Lithosphere deflection on a juvenile oceanic detachment during seafloor spreading promoted the exposure of the mantle rocks of the Troodos ophiolite – inferences from gabbro paleomagnetism

The domal structure in the core of the Troodos ophiolite exposes lower crustal (gabbro suite) and mantle rocks (ultramafic province). This structure is part of a fossil ridge-transform intersection (RTI), where an extinct spreading axis meets the fossil oceanic transform, namely the Arakapas transform. A major feature in the RTI system is the Troodos Forest-Amiandos Fault (TAF), an off-axis and axis parallel fault that was active during the Cretaceous seafloor spreading. Here we investigate the deformation across the TAF by measuring paleomagnetic vectors from 34 sites in the gabbro suite around the domal ultramafic core. Special emphasize was along an E-W transect that crosses the TAF south of the sheeted dike complex and north of the ultramafic province. We also compiled dike dips along an E-W strip (6 km wide) north of the gabbro suite. All results were compared to previous paleomagnetic studies from the sheeted dikes and the gabbro suite. Accordingly, we have found that rotations in the gabbro are very similar to those in the sheeted dikes, suggesting coupling of the upper and the lower oceanic crust during axial deformation of seafloor spreading. All rotation axes were horizontal and parallel to the dike strikes, i.e., parallel to the extinct spreading axis. Rotations increase gradually towards the TAF from both sides, eastward in the footwall and westward in the hanging wall. The most plausible scenario is an upward and downward deflection in the footwall and the hanging wall, respectively, similarly described theoretically for the early stages of detachment development. The orientations of the rotation axes of all paleomagnetic vectors indicate spreading-related deformation. This suggests that the relative uplift of the deep-seated rocks was by the development of a young detachment during seafloor spreading rather than serpentinite diapirism. The detachment occurrence in the outside-corner is explained here by the shift from orthogonal to curved axis, inferred from sheeted dike orientations.