Stability of iron oxides and their role in the formation of rock magnetism |
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| Authors: | Arkady N Pilchin Lev V Eppelbaum |
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| Institution: | (1) Universal Geoscience and Environmental Consulting Company, 205 Hilda Ave., Willowdale, Ontario, M2M 4B1, Canada;(2) Department of Geophysics and Planetary Sciences, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, 69978 Tel Aviv, Israel |
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| Abstract: | Thermodynamic conditions (first of all, temperature) are the main dynamic factors in the transformation process of ferrous
to ferric iron (TFFI). TFFI usually takes place within a temperature range of 473–843 K (most active at temperatures above
673 K) and does not require presence of the oxidizing agents above 673 K. Analysis of the chemical composition of different
rocks and minerals indicates that only for some sedimentary rocks is the relative content of ferrous iron oxide less than
its value in magnetite, and this value is minimal for oceanic sediments. The relative content of ferrous iron oxide in oceanic
magmatic rocks exceeds this value in continental magmatic rocks and depends on the rate of rock cooling. An investigation
of the role of the titanium oxide content of different rocks on stability of ferrous iron oxide against its transformation
to ferric iron oxide shows that a significant correlation (r = 0.79) does exist between the relative content of ferrous iron oxide and ratio of TiO2/Fe2O3. Temperature within the solar nebula at location of the Earth was within the temperature range of the TFFI. During the Earth
accretion and its early evolution, ferric iron oxide was unstable and most likely did not exist. The first magnetic minerals
containing ferric iron could have appeared only after the Earth’s surface had cooled below ∼843 K. The formation of the first
Algoma-type banded iron formations could be used as a marker of the Earth’s surface cooling below ∼843 K. |
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| Keywords: | ferric ferrous remagnetization rock magnetism temperature range |
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