Palaeomagnetic results from the Baër-Bassit ophiolite of northern Syria and their implication for fold tests in sheeted dyke terrains

Abstract

Palaeomagnetic results from 27 sites at five localities within the dismembered Baër-Bassit ophiolite of northern Syria are summarised. The ophiolite forms part of a series of thrust sheets emplaced over Mesozoic carbonates of the Arabian platform in the middle Maastrichtian. A positive inclination-only area-wide fold test applied to four locality mean remanences, and positive fold and reversal tests from palaeohorizontal units (pillow lavas, lava flows) within one of these localities, indicate that the ophiolite preserves pre-deformation magnetizations. Variable directions of remanence between localities indicate that the ophiolite has experienced extreme relative rotations on a kilometric scale. Sub-vertical dykes at one locality have a vertical upwards remanence. Inclusion of data from this locality in the inclination-only fold test invalidates the unequivocally positive result from the other four localities by producing a statistically unacceptable degree of dispersion, both before and after tilt correction. The strike of these dykes lies parallel to the thrust emplacement direction of the ophiolite. The unusual vertical magnetization direction may be explained by tilting about a dyke-normal axis, resulting in no visible change in dyke orientation. Given the potential for this situation to occur in other sheeted dyke complexes, it is suggested that the best strategy for palaeomagnetic analyses of the mid-upper levels of ophiolite terranes is to sample both palaeovertical and palaeohorizontal units and to approach application of tilt corrections and fold tests with care.