Inferences on the Magnetic Domain State of Leg 37 Basalts

Murthy, G.S.; Deutsch, E.R.; Patzold, R.R.

doi:10.2973/dsdp.proc.37.127.1977

Cited by 3 publications

(3 citation statements)

References 9 publications

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“…Specimens dominated by stable single-domain grains do not exhibit loops. Neel [1955] suggested that multidomain grains should exhibit Rayleigh loops; however, with the exception of certain intrusive rocks [Murthy and Patzold, 1982], specimens dominated by multidomain grains apparently do not produce loops visible with the currently available apparatus [Murthy et al, 1977]. The suggestion that Rayleigh loops may not necessarily be indicative of the properties of the bulk of the magnetic grains in a specimen [Clark and Schmidt, 1981] does not invalidate these assumptions.…”

Section: Quadrature Susceptibilitymentioning

confidence: 99%

Correlation between Rayleigh loops and frequency‐dependent and quadrature susceptibility: Application to magnetic granulometry of rocks

Bloemendal¹,

Barton²,

Radhakrishnamurthy³

1985

J. Geophys. Res.

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We report the results of measurements of frequency‐dependent and quadrature low‐field magnetic susceptibility of basalt specimens showing different types of low‐field hysteresis (Rayleigh) loop. A correlation among the three techniques is demonstrated, with specimens showing broad and constricted loops exhibiting relatively high‐frequency dependence of susceptibility and a high ratio of quadrature to in‐phase susceptibility. This result has implications for magnetic granulometry studies of rocks. Broad and constricted Rayleigh loops indicate the significant contribution of hyperfine grains to the magnetic properties of specimens; however, with the current instrumentation, low‐field hysteresis loop measurements are restricted to relatively strongly magnetic specimens. For weakly magnetic rocks and sediments, measurement of the frequency dependence of susceptibility or the quadrature susceptibility permits rapid identification of specimens in which hyperfine grains significantly influence the magnetic properties.

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Section: Quadrature Susceptibilitymentioning

confidence: 99%

Correlation between Rayleigh loops and frequency‐dependent and quadrature susceptibility: Application to magnetic granulometry of rocks

Bloemendal¹,

Barton²,

Radhakrishnamurthy³

1985

J. Geophys. Res.

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“…It does not follow that oxidized basalts normally should not have a distinctive magnetic signature. For example, fine-grained basalts from DSDP Leg 37 include prominently a magnetic sub-type characteristic of hghly cation-deficient magnetite or of maghemite in basalts (see Figs l(d), 2(e), 3(e) and Murthy, Deutsch & Patzold 1976). W e the properties of this sub-type were not observed in untreated Leg 34 samples, they do resemble the properties of originally type 2 samples that became oxidized through heating in the laboratory (Fig.…”

mentioning

confidence: 93%

“…Laboratory MD-type curves are characteri'stic of artificial, coarse magnetite samples and of some (generally older) volcanic rocks, but were not observed on any Nazca Plate core, and Fig. l(c) is the only case found among 46 samples from Leg 37 (Murthy, Deutsch & Patzold 1976). Since, moreover, Johnson & Hall attribute type 1 properties to high-titanium (x = 0.62) stoichiometric TiMt, one would have expected to obtain k-T curves of multidomain type like Fig.…”

mentioning

confidence: 93%

A comment on: 'A detailed rock magnetic and opaque mineralogy study of the basalts from the Nazca Plate' by H. P. Johnson and J. M. Hall

Deutsch

Pätzold

1980

Geophys J Int

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Johnson & Hall (1978) have discussed the results of magnetic measurements and reflected light microscopy of basalts from Legs 34 and 16 of the Deep Sea Drilling Project. Their data form two main groups: (1) Samples from unoxidized or slightly oxidized massive flows tend to be associated with low Curie points (T, < 200°C) and small median demagnetizing fields and with relatively high values of intensity of natural remanence (Jn), of saturation magnetization (J"), of low-field susceptibility ( k ) and of overall ferromagnetic grain size and grain concentration. (2) In the fine-grained pillow lavas T, is in the range 225-40Ooc.

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Magnetic effects of maghemitization of oceanic crust

Prévot¹,

Lecaille²,

Mankinen³

1981

J. Geophys. Res.

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Both theoretical considerations and available experimental results indicate that magnetic effects of maghemitization are strongly dependent on the grain size of the originally unoxidized titanomagnetite. Maghemitization of single‐domain titanomagnetite results in a decrease in coercivity, an increase in susceptibility, and a large decrease in Q ratio. Maghemitization of multidomain titanomagnetite results in an increase in coercivity, a decrease in susceptibility, and no large changes in Q ratio. Single‐domain titanomagnetite is probably resistant to the development of a chemical remanent magnetization (CRM), whereas multidomain titanomagnetite can acquire a CRM during maghemitization. The behavior of pseudo‐single‐domain titanomagnetite, which is the main carrier of remanence in submarine extrusive rocks, is investigated by comparing the magnetic properties of the French‐American Mid‐Ocean Undersea Study (FAMOUS) (less than 0.1 m.y. old) and the Leg 37 (3.5 m.y. old) pillow basalts recovered from the Mid‐Atlantic Ridge near 37°N. Combining electron microprobe analyses, Curie temperature measurements, and cell edge determinations, we find that the FAMOUS rocks are already oxidized (z = 0.38), possibly as a result of some high‐temperature maghemitization during cooling of the magma. Comparison with the more highly oxidized (z = 0.7) Leg 37 pillow basalts indicates that low‐temperature maghemitization of such rocks does not result in appreciable changes of coercivity and susceptibility, although the Q ratio does decrease and CRM seems to be acquired. Such a CRM could account for the anomalously low magnetic inclinations observed at most of the Leg 37 sites.

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Inferences on the Magnetic Domain State of Leg 37 Basalts

Cited by 3 publications

References 9 publications

Correlation between Rayleigh loops and frequency‐dependent and quadrature susceptibility: Application to magnetic granulometry of rocks

Correlation between Rayleigh loops and frequency‐dependent and quadrature susceptibility: Application to magnetic granulometry of rocks

A comment on: 'A detailed rock magnetic and opaque mineralogy study of the basalts from the Nazca Plate' by H. P. Johnson and J. M. Hall

Magnetic effects of maghemitization of oceanic crust

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