Abstract

Graben at oceanic spreading centres may form at on-axis or off-axis positions. Their formation is dependent on the tectonic processes active in the oceanic crust. Evidence for the position of formation of graben in oceanic analogues (ophiolites) can be obtained from the orientation of dykes within sheeted dyke complexes. Dyke orientation data and dyke relations from the Mitsero graben and environs, Troodos ophiolite, Cyprus, have been used to determine the tectonic setting of graben formation. Five major dyke domains were delineated on the basis of orientation of dykes in the Sheeted Dyke Complex in the Mitsero graben. Between domains, the mean strike rotates counter-clockwise by 25°. In the easternmost domain, dyke strikes are roughly 070°, and progressively westward, the mean strikes of dykes within domains are roughly 045°, 026°, 000°, and 324°. Within domains the dyke trends show no systematic changes in strike toward the domain edges. Dyke cross-cutting relations, the degree of their rotation, and relations to other features such as hydrothermal alteration leads to the suggestion that the Mitsero graben formed late in the history of the area, possibly in an off-axis position.

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