Magnetic Lineations in the Shikoku Basin

Shih, T. C.

doi:10.2973/dsdp.proc.58.131.1980

Cited by 34 publications

(28 citation statements)

References 18 publications

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“…In SW Japan subducting Philippine Sea plate is young and warm. The age of the slab at the trench is estimated 15-25 Ma (Shih, 1980) and about 20 Ma by the magnetic anomalies (Okino et al, 1994). The calculated 3 He/ 4 He ratios vary from 0.40Ra to 3.4Ra, suggesting that medium-Ra is available in aqueous fluids derived from the descending slab in some case.…”

Section: Magma Aging Effect On Helium Isotopesmentioning

confidence: 99%

Geographical distribution of 3He/4He ratios and seismic tomography in Japan

Sano

Nakajima

2008

Geochem. J.

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The 3 He/ 4 He ratios (Ra) of natural gas, volcanic fluid, and groundwater are compiled in the Japanese Islands and their geographical distributions are discussed in the tectonic frame work of subduction zone together with preciselydetermined seismic velocity structures. In Northeastern (NE) Japan where typical island arc signatures are developed, there is a clear contrast of 3 He/ 4 He ratios perpendicular to the trench axis, low-Ra in the frontal arc and high-Ra in the volcanic arc. This may reflect the presence or absence of magma with high-Ra in the shallow crust. As a carrier of primordial helium, source melt may be generated in low-V zone of the wedge mantle by dehydration of Pacific slab at about 150 km deep and may flow upward sub-parallel to the slab, which is well constrained by S-wave velocity perturbation. In the Chugoku and Shikoku districts of Southwestern (SW) Japan, there is a geographical contrast of Ra similar to NE Japan except for the region at about 100 km from the volcanic front where medium-Ra was found. High-Ra observed in volcanic arc of the Chugoku district may be attributable to the mantle helium derived from the magma source generated below the Philippine Sea slab. Medium-Ra in the Shikoku district is explained by dehydration of the young slab with a moderate aging effect. These features are again consistent with the results of seismic tomography. In the Kinki district of SW Japan, anomalously high-Ra was observed in the frontal arc region that was called by "Kinki Spot". Since the high-Ra is located at much wider region from the volcanic front when compared with NE Japan, the melt generated below the Philippine Sea slab may penetrate into the fissure of the slab tear and may arrive at the shallow crust by upwelling flow.

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Section: Magma Aging Effect On Helium Isotopesmentioning

confidence: 99%

Geographical distribution of 3He/4He ratios and seismic tomography in Japan

Sano

Nakajima

2008

Geochem. J.

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“…The basement topography in the central part of the Shikoku Basin shows a north northwest-south southeasttrending topographic high and a chain of seamounts that runs approximately parallel to the magnetic anomalies. The central topographic high has been interpreted as a fossil spreading center, and the magnetic anomalies as well as previous drilling results indicate a spreading episode of Oligocene-Miocene age (25 to 15 Ma; Kobayashi and Nakada, 1978;Shih, 1980). A new interpretation of basement topography and magnetic anomalies obtained during the Kaiko Project (Kaiko I Research Group, 1986) showed a north-south trending spreading axis, active during the final stage of opening in the central region and producing a complex topographic mixture of north-south trending transform faults and northwest-southeast trending horst-graben features.…”

Section: Tectonic Setting Of the Nankai Troughmentioning

confidence: 99%

Sediment Deformation and Hydrogeology at the Nankai Accretionary Prism: Synthesis of ODP Leg 131 Shipboard Results

Taira¹,

Hill²,

Firth³

1991

Proceedings of the Ocean Drilling Program

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The Nankai accretionary prism is arguably the best-known clastic prism in the world. The main objective of ODP Leg 131 was to provide data on the deformational processes and associated hydrogeology of the prism. Such information can be incorporated into the existing geophysical and geological data set to characterize the evolution of sediments in this tectonic setting. The objective was approached by drilling Site 808, at which the frontal thrust and décollement of the prism toe were penetrated. Drilling also succeeded, for the first time in the history of ocean drilling, in penetrating the complete sedimentary sequence to basaltic basement, and with good core recovery. Both the frontal thrust and the décollement were clearly recognizable in the cored material. Bedding dips, faults, and shear bands analyzed in the cores confirm the pattern of deformation to be mainly due to northwest-southeast shortening. Below the décollement no significant deformation features were observed. Physical properties data show major discontinuities at the décollement, notably an increase in porosity below the décollement. This might indicate excess pore pressure in the subducted section. An increase in porosity below the frontal thrust is less marked and might reflect only the youthfulness of this feature. Attempts to make downhole measurements were severely hampered by unstable hole conditions, but useful constraints have been placed on the thermal regime, some calibration of laboratory physical properties to in-situ conditions has been provided, and in-situ stress and pore pressure were measured in the uppermost sediments. Evidence of channelized fluid flow is inconclusive because no vein structures were observed in the cores, no unequivocal geochemical anomalies indicative of flow were found, and thermal measurements are not significantly different from those predicted by a purely conductive heat-flow model. We conclude that dewatering probably occurs mainly through diffuse flow at this site.

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“…Analysis of magnetic anomalies suggests multiple episodes of Shikoku Basin spreading during the late Oligocene to middle Miocene (Kobayashi and Nakada, 1978;Shih, 1980). The history of the opening is mainly divided into two episodes: east-west spreading during 27-19 Ma and north-south spreading during 14-12 Ma (e.g., Chamot-Rooke et al, 1987).…”

Section: Geologic Settings Nankai Troughmentioning

confidence: 99%

Sedimentary Facies Evolution of the Nankai Forearc and Its Implications for the Growth of the Shimanto Accretionary Prism

Taira¹,

Ashi²,

Trough³

1993

Proceedings of the Ocean Drilling Program

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A combination of Deep Sea Drilling Project-Ocean Drilling Program drilling results and site survey data in the Shikoku Basin, Nankai Trough, and Nankai landward slope region provides a unique opportunity to investigate the sedimentary facies evolution in the clastic-dominated accretionary forearc. Here, we consider the facies evolution model based on the drilling results, IZANAGI sidescan images, and seismic reflection profiles.The sedimentary facies model of the Nankai forearc proposed in this paper is composed of two parts: the ocean floor-trenchlower slope sedimentary facies evolution and the upper slope to forearc basin sedimentary facies evolution. The former begins with basal pelagic and hemipelagic mudstones overlain by a coarsening upward sequence of trench turbidites which are, in turn, covered by slope apron slumps and lower slope hemipelagic mudstone. This assemblage is progressively faulted and folded into a consolidated accretionary prism that is then fractured and faulted in the upper slope region. Massive failure of the seafloor in the upper slope region produces olistostrome deposits that contain lithified blocks derived from older accretionary prism dispersed in a mud matrix. The contact between the older accretionary prism and the upper slope olistostrome is a submarine unconformity that is the first stratigraphic evidence for the exhumation of an older prism to the seafloor. The olistostrome beds are then overlain by forearc basin-plain mudstone and turbidites which are progressively covered by coarsening-upward delta-shelf sequences. An application of the forearc facies model to the Shimanto Belt was attempted in order to ensure feasibility of this model. Several characteristic lithologies observed in the Shimanto Belt can be interpreted with this model. The unconformities found in the Shimanto Belt were evaluated to provide an estimate for the exhumation rate of the prism. Comparison with independent measurement of exhumation rate provides a 0.5 to 1 km/m.y. vertical growth of the prism.

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Magnetic Lineations in the Shikoku Basin

Cited by 34 publications

References 18 publications

Geographical distribution of 3He/4He ratios and seismic tomography in Japan

Geographical distribution of 3He/4He ratios and seismic tomography in Japan

Sediment Deformation and Hydrogeology at the Nankai Accretionary Prism: Synthesis of ODP Leg 131 Shipboard Results

Sedimentary Facies Evolution of the Nankai Forearc and Its Implications for the Growth of the Shimanto Accretionary Prism

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