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


Piper J., Gursoy H. , Tatar O.

JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, cilt.117, ss.237-262, 2002 (SCI İndekslerine Giren Dergi) identifier identifier

  • Cilt numarası: 117
  • Basım Tarihi: 2002
  • Doi Numarası: 10.1016/s0377-0273(02)00221-4
  • Dergi Adı: JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH
  • Sayfa Sayıları: ss.237-262

Özet

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 Goreme, Akdag-Zelve) from the Cardak Centre are all of normal polarity. Later ignimbrites, partly erupted from the Derinkuyu Centre, comprise the Sarimaden (R), Cemilkoy (R), Tahar (R), Kizilkaya (R), Incesu (N) and Valibaba-Sofular (R) ignimbrites. The overall (reversed) group mean is D/I= 174/-51degrees (N = 10 units, R = 9.84, alpha(95) = 6.6degrees, k= 55) and all magnetisation directions from the Upper Goreme (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 +/- 5degrees in this sector. The rotation rate from 8 to 1 Ma BP was similar to 1.25degrees/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 (similar to400 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