Variation of magnetic directions within pillow basalts

Soroka, William L.; Beske-Diehl, Suzanne

doi:10.1016/0012-821x(84)90085-2

Cited by 12 publications

(3 citation statements)

References 25 publications

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“…However, their calculations are suspect because they fly in the face of much of the recent evidence that CRM due to maghemitisation of fine-grained T M ~O preserves the original TRM direction. This evidence includes observations of NRM directions in variably oxidised pillow lavas from the seafloor (Soroka and Beske-Diehl 1984) as well as laboratory experiments.…”

Section: Recrystallisution Without Change Of Latticementioning

confidence: 97%

Developments in rock magnetism

Dunlop¹

1990

Rep. Prog. Phys.

102

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Rock magnetism is concerned with the remanent magnetisation of ferrimagnetic fine particles in weak fields (2.0.1 mT), at temperatures ranging from ambient to the Curie point, and over times of geological length. Since most magnetisations in rocks or their synthetic analogues are thermally activated, the blocking temperature below which the approach to equilibrium is effectively frozen is of particular importance. The phenomenon of magnetisation blocking and unblocking permits one to simulate changes over geological times that would otherwise be unattainable on a laboratory timescale. As well as thermal and viscous (time-dependent) mechanisms of blocking, the crystallisation or recrystallisation of magnetic minerals in the presence of a field leads to magnetisation blocking when the crystal volume grows past superparamagnetic size. This review summarises current thinking about thermally activated magnetic processes, and puts them in the context of recent discoveries about magnetic domain structure in crystals containing only one or a few domains. Pseudo-single-domain effects in such crystals, which bridge the gap between classic single-domain and multidomain behaviour, are one of the current frontiers in rock magnetism.

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Section: Recrystallisution Without Change Of Latticementioning

confidence: 97%

Developments in rock magnetism

Dunlop¹

1990

Rep. Prog. Phys.

102

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“…The nonglassy parts of basalt pillows show interesting trends of their own (Figure 13). Soroka and Beske‐Diehl [1984] compared companion cores taken from the coarser‐grained interior and the finer‐grained near surface of individual pillows. In almost all cases, lines joining pairs of points for the same pillow trend parallel to the magnetite or TM60 SD + MD mixing curves, in an upward direction consistent with finer average grain sizes toward the chilled margin of the pillow.…”

Section: Data For Oceanic Basalts and Glasses And Intrusive And Plutomentioning

confidence: 99%

Theory and application of the Day plot (M_rs/M_sversusH_cr/H_c) 2. Application to data for rocks, sediments, and soils

2002

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[1] New theoretical curves relating the hysteresis parameters M rs /M s and H cr /H c for single-domain (SD), superparamagnetic (SP), pseudo-single-domain (PSD), and multidomain (MD) grains and their mixtures are applied to published data for natural materials. The Day plot of M rs /M s versus H cr /H c has been used to crudely classify samples into box-like SD, PSD, and MD (or sometimes incorrectly, MD + SP) regions with arbitrary boundaries. New type curves for MD, PSD/SD + MD, and SD + SP grains and mixtures permit more subtle and precise modeling. The predicted MD trend and its junction with the PSD trend are observed in two data sets: for magnetite spherules from carbonate rocks and for temperature-varying hysteresis results spanning the Verwey transition. The latter data are the basis of a suggested new method for pinpointing the PSD-MD threshold size. Selected data for pottery clays, soils, and paleosols generally follow SD + MD type curves and indicate intermediate-size PSD magnetite with narrow to broad size distributions. A lake sediment section with known grain-size progression tracks in the predicted sense along the SD + MD trend. Selected data for glaciomarine and pelagic sediments are also generally compatible with SD + MD trends. Examples of remagnetized carbonate rocks, submarine basaltic glasses, and glassy rims of pillow basalts all follow predicted SP + SD or SP + PSD mixing curves, with a large range in volume fraction of SP grains (0-75%) but a narrow range of SP particle sizes: 10 ± 2 nm. Larger SP grains spanning the range to SD size (25 -30 nm) are absent for unknown reasons. Oceanic dolerites, gabbros, and serpentinized peridotites in some cases fall in a novel region of the Day plot, parallel to but below magnetite SD + MD mixing curves.

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“…Several studies of the effect of oxidation on the NRM directions in natural samples conclude that the resultant chemical remanent magnetization is acquired along the original TRM direction [Marshall and Cox, 1972; R yall and A de- Hall, 1975]. Differences between directions of the oxidized and unoxidized samples have been explained by a viscous remanent magnetization (VRM) acquired by the unoxidized material [Soroka and Beske-Diehl, 1984]. Results of the above studies are not diagnostic with regard to CRM, however, because the ages of most of the pillow basalts were less than 0.7 m.y.…”

Section: Introductionmentioning

confidence: 99%

The effect of low‐temperature hydrothermal alteration on the remanent magnetization of synthetic titanomagnetites: A case for acquisition of chemical remanent magnetization

1991

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The effect of hydrothermal alteration on the thermoremanent magnetization (TRM) of synthetic titanomagnetite (TM40: Fe2.6Ti0.404) has been studied, to simulate the alteration that occurs in the oceanic crust. Pseudo-single-domain titanomagnetite grains, similar in size to those often found in oceanic basalts, were dispersed in a permeable but rigid glass matrix. This resulted in a TRM in the sample which was subsequently oxidized in acidic solutions while a magnetic field (0.1 mT) was applied perpendicular to the TRM direction. The experiments were conducted in a non-magnetic stainless steel pressure vessel at 150øC in solutions of acidity varying from pH=2 to pH=7. In addition to being time and temperature dependent, the acquired chemical remanent magnetization (CRM) was also found to be very pH dependent. The degree of maghemitization increased drastically as the acidity of the hydrothermal solution was increased in accordance with a process controlled by the loss of iron ions in aqueous solutions. Long-term storage experiments at carefully chosen temperatures demonstrated that no significant viscous remanent magnetization was acquired during heating. It was found that during the alteration of TM40 to titanomaghemite the CRM is along the a•nbie. nt field direction from the onset, and not partly or wholly along the TRM direction as has been found in previous air oxidation experiments. This has important implications for the possible cause of anomalous skewness of marine magnetic anomalies and for the anomalous directions of natural remanent magnetization found in some oceanic basalt samples. 19,54519,546 KELSO ET AL.: CRM IN T1TANOMAGNETITE DUE TO HYDROTttERMAL ALTERATION (i.e., the CRM direction) being perpendicular to the original TRM of the sample. They found that CRM and TRM were parallel up to z = 0.7, where z, the oxidation parameter, is the proportion of ferrous iron converted to ferric iron, which varies from 0 to 1.

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Variation of magnetic directions within pillow basalts

Cited by 12 publications

References 25 publications

Developments in rock magnetism

Developments in rock magnetism

Theory and application of the Day plot (M_rs/M_sversusH_cr/H_c) 2. Application to data for rocks, sediments, and soils

The effect of low‐temperature hydrothermal alteration on the remanent magnetization of synthetic titanomagnetites: A case for acquisition of chemical remanent magnetization

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Variation of magnetic directions within pillow basalts

Cited by 12 publications

References 25 publications

Developments in rock magnetism

Developments in rock magnetism

Theory and application of the Day plot (Mrs/MsversusHcr/Hc) 2. Application to data for rocks, sediments, and soils

The effect of low‐temperature hydrothermal alteration on the remanent magnetization of synthetic titanomagnetites: A case for acquisition of chemical remanent magnetization

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Theory and application of the Day plot (M_rs/M_sversusH_cr/H_c) 2. Application to data for rocks, sediments, and soils