.1 + +,,**- Japanese Journal of Structural Geology, No..1, + +,,,**- Some Considerations on the Research History of the Paleo-Ryoke Belt (-) The Median Tectonic Line of Pre-Ichinokawa Stage * ** Ikuo Hara*and Takami Miyamoto** Abstract : Recent research history of Mesozoic tectonics of the Median Tectonic Line (MTL) is briefly described in this paper. Some authors pointed out that MTL has to be distinguished four di#erent faults with reference to tectonic significance, time and place : MTL-* (suture zone between the accretionary complex of the Inner zone and the Kurosegawa-Paleo-Ryoke continent beneath which plate subduction responsible for the formation of the Sambagawa schists occurred), MTL-I (great mylonite zones related to exhumation of high-temperature parts of the Ryoke metamorphic rocks just after intrusion of the older Ryoke granites), MTL-II (great mylonite zones developed along the southern boundary of intrusion field of the younger Ryoke granites) and MTL-III (faulting related to exhumation of the Sambagawa schists). While some others assumed that tectonics described in terms of MTL-*, MTL-I, MTL-II and MTL-III occurred in the same place (MTL as a single fault). Key words : Median Tectonic Line, Kurosegawa-Paleo-Ryoke continent, Ryoke granites, Izumi Group + MTL,**+ MTL MTL,**, b MTL,**, +,,.,**- - +1 * Oyo Corporation, - + -* Minaga, Saeki-ku, Hiroshima 1-+ /+,., Japan ** Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, + - + Kagamiyama, Higashi-Hiroshima 1-3 2/,0, Japan,**, a;,**, MTL MTL MTL + MTL-I MTL-II Kobayashi +3.+ MTL MTL +330 1
MTL +3.3 MTL Hara et al., +32* b +330 MTL-I MTL-II MTL-I MTL MTL Hara et al., +32* b; +330,***,**, a,**, MTL-I MTL-II MTL-I MTL MTL Okudaira et al., +33- MTL MTL-I + MTL-I MTL-I MTL-I MTL-I MTL-I MTL-I MTL-I MTL-I + +33, MTL : a: b: c: 2
.1 MTL-I Sakakibara et al +323 Sakakibara +33/ MTL X +320 +33* +320 +321 +33* Ohtomo +33- Yamamoto +33. + MTL-I MTL-I MTL Suwa +30+ +30/,*** MTL, MTL Okudaira et al +33- MTL-I top-to-the south top-to-the southwest Sakakibara et al., +323 ; +33* ; Ohtomo, +33- ; Sakakibara, +33/ MTL-I MTL +, +321,.,/ :,.,0 : ; +33+,. - :,. + : ; + km,,*** + :, : - :. : / : 0 : MTL-I 3
/ km +* km +321 ; +33+ ; Hara et al., +32* a; + +323 ; Okudaira et al., +33- ; + top-to-the southwest Okudaira et al., +33- MTL + Suwa, +30+ ; +30/ ;,*** ;, Suwa +30+ +30/,***, Okudaira et al., +33- MTL-I MTL-I MTL, MTL-I +33+ MTL Suzuki et al., +330 MTL-I 3* Ma +330,*** MTL MTL MTL CHIME Suzuki and Adachi, +332 +** Ma, MTL-II : MTL MTL Hara et al., +32* b MTL-II Michi bayashi and Masuda, +33- ; +330 MTL-II MTL-II MTL-I MTL-I MTL-II MTL-II MTL +33, MTL-II MTL-II MTL-I MTL +, Yoshizawa et al., +300 Yoshizawa et al., +300 +310 +311 ; Ohtomo, +33- +31. +32/ ; Sakakibara, +33/ MTL-I MTL Hara et al., +32* b ; Ohtomo, +33- +310 +311 ; Ohtomo, +33- MTL-I +310 +311 ; Ohtomo, +33- MTL-I 4
.1 MTL-I +321 ; +33+ ; - MTL-I 31 Ma K-Ar +321 MTL-I, - +321 +* 1,/* /** m +331 - +31* ; +31-,*** +*- +*0 Ma K-Ar +*2 Ma K-Ar - MTL-I + :, : A: B: C: D: MTL-I - 31 Ma K-Ar MTL-I MTL-I +33- ; +332 ; +332 Yamamoto, +30, ; +323 MTL-I MTL-I,. MTL-I ;. Hayama and Yamada +32* +330 +31* ; +33/ MTL-I. eastward younging +311 ;,*** MTL eastward younging +31* ; +311 ; Nakajima et al., +33* eastward younging eastward younging +311 eastward young- 5
ing Hara et al., +33, - MTL-I + + MTL-II,*** +332 +,**+ MTL-II - MTL-III : +30- I III MTL MTL. MTL-I,*** a: b : MTL-I c: d: e: K: M: Ma 6
.1 MTL-I MTL-I eastward younging eastward younging,**+,**, b,**+ +,**+ +330 Ichikawa, +32+ ; +32, +33* +33+ ; Hara et al., +33, MTL-II MTL-III MTL-I MTL-III MTL-I MTL-II MTL-III MTL-II MTL-III Hara et al., +33, ; +330 MTL-III MTL MTL-III 10./ 1,., Ma +33- K-Ar 11 Ma +33+ MTL-III 1/ Ma Hara et al., +33, ; +330 MTL-III Hara et al +33, +330 downward younging downward younging downward younging K-Ar 11 Ma 7
; Hara et al., +33, ; +330 MTL-II MTL-III MTL-III MTL-II Hara et al., +33, ; +330 MTL-III MTL Otoh and Yamakita +33/ MTL +33, ; +33, MTL +330 +330 MTL MTL MTL +330 MTL - decollement master fault MTL MTL +* km +322 master fault +* km MTL MTL-II MTL MTL MTL-II +31* +33- MTL F, F+ F. +33+ ; +33+ MTL-II. : MTL-* MTL-* MTL-* MTL +330,*** MTL MTL MTL MTL-I MTL-II MTL-III MTL-* MTL-III MTL-I, MTL-II, MTL-III MTL-*,**+ +330,*** MTL MTL-I 8
.1,**, b MTL MTL-I MTL-II MTL-* +33* ; +33+,**, a; +330 MTL-* ; +3/3 ; +311 ; ++* Ma ;,***,*** +0. Ma Rb-Sr +33- ++, +*- Ma K-Ar +321 ;,*** +*1 Ma SHRIMP,**+,**, b,*** MTL-* MTL + MTL MTL-I MTL-II MTL-III MTL-*, MTL-I MTL-I MTL MTL - MTL-I. / MTL-II MTL-II MTL MTL-II 0 eastward younging 1 2 MTL-* 3 MTL-* MTL +* MTL-III ++ MTL-III +, +- MTL-III,**+ MTL,**, a, b 9
MTL,***,***,**, a, b MTL-III +33, +** + - +330,*,,+*.,**+ no../ 3,*.,**, a no. ++3, +2.,**, b no. +,*, 2. Hara, I., Sakurai, Y., Arita, S. and Paulitsch, P., +32* a, Distribution pattern of quartzin granites- Evidence of their high-temperature deformation during cooling. N. Jb. Miner. Mh. +,,* -*. +33+ 33 +,*. +330 -/ km no.,2, + 10. Hara, I., Shiota, T., Hide, K., Kanai, K., Goto., M., Seki, S., Kaikiri, K., Takeda, K., Hayasaka, Y., Miyamoto, T., Sakurai, Y. and Ohtomo, Y., +33,, Tectonic evolution of the Sambagawa schists and its implications in convergent margin processes. Jour. Sci. Hiroshima Univ. Ser. C, 3,.3/ /3/. Hara, I., Shyoji, K., Sakurai, Y., Yokoyama, S. and Hide, K., +32* b, Origin of the Median Tectonic Line and its initial shape. Mem. Geol. Soc. Japan, no. +2,,1.3. +31. no. +, 3 +.. +33* 31 3 +-. Hayama, Y. and Yamada, T., +32*, Median Tectonic Line at the stage of its origin in relation to plutonism and mylonitization in the Ryoke belt. Mem. Geol. Soc. Japan, no. +2, /,0.,**+ +*2 ++3. Ichikawa, K., +32+, Closure of the Jurassic sea in and around the Ryoke-Sambagawa region. In Hara, I. ed., Tectonics of Paired Metamorphic Belts, Tanishi Print Kikaku, ++- ++0. +32,.,.+..,*. +33, 3-1+ p. +33+.-1 p. Kobayashi, T., +3.+, The Sakawa orogenic cycle and its bearing on the origin of the Japanese Islands. Jour. Fac. Sci. Imp. Univ. Tokyo, Ser.,, /, + /12. +3.3,2 p. +31-,/-,0+. +320 S C +,, 1/ 21. Michibayashi, K. and Masuda, T., +33-, Shearing during progressive retrogression in granitoids : abrupt grain size reduction of quartz at the plastic-brittle transiton for feldspar. Jour. Struct. Geol., +/, +.,* +.-,. +3/3 II -,,1+,2-. +330 10
.1 21 32.,*** no. /0, +-,,. +30/./2 p. +330,,*,,0. +33- / + +322 +3 --.,*** +*1,3/. Nakajima, T., Shirahase, T. and Shibata, K., +33*, Along-arc lateral variation of Rb-Sr and K-Ar ages of Cretaceous granitic rocks in Southwest Japan. Contrib. Mineral. Petrol., +*., -2+ -23. +321 0,31 p. +311 2-, /.- /... +31* : +31* 10,.3- /+2. +320 3- /.3. +33* +,,.1-.11. Ohtomo, Y., +33-, Origin of the Median Tectonic Line. Jour. Sci. Hiroshima Univ., Ser. C, 3, 0++ 003. +330 +3+,*+. +323 no. --,+21 +32. Okudaira, T., Hara, I., Sakurai, Y. and Hayasaka, Y., +33-, Tectono-metamorphic processes of the Ryoke belt in the Iwakuni-Yanai district, southwest Japan. Mem. Geol. Soc. Japan, no..,, 3+ +,*.,*** no..3, 01 2*. +33- Rb-Sr no..,, +-/ +/*. Otoh, S. and Yamakita, S., +33/, Late Cretaceous structural features and tectonics of Southwest Japan. Proceedings of +/ th International Symposium of Kyungpook Natinal University, +3-,*,. Sakakibara, N., Hara, I. and Ohtomo, Y., +323, Deformation of granitic rocks in the Ryoke belt (+) Deformation styles of quartz. DELP Publication, no.,2,.1 /+. Sakakibara, N., +33/, Structural evolution of multiple ductile shear zone system in the Ryoke belt, Kinki Province. Jour. Sci. Hiroshima Univ., Ser. C, +*,,01 --,. +332, SHRIMP U-Pb +*/,+..,*** SHRIMP U-Pb no. /0,+03 +2,. +323 +,,./1.0,. +321-2, -2/.,,.,**, +/, 2+ 3+. Suwa, K., +30+, Petrological and geological studies on the Ryoke metamorphic belt. Jour. Earth Sci. Nagoya Univ., 3,,.. -*-. +33+ 2,00 p. +332 CHIME +*/,+,. Suzuki, K. and Adachi, M., +332, Denudation history of the high T/P Ryoke metamorphic belt, southwest Japan : constraints from CHIME monazite ages of gneisses and granitoids. Jour. Metamorphic Geol., +0,,- -1. Suzuki, K., Adachi, M. and Nureki, T., +330, CHIME age dating of monazites from metamorphic rocks of the Ryoke belt in the Iwakuni area, Southwest Japan. Island Arc, /,.- //. 11
+32/ 3+, 0-1 0/+. +330,++,+3.,*** no. /0, + +,.,*** K-Ar no. /0,,+-,,*.,**+ +*2 ++2.,*** K-Ar no. /0, +.1 +01.,**, a no. +,*,,,.,**, b +*3 +1*. +330 +2, 1.2 1/.. +31*,-1 p. +311.+3.--. +33/ +*, 31 ++,. +310 A no. +, 2+ 2-. +311 A no.,, 3-30. +30-1,, ++* ++.. +332 +331 +, -. -1.,*** no..3, 3- +*.. Yamamoto, H., +30,, Plutonic and metamorphic rocks along the Usuki-Yatsushiro tectonic line in the western part of central Kyushu. Bull. Fukuoka Gakugei Univ., Part III, +,, 3- +1,. Yamamoto, H., +33., Kinematics of mylonitic rocks along the Median Tectonic Line, Akaishi Range, central Japan. Jour. Struct. Geol., +0, 0+ 1*. +321 3. /13. +33* no. +0,,/.1. +331 +3, +,2 +-, +330 +33/ ++ no.,0/, -- -0. +33, no..*, +11 +20. Yoshizawa, H., Nakajima, W. and Ishizawa, K., +300, The Ryoke metamorphic zone of the Kinki district, southwest Japan ; Complishment of a regional map. Mem. Coll. Sci., Univ. Kyoto, Ser. B, -,,.-1./.. +33,./. +33,+,. 12