Magnetite-out and pyrrhotite-in temperatures in shales and slates

Charles Aubourg, Mike Jackson, Maxime Ducoux, Mohannad Mansour

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

Clay-rich basins have undergone varying degrees of magnetic transformation during burial, affecting their ability to retain accurate records of Earth's dynamic magnetic field. We propose to bracket the magnetite-out and pyrrhotite-in temperatures in shales and slates from Taiwan and the Pyrenees by using a combination of low-temperature magnetic transitions and geothermometers. For Tburial < 340°C, the magnetic assemblage is dominated by magnetite. Gradually with increasing burial temperature, the concentration of magnetite decreases to a few ppmv. We observe the magnetite-out isograd at Tburial ~350°C. At Tburial >60°C and Tburial >340°C respectively, fine-grained and coarse-grained pyrrhotite develop. In the course of burial, a clay-rich basin gradually loses its capability to retain a record of Earth's magnetic field. It is only during basin uplift, that coarse pyrrhotite might acquire a thermo remanent magnetization. Our results point out therefore highly contrasted magnetic properties and palaeomagnetic records between deeply buried basins and exhumed ones.

Original languageEnglish (US)
Pages (from-to)534-539
Number of pages6
JournalTerra Nova
Volume31
Issue number6
DOIs
StatePublished - Dec 1 2019

Bibliographical note

Funding Information:
We would like to thank the reviewers and the editor for their meticulous work, which has led to an improvement of the manuscript. This study benefited from numerous discussions with J‐P. Pozzi and M. Kars who accompanied C.A. during preliminary works on magnetite. We also thank E. Péré (IPREM) to gave us access to Raman facilities. Y‐M. Chou provided us efficient logistics in Taiwan for sampling. This work, particularly the low‐temperature magnetic measurements, benefited from several fellowships of C.A. at the Institute of Rock Magnetism (IRM, University of Minnesota). The IRM is supported by the Instruments and Facilities program of the US National Science Foundation.

Funding Information:
We would like to thank the reviewers and the editor for their meticulous work, which has led to an improvement of the manuscript. This study benefited from numerous discussions with J-P. Pozzi and M. Kars who accompanied C.A. during preliminary works on magnetite. We also thank E. P?r? (IPREM) to gave us access to Raman facilities. Y-M. Chou provided us efficient logistics in Taiwan for sampling. This work, particularly the low-temperature magnetic measurements, benefited from several fellowships of C.A. at the Institute of Rock Magnetism (IRM, University of Minnesota). The IRM is supported by the Instruments and Facilities program of the US National Science Foundation.

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