Some Magnetic Properties of Some Leg 37 Samples

Brecher, A.; Atwater, T.; Stein, J; Carter, E.

doi:10.2973/dsdp.proc.37.119.1977

Cited by 3 publications

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“…Although the remanence is the dominant magnetization component in Holes 470, 470A, and 472, induced magnetization components become dominant at Sites 469, 471, and 473. The Q n ratios also suggest (Brecher et al, 1977;Petersen et al, 1979) that the remanence of the basalts from Holes 470, 470A, and 472 is the result of fine-grain carriers (Q > 1; single or pseudo-single domain grains), whereas coarse-grain carriers {Q< 1; multi-domain grains) are responsible at the other three sites. Hamano et al (1979) have observed an inverse correlation between susceptibility and NRM intensity.…”

Section: Coercive Force (H C ) Remanent Coercivementioning

confidence: 93%

“…The magnetic susceptibility x of Leg 63 samples ranges from 1.5 to 54 × I0" 3 emu cm" 3 oe-1 . Many samples from Sites 469, 471, and 473 show rather high susceptibility values, compared to most oceanic basalts and massive flows (e.g., Lowrie, 1974;Lowrie and Israfil, 1974;Lowrie and Hayes, 1975;Brecher et al, 1977;Petersen et al, , 1979Hamano et al, 1979).…”

Section: Coercive Force (H C ) Remanent Coercivementioning

confidence: 99%

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Magnetic Properties of Igneous Rocks from Deep Sea Drilling Project Leg 63

Verma¹,

Banerjee²

1981

Initial Reports of the Deep Sea Drilling Project

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This study reports the magnetic properties of 30 samples of igneous rocks recovered from Sites 469 through 473 of Leg 63 of the Deep Sea Drilling Project. Such studies are relevant for determining the thickness and composition of the source layer of the marine magnetic anomalies. These studies are also relevant to the study of ophiolites, in which direct comparison of magnetic properties can lead to important inferences (e.g., Butler et al., 1976; Levi et al., 1978; Beske-Diehl and Banerjee, 1979). We made routine measurements of Paleomagnetism on all samples. The magnetic properties reported here include the following: 1) Intensity and stability of natural remanent magnetization (NRM). 2) Intensity and stability of anhysteretic remanent magnetization (ARM). 3) Intensity and stability of viscous remanent magnetization (VRM). 4) Saturation magnetization (M s). 5) Hysteresis parameters, i.e., saturation remanent magnetization (M r), the ratio (M r /M s) of saturation remanent magnetization to saturation magnetization, coercive force (H c), remanent coercive force (H cr), and initial and high-field susceptibilities (x, and x P) 6) Weak-field susceptibility (x). 7) Thermomagnetic properties, i.e., Curie temperature (7^.) and thermomagnetic curve characteristics. EXPERIMENTAL METHODS We measured the intensity and stability of NRM, ARM, and VRM on a Schonstedt spinner magnetometer coupled to a Hewlett-Packard computer and a Schonstedt single-axis alternating field demagnetizer. For the acquisition of ARM we applied a lOOQπoe alternating field (H) in the presence of a steady 1-oe direct field (H) and then reduced the alternating field (A.F.) slowly to zero oe. We then normalized the measured ARM intensity to 0.5 oe by dividing the measured value by 2; this was done so that the NRM and ARM intensities could be compared. We studied the acquisition of VRM in all samples by monitoring the magnetization acquired in 0.5 oe direct field for periods ranging from 15,000 to 28,800 min. For each sample we made 10 or more measurements of remanence and computed the VRM component.

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Section: Coercive Force (H C ) Remanent Coercivementioning

confidence: 93%

Section: Coercive Force (H C ) Remanent Coercivementioning

confidence: 99%

Magnetic Properties of Igneous Rocks from Deep Sea Drilling Project Leg 63

Verma¹,

Banerjee²

1981

Initial Reports of the Deep Sea Drilling Project

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“…These authors attribute this behavior to multidomain (MD) and pseudo-single domain (PSD) contributions to the total VRM. Other authors do not see multi-stage acquisition curves [Wayman and Evans, 1977;Brecher et al, 1977]. Dunlop and Hale [1977], using vis-and cell parameter versus z data [Ozima and Sakamoto, 1971;Readman and O'Reilly 1972;Nishitani, 1979;Keefer and Shive, 1981].…”

mentioning

confidence: 99%

A comparison of the magnetic properties of synthetic titanomaghemites and some oceanic basalts

Moskowitz¹,

Banerjee²

1981

J. Geophys. Res.

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The variation of some magnetic properties of (1) synthetic titanomaghemites and (2) oceanic basalts from DSDP site 417 D as a function of grain size and oxidation is presented. The synthesis of the initial titanomagnetite (x = 0.6) was carried out, using controlled fugacity and self-buffering techniques. Singlephase titanomaghemites were produced by heating the titanomagnetite in air at low temperatures (<350øC). The magnetic properties studied on the synthetic titanomagnetite (grain size --, 1/•m) show the following variations with increasing degrees of oxidation (0 _< z <_ 0.6): (1) Curie temperature (Tc) increases, (2) saturation magnetization (Js) at room temperature increases, (3) J, measured at 77øK decreases for z •< 0.3 and then increases for 0.3 < z • 0.6, (4) bulk and reinanent coercivities (He and Hr) increase slightly initially (z < 0.2) and then decrease at both room temperature and 77•'K, (5) susceptibility (Xo) decreases for z • 0.3 and then increases, (6) the magnetic viscosity acquisition and decay coefficients (Sa and Sa) increase and (7) the median destructive fields for an anhystretic reinanent magnetization and a viscous reinanent magnetization increase for z •< 0.3 and then decrease. These magnetic data also suggest that the synthetic titanomaghemites are pseudo-single domained (PSD) and with increasing degrees of oxidation these PSD grains become more SD-like. The basalt samples from site 417D are divided into fine-grained pillow basalts and coarse-grained massive flows. Most of the magnetic properties measured are distinctly different between these two groups. The magnetic data indicate that the domain states of these basalts are probably PSD. Although it is difficult to separate the effects of grain size and oxidation on the magnetic properties of these basalts, it appears that grain size effects predominate. A preliminary investigation of the magnetic viscosity of the synthetic and oceanic titanomaghemites suggests that a combination of thermally activated and diffusive magnetic viscosity is responsible for their viscous behavior. Finally, we will discuss the roles of grain size and oxidation variation in oceanic basalts and their separate and combined effects on their magnetic behavior. vasiveness of low-temperature oxidation and its effect on their magnetic properties [Marshall and Cox, 1972; Johnson and Hall, 1978; Marshall, 1978]. A degradation of the magnetic signature of the oceanic crust with distance from the ridge seems to be associated with this low-temperature (lt) oxidation. Stoichiometric titanomagnetite (Fe3_xTixO4) with a restricted range of composition around x --0.6 -0.65 is ubiquitous in almost all young (<1 m.y.) submarine basalts [Johnson and Hall, 1978; Marshall, 1978; Pr•vot et al., 1979]. Subsequent to formation, the titanomagnetite is subjected to various degrees of It oxidation, producing single-phase titanomaghemite [Marshall and Cox, 1972; Ozima et aL, 1974; Marshall, 1978; Pr•vot et al., 1979]. Many studies indicate that oxidation of submarine basalt occurs re...

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Magnetization of the oceanic crust

Johnson¹

1979

Reviews of Geophysics

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Introduction.The ¾ine-Matthew8 [1963] model of the magnetic structure of the igneous oceanic crust, in which basement is considered to be made up of alternating normal and reverse magnetic polarity blocks with a one-to-one match with linear marine magnetic anomalies, has received wide acceptance in the geological and geophysical community.Comparison of the results from studies of samples obtained by dredging, submersible, and shallow drilling, with magnetic anomaly inversion and modeling are generally consistent with this model if the sections of magnetic crust are considered relatively thin --of the order of a kilometer in vertical thickness. However, work that has taken place in the last four years seems to indicate that the magnetic structure of the oceanic crust is a great deal more complicated than originally envisaged. Recent studies of the oceanic basement basalt recovered by the GLOMAR CHALLENGER, particularly from deep basement holes in the Atlantic, have indicated that the net magnetization of the upper 600 meters of igneous crust may s in some places, appear to be insufficient to contribute much to the overlying anomaly amplitudes.A number of phenomena are responsible for this apparent inadequate magnetization, including polarity reversals in vertical crustal sections, non-dipolar magnetic directions, pervasive low-temperature alteration of the magnetic minerals with the corresponding decrease in remanent magnetization, and the presence of even occasional plutonic rocks within the upper volcanic rock units.This review and the following bibliography will try to describe some of the studies that have had a major impact on our understanding of the magnetization of the oceanic crust, and also some of the models that have resulted from these studies. Generally only those investigations that have addressed the problem of the source of the linear marine magnetic anomalies will be referred here.Papers that use magnetic anomalies to solve tectonic problems as well as those which are largely concerned with rock magnetics will be discussed elsewhere in this volume. Previous reviews by Lowtie [1974], BZak•Zy •t aZ. [1975], and Larson [1975] describe the pre-1974 papers on the subject of oceanic crustal magnetization, and two excellent review articles (Har•i8om, 1976; Low•, 1977) have recently been published. An entire issue of the Journal of Geophysical Research (81, pp. 4041 to 4380, 1976) was devoted to papers on problems associated with the structure of the oceanic crust. magnetization at Cambridge, England during September, 1978. The last four years have provided several direct tests of the Vine-Matthews hypothesis --a sufficient number at least to see some of the difficulties associated with the geological magnetic tape recorder. A number of attempts at deep crustal drilling by the GLOMAR CHALLENGER, beginning somewhat modestly with Leg 34 and followed by the more successful penetration of nearly 600 meters in the Atlantic by Legs 37 and 45, and over 400 meters by Leg 46, have provided a look at the previousl...

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Some Magnetic Properties of Some Leg 37 Samples

Cited by 3 publications

References 0 publications

Magnetic Properties of Igneous Rocks from Deep Sea Drilling Project Leg 63

Magnetic Properties of Igneous Rocks from Deep Sea Drilling Project Leg 63

A comparison of the magnetic properties of synthetic titanomaghemites and some oceanic basalts

Magnetization of the oceanic crust

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