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Boudinage Structure in the Cretaceous Izumi Group along the Median Tectonic Line, western Izumi Range, Southwest Japan - (1)

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  • Earth Science
  • Mathematics


Journal of Geosciences, Osaka 'City UniversUy Vol. 19. A{t. 3, p. 63-80. December,E975 B'oudril'nage Stryc:tiu.rel i'n'i t,he: C:問 t_aceous!1 :~Qm1i G'roup" aLI¥Qog' the Med,'i'an,' Tectonic 'Li,'n,e" wesltern .Izum,i', - Rang~, S'Qutrh~west Japan*一(1:) Takao MIYATA (Wiltir.l 5τables, 111 Fi例代saud 1 Plate) 1. Introduction The Median tectomic line、ofthe Killki distriet bas a ]ong and complex rustory of dis- 】ocation. lts movemen~ pictufe' in the pre-Miocene time was discussed in previQus paf)ers (ICHIKAWA and MIYA'fA, 1973; MrvATA et a人 1974). Boudinage structure" wbich is de- veloped in the Izumi Group along the tectonic line, is regarded to have occurred in the pre圃 Miocene time. In this paper, the $tate of thestrain in soutfuern margin>al zone ef the I~umi. Group atぬistIJme will be discussed using the boud.inage as a 'Clue. The forrnatiom of boudins in a rock layer or v1em has been 8'0 far studied by man.y authors (cf. S,TROM(JARD, ~973). ln a compar1som rof natural boudins with experi.mental :resmts, the geometric property an:d tbe state df st:rarn in boudins may be faotors which en:aole oomparison, white the applぬdstress and the viscosity ratio of the host layer and the Sll!rrouJild¥Ing layer are the factors which ar.e ,gemeraHy unknow:n with respect to matural boudins.. la the p:resen.t inves,tigatio丸山efefore,it is airned to clarify quantifatively the geometric prop,errty of s-bape and the state ,of st~ain about boudias in field. Problems of the stress distribution amd the viscosity ratio wil[ be dilsoussed in a future paper. ll. Geologic se“hg O,utline ,of geology Tlnle westem Izumi Range" KiDki dis:trict, oonsists of the Late 'Cretaceous (Campania~ Maas仕おhtian)J.ZUffi.rI Grou, (F~g. 1). The Medias tectomc line, a large-sω10 fault separat .. img geotectonically the Iz;umi 'Group (north~ fFOm tbe Sambagawa metamorphic rocKs (south), runs, in the diFection of N鈎OEthrough the southem foot of th:e mountain-rallge. The traoe of this tectoruc iine is alm

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