Palaeomagnetism and magnetic properties of the Cappadocian ignimbrite succession, central Turkey and Neogene tectonics of the Anatolian collage

Abstract

The Cappadocian ignimbrite succession of central-southern Anatolia comprises at least nine major and two minor calc-alkaline rhyolitic sheets emplaced at 1–2-Ma intervals between 11.2 and 1.1 Ma. It records the last phase of Neotethyan subduction during final emplacement of the Tauride orogen in southern Turkey. This study reports magnetostratigraphy and describes associated rock magnetic properties. Remanence resides in Ti-poor titanomagnetites. Haematisation is locally produced by post-emplacement oxidation but does not contribute significantly to the palaeomagnetic signature although secondary processes within the ignimbrite sheets have produced composite isothermal remanent magnetisation spectra and variable intensities of magnetisation. Weak anisotropy of magnetic susceptibility describes tensors with maximum axes close to bedding and minimum axes perpendicular to this plane. Directions of k max with weak imbrication mostly suggest flow away from centres of eruption located by gravity and remote sensing. Older ignimbrites (Upper and Lower Göreme, Akdag-Zelve) from the Çardak Centre are all of normal polarity. Later ignimbrites, partly erupted from the Derinkuyu Centre, comprise the Sarımaden (R), Cemilköy (R), Tahar (R), Kızılkaya (R), Incesu (N) and Valibaba-Sofular (R) ignimbrites. The overall (reversed) group mean is D/ I=174/−51° ( N=10 units, R=9.84, α 95=6.6°, k=55) and all magnetisation directions from the Upper Göreme (9.0 Ma) onwards are rotated anticlockwise with respect to Eurasian and African palaeofields. This sense of rotation characterises most of central Anatolia and averages 9±5° in this sector. The rotation rate from 8 to 1 Ma BP was ∼1.25°/Ma but it appears to have accelerated during the latter part of the Quaternary to about an order higher than rates determined from GPS. Rotation has resulted from extrusion of fault blocks during tectonic escape of the Anatolian collage to the southwest and followed crustal thickening as the Afro-Arabia Plate has continued to impinge differentially into Eurasia. Cenozoic magnetic inclinations are systematically shallower across Anatolia than inclinations expected from the geocentric dipole model and the apparent polar wander of bordering major plates. Only part of this difference (∼400 km) can be accommodated by northward movement and crustal thickening in Central Anatolia since mid-Miocene times. Shallow inclinations observed in the Aegean region extend into Turkey; they are observed in young volcanics and appear to reflect a regional geomagnetic anomaly. The pattern of neotectonic declinations across Anatolia shows rotations that are strongly anticlockwise rotated in the east near the Arabian pincer but diminish towards the west to become zero or slightly clockwise at the western extremity of the collage. Rotations also seem to become generally younger towards the south. Crustal deformation has therefore been distributed and the net effect of terrane extrusion to the west and south has been to expand the curvature of the Tauride Arc and, by inference, the Cyprus Arc.