Exhumed mantle at ultra-slow spreading ridges and magma-poor rifted margins : what can we learn from marine magnetic anomalies ?

• Main Author: Bronner, Adrien
• Other Authors: Institut de physique du globe de Strasbourg (IPGS), Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Université de Strasbourg, Daniel Sauter, Gianreto Manatschal
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2013
• Subjects: Magnetic anomaly; Serpentinized peridotite; Mid-oceanic ridge; Rifted margin; Marge passive; Dorsale océanique; Péridotite serpentinisée; Anomalie magnétique; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Dorsale; Indian; Newfoundland
• Online Access: https://tel.archives-ouvertes.fr/tel-01001830; https://tel.archives-ouvertes.fr/tel-01001830/document; https://tel.archives-ouvertes.fr/tel-01001830/file/Bronner_Adrien_2013_ED413.pdf

The aim of this work is to constrain (1) whether exhumation of mantle rocks at mid oceanic ridges is compatible with the record of polarity reversals of the Earth magnetic field, (2) what is the origin and the processes responsible for the magnetic anomalies observed at magma-poor rifted margins and (3) what are the consequences of these processes on continental breakup. In a first part, in order to work with high-resolution data, we develop a method for calibration and interpretation of deep-tow three component magnetic data. In a second part, we apply these methods to the data acquired above the large exhumed mantle domains of the ultraslow-spreading Southwest Indian Ridge. We show that, in these areas, neither the magnetic properties of the dredge samples nor the deep-tow magnetic data are consistent with the seafloor-spreading magnetic pattern commonly observed at mid oceanic ridges. We further suggest that in contrast to mid oceanic ridges basalts the exhumed serpentinized mantle rocks do not carry a sufficiently stable remanant magnetization to produce marine magnetic anomalies. In the last part, we show that the “J” anomaly, previously interpreted as the first seafloor-spreading anomaly of the Iberia and Newfoundland passive margins, is associated with locally high topography and thickened crust. We propose that this peculiar crustal structure results from voluminous magma both erupted at the surface and added beneath the exhumed mantle domain. We therefore propose that the J anomaly did not form during seafloor spreading but instead represents a pulse of magmatism that have triggered continental breakup. L’objectif de cette thèse est de comprendre (1) si l’exhumation des roches mantelliques aux dorsales océaniques est compatible avec l’enregistrement des inversions de polarité du champ magnétique terrestre, (2) quels sont les processus associés aux anomalies magnétiques observées à l’aplomb des transitions océan-continent et (3) quelles sont les conséquences de ces processus sur les mécanismes de ...