Moessbauer effect observations of the "X-phase" in the ilmenite-hematite series.

Allen, James L.; Shive, Peter N.

doi:10.5636/jgg.26.329

Cited by 4 publications

(2 citation statements)

References 3 publications

(3 reference statements)

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“…Hoffman supports this contention by presenting good evidence that the x-phase has a narrowly restricted Curie temperature near 350~ an observation consistent with the x-phase being a hematite-rich exsolved phase with roughly 40 mole 70 ilmenite in solid solution. This is consistent with the work of Allan and Shive (1974), who use M6ssbauer analysis to find that at least part of the x-phase has a Curie temperature close to the 350~ temperature cited by Hoffman. However, Hoffman (1975) also indicated that his mechanism will work only if the temperature of the solvus in the vicinity of y--0.5 to y = 0.6 is far higher than that allowed by Lindsley (1973).…”

Section: Self-reversal In Titanohematitessupporting

confidence: 79%

Magnetic effects associated with chemical changes in igneous rocks

Merrill

1975

Geophysical Surveys

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Experimental evidence and theory indicate that chemical changes occur in many igneous rocks at sufficiently low temperatures to significantly affect the remanent magnetization. Some chemical changes lead to self-reversals of magnetization that are not reproducible in laboratory experiments. Such self-reversals appear to be very rare in subaerially-erupted basalts, but they probably are much more common in some other rock types, such as granites and diorites. The stability of the natural remanent magnetization in igneous rocks can be decreased, left unaltered, or increased by chemical changes. In addition, chemical changes will usually affect the intensity of magnetization in a rock; the intensity can increase, decrease, or (rarely) be left unaltered by a chemical change. Such changes are important to consider in the development of improved techniques for obtaining reliable estimates of the intensity of the Earth's magnetic field in the past and in correctly interpreting marine magnetic anomalies. Finally, experiments and theory are presented which suggest that many of the chemical changes in igneous rocks will only occasionally produce significant changes in the direction of the magnetization.

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Section: Self-reversal In Titanohematitessupporting

confidence: 79%

Magnetic effects associated with chemical changes in igneous rocks

Merrill

1975

Geophysical Surveys

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“…8), and that they may be as small as a few atoms across in some cases (Lawson et al 1981;Lawson & Nord 1984;Nord & Lawson 1989). The possibility of a self-reversed thermal remanent magnetization (TRM) within ferrian ilmenites (Ishikawa & Syono 1963;Allen & Shive 1974;Lawson et al 1981;Lawson & Nord 1984;Nord & Lawson 1989;Hoffman 1992) is not directly relevant in the present study because, as detrital particles, the dominant remanence component, which might have been originally self-reversed, would align with the ambient geomagnetic field in the depositional environment. Although the grains identified as the likely remanence carriers in this study have somewhat higher Ti (and Mn) contents than those in the above-cited studies, the magnetic properties of the ilmenite grains in the Wanganui basin sediments can be attributed to a similar mechanism to that discussed by Lawson & Nord (t984) and Nord & Lawson (1989).…”

Section: Reconciling the Apparent Conflict Between Magnetic Behaviourmentioning

confidence: 97%

Diagenesis of magnetic mineral assemblages in multiply redeposited siliciclastic marine sediments, Wanganui basin, New Zealand

Wilson¹,

Roberts²

1999

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In many sedimentary environments, early diagenetic sulphidization reactions cause extensive dissolution of detrital magnetic minerals which can alter or destroy the palaeomagnetic signal. Pliocene sediments from the Wanganui basin, North Island, New Zealand, have been subjected to multiple cycles of erosion and redeposition in sulphatereducing environments before reaching their present setting. Despite this, the sediments retain a measurable and stable remanent magnetization. The only Fe-Ti oxide recognized from detailed sedimentary petrographic characterization of magnetic extracts and bulk sediments is ilmenite, with compositions that lie within the range from which paramagnetic behaviour is expected. There are no Fe-Ti oxide grains with compositions from which ferrimagnetic behaviour is expected (except for rare chromite). A direct link was made between magnetic behaviour and mineralogy by conducting electron probe microanalysis and back-scattered electron imaging of the same grains that were subjected to magnetic analysis. These studies demonstrate that stable magnetic behaviour is displayed by grains that appear to be homogeneously composed of ilmenite. This magnetic behaviour is attributed to the presence of ferrimagnetic Fe-enriched (hemo-ilmenite) microstructural domains that have been previously reported from ilmenite grains. These hemo-ilmenite domains appear to be dominantly responsible for the remanence of the Wanganui basin Pliocene sediments. Calculations of the reactivity of detrital iron-bearing minerals to sulphidization indicate that ilmenite is much less reactive than magnetite and other detrital magnetic minerals. Given the resistance of hemo-ilmenite, to dissolution, it is suggested that microstructural ferrimagnetic domains withiia ilmenite grains may be a source of palaeomagnetic information in sediments that have undergone diagenetic magnetic mineral dissolution during multiple episodes of erosion and redeposition.

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References

1983

International Geophysics

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Moessbauer effect observations of the "X-phase" in the ilmenite-hematite series.

Cited by 4 publications

References 3 publications

Magnetic effects associated with chemical changes in igneous rocks

Magnetic effects associated with chemical changes in igneous rocks

Diagenesis of magnetic mineral assemblages in multiply redeposited siliciclastic marine sediments, Wanganui basin, New Zealand

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