Stratigraphy and sedimentary facies of the Tertiary Shimizu and Misaki Formations in the southwestern part of Shikoku

Kimura, Koshi

doi:10.5575/geosoc.91.815

Cited by 15 publications

(11 citation statements)

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“…Although the R max value of 0.7–1.9% in the Early Miocene Misaki group overlying the Shimizu Formation ( Kimura 1985) is lower than that of the other formations around the granitic body, this has a higher temperature than that of the shelf basin sediment.…”

Section: Thermal Structural Analysismentioning

confidence: 92%

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Thermal structure and paleo‐heat flow in the Shimanto accretionary prism, Southwest Japan

Sakaguchi

1999

Island Arc

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Thermal structural analysis and paleo‐heat flow estimation provide clues to understanding the thermal evolution of the accretionary complex. The thermal structure and heat flow in the Jurassic Chichibu and Cretaceous to Tertiary Shimanto accretionary complex, Southwest Japan, have been investigated by vitrinite reflectance measurement and fluid inclusion analysis. As a result, the local and multistage metamorphisms were recognized as follows. First, the Tertiary complex around the Miocene Ashizuri granite underwent exposure to extra‐high temperatures. Second, the Okitsu Melange underwent exposure to higher temperatures than the surrounding strata and was formed concurrently with the Kula‐Pacific ridge subduction beneath the Japanese Islands in the Eocene. Finally, the thermal structure of most of the Cretaceous and southern Jurassic complexes is independent of the geologic structure, indicating that these areas suffered thermal overprint. Regional radiometric dating studies show that most of the Cretaceous Shimanto complex was heated in the Eocene; the thermal overprint might have occurred as a result of ridge subduction. The heat flow during peak heating was estimated to be 95–120 mW/m2 except for the Cretaceous Okitsu melange and the Cretaceous Nonokawa formation, north of the Okitsu Melange; a much higher value of heat flow of ~200 mW/m2 was estimated in the Okitsu Melange. An estimation of heat flow failed for the non‐okawa formation because thermal equilibrium between the fluid and rocks has not yet been reached. It is probable that the southern strata underwent a higher heat flow. Such a trenchward increase in heat flow resembles the present situation of the Nankai Trough, although the heat flow in the Eocene was much higher.

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Section: Thermal Structural Analysismentioning

confidence: 92%

“…1). These complexes are underlain unconformably by the shelf and forearc facies of the Cretaceous Monobegawa Group, Torinosu group, Doganaro formation, Uwagumi formation, Uwajima Group and Miocene Misaki Group ( Kimura 1985; Okamura 1992; Morino 1993).…”

Section: Geologic Settingmentioning

confidence: 99%

Thermal structure and paleo‐heat flow in the Shimanto accretionary prism, Southwest Japan

Sakaguchi

1999

Island Arc

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“…The best evidence for regional uplift prior to the Middle Miocene, as summarized by Sakai (1988) and Hibbard and Karig (1990b), comes from the unconformities that separate the Shimanto Belt from overlying fore-arc-basin successions, such as the Kumano Group (Kii Peninsula), the Shijujiyama Formation (Muroto Peninsula) and the Misaki Group (Hata Peninsula). We believe, however, that these contacts are submarine unconformities, particularly because the fore-arc and slope-basin successions grade up-section from basal units that were deposited at middle bathyal depths into shallow-water facies (Kimura 1985;Chijiwa 1988;Hisatomi 1988;Osozawa 1988). Submarine uplift of the Eocene-Oligocene accretionary prism almost certainly did occur, perhaps in response to underplating of the Oligocene-Miocene sediments (Fig.…”

Section: Thermal Overprint Of Palaeogene Cleavage?mentioning

confidence: 97%

Thermal evolution of the Tertiary Shimanto Belt, Muroto Peninsula, Shikoku, Japan

et al. 1992

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The Shimanto accretionary complex on the Muroto Peninsula of Shikoku comprises two major units of Tertiary strata: the Murotohanto Sub-belt (Eocene-Oligocene) and the Nabae Sub-belt (Oligocene-Miocene). Both sub-belts have been affected by thermal overprints following the peak of accretion-related deformation. Palaeotemperatures for the entire Tertiary section range from -140 to 315"C, based upon mean vitrinite reflectance values of 0.9-5.0%Rm. Values of illite crystallinity index are consistent with conditions of advanced diagenesis and anchimetamorphism. Illite/mica b, lattice dimensions indicate that burial pressures were probably no greater than 2.5 kbar. In general, levels of thermal maturity are higher for the Murotohanto Sub-belt than for the Nabae Sub-belt. The EoceneOligocene strata also display a spatial decrease in thermal maturity from south to north and this pattern probably was caused by regional-scale differential uplift following peak heating. Conversely, the palaeothermal structure within the Nabae Sub-belt is fairly uniform, except for the local effects of mafic intrusions at the tip of Cape Muroto. There is a paleotemperature difference of -90°C across the boundary between the Murotohanto and Nabae Sub-belts (Shiina-Narashi fault), and this contrast is consistent with approximately 1200 m of post-metamorphic vertical offset.Subduction prior to Middle Miocene probably involved the Kula or fused Kula-Pacific plate and the background geothermal gradient during the Eocene-Oligocene phase of accretion was -30-35"Ckm.Rapid heating of the Shimanto Belt evidently occurred immediately after a Middle Miocene reorganization of the subduction boundary. Hot oceanic lithosphere from the Shikoku Basin first entered the subduction zone at -15 Ma; this event also coincided with the opening of the Sea of Japan and the rapid clockwise rotation of southwest Japan. The background geothermal gradient at that time was -70"Ckm.Whether or not all portions of the inherited (Eocene-Oligocene) palaeothermal structure were overprinted during the Middle Miocene remains controversial.

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“…The best evidence for an early phase of uplift is the unconformity that separates the basal Misaki Group (~18 Ma) from the underlying Shimanto Belt (Kimura, 1985;Sakai, 1988). This contact probably is a submarine unconformity, however, separating the accretionary prism from overlying slope-basin deposits (similar to the basal Shijujiyama deposits of Muroto).…”

Section: Coeval Rocks In Southwest Japanmentioning

confidence: 99%

The effects of ridge subduction on the thermal structure of accretionary prisms: A Tertiary example from the Shimanto Belt of Japan

Underwood

Byrne²,

Hibbard³

et al. 1993

Geological Society of America Special Papers

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The Shimanto accretionary complex on the Muroto Peninsula of Shikoku comprises two major units of Tertiary strata: the Murotohanto subbelt (Eocene-Oligocene) and the Nabae subbelt (Oligocene-Miocene). Field-based structural analyses and laboratory measurements of thermal maturity show that both subbelts were affected by thermal overprints long after the initial stages of accretion-related deformation. Paleotemperatures for the entire Tertiary section range from about 140 to 315°C, based upon mean vitrinite reflectance values of 0.9 to 5.0%R m . In general, older rocks of the Murotohanto subbelt display higher levels of thermal maturity and better cleavage than rocks of the Nabae subbelt. The Murotohanto subbelt also displays a spatial decrease in thermal maturity from south to north, and this pattern probably was caused by regionalscale differential uplift following peak heating. Conversely, the paleothermal structure exposed within the Nabae subbelt is fairly uniform, except for the local effects of mafic intrusions at the tip of Cape Muroto. The most important structural discontinuity to display a large component of post-metamorphic vertical offset is the Shiina-Narashi fault; this out-of-sequence thrust forms the boundary between hanging-wall rocks of the Murotohanto subbelt and the younger Nabae subbelt. Rapid heating of the Shimanto Belt evidently occurred immediately after a middleMiocene reorganization of the subduction boundary of southwest Japan. Whether or •Present addresses: DiTullio, 326 12th St., Apt. 2L, Downloaded from 152 M. B. Underwood and Others not all portions of the inherited (Eocene-Oligocene) paleothermal structure were overprinted during the middle Miocene remains controversial. Subduction prior to middle Miocene time probably involved the Kula, or fused Kula/Pacific, Plate. Hot oceanic lithosphere from the Shikoku Basin back-arc spreading ridge first entered the subduction zone at approximately 15 Ma; this event also coincided with the opening of the Sea of Japan and the rapid clockwise rotation of southwest Japan. Middle Miocene thermal overprints elsewhere in the Shimanto Belt are spatially related to and, therefore, probably synchronous with widespread acidic magmatism, local mafic intrusions, and formation of anthracite coals in the forearc. The Kii Peninsula of Honshu appears to be the hottest spot along the strike of the subduction zone; this locality may well correspond to the collision point between the Shimanto accretionary complex and the central ridge of the Shikoku Basin. However, the spreading ridge probably was unstable and disorganized at the time of the collision, which allowed widespread, strike-parallel flux of mantle heat and magma into the accretionary prism. Apatite fission-track data show that most of the Eocene-Oligocene Shimanto strata experienced differential uplift and cooling through the 100°C isotherm shortly after the ridge-trench collision (11 to 8 Ma).The Shimanto Belt provides an excellent example of an ancient accretionary complex that does not follow the...

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Stratigraphy and sedimentary facies of the Tertiary Shimizu and Misaki Formations in the southwestern part of Shikoku

Cited by 15 publications

References 0 publications

Thermal structure and paleo‐heat flow in the Shimanto accretionary prism, Southwest Japan

Thermal structure and paleo‐heat flow in the Shimanto accretionary prism, Southwest Japan

Thermal evolution of the Tertiary Shimanto Belt, Muroto Peninsula, Shikoku, Japan

The effects of ridge subduction on the thermal structure of accretionary prisms: A Tertiary example from the Shimanto Belt of Japan

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