The Oligocene Xanthi pluton, northern Greece: a granodiorite emplaced during regional extension

Abstract

The Xanthi pluton is one of a series of Oligocene subduction-related granodiorites in northern Greece. Its emplacement was controlled by major faults. It is located on the ENE-trending Kavala–Komotini fault zone, which probably originated as a strike-slip fault. Geophysical data show that the pluton is laccolith-shaped, extending many kilometres south of the fault. Andesitic dykes several million years older than the pluton indicate a NE–SW-directed extensional stress field. Mineral lineations plunging to the SW reflect continued extension during cooling of the pluton. Subsequent jointing and dykes of aplite and lamprophyre reflect continued extension. Although this could result from extensional pull-apart at a bend during dextral strike-slip motion on the Kavala–Komotini fault, there is no evidence for subsequent strike-slip deformation. Furthermore, two similar laccolithic plutons are unrelated to the Kavala–Komotini fault and the regional extent of thick Oligocene sediments suggests an extensional environment. During the extension that created a ramp space along the listric fault bounding the Xanthi basin, into which the granite was intruded, the Kavala–Komotini fault acted as a transfer fault. Reactivation of early joints occurred during late Oligocene–Early Miocene compression. Faults within the pluton parallel to the Kavala–Komotini fault accompanied extension during Neogene basin formation. Emplacement of subduction-related magma into ramp space developed along listric faults, to produce laccolith-like plutons, may be a common feature of back-arc extension.