Micromagnetic, rockmagnetic and mineralogical studies on Dacitic Pumice from the Pinatubo Eruption (1991, Phillipines) Showing self‐reversed TRM

Hoffmann, V.; Fehr, Karl Thomas

doi:10.1029/96gl01317

Cited by 22 publications

(46 citation statements)

References 14 publications

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“…C: core, R: rim. Data of Nevado del Ruiz (Hoffmann, private communication, 1999) and Pinatubo (one is from Hoffmann and Fehr (1996) and the other is from our study) indicate the distribution of the TiO 2 -content of core to rim in each single crystal.…”

Section: Electron Microprobe Analysismentioning

confidence: 58%

“…The possible physical mechanisms of SRTRM of this type have been proposed by several authors (Uyeda, 1958;Ishikawa andSyono, 1962, 1963;Nord and Lawson, 1989;Hoffman, 1992;Haag et al, 1993;Hoffmann and Fehr, 1996). Among those, the spin rotation model of Hoffman (1992) is slightly different from the other five.…”

Section: Introductionmentioning

confidence: 99%

“…If we suppose Ishikawa's data are a little different from the magnetic properties of natural hemoilmenite concerned here (such a case is possible in nature), and Hoffmann and Fehr's (1996) model is true, then their proposed mechanism should be adaptable for at least the SRTRM in Haruna dacite pumice. This means that at least two intergrown hemoilmenite phases, one being ferrimagnetic and the other WF, should coexist in single crystals of hemoilmenite of Haruna dacite pumice, whatever the structure may be.…”

Section: Introductionmentioning

confidence: 99%

“…Ishikawa and Syono's model was so clever and firmly based on the physical data that it has been a unique model for many years, until Nord and Lawson (1989) proposed a model of the twin-(cation-ordered)domain boundary and some other models were successively proposed. Hoffmann and Fehr (1996) tried to explain the mechanism of SRTRM of this type on the basis of detailed micromagnetic, rockmagnetic, and mineralogical investigations on dacitic pumice from the 1991 eruption of Mt. Pinatubo.…”

Section: Introductionmentioning

confidence: 99%

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Magnetic properties of hemoilmenite single crystals in Haruna dacite pumice revealed by the Bitter technique, with special reference to self-reversal of thermoremanent magnetization

Ozima

Funaki

2014

Earth Planet Sp

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In order to reconsider the mechanism of the self-reversal of TRM (SRTRM) of hemoilmenite in dacite pumice, magnetic properties of newly collected Haruna dacite pumice near the historical sampling site (more than 50 years ago) were investigated again. All Haruna dacite pumice samples collected showed SRTRM or at least partial SRTRM. This time, the methods of microprobe analysis and the Bitter technique which were not available 50 years ago, were added to examine hemoilmenite crystals. Contrary to the result which was first reported by Hoffmann and Fehr on the basis of the micromagnetic observation of hemoilmenite crystals in Pinatubo dacite pumice, our hemoilmenite crystals are considerably more homogeneous in TiO 2 -content in a single crystal than those of Hoffmann and Fehr. Also, we could not find any "shell structure" with two phases having different magnetism and compositions in a single crystal of hemoilmenite in Haruna dacite pumice. We came to the conclusion that the intergrown shell-structure itself in Hoffmann and Fehr's model may not be essential but only the coexistence of the intergrown two phases in a single crystal of hemoilmenite must be essential for the acquisition of SRTRM of hemoilmenite. Both models, one by Ishikawa and Syono and the other by Hoffmann and Fehr are basically similar to each other, regardless of the structure involved.

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Section: Electron Microprobe Analysismentioning

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Magnetic properties of hemoilmenite single crystals in Haruna dacite pumice revealed by the Bitter technique, with special reference to self-reversal of thermoremanent magnetization

Ozima

Funaki

2014

Earth Planet Sp

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“…The model of the mechanism of SRTRM in hemoilmenite, established by Syono (1962, 1963), has subsequently been questioned and some alternate models proposed (Lawson et al, 1987;Hoffman, 1992;Hoffmann and Fehr, 1996;Prévot et al, 2001). Some of the alternative models are based on micromagnetic observational results (Bitter patterns) on hemoilmenite crystals of Pinatubo samples.…”

Section: Introduction and Geologic Settingmentioning

confidence: 99%

Magnetic properties of pyroclastic rocks from the later stage of the eruptive activity of Haruna Volcano in relation to the self-reversal of thermo-remanent magnetization

Ozima¹,

Oshima

Funaki

2014

Earth Planet Sp

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Focusing to the self-reversal of Thermo-Remanent Magnetization (TRM), we examined magnetic properties of 32 pieces of unoriented pumice samples, which were systematically collected from eight layers of pumice-fall and pumice-flow deposits at Haruna Volcano, Japan in the two stages of the eruption, i.e., Futatsu-dake stage (the 5th stage) and caldera-forming stage (the 4th stage). The magnetic behaviors of TRM well correlated with the primary chemical composition (TiO 2 -content or x (molecular fraction value of ilmenite in xFeTiO 3 -(1-x)Fe 2 O 3 )) of the hemoilmenite phenocrysts in the samples. That is, the samples of which chemical composition of hemoilmenite is TiO 2 ∼ 30 wt% (x ∼ 0.582) showed various types of TRM including typical intense Self-Reversed ThermoRemanent Magnetization (SRTRM), whereas the samples of which chemical composition of hemoilmenite is TiO 2 ∼ 32 wt% (x ∼ 0.620) showed one type of TRM; weak intensity of self-reversed component of TRM. This result harmonizes with the well-known diagram by Uyeda, where the intensity of SRTRM of hemoilmenite (quenched) is an explicit function of the chemical composition, and only in the restricted narrow range of the chemical composition, intense SRTRM is acquired. Moreover, the hemoilmenite samples of which chemical composition is less than TiO 2 ∼ 31 wt% (x ∼ 0.60) are capable to acquire various intensities of SRTRM on annealing according to its condition. In our TiO 2 -poorer (or smaller-x) samples, the variety in the behavior of TRM is well explained with this annealing effect in this compositional range.

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Importance of titanohematite in detrital remanent magnetizations of strata spanning the Cretaceous‐Paleogene boundary, Hell Creek region, Montana

Sprain

Feinberg

Renne

et al. 2016

Geochem Geophys Geosyst

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Intermediate composition titanohematite, Fe 2-y Ti y O 3 with 0.5 y 0.7, is seldom the focus of paleomagnetic study and is commonly believed to be rare in nature. While largely overlooked in magnetostratigraphic studies, intermediate titanohematite has been identified as the dominant ferrimagnetic mineral in an array of Late Mesozoic and early Cenozoic Laramide clastic deposits throughout the central United States. Intermediate titanohematite is ferrimagnetic and has similar magnetic properties to titanomagnetite, except its unique self-reversing property. Due to these similarities, and with detrital remanent magnetizations masking its self-reversing nature, intermediate titanohematite is often misidentified in sedimentary deposits. Past studies relied upon nonmagnetic techniques including X-ray diffraction and electron microprobe analysis. While these techniques can identify the presence of intermediate titanohematite, they fail to test whether the mineral is the primary recorder. To facilitate the identification of intermediate titanohematite in sedimentary deposits, we characterize this mineral using low-temperature magnetometry and high-temperature susceptibility experiments, and present a new identification technique based on titanohematite's self-reversing property, for sediments that span the Cretaceous-Paleogene boundary (Hell Creek region, Montana). Results from the self-reversal test indicate that the majority of remanence is held by minerals that become magnetized parallel to an applied field, but that intermediate, selfreversing titanohematite (y 5 0.53-0.63) is an important ancillary carrier of remanence. While earlier literature suggests that intermediate titanohematite is rare in nature, reanalysis using specialized rock magnetic techniques may reveal that it is more abundant in the rock record, particularly within depositional basins adjacent to calc-alkaline volcanics, than previously thought.

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Micromagnetic, rockmagnetic and mineralogical studies on Dacitic Pumice from the Pinatubo Eruption (1991, Phillipines) Showing self‐reversed TRM

Cited by 22 publications

References 14 publications

Magnetic properties of hemoilmenite single crystals in Haruna dacite pumice revealed by the Bitter technique, with special reference to self-reversal of thermoremanent magnetization

Magnetic properties of hemoilmenite single crystals in Haruna dacite pumice revealed by the Bitter technique, with special reference to self-reversal of thermoremanent magnetization

Magnetic properties of pyroclastic rocks from the later stage of the eruptive activity of Haruna Volcano in relation to the self-reversal of thermo-remanent magnetization

Importance of titanohematite in detrital remanent magnetizations of strata spanning the Cretaceous‐Paleogene boundary, Hell Creek region, Montana

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