The magnetization of clay-rich rocks in sedimentary basins; low-temperature experimental formation of magnetic carriers in natural samples

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doi: 10.1016/j.epsl.2004.11.013
Authors:Moreau, M. G.; Ader, M.; Enkin, R. J.
Author Affiliations:Primary:
Institut de Physique du Globe de Paris, Paris, France
Geological Survey of Canada, Canada
Volume Title:Earth and Planetary Science Letters
Source:Earth and Planetary Science Letters, 230(1-2), p.193-210. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X
Publication Date:2005
Note:In English. 45 refs.; illus., incl. 5 tables, 3 plates
Summary:Rocks are often magnetically altered during burial, thus providing a useful method to study their thermo-chemical history. In order to improve the understanding of burial diagenetic magnetization, we experimentally synthesized magnetite in natural samples. Lower Jurassic argillites from the Paris Basin were heated to 150 °C, under a confined atmosphere of argon. When a magnetic field was applied during the heating, a chemical remanent magnetization was acquired. Rock magnetism studies reveal that most of the newly formed magnetic carriers were magnetite. Using anhysteretic remanent magnetization as a measure of the quantity of magnetite, an increase of up to 150% after heating was observed. Ferrimagnetic iron sulphide and hematite are observed to have formed in samples composed of less than 3% calcite, and new magnetite is sometimes completely absent in samples containing less than 0.5% calcite. Hysteresis measurements suggest that the new magnetite is in the pseudo-single domain state. Scanning electron microscope studies indicate that the new magnetic carriers are associated with pre-existing pyrite. The magnetic transformations during the experiments involved a fluid which reacted with iron-bearing and sulfur-bearing minerals in ways depending on local redox conditions. This study shows that magnetite can be produced in argillaceous sediments at the normal temperatures and pressures found in sedimentary basins, without any external supply from long-range fluid flow. Abstract Copyright (2005) Elsevier, B.V.
Sections:Clay minerals; Experimental mineralogy; Physical properties of rocks and minerals
Subsections:Sedimentary rocks
Subjects:Anhysteretic remanent magnetization; Argillite; Basins; Burial; Clastic rocks; Crystallization; Demagnetization; Diagenesis; Experimental studies; Fluid phase; Isothermal remanent magnetization; Jurassic; Low temperature; Lower Jurassic; Magnetic minerals; Magnetite; Magnetization; Mesozoic; Mineral composition; Oxides; Paleomagnetism; Petrography; Remanent magnetization; Sedimentary basins; Sedimentary rocks; Sedimentation; Sulfides; Temperature; Textures; Europe; France; Paris Basin; Western Europe
Coordinates:N480000 N500000 E0050000 E0010000
Abstract Numbers:05M/623
Record ID:2006016313
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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