Occurrence and geochemistry of greenstones from the Makimine Formation in the Upper Cretaceous Shimanto Supergroup in Kyushu, Japan.

和雄, 君波; 純夫, 宮下

doi:10.5575/geosoc.98.391

Cited by 20 publications

(5 citation statements)

References 13 publications

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“…The Makimine mélange has biostratigraphically determined ages of Santonian to Campanian in eastern Kyushu and Turonian to Santonian in western Kyushu (Teraoka & Okumura, 1992). Vitrinite reflectance is consistent with maximum paleotemperatures of 130–150°C, 170–200°C, and 340°C for the Lower Mugi, Upper Mugi, and Makimine, respectively (Ikesawa et al., 2005; Kiminami & Ohno, 1999; Ohmori, 1999). These temperatures of 130°C–340°C span the range of the seismogenic zone (Hyndman et al., 1997).…”

Section: Geological Settingmentioning

confidence: 60%

“…The mélange zones, which are stratally disrupted during underthrusting (Fisher & Byrne, 1987), are subsequently imbricated during duplex accretion, with faults marked by basaltic greenstones in the hanging wall and stratally disrupted sand‐shale lithologies of the mélange in the footwall (Kimura et al., 2012; Kitamura & Kimura, 2012; Yamaguchi et al., 2012). Vitrinite reflectance and fluid inclusion analyses show evidence that the mélange zones experienced temperature conditions that are expected within the seismogenic zone of active subduction zones (Ikesawa et al., 2005; Kiminami & Ohno, 1999; Matsumura et al., 2003; Ohmori, 1999). In this study, we concentrate on three mélange belts in the northern Shimanto sub‐belt that collectively preserve a record of paleotemperatures that spans the full range, from the updip to the downdip boundaries, of the seismogenic zone: the Lower Mugi, Upper Mugi, and Makimine mélanges (Figures 1b and 1c).…”

Section: Geological Settingmentioning

confidence: 99%

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Constraints on Element Mobility During Deformation Within the Seismogenic Zone, Shimanto Belt, Japan

Ramirez¹,

Smye

Fisher

et al. 2021

Geochem Geophys Geosyst

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Subduction interfaces exhibit a variety of slip behaviors, including megathrust and slow earthquakes. Field observations are consistent with crack‐seal deformation, in which tensile cracks are sealed by fluid‐transported solute. However, there are few constraints on the mass fluxes and length and time scales of such deformation and attendant increases in cohesion within the seismogenic zone. Here, we present a systematic geochemical investigation of mass transport associated with development of crack‐seal veins in the Shimanto Belt—an accretionary complex that preserves a record of plate boundary slip behavior at temperatures relevant to the seismogenic zone: 150–350°C. These mélanges show evidence for shear across decameter‐scale zones of deformation dominated by anastomosing scaly fabrics and pervasive veins. We use meso‐ and microstructural observations with geochemical observations of scaly fabrics and crack‐seal veins to evaluate the role of silica redistribution in healing fracture porosity along the plate interface and modulating slip behavior. Crack‐seal veins contain primarily quartz with albite and calcite, and vein textures provide evidence for partial sealing. Bulk rock analyses determined that the amount of phyllosilicates, specifically illite and chlorite, increases with temperature. A simple mass‐balance model based on the immobile chemical component TiO2 shows a systematic trend in mobility for all three mélanges and increased element mobility as a function of temperature. Scaly fabrics and veins show compositional evidence for locally sourced mineral redistribution. This study supports a model where development of scaly slip surfaces and fracture healing through temperature‐dependent mineral redistribution can impact slip behavior and fluid flow along the subduction plate interface.

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Section: Geological Settingmentioning

confidence: 60%

Section: Geological Settingmentioning

confidence: 99%

Constraints on Element Mobility During Deformation Within the Seismogenic Zone, Shimanto Belt, Japan

Ramirez¹,

Smye

Fisher

et al. 2021

Geochem Geophys Geosyst

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“…The chert and phyllite are commonly directly overlain by basaltic rocks that consist of pillow and massive lava, dolerite, volcaniclastics, and tuff. The dolerites are intruded into pelitic rock (Kiminami & Miyashita 1992; Kiminami et al. 1994).…”

Section: Geological and Tectonic Settingsmentioning

confidence: 99%

Metamorphic and cooling history of the Shimanto accretionary complex, Kyushu, Southwest Japan: Implications for the timing of out‐of‐sequence thrusting

Hara

Kimura

2008

Island Arc

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Illite crystallinity, K–Ar dating of illite, and fission‐track dating of zircon are analyzed in the hanging wall (Sampodake unit) and footwall (Mikado unit) of a seismogenic out‐of‐sequence thrust (Nobeoka thrust) within the Shimanto accretionary complex of central Kyushu, southwest Japan. The obtained metamorphic temperatures, and timing of metamorphism and cooling, reveal the tectono‐metamorphic evolution of the complex, and related development of the Nobeoka thrust. Illite crystallinity data indicate that the Late Cretaceous Sampodake unit was metamorphosed at temperatures of around 300 to 310°C, while the Middle Eocene Mikado unit was metamorphosed at 260 to 300°C. Illite K–Ar ages and zircon fission‐track ages constrain the timing of metamorphism of the Sampodake unit to the early Middle Eocene (46 to 50 Ma, mean = 48 Ma). Metamorphism of the Mikado unit occurred no earlier than 40 Ma, which is the youngest depositional age of the unit. The Nobeoka thrust is inferred to have been active during about 40 to 48 Ma, as the Sampodake unit started its post metamorphic cooling after 48 Ma and was thrust over the Mikado unit at about 40 Ma along the Nobeoka thrust. These results indicate that the Nobeoka thrust was active for more than 10 million years.

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“…Its areal extent is more than 80 × 20 km. This conclusion is consistent with a subduction of young, hot slab, as has been proposed based on other geological observations for the CSAC, such as the mode of occurrence of greenstones (Sakai & Kammera, 1981; Kiminami & Miyashita, 1992; Kiminami et al ., 1994), homogenization temperatures of the fluid inclusions (Sakaguchi, 1996; Ohmori et al ., 1997), and illite crystallinity (Awan & Kimura, 1996).…”

Section: Application To Regional Prehnite‐bearing Metamorphic Rocks Omentioning

confidence: 99%

“…Finally, we apply the results of the simple thermal modelling to low grade metamorphism of the Cretaceous Shimanto Accretionary Complex (CSAC) in Kyushu, Japan. The mode of the greenstone occurrence in the CSAC indicates that some basaltic protoliths were both intruded into and extruded upon unconsolidated terrigenous clastic sediments (Sakai & Kammera, 1981; Kiminami & Miyashita, 1992; Kiminami et al ., 1994). This observation suggests that an active ridge and young slab were descending during the formation of the CSAC.…”

Section: Introductionmentioning

confidence: 99%

Thermal modelling in shallow subduction: an application to low P/T metamorphism of the Cretaceous Shimanto Accretionary Complex, Japan

Miyazaki

Okumura

2002

Journal Metamorphic Geology

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This paper presents the results of numerical modelling to investigate the regional occurrence of prehnite‐bearing metamorphic rocks at shallow levels in subduction zones. The modelling assumes a simple geometrical configuration in which the thermal structure in a prism is controlled by boundary conditions at the top and base of the prism. It is expected that the predominant metamorphic facies in a prism will change with decreasing age of the descending slab. The results of thermal modelling show that the facies boundary between pumpellyite–actinolite and prehnite–actinolite facies (including prehnite–pumpellyite facies) overlaps with an array of P–T conditions in the prism when the age of a descending slab is younger than 10 Myr. This implies that the change of the predominant metamorphic facies from pumpellyite–actinolite to prehnite–actinolite facies will switch drastically. The critical age of the switch depends on subduction parameters. In particular, the critical age of the descending slab is <5 Myr in the case of no shear heating, with a subduction rate of v=75–200 mm y−1 and subduction angle of θ=5–15°. For shear heating (constant shear stress=30 MPa) with a subduction rate of v=75 mm y−1 and subduction angle of θ=10° the critical age is 7 Myr. To test this switching behaviour in the development of prehnite–actinolite facies in the prism, petrologic data from the Cretaceous Shimanto Accretionary Complex (CSAC) in Kyushu, Japan were compiled. The regional occurrence and mineral assemblages of prehnite‐bearing metamorphic rocks suggest that the most of CSAC was metamorphosed under prehnite–actinolite facies. This conclusion is consistent with subduction of a young, hot slab, as has been proposed based on other geological observations. This suggests that the regional extent of the prehnite–actinolite facies metamorphic rocks may be a unique evidence for the subduction of a young, hot slab.

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Occurrence and geochemistry of greenstones from the Makimine Formation in the Upper Cretaceous Shimanto Supergroup in Kyushu, Japan.

Cited by 20 publications

References 13 publications

Constraints on Element Mobility During Deformation Within the Seismogenic Zone, Shimanto Belt, Japan

Constraints on Element Mobility During Deformation Within the Seismogenic Zone, Shimanto Belt, Japan

Metamorphic and cooling history of the Shimanto accretionary complex, Kyushu, Southwest Japan: Implications for the timing of out‐of‐sequence thrusting

Thermal modelling in shallow subduction: an application to low P/T metamorphism of the Cretaceous Shimanto Accretionary Complex, Japan

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