Tectonics of the circum-Troodos sedimentary cover of Cyprus, from rock magnetic and structural observations

Abstract

The calcareous sedimentary cover of the Troodos Ophiolite Complex dips gently away from the Troodos Complex. It has rare, usually open folds and, locally, stylolitic cleavage ( S 1). Stylolitic cleavage is ∼50% more effective than primary bedding-stylolites in removing matrix and the variation in the S 1 vergence directions are compatible with gravitational sliding radially away from the Troodos range and into sedimentary basins. Two different types of magnetic fabric, anisotropy of magnetic susceptibility (AMS) and anisotropy anhysteretic remanence (AARM), reveal the sequence of preferred orientations of different minerals, and the vergence of their magnetic foliations with respect to bedding reveals the sense of over-shearing of the stratigraphic sequence. AMS defines crystallographic alignments of clay minerals and dimensional alignments of magnetite in the limestones. AARM isolates the preferred dimensional orientation of magnetite. Although traces of magnetite dominate the bulk susceptibility, its anisotropy is low in comparison with phyllosilicates so that AMS essentially records the clay-fabric. Throughout the study area, AMS foliation indicates S-vergence and AMS lineation indicates N–S extension. AMS foliation-vergence indicates shearing of the entire sedimentary cover southward from Troodos. This motion is attributed to gravity sliding controlled by regional uplift to the north. In contrast, AARM foliation indicates a subsequent ESE vergence due to later WNW–ESE extension. The NNE, AARM lineation is a composite of bedding and tectonic fabric contributions that do not directly yield a faithful extension direction. The shapes of the magnetic fabrics indicate that AMS (clay) fabrics have a broad range of shapes about the neutral ellipsoid shape, whereas AARM (magnetite) fabrics are bimodal, with equally developed bedding-oblate and tectonic linear–planar ( L= S) components. Hysteresis properties, plotted on a new three-dimensional diagram, show clearly that the magnetite has a pseudosingle domain response, so there is no reason to expect complications from inverse fabrics due to single-domain magnetite. Moreover it shows that hysteresis properties vary systematically with depositional depth, reflecting systematic changes in magnetite granulometry with sedimentary environment.