Magnetic Petrology and Magnetic Properties of Western Pacific Guyots: Implications for Seamount Paleopoles

Gee, J. S.; Nakanishi, Masao

doi:10.2973/odp.proc.sr.144.020.1995

Cited by 7 publications

(10 citation statements)

References 35 publications

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“…? and Gee and Nakanishi, 1995). The intensity of 10.7 A/m by Ueda (1985) is high as compared with our results and Ishikawa and Den (1984).…”

Section: Discussionsupporting

confidence: 89%

Three-dimensional magnetization vector inversion of a seamount

Kubota¹,

Uchiyama²

2005

Earth Planet Sp

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A three-dimensional non-uniform magnetic modeling is proposed to obtain information about a magnetization of a seamount, which was divided into many blocks modeled by layered and rectangular prisms, and parameters were assigned to each block describing magnetic three components. Our data were the magnetic total force on the sea. A set of linear observation equations was formulated in terms of three components of magnetization for each block. The solution was obtained by using the conjugate gradients method because of its fast and accurate advantages of calculation. In this inversion, a common set of three components was defined for several blocks to decrease the number of unknown parameters. A computer program has been tested with artificial data and applied to data of Daiichi Kashima Seamount observed during the first phase of the Kaiko project carried out with the R/V Jean Charcot in 1984. In the real application, the crustal structure was divided into three layers (top depth to 5 km depth, 5-6.5 km depth and 6.5-8 km depth). The result of the inversion shows that the top portion and the submerged western half of this seamount are covered with the low magnetization layers, and in the middle layer (5-6.5 km depth) of eastern half side, declinations, inclinations and intensities are almost northward, 15• and 3-5 A/m, respectively. In the third layer (6.5-8 km depth), the reverse magnetizations are revealed in the southeastern and northern sides of Daiichi Kashima Seamount and around Katori Seamount. These reverse magnetizations may reflect part of the magnetic lineations of the Pacific plate.

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“…? and Gee and Nakanishi, 1995). The intensity of 10.7 A/m by Ueda (1985) is high as compared with our results and Ishikawa and Den (1984).…”

Section: Discussionsupporting

confidence: 89%

Three-dimensional magnetization vector inversion of a seamount

Kubota¹,

Uchiyama²

2005

Earth Planet Sp

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“…However, it is widely accepted that the secondary magnetization makes only a minor contribution to the total magnetization in comparison with the thermal one (Hildebrand and Staudigel, 1986;Sager, 1987). The opposite results, which indicate the significant contribution of the secondary and induced magnetizations to paleomagnetism of the oceanic rocks, are also presented (Gee et al, 1993;Gee and Nakanishi, 1995). However, in the present study, the au-thor accepts the former concept, and then points out the cases which show the contribution of secondary magnetization for individual cases.…”

Section: Resultssupporting

confidence: 51%

Paleomagnetism of seamounts in the West Philippine Sea as inferred from correlation analysis of magnetic anomalies

Ueda

2014

Earth Planet Sp

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Magnetization vectors of seamounts and edifices in the West Philippine Sea were determined with a direct searching method in the space domain using the topography and magnetic anomaly data at the sea surface. The data analyzed were surveyed by the Hydrographic and Oceanographic Department of Japan since the 1980s. Several seamounts in the eastern part of the Minami Daito Basin are magnetized in the N70 • W to N80 • W directions with negative shallow inclinations, whereas edifices of the Kyushu-Palau Ridge have directions of N30 • W with downward inclinations. The paleolatitude of the Oki-Daito Ridge as a whole is 4.4 • S±11.0 • and that of the Amami Plateau and the Daito Ridge, 15.1 • N±4.6 • and 20.1 • S±8.2 • , respectively. These results are inconsistent with the proposed clockwise rotation of the West Philippine Sea exceeding 80 •. Furthermore, the results also suggest that the Oki Daito Ridge was generated in the Southern Hemisphere and then migrated northward. The large shortening between the Oki-Daito Ridge and the Amami-Daito Ridge regions may suggest the convergence boundary between them.

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“…In natural samples magnetic evidence for maghemite with a thermal stability around 870 K has been reported from basaltic rocks (e.g. Gee & Nakanishi 1995; Chévrier et al 2006) and from loess sediments (e.g. Spassov et al 2003).…”

Section: Introductionmentioning

confidence: 99%

High temperature stability of natural maghemite: a magnetic and spectroscopic study

Gehring¹,

Fischer²,

Louvel³

et al. 2009

Geophysical Journal International

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S U M M A R YA combined magneto-mineralogical approach is used to diagnose maghemitization in magnetic grains of basaltic rock fragments from sand dunes in the Namibian desert in SW Africa. Data were obtained from static magnetic analysis, ferromagnetic resonance (FMR) spectroscopy, micro-Raman spectroscopy and electron microscopy. Micro-Raman spectroscopy showed that the magnetic grains in the lithic fragments form oxidative solid solution series with magnetite and maghemite as end-members. The five active Raman modes at 712, 665, 507, 380 and 344 cm −1 indicate that maghemite in the magnetic grains has well-defined structural properties. The FMR spectral analysis provides evidence for long-range dipolar coupling, which suggests intergrowth of the magnetic phases of the oxidative solid solution series. Thermomagnetic experiments and hysteresis measurements reveal a Curie temperature of about 890 K for this maghemite. Upon heating to 970 K part of the maghemite is altered to thermodynamically more stable hematite. After selective thermal decomposition of the maghemite in a protected atmosphere, the remaining magnetic phase has a Curie temperature of 850 K, characteristic for magnetite. The unique thermal stability of this natural maghemite above its Curie temperature is explained by the well-defined mineral structure, which formed during slow oxidative alteration of magnetite under arid climate conditions.

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Magnetic Petrology and Magnetic Properties of Western Pacific Guyots: Implications for Seamount Paleopoles

Cited by 7 publications

References 35 publications

Three-dimensional magnetization vector inversion of a seamount

Three-dimensional magnetization vector inversion of a seamount

Paleomagnetism of seamounts in the West Philippine Sea as inferred from correlation analysis of magnetic anomalies

High temperature stability of natural maghemite: a magnetic and spectroscopic study

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