Reply to: 'A late Pleistocene clockwise rotation phase of Zakynthos (Greece) and implications for the evolution of the western Aegean Arc'

During the 80s, a number of seminal papers were published by the Gif-sur-Yvette group of Carlo Laj and co-workers, on the late Neogene palaeomagnetic rotations of the Aegean and, in particular, of the Aegean Arc system. These studies shed new light on the tectonic evolution of the region (e.g. [1,2]). Then, similar work on the Calabrian^ Sicilian arc system established that major tectonic rotations were of very young (middle Pleistocene) age [3], and it became clear to us that it was warranted to have a closer and more detailed look at the tectonic history of the Aegean Arc. In particular, the advent of more accurate, astronomically calibrated time scales during the 90s provided the opportunity to correlate tectonic (or other, e.g. climatic) events over a large geographical area, and to constrain their age and duration and hence their (a)synchrony. This would aid in testing a dynamical model of subduction- related geodynamics of the (central) Mediterranean area [4]. Many studies, e.g. on numerical modelling of stress patterns, tomography, vertical motions and depot centre migration, and on tectonostratigraphy, have aided in testing this hypothesis (see [5] for references). Meanwhile, the accurate time control has provided increasing evidence for relatively short periods of rapid, pulsed tectonic rotations (see [5] for references and discussion). This is in contrast to a more continuous deformation over a longer time interval, as was earlier suggested by Laj et al. [1] for the western Aegean Arc

Astronomical dating of a tectonic rotation on Sicily and consequences for the timing and extent of a middle Pliocene deformation phase

A detailed palaeomagnetic study of long and continuous middle Pliocene sections from the Caltanisetta basin on Sicily reveals a differential clockwise rotation occurring around 3.21 Ma. The rotation appears to be a rapid event (80,000100,000 years) which suggests that the responsible tectonic processes also occur rapidly. Its timing corresponds closely to the transition from the Trubi to the Narbone Formation at 3.19 Ma. This transition marks a major change in sedimentary environment on Sicily and in Calabria, and it is coeval, for instance, with the onset of sapropel formation in the eastern Mediterranean. Apparently it marks a synchronous and centraleastern Mediterranean-wide event. Data from the oldest sediments overlying the Tyrrhenian basement (ODP Leg 107) suggest an acceleration in opening of the Tyrrhenian Sea during the middle Pliocene. We speculate that this acceleration is related to a transpressional event in the Sicilian fold-and-thrust belt and extension which formed troughs in the foreland, the Strait of Sicily. Thrust imbrication accompanying the transpressional event on Sicily induced the middle Pliocene clockwise rotation and resulted in shallowing of the Caltanisetta basin causing the change in sedimentation regime characterised by the TrubiNarbone transition. Following this middle Pliocene tectonic phase, no rotation took place in the southern Apennines, Calabria and Sicily until the middle Pleistocene (1.00.7 Ma). Ó 1998 Elsevier Science B.V. All rights reserved

Post-early Messinian counterclockwise rotations on Crete: implications for Late Miocene to Recent kinematics of the southern Hellenic arc

Most geodynamical models for the kinematics of the central Mediterranean recognise that major tectonic rotations must have played an important role during the Neogene. The Hellenic arc is believed to have been subjected to clockwise rotations in the west and counterclockwise rotations in the east, while the southern part (Crete) shows no rotations (Kissel and Laj, 1988). Many qualitative and quantitative models are based on the idea that Crete did not rotate. We present new palaeomagnetic data which show that post-early Messinian counterclockwise rotations have occurred on Crete. The amount of counterclockwise rotation generally varies between 10º and 20º, but in central Crete much larger rotations (up to 40º counterclockwise) were found. Only a few sections did not show any rotation. The anisotropy of magnetic susceptibility (AMS) shows lineations, which are consistently WNWESE throughout Crete, indicating post-rotational WNW-ESE extension, or NNE-SSE compression. The observed counterclockwise rotations are consistent with the results of tectonic modelling by Ten Veen and Meijer (1998). The latter study compares the late-Middle Miocene to Recent kinematics with modelled intra-plate stresses for various possible distributions of plate boundary forces. Observations reveal that motion along left-lateral and right-lateral faults occurred during the Pliocene. The model analysis shows these motions to be consistent with transform resistance along the eastern segment of the overriding margin. The counterclockwise block rotations observed by us are probably a consequence of displacements along the left-lateral and right-lateral faults and could reflect a similar tectonic regime that involved transform resistance. Ó 1998 Elsevier Science B.V. All rights reserved

Neogene evolution of the Aegean arc: paleomagnetic and geodetic evidence for a rapid and young rotation phase

New paleomagnetic data of the entire Aegean outer-arc are presented. The results indicate a young Pleistocene and rapid clockwise rotation phase in the western Aegean arc, covering at least Zakynthos and the Peloponessos. The eastern Aegean arc, incorporating Kassos, Karpathos and Rhodos, also experienced Pleistocene anticlockwise rotations. The anisotropies of the magnetic susceptibility (AMS) data are in agreement with arc-parallel extension in the south and south-eastern Aegean arc and arc-normal compression in the north-west, in agreement with structural and geodetic observations. We compare the paleomagnetic results with the present-day pattern of rotation as computed from geodetic data, and we find good agreement. The onset of the Pleistocene rotations coincides with the beginning of uplift and a change in the stress pattern of extension. We compare our findings with existing models for the Aegean area

Comment on: 'A late Pleistocene clockwise rotation phase of Zakynthos (Greece) and implications for the evolution of the western Aegean Arc'

In a recent paper, Duermeijer et al. [1] report new palaeomagnetic results from the island of Zakynthos (Greece). In many cases, these authors have re-sampled the original sites of Laj et al. [2] and the results are virtually identical to those of the earlier study except for much more precise biostratigraphic age control. Three middle Pleistocene sites (Bochali, Zakynthos town and Porto Roma) which were not sampled by Laj et al. document signi¢cant clockwise rotations. From the results obtained from these three new sites, the authors conclude that the 25° clockwise rotation of Zakynthos described by Laj et al. as affecting the entire western Hellenic margin more or less progressively over the last 5 Myr is much more recent (early Pleistocene)

A Late Pleistocene clockwise rotation phase of Zakynthos (Greece) and implications for the evolution of the western Aegean arc

Palaeomagnetic measurements have been carried out on Eocene to Pleistocene sediments on the Ionian island of Zakynthos, NW Greece. Magnetostratigraphic constraints, biostratigraphic analyses of planktonic foraminifera and calcareous nannofossils provide a reliable time frame for these deposits. The results show that no significant rotation occurred between 8.11 and 0.77 Ma, but that Zakynthos underwent a 21.6º 7.4º clockwise rotation between 0.77 Ma and Recent. Thus, our data indicate a rapid rotational event, in contrast to continuous rotation since 5 Ma as previously postulated [Laj et al., Tectonophysics 86 (1982) 45 67]. We speculate this late Pleistocene tectonic rotation phase to be linked to rapid uplift in the Greek region which results from rebound processes caused by (African) slab detachment underneath the Ionian islands. Ó 1999 Elsevier Science B.V. All rights reserved

A record of the Messinian salinity crisis in the eastern Ionian tectonically active domain (Greece, eastern Mediterranean)

This integrated study (field observations, micropalaeontology, magnetostratigraphy, geochemistry, borehole data and seismic profiles) of the Messinian\u2013Zanclean deposits on Zakynthos Island (Ionian Sea) focuses on the sedimentary succession recording the pre-evaporitic phase of the Messinian salinity crisis (MSC) through the re-establishment of the marine conditions in a transitional area between the eastern and the western Mediterranean. Two intervals are distinguished through the palaeoenvironmental reconstruction of the pre-evaporitic Messinian in Kalamaki: (a) 6.45\u20136.122\ua0Ma and (b) 6.122\u20135.97\ua0Ma. Both the planktonic foraminifer and the fish assemblages indicate a cooling phase punctuated by hypersalinity episodes at around 6.05\ua0Ma. Two evaporite units are recognized and associated with the tectonic evolution of the Kalamaki\u2013Argassi area. The Primary Lower Gypsum (PLG) unit was deposited during the first MSC stage (5.971\u20135.60\ua0Ma) in late-Messinian marginal basins within the pre-Apulian foreland basin and in the wedge-top (<300\ua0m) developed over the Ionian zone. During the second MSC stage (5.60\u20135.55\ua0Ma), the PLG evaporites were deeply eroded in the forebulge\u2013backbulge and the wedge-top areas, and supplied the foreland basin's depocentre with gypsum turbidites assigned to the Resedimented Lower Gypsum (RLG) unit. In this study, we propose a simple model for the Neogene\u2013Pliocene continental foreland-directed migration of the Hellenide thrusting, which explains the palaeogeography of the Zakynthos basin. The diapiric movements of the Ionian Triassic evaporites regulated the configuration and the overall subsidence of the foreland basin and, therefore, the MSC expression in this area