DYKE DOMAINS IN THE MITSERO GRABEN, TROODOS OPHIOLITE, CYPRUS - AN OFF-AXIS MODEL FOR GRABEN FORMATION AT A SPREADING CENTER

Graben at oceanic spreading centres may form at on-axis or off-axis po sitions. Their formation is dependent on the tectonic processes active in the oceanic crust. Evidence for the position of formation of grabe n in oceanic analogues (ophiolites) can be obtained from the orientati on of dykes within sheeted dyke complexes. Dyke orientation data and d yke relations from the Mitsero graben and environs, Troodos ophiolite, Cyprus, have been used to determine the tectonic setting of graben fo rmation. Five major dyke domains were delineated on the basis of orien tation of dykes in the Sheeted Dyke Complex in the Mitsero graben. Bet ween domains, the mean strike rotates counter-clockwise by 25 degrees. Zn the easternmost domain, dyke strikes are roughly 070 degrees, and progressively westward, the mean strikes of dykes within domains are r oughly 045 degrees, 026 degrees, 000 degrees, and 324 degrees. Within domains the dyke trends show no systematic changes in strike toward th e domain edges. Dyke cross-cutting relations, the degree of their rota tion, and relations to other features such as hydrothermal alteration leads to the suggestion that the Mitsero graben formed late in the his tory of the area, possibly in an off-axis position.