Self-reversed thermoremanent magnetization in a late Brunhes dacite pumice.

Kennedy, Lawrence P.

doi:10.5636/jgg.33.429

Cited by 11 publications

(6 citation statements)

References 20 publications

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“…Recently, similar cases of SRTRM in some other dacite/andesite pumices have been reported (Kennedy, 1981;Heller et al, 1986;Lawson et al, 1987;Ozima et al, 1992). For thirty years, after SRTRM was first discovered in Haruna dacite pumice, SRTRM of this type was believed to be uncommon in nature.…”

Section: Introductionmentioning

confidence: 88%

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: Introductionmentioning

confidence: 88%

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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“…Intermediate titanohematite received much interest after Nagata et al's [1951] discovery of a reversed thermoremanent magnetization (RTRM) in the Haruna dacite tuff from Japan, which complicated early recognition of geomagnetic polarity reversals [Cox et al, 1963;McDougall and Tarling, 1963]. Since that time, intermediate titanohematite has been identified only in a handful of other locations, most involving rapidly cooled intermediate calc-alkaline volcanic rocks [Kennedy, 1981;Heller et al, 1986;Lawson et al, 1987;Ozima et al, 1992]. Aside from rock magnetic studies of self-reversal mechanisms, intermediate titanohematite is often viewed as a magnetic rarity of negligible importance to most paleomagnetic studies.…”

Section: Introductionmentioning

confidence: 99%

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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“…Furthermore very little knowledge exists about the frequency of this effect in nature. The few well documented examples of total self-reversal of NRM which were repr.odueible in the laboratory are found in dacitic or andesitic pumices only (Nagata 1952;Kennedy 1981;Heller et al, 1986,' Lawson et al, 1987,' Ozima et al, 1992 and therefore refer to a self-reversal of the thermoremanent magnetization (SR-TRM). Already N•el (1951) and Uyeda (1958) discussed the possibility that self-reversal could be due to a physical interaction of two chemically very similar magnetic phases intergrown in a specific manner.…”

Section: Introductionmentioning

confidence: 99%

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

Hoffmann¹,

Fehr²

1996

Geophysical Research Letters

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Detailed micromagnetic, rockmagnetic and mineralogical investigations on dacitic pumice from the eruption of Mt. Pinatubo (1991, Phillipines) showing reversed NRM/TRM are presented. Two intergrown hemoilmenite‐phases in chemically zoned particles were detected as being responsible: a rim‐(or covering) phase consisting of a weak‐ferromagnetic (disordered) hemoilmenite phase (low saturation magnetization but magnetically hard like hematite, FeTiO3 content 53–57 mol percent) and a core‐phase consisting of a ferrimagnetic (ordered) hemoilmenite phase (high saturation magnetization but magnetically softer, constant FeTiO3 content ≈ 58 mol percent). Preliminary studies were carried out in order to elucidate the magnetic interactions (possibly exchange coupling) responsible for the self‐reversal of the NRM/TRM. A preliminary and schematic model is presented which summarizes the main points of acquisition of a self‐reversed TRM according to our results.

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Self-reversed thermoremanent magnetization in a late Brunhes dacite pumice.

Cited by 11 publications

References 20 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

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

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

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