessor's footwall with an opposite polarity, causing part of the footwall lithosphere to experience further deformation, hydrothermal alteration, sparse magmatism and possibly thermal rejuvenation, in a hanging wall position. The accretion of the oceanic lithosphere in this context therefore occurs in two distinct stages over the lifetime of two successive detachment faults. We examine the transition from this nearly amagmatic detachment-dominated mode to the more common volcanic mode of spreading, showing that it occurs along-axis over distances <= 30 km. It involves a significant thinning of the axial lithosphere and a gradual decrease of the amount of tectonic displacement on faults, as the magmatic contribution to the divergence of the two plates increases. We develop a conceptual model of this transition, in which magma plays a double role: it fills the space between the diverging plates, thus reducing the need for displacement along faults, and it modifies the thermal state and the rheology of the plate boundary, affecting its thickness and its tectonic response to plate divergence. Based on a comparison of the ultraslow eastern SWIR, with the faster spreading Mid-Atlantic Ridge, we show that the activation of the volcanic, or of the detachment-dominated modes of spreading is connected with the volume of magma supplied per increment of plate separation, over a range of axial lithosphere thickness, and therefore over a range of the M ratio defined by (Buck et al., 2005) as the relative contribution of magma and faults to plate divergence (M is smaller, for a given volume of melt per increment of plate separation, if the plate is thicker). We therefore propose that M does not fully explain the variability in faulting styles observed at slow and ultraslow ridges and propose that rheological changes induced by magma also play a key role (melt itself is weak, hydrothermally altered gabbro-peridotite mixtures are weak, and melt heat sustains more vigorous hydrothermal circulation), resulting in contrasted potentials for strain localization, footwall flexure on faults and the development of detachment faults. (C) 2019 Elsevier B.V. All rights reserved. 
PY 2019
PD AUG
SO Earth And Planetary Science Letters
SN 0012-821X
PU Elsevier Science Bv
VL 519
UT 000472689200022
BP 223
EP 233
DI 10.1016/j.epsl.2019.05.012
ID 87880
ER

EF