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Magnetite‐out and pyrrhotite‐in temperatures in shales and slates
Author(s) -
Aubourg Charles,
Jackson Mike,
Ducoux Maxime,
Mansour Mohannad
Publication year - 2019
Publication title -
terra nova
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.353
H-Index - 89
eISSN - 1365-3121
pISSN - 0954-4879
DOI - 10.1111/ter.12424
Subject(s) - pyrrhotite , geology , magnetite , slates , remanence , geochemistry , magnetic mineralogy , mineralogy , magnetization , magnetic field , paleontology , pyrite , physics , quantum mechanics
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 T burial < 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 T burial ~350°C. At T burial >60°C and T burial >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.