Determination of lattice parameter, oxidation state, and composition of individual titanomagnetite/titanomaghemite grains by transmission electron microscopy

Zhou, Weiming; Peacor, Donald R.; Voo, Rob Van der; Mansfield, John F.

doi:10.1029/1999jb900095

Cited by 26 publications

(29 citation statements)

References 53 publications

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“…It is not clear, however, whether this peak originates from titanomaghemite or it is a “contamination signal” due to X‐ray fluorescence from the adjacent silicate minerals (e.g., plagioclase). The latter explanation is consistent with the observation of a comparable peak from Si (Figure 3c); Si is not usually present in significant quantities in natural titanomagnetites [e.g., Creer and Ibbetson , 1970; Zhou et al , 1999]. Assuming that the entire Al signal comes from titanomaghemite, we calculated the maximum degree of Al substitution (0.10 ≤ δ max ≤ 0.16) using the following formula:

where (Fe/Al) and (Ti/Al) are the atomic ratios estimated from the quantification of EDS data.…”

Section: Rock Magnetic and Compositional Datasupporting

confidence: 90%

On the compositional field of self‐reversing titanomaghemite: Constraints from Deep Sea Drilling Project Site 307

Doubrovine

Tarduno

2005

J. Geophys. Res.

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[1] In 1956, Verhoogen proposed that ionic reordering during low-temperature oxidation of titanomagnetite could result in self-reversal of natural remanent magnetization. Later, in 1966, O'Reilly and Banerjee concluded that (1) the compositional field of self-reversing titanomaghemite was restricted to very high oxidation states and (2) that high oxidation temperature (!250°C) would be required to reach these oxidation levels, which would in turn be inconsistent with stability of the cation-deficient structure of titanomaghemite in nature. However, an example of the process has been reported, in some altered pillow basalt lavas of Late Cretaceous age from Detroit Seamount (Ocean Drilling Program (ODP) sites 883, 1203, and 1204) in the northwestern Pacific Ocean. Here we present new paleomagnetic, rock magnetic and compositional data from mid-ocean ridge tholeiitic basalts of Late Jurassic age collected at Deep Sea Drilling Project (DSDP) Site 307. Although severely oxidized, the DSDP Site 307 basalt samples lack the clear self-reversed magnetizations seen in some samples from Detroit Seamount. These data constrain the compositional field of self-reversing titanomaghemite to extremely high oxidation states (z ! 0.95), consistent with the first conclusion of O'Reilly and Banerjee. The comparison of results from ODP sites 883, 1203, and 1204 on Detroit Seamount and those from the DSDP Site 307 basalts suggests that the presence of self-reversed magnetizations may signify unusually vigorous and sustained fluid flow that resulted in very efficient removal of Fe from titanomaghemite producing the extremely high oxidation states required for self-reversal.Citation: Doubrovine, P. V., and J. A. Tarduno (2005), On the compositional field of self-reversing titanomaghemite:

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where (Fe/Al) and (Ti/Al) are the atomic ratios estimated from the quantification of EDS data.…”

Section: Rock Magnetic and Compositional Datasupporting

confidence: 90%

On the compositional field of self‐reversing titanomaghemite: Constraints from Deep Sea Drilling Project Site 307

Doubrovine

Tarduno

2005

J. Geophys. Res.

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“…According to the semiquantitative EDS spectra, the Ti content of these particles can reach from 1 to 20% corresponding to a (fresh) Tmt composition of TM3 to TM60 (Figure 3). Averaged over many individual Tmt grains, the mean composition of all sites corresponds approximately to TM30 (Table 2b), which is consistent with the observations for MORB titanomagnetites by Zhou et al [1999Zhou et al [ , 2000.…”

Section: Fragmental and Euhedral Titanomagnetitesupporting

confidence: 78%

Magnetic petrology of equatorial Atlantic sediments: Electron microscopy results and their implications for environmental magnetic interpretation

et al. 2007

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[1] The magnetic microparticle and nanoparticle inventories of marine sediments from equatorial Atlantic sites were investigated by scanning and transmission electron microscopy to classify all present detrital and authigenic magnetic mineral species and to investigate their regional distribution, origin, transport, and preservation. This information is used to establish source-to-sink relations and to constrain environmental magnetic proxy interpretations for this area. . Sediments from two depths corresponding to marine isotope stages 4 and 5.5 were processed. This selection represents glacial and interglacial conditions of sedimentation for the western, central, and eastern equatorial Atlantic and avoids interferences from subsurface and anoxic processes. Crystallographic, elemental, morphological, and granulometric data of more than 2000 magnetic particles were collected by scanning and transmission electron microscopy. On basis of these properties, nine particle classes could be defined: detrital magnetite, titanomagnetite (fragmental and euhedral), titanomagnetite-hemoilmentite intergrowths, silicates with magnetic inclusions, microcrystalline hematite, magnetite spherules, bacterial magnetite, goethite needles, and nanoparticle clusters. Each class can be associated with fluvial, eolian, subaeric, and submarine volcanic, biogenic, or chemogenic sources. Large-scale sedimentation patterns are delineated as well: detrital magnetite is typical of Amazon discharge, fragmental titanomagnetite is a submarine weathering product of mid-ocean ridge basalts, and titanomagnetite-hemoilmenite intergrowths are common magnetic particles in West African dust. This clear regionalization underlines that magnetic petrology is an excellent indicator of source-to-sink relations. Hematite encrustations, magnetic spherules, and nanoparticle clusters were found at all investigated sites, while bacterial magnetite and authigenic hematite were only detected at the more oxic western site. At the eastern site, surface pits and crevices were seen on the crystal faces indicating subtle early diagenetic reductive dissolution. It was observed that paleoclimatic signatures of magnetogranulometric parameters such as the ratio of anhysteretic and isothermal remanent magnetizations can be formed either by mixing of multiple sources with separate, relatively narrow grain size ranges (western site) or by variable sorting of a single source with a broad grain size distribution (eastern site). Hematite, goethite, and possibly ferrihydrite nanoparticles occur in all sediment cores studied and have either high-coercive or superparamagnetic properties depending on their partly ultrafine grain sizes. These two magnetic fractions are generally discussed as separate fractions, but we suggest that they could actually be genetically linked.

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“…Cation-deficient spinel ss was previously regarded as ''titanomaghemite'', which is formed by an oxidation process analogous to the formation of maghemite (c-Fe 2 O 3 ) (Basta 1959, Collyer et al 1988, Zhou et al 1999 …”

Section: Direct Exsolution Of Ilmenitementioning

confidence: 99%

“…A minor amount of cationic vacancies (A) can also be present in cationdeficient spinel ss (Collyer et al 1988, Senderov et al 1993, Lattard et al1995, Zhou et al 1999. Spinel ss in mafic-ultramafic intrusive rocks would experience intensive sub-solidus re-equilibration on slow cooling (Frost & Lindsley 1991), resulting in various types of exsolution in Ti-rich magnetite.…”

Section: Introductionmentioning

confidence: 99%

Mineralogy and Origin of Exsolution In Ti-Rich Magnetite From Different Magmatic Fe-Ti Oxide-Bearing Intrusions

Tan

Liu

et al. 2016

Can Mineral

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Titanium-rich magnetite from different magmatic Fe-Ti oxide-bearing intrusions consists of host magnetite (nearly pure Fe 3 O 4 ) and different types of exsolution. The exsolution of Ti-rich magnetite is indicative of the physical and chemical conditions at which the host intrusions formed. However, the mechanisms to form these types of exsolution have been debated. To examine the formation mechanisms of the different types of exsolution, multiple microanalytical techniques, such as electron microprobe analysis, micro Raman spectroscopy, and micro X-ray diffraction, were used to examine the chemical composition, morphology, and crystalline structure of exsolved minerals in Ti-rich magnetite from different Fe-Ti oxidebearing intrusions in China. The characterization results indicate that pleonaste and ilmenite are the two dominant exsolution phases in the Ti-rich magnetite, whereas the ulvöspinel phase is barely found. The ilmenite exsolution may have different origins: (1) the cloth-texture lamellae primarily exsolved as ulvöspinel, which was oxidized to ilmenite later at ,600 8C; (2) most of the trellis-and sandwich-type lamellae formed by ''oxy-exsolution'' at .600 8C; (3) some ilmenite lamellae exsolved directly from cation-deficient solid solution due to the substitution of Ti 4þ þ A 2Fe 2þ ; (4) sub-solidus re-equilibration of coexisting Fe-Ti oxides can also lead to ilmenite exsolution in Ti-rich magnetite and magnetite exsolution in ilmenite.

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Determination of lattice parameter, oxidation state, and composition of individual titanomagnetite/titanomaghemite grains by transmission electron microscopy

Cited by 26 publications

References 53 publications

On the compositional field of self‐reversing titanomaghemite: Constraints from Deep Sea Drilling Project Site 307

On the compositional field of self‐reversing titanomaghemite: Constraints from Deep Sea Drilling Project Site 307

Magnetic petrology of equatorial Atlantic sediments: Electron microscopy results and their implications for environmental magnetic interpretation

Mineralogy and Origin of Exsolution In Ti-Rich Magnetite From Different Magmatic Fe-Ti Oxide-Bearing Intrusions

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