Hostname: page-component-78c5997874-xbtfd Total loading time: 0 Render date: 2024-11-02T23:18:36.700Z Has data issue: false hasContentIssue false
  • English
  • Français

Flow direction and groundmass shear zones in dykes, Shimane Peninsula, Japan

Published online by Cambridge University Press:  01 May 2009

J. V. Smith ,
Y. Miyake  and
S. Yamauchi
J. V. Smith
Affiliation:
Geology Department, Shimane University, Matsue, Shimane 690, Japan
Y. Miyake
Affiliation:
Department of Geology, Shinshu University, Matsumoto, Nagano 390, Japan
S. Yamauchi
Affiliation:
Geology Department, Shimane University, Matsue, Shimane 690, Japan
Get access Rights & Permissions [Opens in a new window]

Abstract

The groundmass of andesitic dykes at Sezaki, southwest Japan, has trachytic texture and contains microscopic shear zones. The shear zones comprise a conjugate pair formed by flattening of the solidifying dyke rock, probably caused by the magma pressure of the still molten part of the dyke. This pressure shortened the solidifying rock perpendicular to the dyke margins and caused it to extrude parallel to the magma flow direction. The groundmass shears indicate that locally the magma flowed 60° upward in the dykes. It is concluded that while groundmass shears are a useful indicator of flow direction in dykes, phenocryst alignment in dykes is strongly influenced by magma-pressure flattening and thus may be a poor indicator of flow direction

Type
Articles
Information
Geological Magazine , Volume 130 , Issue 1 , January 1993 , pp. 117 - 120
Copyright
Copyright © Cambridge University Press 1993

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Gudmundsson, A. 1984. Formation of dykes, feeder-dykes, and the intrusion of dykes from magma chambers. Bulletin of Volcanology 47, 537–50.Google Scholar
Harding, T. P. 1974. Petroleum traps associated with wrench faults. American Association of Petroleum Geologists, Bulletin 58, 1290–304.Google Scholar
Morris, P. A., Itaya, T., Watanabe, T. & Yamauchi, S. 1990. Potassium/argon ages of Cenozoic igneous rocks from eastern Shimane Prefecture–Oki Dozen Island, southwest Japan and the Japan Sea opening. Journal of Southeast Asian Earth Science 4, 125–31.Google Scholar
Otofuji, Y.-L, Itaya, T. & Matsuda, T. 1991. Rapid rotation of southwest Japan – palaeomagnetism and K-Ar ages of Miocene volcanic rocks of southwest Japan. Geophysical Journal International 105, 397–405.Google Scholar
Ramsay, J. G. 1980. Shear zone geometry: a review. Journal of Structural Geology 2, 83–99.Google Scholar
Ramsay, J. G. 1982. Rock ductility and its influence on the development of tectonic structures in mountain belts. In Mountain Building Processes (ed Hsü, K. J.), pp. 111–27. Academic Press.Google Scholar
Rickwood, P. G. 1990. The anatomy of a dyke and the determination of propagation and magma flow directions. In Mafic Dykes and Emplacement Mechanisms. (eds Parker, A. J. Rickwood, P. C. and Tucker, D. H.), pp. 81–100. Rotterdam: Balkema.Google Scholar
Shelley, D. 1985. Determining paleo-flow directions from groundmass fabrics in the Lyttelton radial dykes, New Zealand. Journal of Volcanology and Geothermal Research 25, 69–79.CrossRefGoogle Scholar
Wada, Y. 1992. Magma flow directions inferred from preferred orientations of phenocrysts in a composite feeder dyke, Miyake-Jima, Japan. Journal of Volcanology and Geothermal Research 49, 119–26.Google Scholar
Wilcox, R. E., Harding, T. P. & Seely, D. R. 1973. Basic wrench tectonics. American Association of Petroleum Geologists, Bulletin 57, 74–96.Google Scholar