Inclusion‐trail geometry of albite porphyroblasts in a fold structure in the Sambagawa Belt, central Shikoku, Japan

Okamoto, K.

doi:10.1046/j.1440-1738.1998.00176.x

Cited by 11 publications

(5 citation statements)

References 39 publications

(56 reference statements)

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“…Ds is associated with a west–east to northwest–southeast oriented stretching lineation (Figure 4; Wallis et al, 1992; Wallis, 1998; Takeshita & Yagi, 2004) and developed during exhumation of the belt. Earlier deformation stages are also recognized and are best documented in the high‐grade parts of the belt (Aoya, 2001; Aoya & Wallis, 1999; Endo et al, 2012; Okamoto, 1998; Wallis, 1998). The stretching direction of these earlier phases is variable but dominantly north–south (Endo et al, 2012; Toriumi & Kohsaka, 1995).…”

Section: Geological Settingmentioning

confidence: 99%

Recognition of broad thermal anomaly around the median tectonic line in central Kii peninsula, southwest Japan: Possible heat sources

Yamaoka

Wallis

2022

Island Arc

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Application of Raman spectroscopy of carbonaceous material thermometry to samples of metasedimentary rock from the low‐grade Sanbagawa belt in the central Kii peninsula reveals a progressive decrease in temperature from ~390 °C close to the northern boundary, a major continental shear zone—the median tectonic line (MTL)—to ~270 °C and ~7 km to the south and roughly constant temperature distribution thereafter. Within the Sanbagawa belt, the thermal structure is not significantly modified by slip‐on fault boundaries between different geological units or folding. Meso‐ and microstructural observations combined with strain analysis using detrital grains in meta‐mudstone indicate a similar deformation history throughout the area and no correlation between ductile strain and temperature gradients. These observations suggest the observed thermal structure was developed after the main stages of ductile deformation of the Sanbagawa belt were complete and are not due to localized preferential exhumation along with the MTL. The observations also require a heat source along with the MTL. Order of magnitude estimates suggest the influx of warm fluid along the MTL are viable causes of the observed thermal anomaly. Although shear heating would be another possible explanation, thermal calculations require anomalous fast slip rates along the MTL and much greater frictional strength than generally considered reasonable. For these reasons, fluid infiltration is our preferred model.

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Section: Geological Settingmentioning

confidence: 99%

Recognition of broad thermal anomaly around the median tectonic line in central Kii peninsula, southwest Japan: Possible heat sources

Yamaoka

Wallis

2022

Island Arc

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“…In the Sanbagawa metamorphic belt several studies provide fabric data, e.g., garnet and clinopyroxene CPO from the Higashi-Akaishi peridotite body (Muramoto et al, 2011), inclusion-trail geometry of albite in basic schists (Okamoto, 1998), and misorientation of garnet aggregates in vein in the mafic schists (Okamoto & Michibayashi, 2006 research provides the first report on the fabric of eclogitefacies and retrograde-stage minerals as well as useful insights into the rheological mineral behaviour during eclogite formation and exhumation.…”

Section: Deformation Regime Of the Eclogite-facies Stagementioning

confidence: 99%

EBSD-measured crystal preferred orientation of eclogites from the Sanbagawa metamorphic belt, central Shikoku, SW Japan

Rehman¹,

Mainprice²,

Barou³

et al. 2016

ejm

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Electron back-scattered diffraction (EBSD) maps and crystal-preferred orientation (CPO) of eclogite-facies (omphacite and garnet) and amphibolite-facies (hornblende and actinolite) phases are reported for understanding the rheological behaviour of crust during subduction. Two types of eclogites from the subduction-related high-pressure/low-temperature type Sanbagawa metamorphic belt, Japan, have been investigated. Type-I eclogite (sample Sb-1) is composed of garnet, omphacite, secondary actinolite and hornblende. Type-II eclogite (samples Sb-2 and Sb-2a) are mainly composed of omphacite, garnet, and retrograde hornblende with no actinolite. Omphacite, the peak eclogite-facies phase, exhibits L-type CPO (maximum density of [001] axes parallel to and high density of {110} poles normal to the lineation) in Type-I eclogite, suggesting intra-crystalline plasticity with [001] {110} and 〈110i{110} active slip systems, indicating a constrictive strain regime at mantle depths. Omphacite in Type-II eclogite exhibits a similar fabric but with much weaker CPO. Using the LS-index symmetry analysis (one for the end-member L-type, zero for the end-member S-type, and intermediate values for LS-types), a progressive change in LS index of 0.80 for Type-I and 0.61 to 0.44 for Type-II eclogites is observed. These values suggest a transition from axial extension parallel to the lineation for Sb-1 and weaker CPO associated with pure or simple shear for Sb-2 and Sb-2a. Garnet, the second dominant phase in the eclogite-facies stage, exhibits weak and complex fabric patterns in all eclogite types, behaved like rigid bodies and does not show plastic deformation. Amphibolite-facies phases (e.g., hornblende and actinolite) exhibit more than two types of CPO. Hornblende and actinolite in Type-I eclogite have a strong CPO along [001] axes aligned parallel to the lineation, indicating homotactic crystal growth probably by the replacement of omphacite during the early stages of retrogression. Type-II eclogites have weak CPO in hornblende but with characteristic alignment of [001] parallel to the lineation and other poles to planes (100), (010), and {110} normal to the lineation. This fabric might have resulted from a cataclastic deformation and could be related to the late-"D1" deformation stage in the Sanbagawa metamorphic belt.

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“…Burchfiel & Royden 1985; Brunel 1986; Kaneko 1997). Alternatively, early deformation structures of some metamorphic belts are subparallel to their long axes; for example, the Sanbagawa belt ( Faure 1985; Wallis 1992; Okamoto 1998), Fiordland in New Zealand ( Hill 1995), Scandinavian Caledonides ( Gilotti & Hull 1993; Northrup & Burchfiel 1996) and Kokchetav metamorphic belt (present study). Orogen‐parallel subhorizontal shearing is recognized as a common feature from these regions.…”

Section: Implications For the Exhumation Of Ultrahigh‐pressure Metamomentioning

confidence: 71%

Kinematic analysis of ultrahigh‐pressure–high‐pressure metamorphic rocks in the Chaglinka–Kulet area of the Kokchetav Massif, Kazakhstan

Yamamoto¹,

Ishikawa²,

Anma

et al. 2000

Island Arc

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The central part of the Kokchetav Massif is exposed in the Chaglinka–Kulet area, northern Kazakhstan. The ultrahigh‐pressure–high‐pressure (UHP–HP) metamorphic belt in this area is composed of four subhorizontal lithological units (Unit I–IV) metamorphosed under different pressure–temperature (P–T) conditions. The coesite‐ and diamond‐bearing Unit II, which consists mainly of whiteschist and eclogite blocks, is tectonically sandwiched between the amphibolite‐dominant Unit I on the bottom and the orthogneiss‐dominant Unit III on the top. Total combined thickness of these units is less than 2 km. The rocks of the UHP–HP metamorphic belt are affected by at least four deformational events post‐dating peak metamorphism: (i) The earliest penetrative deformation is characterized by non‐coaxial ductile flow in a NW–SE direction. The shear sense indicators in oriented samples from Unit I provide consistent top‐to‐the‐northwest motions and those from Unit III provide top‐to‐the‐southeast, south or south‐west motions; (ii) Upright folds with subhorizontal enveloping surface refold earlier foliations including shear‐indicators throughout the metamorphic belt; (iii) The third stage of deformation is denoted by large‐scale bending around a subvertical axis; and (iv) Late localized fault (or shear) zones cut all earlier structures. The fault zones have subvertical shear planes and their displacements are essentially strike‐slip in manner. The subhorizontal structure and opposite shear directions between Unit I and Unit III during the earlier deformation stage suggest north‐westward extrusion of UHP Unit II.

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Inclusion‐trail geometry of albite porphyroblasts in a fold structure in the Sambagawa Belt, central Shikoku, Japan

Cited by 11 publications

References 39 publications

Recognition of broad thermal anomaly around the median tectonic line in central Kii peninsula, southwest Japan: Possible heat sources

Recognition of broad thermal anomaly around the median tectonic line in central Kii peninsula, southwest Japan: Possible heat sources

EBSD-measured crystal preferred orientation of eclogites from the Sanbagawa metamorphic belt, central Shikoku, SW Japan

Kinematic analysis of ultrahigh‐pressure–high‐pressure metamorphic rocks in the Chaglinka–Kulet area of the Kokchetav Massif, Kazakhstan

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