France Lagroix MSc thesis abstract

Thesis Title: 
Neo-Tectonic and Rock Magnetic Study of the Circum Troodas Sedimentary Succession, Cyprus

The circum Troodos Sedimentary Succession (Late Cretaceous to Recent) overlies the Troodos ophiolite of Cyprus, located in the Eastern Mediterranean.  The pattern of neo-tectonic deformation was investigated through magnetic analysis of the tectonic petrofabrics.  Anisotropy of magnetic susceptibility (AMS), anisotropy of anhysteretic remanence magnetization (AARM) and hysteresis loop parameters were determined in order to define the magnetic fabric and the magnetic mineralogy.

The study area extends over approximately 1000 km2 mainly to the south of the exposed Troodos ophiolite.  The sample suite includes 432 oriented hand samples, predominantly of the Lefkara and Pakhna Formations.

Field measurements indicate bedding predominantly dips less than 10° to the south, while stylolitic cleavage dips steeper than bedding in various directions.  The bedding-cleavage relationship yields variable vergence directions suggesting gravity sliding of the sediments towards local sedimentary basins.  Southwest of the Limassol Forest Block axial planar cleavage consistently defines a SW vergence with respect to bedding due to a locally different, Early to Middle Miocene compression along NNE to NE - SSW to SW azimuth. Hysteresis loop analysis show that pseudo-single domain magnetitel is the ferromagnetic contributor.  Furthermore, in 71% of the samples, the ferromagnetic contribution provided more than 50% of the total susceptibility.  Thus, the petrofabrics of traces of magnetite largely control the magnetic fabrics.

The AMS fabric, in part tectonic, is controlled by the preferred crystallographic orientation of diamagnetic calcite and paramagnetic clay minerals as well as magnetite.  Orientation directions of the principal axes relative to bedding and cleavage indicate incomplete overprinting of the primary sedimentary fabric in many cases.  AMS foliation preferentially dips shallowly to the east and west.  AMS lineation varies regionally, from west to east across the study area, from a NNE to NNW trends, respectively.  The tectonic AMS fabric registers either a late Miocene supra-subduction extension regime due to southward migration of the reactivation Cyprean Arc or due to Pleistocene gravity sliding due to uplift of the Troodos Ophiolite Complex. 

The AARM fabric is controlled exclusively by the preferred dimensional orientation of pseudo single domain magnetite.  Exluding the area in proximity to the Limassol Forest Block, the AARM  fabric orientations are regionally consistent.  AARM foliation planes dip ~45° to the NW and AARM lineation is directed NE and SW, almost orthogonal to AMS lineation.  In some cases, in proximity to the Limassol Forest, the AARM lineation results from the combined magnetic fabrics, parallel to cleavage and bedding and is parallel to the bedding-cleavage intersection lineation.  The actual extension direction is to the WNW, represented by the AARMint principal axes.  Southwest of the Limassol Forest Block of the AARM fabric registers the Early to Middle Miocene SW - NE compression, and its tectonic expression is conventional, with AARMmax oriented NW and SE, perpendicular to the maximum compression direction.

A copy of the thesis can be downloaded here