Ophiolite Tectonics, Rock Magnetism and Palaeomagnetism, Cyprus

Abstract

Magnetic properties of minerals may be sensitive indicators of provenance. Remanence-bearing minerals (RBM) such as iron-titanium oxides, and matrix-forming minerals such as paramagnetic phyllosilicate or diamagnetic calcite yield different clues to provenance, strain history and tectonics, and are essential supplements for the full interpretation of palaeomagnetic data. Moreover, mineral magnetic properties provide magnetic-petrofabric indicators of tectonic strain, determine the suitability of sites for palaeomagnetism, and permit the restoration of palaeomagnetic vectors in some strained rocks. In the Cretaceous Troodos ophiolite (*88 Ma) magnetic properties are dictated by the relative importance of mafic silicates and largely primary, ophiolite-derived RBM. In its cover of deformed pelagic sedimentary rock, magnetic properties are dictated by the balance of clastic RBM versus matrix calcite and in some cases clay. The two larger Cretaceous ophiolite outcrops (Troodos & Akamas) share a common orientation of their plutonic flow fabrics, determined by magnetic methods. The dike complex shows fabrics indicating plumelike feeders spaced along and perpendicular to the spreading axis, with longevities[0.5 Ma. South of the ophiolite, its Cretaceous-Miocene limestone cover possesses ubiquitous tectonic petrofabrics inferred from anisotropy of magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent susceptibility (AARM). Its foliation and maximum extension dip and plunge gently northward, sub-parallel to a common but previously unreported North-dipping stylolitic cleavage. In well-known localized areas, there are S-vergent thrusts and overturned folds. The S-vergent deformation fabrics are due to Late Miocene (pre-Messinian *8 Ma) deformation. The structures are geometrically consistent with overthrusting of the Cretaceous Troodos-Akamas ophiolite, and its sedimentary cover, onto the underlying Triassic Mamonia terrane. The northern limit of pre-Messinian tectonic fabrics, the TroodosMamonia terrane boundary and the Arakapas-Transform fault form an approximate E-W composite boundary that we term the Troodos Tectonic Front. Miocene deformation remagnetized the ophiolite and its sedimentary cover in many places and also affects the Mamonia terrane to the SW, with which the Troodos terrane docked in the late Cretaceous. Magnetic mineralogy, particularly of the RBM traces the progressive un-roofing of the ophiolite during the deposition of its sedimentary cover. During the submarine exposure and erosion of the ophiolite, the contribution of RBM clasts to the overlying sedimentary cover changed qualitatively and quantitatively. Thus, magnetic mineralogy of the sedimentary rock cover records the progressive denudation of the ophiolite from lavas, down through dikes, to gabbros and deeper mantle rocks. Palaeomagnetic studies previously revealed the anticlockwise rotation of the Troodos terrane and its northwards migration. Characteristic remanent magnetism (ChRM) is most reliable for lavas and dikes although it...

Newly developed paleomagnetic map of the EasternmostMediterranean joined with tectono-structural analysis unmaskgeodynamic history of this region

“…Among the employed materials were geological maps of Israel [76], Jordan [77], Egypt [72] and photomaps of Israel and adjacent areas [78]. Radiometric data displayed in [22,73,[79][80][81][82][83] were explored. Available paleontological data for the region under study [9,18,[84][85][86] were studied.…”

Magnetostratigraphy of the Apalós Formation (early Pleistocene): Evidence for pulsed uplift of Cyprus

“…In addition, significant amounts of hematite could be identified, especially in the NRM experiments. Continued oxidation and alteration of the ferromagnetic mineral phases during and/or after sedimentation has produced higher H cr /H c values (Figure 8b) than those observed by Borradaile et al [2010] in the original Troodos ophiolites.…”

“…Irreversible thermomagnetic curves, Curie temperatures and hysteresis properties point to the presence of magnetite between the SD‐MD and SP‐SD mixing lines and maghemite. No clear evidence of the original TM60 extensively occurring in the Troodos ophiolites [ Borradaile et al , 2010] has been detected in the Apalós sediments. High‐temperature exsolution with micrometer‐sized ilmenite lamellae in magnetite is well documented (Figure 6).…”

“…The offset of the Hcr/Hc values to the right from the magnetite SD‐MD mixing curve may be due to superparamagnetic contributions and hematite, which have been created by continued alteration and oxidation of the ferromagnetic minerals during sedimentation. Shaded area indicates hysteresis data from the original Troodos ophiolites as given by Borradaile et al [2010]. (c) Thermomagnetic curves with two major inflexions representing mineral phases with Curie temperatures at 380°C–400°C and just below 600°C.…”

“…Alternatively titanomagnetite of intermediate composition, although not observed in the thermomagnetic curves, may shift the data to higher H cr /H c values. [22] Titanomagnetite from the ophiolites of the Troodos Massif is supposed to be the ferromagnetic source mineral of the sediments at the Vlokkariá locality [Borradaile et al, 2010]. Titanomagnetite of intermediate composition (TM60 with x = 0.6 in the solid solution series Fe 3-x Ti x O 4 with 0 < x < 1) formed originally in the pillow basalts, sheeted dykes and gabbros.…”