Magnetic Anomalies and Tectonic Evolution of the Shikoku Inter-Arc Basin

Kobayashi, Kazuo; Nakada, Masayuki

doi:10.4294/jpe1952.26.supplement_s391

Cited by 131 publications

(73 citation statements)

References 22 publications

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“…The eastern margin of the basin consisted of Eocene arc volcanic rocks, including boninites, that form the basement of Jie outer-arc high at Leg 125 Sites 782 and 786 (Fryer, Pearce, et al, 1990). Rocks that were to the west of this basin in the Oligocene were split into two parts by the Miocene opening of the Shikoku Basin: one part is beneath the modern volcanic front; the other is beneath the Palau-Kyushu Ridge (Kobayashi and Nakada, 1979). These volcanic rocks are also Eocene, as proved by a radiometric date of 48.5 ± 1.4 Ma for volcanic rocks of the Palau-Kyushu Ridge (Matsuda, 1985).…”

Section: Introductionmentioning

confidence: 97%

Sedimentology of Deep-Water Volcaniclastics, Oligocene Izu-Bonin Forearc Basin, Based on Formation MicroScanner Images

Hiscott¹,

Colella²,

Pezard³

et al. 1992

Proceedings of the Ocean Drilling Program

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Three sites were drilled in the Izu-Bonin forearc basin during Ocean Drilling Program (ODP) Leg 126. High-quality formation microscanner (FMS) data from two of the sites provide images of part of a thick, volcaniclastic, middle to upper Oligocene, basin-plain turbidite succession. The FMS images were used to construct bed-by-bed sedimentary sections for the depth intervals 2232-2441 m below rig floor (mbrf) in Hole 792E, and 4023^330 mbrf in Hole 793B. Beds vary in thickness from those that are: near or below the resolution of the FMS tool (2.5 cm) to those that are 10-15 m thick. The bed thicknesses are distributed according to a power law with an exponent of about 1.0. There are no obvious upward thickening or thinning sequences in the bed-by-bed sections. Spaced packets of thick and very thick beds may be a response to (1) low stands of global sea level, particularly at 30 Ma, (2) periods of increased tectonic uplift, or (3) periods of more intense volcanism.Graded sandstones, most pebbly sandstones, and graded to graded-stratified conglomerates were deposited by turbidity currents. The very thick, mainly structureless beds of sandstone, pebbly sandstone, and pebble conglomerate are interpreted as sandy debris-flow deposits. Many of the sediment gravity flows may have been triggered by earthquakes. Long recurrence intervals of 0.3-1 m.y. for the very thickest beds are consistent with triggering by large-magnitude earthquakes (M = 9) with epicenters approximately 10-50 km away from large, unstable accumulations of volcaniclastic sand and ash on the flanks of arc volcanoes.Paleocurrents were obtained from the grain fabric of six thicker sandstone beds, and ripple migration directions in about 40 thinner beds; orientations were constrained by the FMS images. The data from ripples are very scattered and cannot be used to specify source positions. They do, however, indicate that the paleoenvironment was a basin plain where weaker currents were free to follow a broad range of flow paths. The data from sandstone fabric are more reliable and indicate that turbidity currents flowed toward 150° during the time period from 28.9 to 27.3 Ma. This direction is essentially along the axis of the forearc basin, from north to south, with a small component of flow away from the western margin of the basin.

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Section: Introductionmentioning

confidence: 97%

Sedimentology of Deep-Water Volcaniclastics, Oligocene Izu-Bonin Forearc Basin, Based on Formation MicroScanner Images

Hiscott¹,

Colella²,

Pezard³

et al. 1992

Proceedings of the Ocean Drilling Program

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“…New subduction of the Philippine Sea plate began from the south to the north under the Kuroshio Paleoisland mass of the Southwest Japan arc. Opening of the Shikoku Basin in the Oligocene and Early Miocene time has been well clarified (KOBAYASHI and NAKADA, 1978;KOBAYASHI, 1983). It was followed by off-ridge volcanism in the basin, subduction of the new slab of the Shikoku Basin, and upward intrusion of magma through the remnant fissure of transform fault of the Shikoku Basin opening.…”

Section: Geotectonic History Of the Northern Philippine Seamentioning

confidence: 99%

Continental Slope Structural High Igneous Activity and Its Bearing on the Geotectonic History of the Philippine Sea

Shiki

Miyake²

1988

J,Phys,Earth

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“…The lithosphere beneath the Philippine Sea, called the Philippine Sea plate, presently moves approximately toward the west-northwest and sinks down at trenches constituting the other boundaries of the Philippine Sea plate, such as the Ryukyu and Philippine Trenches. The seismological structure of the crust generally shows an oceanic nature (MURAUCHI et al, 1968), and also magnetic lineations have been recognized in some places (KOBAYASHI and NAKADA, 1978;ISEZAKI and MIKI, 1978).…”

Section: Tectonic Settingmentioning

confidence: 99%

Electrical conductivity structure beneath the northwestern philippine sea as inferred from the island effect on Minami-Daito Island.

Honkura

Isezaki

Yaskawa

1981

J. geomagn. geoelec

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Observations of short-period geomagnetic variations were carried out at three sites on Minami-daito Island in the northwestern Philippine Sea. The observed results clearly show the island effect; anomalous Z variations on the island, particularly characterized by a reversal of sign in Z variations between northern and southern stations for north-south magnetic fields. Response and current functions are determined from transfer function A obtained for the period range from 7 to 240 min.Numerical calculations of the island effect made on the basis of thin-sheet approximation can well account for the anomalous Z variations. Then, the response or current function obtained from the observed results is compared with those determined from the results of numerical calculations for underground conductivity models. It is concluded that a highly conducting layer exists at a likely depth range from 80 to 120 km beneath the northwestern Philippine Sea where Minami-daito Island is located. The conductivity of the layer is estimated as 0.5 S/m or so.

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Magnetic Anomalies and Tectonic Evolution of the Shikoku Inter-Arc Basin

Cited by 131 publications

References 22 publications

Sedimentology of Deep-Water Volcaniclastics, Oligocene Izu-Bonin Forearc Basin, Based on Formation MicroScanner Images

Sedimentology of Deep-Water Volcaniclastics, Oligocene Izu-Bonin Forearc Basin, Based on Formation MicroScanner Images

Continental Slope Structural High Igneous Activity and Its Bearing on the Geotectonic History of the Philippine Sea

Electrical conductivity structure beneath the northwestern philippine sea as inferred from the island effect on Minami-Daito Island.

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