This research exploits a combination of field, paleomagnetic and rock-magnetic techniques to correlate locate the source and investigate several ignimbrites from two selected regions of Turkey, belonging to two large silicic ignimbrite systems : the well-investigated Cappadocia region (central Anatolia) and the poorly studied Afyon-Eskişehir region (western Anatolia). Investigation of the Upper Miocene Kızılkaya ignimbrite (Cappadocia region) consisted in a stratigraphic rock-magnetic study of the ignimbrite unit, which is considered to be a single flow and cooling unit. Remanent magnetization, magnetic fabric (AMS, AIRM and AARM) and magnetic mineralogy investigations were performed at 35 sites in 7 areal distributed localities at different distance from the vent position inferred by Le Pennec et al. (1998) and different stratigraphic heights, for a total of 444 specimens. Magnetic remanences are not vertically homogenous through the deposits. Two cases are distinguished: (1) a stable TRM, whose direction is consistent with previous literature data (Piper et al., 2002) and (2) two magnetization components with overlapping blocking temperature and coercivity spectra. These situations have been referred respectively to the occurrence of only primary Ti-magnetite, and primary Timagnetite plus secondary magnetic phases (alterated Timagnetite and/or hematite). The AMS fabric varies vertically throughout the deposit; based on the angle between the direction of the magnetic lineation K1 and that of the foliation plunge K3, three types of fabric are evidenced: normal, oblique and transverse. After have attested a primary origin of the magnetic fabric, the AMS was firstly enhanced by discarding all specimens whose density values differ more than +/- 1σ from the site mean value. This resulted in the elimination of the oblique fabrics, which are interpreted as an orientation disturbance due to local occurrence of pumices and lithic clasts in the specimens. Measurement of the AIRM and AARM pointed out that MD Timagnetite is the main carrier of the fabric, which suggests that the magnetic fabric is a reliable proxy for flow directions. Investigation of the Early-Upper Miocene ignimbrite succession exposed in the region of Afyon- Eskişehir consisted in a stratigraphic-sedimentologic and rock-magnetic study of the ignimbrite deposits over a ≈14,300 km2 extended area, in order to locate the source by combining field data and magnetic fabric flow directions. Measurement of the stratigraphic sections, performed at 76 distributed localities, led to ignimbrite correlations and production of isopach and isopleth maps. The ignimbrite succession consists of at least three distinct eruptions that originated the Incik, Sabuncu and Seydiler ignimbrites, different for age, areal distribution, structure and textural features of the deposits. Magnetic investigation consisted in magnetic mineralogy and magnetic fabric analyses (AMS and AIRM), was performed at 22 distributed localities for a total of 36 sites at different stratigraphic heights and 600 specimens. Both field data and magnetic fabric results concur for two source areas. The source area of the Incik and Sabuncu ignimbrites is identified with the Kırka caldera, a ≈20 x 20 km extended area where the presence of a resurgent dome has been detected; source area of the Seydiler ignimbrite is identified in the proximity of the village of Bayat. Volume calculations based on field data pointed out a VEI index of 7 for the Incik and Seydiler ignimbrite, 6 for Sabuncu ignimbrite, evidencing Plinian eruptions; the correspondent magnitude M (Pyle, 2000) is greater than 7 for each ignimbrite.
| Identifer | oai:union.ndltd.org:CCSD/oai:tel.archives-ouvertes.fr:tel-00999468 |
| Date | 14 March 2014 |
| Creators | Agro, Alessandro |
| Publisher | Université Blaise Pascal - Clermont-Ferrand II |
| Source Sets | CCSD theses-EN-ligne, France |
| Language | English |
| Detected Language | English |
| Type | PhD thesis |
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