Magnetic Properties of Oxidized (Cation-Deficient) Titanomagnetites (Fe, Ti, _??_)43O4

Readman, P. W.; O’Reilly, W.

doi:10.5636/jgg.24.69

Cited by 267 publications

(214 citation statements)

References 24 publications

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“…The contour lines of Readman and O'Reilly (1972) are in reasonable agreement with those of Nishitani and Kono (1983) with a few exceptions. Plotting our results in this fashion assumes that the content of impurity cations in the natural titanomaghemites is small.…”

Section: Site 747supporting

confidence: 78%

Rock-Magnetic Investigation of Basalts from the Southern Kerguelen Plateau (Leg 120)

Helder¹,

Geiss²,

Dunlop³

et al. 1992

Proceedings of the Ocean Drilling Program

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Basalt samples recovered on Ocean Drilling Program Leg 120 from the Kerguelen Plateau were investigated by thermomagnetic analysis, X-ray diffraction, and ore microscopy. The basement samples could be divided into two groups based on Curie temperatures, cell-edge parameters, and optical magnetic mineralogy. Samples from Sites 748 and 750 underwent only low-temperature oxidation and displayed Curie temperatures for the titanomaghemites that ranged from 340° to 395°C. The basalts from Sites 747 and 749 mainly experienced high-temperature oxidation. High-temperature oxidation produced titanium-poor titanomagnetites with ilmenite-exsolution lamellae. Curie temperatures of the deuterically oxidized titanomaghemites varied from 490° to 620°C.

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Section: Site 747supporting

confidence: 78%

Rock-Magnetic Investigation of Basalts from the Southern Kerguelen Plateau (Leg 120)

Helder¹,

Geiss²,

Dunlop³

et al. 1992

Proceedings of the Ocean Drilling Program

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“…However, in the case of G205-3-34 which is considerably altered, unmixing of titanomaghemite seems to be more likely ex- planation for the existence of ilmenite. Similarly ilmenite and hematite in sample 133D and 144D can be explained as alteration products of titanomaghemite (READMAN and OREILLY, 1972), since the samples are the most altered among all the samples. The reduction in the magnetization in heating in these two samples could be due to oxidation of magnetite to hematite during the thermomagnetic analysis.…”

Section: Chemical Analysesmentioning

confidence: 99%

“…W10-3 shows faint ilmenite peaks. Coexistence of ilmenite with Ti-poor titanomagnetite can be explained either as an exsolution of ilmenite in titanomagnetite matrix due to a high temperature oxidation (BUDDINGTON and LINDSLAY, 1964) or as an unmixing of titanomaghemite (READMAN and Properties of Submarine Basalts and the Implications 341 OREILLY, 1972). Since the Cobb seamount sample was obtained at very shallow depth (34 m) and the sea level at the early Quaternary is supposed to be significantly lower than the present time (HOLMES, 1965), it is almost certain that the basalt was formed by eruption in air.…”

Section: Chemical Analysesmentioning

confidence: 99%

“…Lately much efforts have been made to understand the magnetic properties of titanomaghemites by two groups (OZIMA and SAKAMOTO, 1971;READMAN and OREILLY, 1972), where the studies were made on synthesized titanomaghemites. However, for titanomaghemites of high Ti content, there is a considerable difference in the Curie temperatures and the lattice parameters between the two groups.…”

Section: Introductionmentioning

confidence: 99%

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Magnetic properties of submarine basalts and the implications on the structure of the oceanic crust.

Ozima

Joshima

Kinosmta³

1974

J. geomagn. geoelec

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X-ray, chemical and thermomagnetic analyses were made on ferromagnetic minerals separated from six submarine basalts of various ages, which are dredged from seamounts and ridge or drilled from sea floor. Lattice parameters, Curie temperatures and oxidation parameters are determined for these samples. From a comparison between K-Ar or Ar39-Ar40 ages and the magnetic properties, it is evident that major ferromagnetic minerals in young submarine basalts are titanomagnetites, whereas older submarine basalts contain essentially titanomaghemites. We conclude that the primary titanomagnetites have undergone maghemitization in suboceanic environment. The maghemitization process is estimated to have a time constant of a few tens of millions of years and maghemitized depth may extend to a few tens of meters in older (say older than 5X10y) oceanic crust.NRM of several maghemitized submarine basalts are subjected to a-f, pressure and low temperature demagnetization, hoping to see if any of the demagnetization techniques could discriminate a secondary magnetization which might be acquired during the maghemitization. Although the demagnetization techniques erased considerable portion of the NRMs, none of them was successful to demagnetize preferentially a remanent magnetization carried by titanomaghemites.

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“…1oHNSON andMERRILL (1972, 1973) carried out an oxidation experiment on synthetic samples using oxygen plasma and examined the intensity and stability of anhysteretic remanent magnetization (ARM) and CRM. Their thermomagnetic are not consistent with any of the results of complete syntheses of titanomaghemites (READMAN and O'REILLY, 1972;KEEFER and SHIVE, 1981;NISHITANI and KONG, 1983). As pointed out by JOHNSON and MERRILL (1973), the X-ray diffraction patterns showed two spinels and other phases.…”

mentioning

confidence: 79%

Effect of low-temperature oxidation on the remanence properties of titanomagnetites.

Nishitani

Kono

1989

J. geomagn. geoelec

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Changes in remanent magnetization and hysteresis parameters associated with low-temperature oxidation have been investigated using x=0.3, 0.5 and 0.7 synthetic titanomagnetite samples and natural submarine basalts. The intensity of remanence and the median destructive field (MDF) of TRM decreases with increasing oxidation. As oxidation proceeds, the intensity of CRM increases and its MDF decreases, except for x=0.7 titanomagnetite samples, which show maximum intensity and MDF around 0.6 of oxidation state (z). The intensity and stability of CRM become almost comparable to those of TRM in a high oxidation state. Saturation magnetization (Js) Understanding of the processes affecting the remanent magnetization of rocks is important in all paleomagnetic studies, in particular for the origin of the magnetic anomalies over the sea floor. Numerous factors affect the amplitude of marine magnetic anomalies; these include low-temperature oxidation of oceanic basalts, increase in the thickness of the magnetized layer with distance from the spreading center ($LAKELY, 1983), and the acquisition of viscous remanent magnetization (VRM) (JOHNSON and MERRILL, 1973; OZDEMIR and $ANERJEE, 1981). Among these factors, chemical changes due tolow-temperature oxidation are very important because of their relevance to the origin of the remanence of the oceanic basalts. Some authors consider that chemical remanent magnetization (CRM) due to lowtemperatureoxidation isthe origin of the remanence, while others take the view that

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Magnetic Properties of Oxidized (Cation-Deficient) Titanomagnetites (Fe, Ti, _??_)43O4

Cited by 267 publications

References 24 publications

Rock-Magnetic Investigation of Basalts from the Southern Kerguelen Plateau (Leg 120)

Rock-Magnetic Investigation of Basalts from the Southern Kerguelen Plateau (Leg 120)

Magnetic properties of submarine basalts and the implications on the structure of the oceanic crust.

Effect of low-temperature oxidation on the remanence properties of titanomagnetites.

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