Determination and appraisal of pyroclastic flow directions using magnetic anisotropy on ignimbrites from Mount Aragats, Armenia

• Applicant: Professor Dr. Valerian Bachtadse
• Subject Area: Geophysics
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 273101564

Mount Aragats, one of the largest stratovolcanoes on the Turkish-Iranian plateau, is located rather close to Yerevan and only about 30 km from the only nuclear power plant in Armenia (ANPP). Besides a series of lava flows, Mt. Aragats is believed to be the locus nascendi of at least one huge pyroclastic eruption resulting in a widespread ignimbrite sheet with a radius of about 50 km. In contrary to well studied ignimbrite deposits in Europe (e.g. Campanian Ignimbrite, Italy) or the USA (e.g. Bishop Tuff, California), the precise eruption evolution and succession is still rather unconstrained and whether all ignimbrites have originated from Mt. Aragats is still debated. The diversity of geochemical composition and color of the ignimbrites add some uncertainty to the problem. We propose a study using paleomagnetic parameters to add important constraints to the py- roclastic eruption. The workflow will start by constraining the temporal relationship between ignimbrites with different lithological properties by applying paleomagnetic methods in order to determine the direction of the natural remanence. Based on the fact that ignimbrites have a rather fast cooling history it is a well known fact that these rocks record secular variation of the geomagnetic field which can be used to differentiate between flows of different age. In a next step we will analyse the magnetic anisotropy of the rocks and attempt to document how the pyroclastic flows (or flow) evolves and whether and how it is changing its flow characteristics (i.e. radially away from the center or topography controlled). This result can be used to investigate if a large eruption in the future is likely to hit the ANPP or maybe even the capital Yerevan. Finally, we will add rock-magnetic measurements to distinguish the carrier of the magnetic signal, which might help to get information about the thermal evolution of the flow during deposition. During a previous field trip twelve ignimbrite outcrops had already been sampled. Preliminary results show that (a) the magnetic signal of the ignimbrites is very strong, (b) characteristic magnetization directions of ten out of twelve outcrops are of normal polarity, (c) whereas the remaining two are of inverse polarity and (d) the magnetic mineral content varies slightly. These results will be enlarged in order to obtain a statistically significant data set. Preliminary results of the anisotropy of magnetic susceptibility at one outcrop to the south of Mt. Aragats (IG3) shows a tight clustering and suggests a southward direction of the flow radially away from Mt. Aragats. A short fieldtrip to Armenia will be used to add additional samples from sites previously unsam- pled to the collection.

• DFG Programme: Research Grants
• International Connection: Armenia, Austria
• Cooperation Partners: Dr. Roman Leonhardt; Dr. Khachatur Meliksetian; Dr. Gevorg Navasardyan