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Controls on the structural development of an accretionary complex: the Shimanto Belt, Southwest Japan
SELECTED
433
ABSTRACTS
Controls on the structural development of an accretionary complex: the Shimanto Belt, Southwest Japan D.T. Needham
a, S.M. Agar b and J.S. Mackenzie
’
a Department of Earth Sciences,Goldsmiths’ College, Rachel McMillan Building, Creek Road, London SE8 3BU, UK ’ Department of Geology, Imperial College, London S W7 ZBP, UK ’ Department of Geology, Imperial College, London S W7 2BP, UK (Received November 27.1989)
Abstract
In order to study the detailed internal geometry and mechanisms of deformation within accretionary complexes, ancient on-land examples must be investigated. The Early Cretaceous-Early Miocene Shimanto Belt of Southwest Japan provides an excellent example of such a complex. It is exposed on the islands of Shikoku and Kyushu,
ted as being tectonic in origin, are characteristic of both areas. It appears that shale-rich sequences acted as broad shear zones during accretion, with interbedded sandstone beds, becoming progressively dismembered. In contrast, fabrics are much more strongly developed on Kyushu, penetrative cleavages replacing scaly fabrics in shales, while fault zones appear to have undergone more com-
where a series of transects have been completed. These provide information on the overall structural pattern, as well as a more detailed insight
plex histories on Shikoku. The observed structural variations will be discussed and placed in the
into the processes active at varying depths within
context of the know Late Cretaceous-Palaeogene
an accretionary prism. Considerable along-strike variation exists. The Shimanto Belt of Shikoku preserves higher-level structures, while deeper
tectonic history of the region. The effect of variables such as angle and rate of subduction will be
levels are exposed on Kyushu. Melanges, interpre-
Elsevier Science Publishers B.V.
assessed, the results being generally applicable other accretionary complexes.
to
433
ABSTRACTS
Controls on the structural development of an accretionary complex: the Shimanto Belt, Southwest Japan D.T. Needham
a, S.M. Agar b and J.S. Mackenzie
’
a Department of Earth Sciences,Goldsmiths’ College, Rachel McMillan Building, Creek Road, London SE8 3BU, UK ’ Department of Geology, Imperial College, London S W7 ZBP, UK ’ Department of Geology, Imperial College, London S W7 2BP, UK (Received November 27.1989)
Abstract
In order to study the detailed internal geometry and mechanisms of deformation within accretionary complexes, ancient on-land examples must be investigated. The Early Cretaceous-Early Miocene Shimanto Belt of Southwest Japan provides an excellent example of such a complex. It is exposed on the islands of Shikoku and Kyushu,
ted as being tectonic in origin, are characteristic of both areas. It appears that shale-rich sequences acted as broad shear zones during accretion, with interbedded sandstone beds, becoming progressively dismembered. In contrast, fabrics are much more strongly developed on Kyushu, penetrative cleavages replacing scaly fabrics in shales, while fault zones appear to have undergone more com-
where a series of transects have been completed. These provide information on the overall structural pattern, as well as a more detailed insight
plex histories on Shikoku. The observed structural variations will be discussed and placed in the
into the processes active at varying depths within
context of the know Late Cretaceous-Palaeogene
an accretionary prism. Considerable along-strike variation exists. The Shimanto Belt of Shikoku preserves higher-level structures, while deeper
tectonic history of the region. The effect of variables such as angle and rate of subduction will be
levels are exposed on Kyushu. Melanges, interpre-
Elsevier Science Publishers B.V.
assessed, the results being generally applicable other accretionary complexes.
to