Neotethyan intraoceanic microplate rotation and variations in spreading axis orientation: Palaeomagnetic evidence from the Hatay ophiolite (southern Turkey)

Insights into tectonic processes operating in ancient ocean basins are provided by analyses of fragments of oceanic lithosphere preserved as ophiolites during collisional orogenesis. Here we present a palaeomagnetic analysis of the Upper Cretaceous Hatay (Kizil Dag) ophiolite of Turkey that provides evidence for intraoceanic microplate rotation and variations in ridge axis orientation in a Neotethyan ocean basin. Magnetizations at 46 sites are shown to be pre-deformational in origin and rotated from the relevant reference direction. A net tectonic rotation approach to the analysis of the data provides information on permissible net rotation poles and angles and allows uncertainties in input vectors to be considered. Results demonstrate that all levels of the ophiolite have been rotated anticlockwise by angles in excess of 90 degrees around steeply inclined axes. The Hatay ophiolite formed in the same supra-subduction zone spreading system as the Troodos ophiolite (Cyprus), which is known to have rotated 90 degrees anticlockwise in an intraoceanic setting in the Late Cretaceous to Early Eocene. By considering our results in the context of the known timing of the Troodos rotation, we infer that 50-60 degrees of rotation of the Hatay ophiolite took place as part of an a really extensive "Troodos microplate". This phase of rotation was triggered by initial impingement of the Arabian continental margin with the Neotethyan subduction trench, consistent with models for modem day oceanic microplate rotation in complex convergent plate boundaries. The Hatay ophiolite then became detached from the actively rotating microplate and was emplaced onto the Arabian margin in the Maastrichtian, undergoing a further 30-40 degrees of anticlockwise rotation during thrusting. Back-stripping of rotations allows correction of the Hatay sheeted dykes to their initial orientations. The restored dyke trend of 020 degrees differs from that inferred previously for the Troodos sheeted dyke complex, demonstrating a primary variation in orientation of Neotethyan spreading axes. Such variability is commonly observed in modem spreading systems in marginal basins; these may act as analogues for the supra-subduction zone spreading inferred for many ophiolites. (C) 2009 Elsevier B.V. All rights reserved.