Broadley, L.N.S.; (2011) Tectonic evolution of the Ionian thrust belt, NW Greece. Doctoral thesis , UCL (University College London).

Abstract

The Ionian Zone is a classic thin-skinned fold and thrust belt that has been believed to have undergone a multiphase clockwise vertical axis rotation of 40°-60° since the Miocene, based on palaeomagnetism and geodesy. Timings, however, are disputed and spatial variations have largely been ignored. In this study, data from 21 new palaeomagnetic sites are presented alongside a reappraisal of previous results from the Ionian Zone. These results are integrated with basement geometry derived from gravity modelling and an estimate of the variation in shortening across the thrust belt, both of which were performed as part of this study. The palaeomagnetic analysis supports a bulk ~55° clockwise rotation of the Ionian Zone, albeit with significant local variations. It is suggested that the Gulf of Amvrakia (GoA), which divides the present day Ionian Zone into the geographic provinces of Epiros and Akarnania, formed an important boundary during thrusting; distinctly different patterns of rotational deformation are observed in the two provinces. In Epiros, north of the GoA, relative rotations between adjacent sections of neighbouring thrust sheets suggest that rotation occurred during thrust sheet emplacement, initially slowly just prior to emplacement, followed by rapid rotation during emplacement. Conversely, in Akarnania, all thrust sheets have undergone a consistent ~70° clockwise rotation, and it is suggested that this was accommodated on the Ionian Thrust, with the largest part of the horizontal displacement taken up by subduction. Foreland basement geometry, derived from gravity modelling, is proposed to have been influential in the tectonic evolution of the Ionian Zone. Interaction with basement obstacles resulted in lower rotations in the northernmost Ionian Zone, duplexing in central Epiros and, possibly, out-of-sequence thrusting Akarnania. The conclusions of this study are distinct from previous findings as they imply no rotation of the most external Ionian Zone and the Paxos Zone occurred prior to the advance of thrusting into this region, rather than a multiphase rotation of the whole zone.

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