Inhomogeneous deformation of metamorphic tectonites of contrasting lithologies: Strain analysis of metapelite and metachert from the Ryoke metamorphic belt, SW Japan

Mid-crustal horizontal shear zone in the forearc region of the mid-Cretaceous SW Japan arc, inferred from strain analysis of rocks within the Ryoke metamorphic belt

“…Alternatively, it is possible that the plane strain to general flattening strain exhibited by the metachert and metapelite may have resulted in large part from the schistosity-forming deformation, because the radiolarian fossils are not deformed in the non-metamorphosed rocks in the Mino-Tamba accretionary complex but are deformed in the metamorphic rocks with a distinct schistosity (Yao et al, 1980;Okada, 1990;Fukui and Kano, 2007;Okudaira and Beppu, 2008). In such a case, the strain geometry inferred from radiolarian fossils in the metacherts (k = 0.6-1.2) would represent the strain geometry for D 1 in the Wazuka-Kasagi district.…”

“…Therefore, we took the data in the low-grade zone into account of the strain geometry of rocks in the Shiojiri-Ina district at D 1 . In the Wazuka-Kasagi and Iwakuni-Yanai districts, the stretching lineation is also defined by stretched sandstone clasts within a pelitic matrix Okudaira and Beppu, 2008;this study). The orientations of measured D 1 stretching lineations are summarized in Fig.…”

“…Maximum stretching direction of the schistosity-forming deformation (D 1 ) measured at different sites throughout the Ryoke metamorphic belt. Data sources: ShiojiriIna, Toriumi (1985) and Toriumi and Kuwahara (1988); Mikawa, Adachi and Wallis (2008); Wazuka-Kasagi, this study; Iwakuni-Yanai, Beppu and Okudaira (2008) and Okudaira and Beppu (2008). Orientations of horizontal minimum stress axis (rH min ) during D 1 are from Yokoyama (1984) and Okudaira et al (1995).…”

“…Recently, by comparing the strain geometry data of Toriumi (1985) and Toriumi and Kuwahara (1988) with the results of the three-dimensional numerical simulations, Iwamori (2003) suggested that the most suitable geodynamic model for the forearc region of the Cretaceous SW Japan is a three-dimensional corner flow in the forearc wedge associated with subduction with moderate obliquity ($45°for the angle between the trench normal and the subduction direction). However, data of the strain analysis on the Ryoke metamorphic rocks (Toriumi, 1985;Toriumi and Kuwahara, 1988) is problematic, because the dominant strain is not prolate but plane strain to oblate in the western part of the metamorphic belt (Iwakuni-Yanai district; Okudaira and Beppu, 2008;Beppu and Okudaira, 2008). It is necessary to determine reliable strain geometry for the Ryoke metamorphic rocks based on appropriate and accurate analysis throughout the metamorphic belt.…”

Cretaceous Events at the Eastern Margin of East Asia Recorded in Rocks of the Ryoke Belt, SW Japan

“…) 。古期花崗岩類と高変 成度岩が密接に伴うことや変成帯内の温度-圧力 構造 温度-圧力経路などから 領家変成作用は 古期花崗岩の貫入・定置による広域的な接触変成 作用であるとされている (Okudaira et al, , 2001Okudaira, 1996;Ikeda, 1998;Miyazaki, 2007;Tirone and Ganguly, 2010 まで提出されている領家変成帯の熱モデル (Okudaira, 1996;Okudaira et al, 2001;Miyazaki, 2007) (Toriumi, 1985;Toriumi and Kuwahara, 1988) これは D1 と D2 / D3 の歪みが重複 した結果であり 最も主要な変形である D1 の歪楕 円は最小伸長軸が層面片理の法線方向で最大伸長 軸がほぼ東西に配置するような一軸圧縮歪～平 面歪である (Okudaira and Beppu, 2008;Adachi and Wallis, 2008;Okudaira et al, 2009) 。この (Sakurai et al, 1983;原ほか, 1991;Ohtomo, 1993;Sakakibara, 1995 Ishihara, 1977;Kagami et al, 1992;Kutsukake, 1993;Nakajima, 1996;Takagi, 2004) 。系統的な CHIME モ…”