The western Eger Rift in the Czech Republic is a currently inactive volcanic area characterized by earthquake swarms and degassing of mantle-derived fluids. Gases obtained from minerals and from repeatedly sampled free gases are used to trace the origin and evolution of volatiles and determine the conditions of the magma reservoir. Helium isotopes in fluids and minerals are up to 5.95 RA, with 20Ne/22Ne ratios up to ~11.0 and 21Ne/22Ne ratios up to ~0.048, suggesting a mixed atmospheric-mantle source for neon. Some crustal input may also be present. The slightly lower-than-mantle He isotopic ratios and the variability in Ne isotopic compositions indicate that these gases may have been impacted by a subduction-related crustal component during the Variscan (or Hercynian) Orogeny. 40Ar/36Ar ratios are higher than atmospheric levels and arrive up to 4680, indicating a mixture of atmospheric and mantle sources. Thermobarometry of pyroxene mineral grains reveals temperatures and pressures suggesting that the crystallization started at ~75 km depth and ended at ~20 km depth following a smooth p-T course. This implies diverse magma ascent conditions.
A total of 56 gas samples were collected from two intensively degassing areas in the western Eger Rift (Czech Republic), namely the mofette fields of Bublák and Hartoušov. From the Hartoušov mofette field, 24 gas samples of fluids ascending in two boreholes (F1:∼28 m depth and F2: ∼108 m depth) and 22 samples of gases emerging in two nearby ponds [surface expressions Hartoušov Mofette (HM) and Hartoušov Mofette South (HMS)] were taken. Ten samples were collected from a pond in the Bublák mofette field (Bbl). In addition to the gas samples, ten rock samples were collected from rock exposures [i.e. Libá (LI) and Číhaná (CI) in quarries, Horní Slavkov (HS1&2), Pila (PI), Dolní Dražov (DD), Kadaň (KN), Horní Paseky (HP), and Slapany (SL) in natural cliffs, and Hlinky (HL) in an outcrop] within the western Eger rift area. In addition, six samples of ultramafic nodules/xenoliths were obtained from the Quaternary tephra deposit of the Mýtina maar and from Železná hůrka scoria cone.
Gas and rock sampling:
This SNF proposal seeks funding for the continuation of the Swiss contribution to the Lake Van Drilling Project executed by the International Continental Scientific Drilling Program (ICDP). Among other previous Swiss ICDP engagements, the Lake Van Drilling project was pivotal in triggering the newly established SNF-supported Swiss membership in ICDP. Further, the SNF Swiss contribution is a central building block of the entire ICDP PaleoVan initiative. Lake Van is the fourth-largest terminal lake in the world, extending 130 km WSW-ENE 1674 m above sea level on a high plateau in eastern Anatolia, Turkey. The lake is surrounded by active volcanoes within a tectonically active area and it is known to accumulate fluids emanating from the Earths mantle. The partly annually-laminated sedimentary record down to 220 m depth recovered from Lake Van during the ICDP PaleoVan drilling operations in 2010 has been shown to be an excellent palaeoclimate and palaeoenvironment archive. The continuous, high-resolution continental sequence, which covers several glacial-interglacial cycles (greater than 500 kyr), represents a unique possibility to investigate in detail the climatic, environmental, and volcanic changes that occurred in the Near East, the cradle of human civilization, during much of the Quaternary Period. Furthermore, the sediments contain an invaluable record of past earthquake activities, allowing the construction of a catalogue of prehistoric earthquakes and making it possible to study fluid transport in the continental crust that was triggered by seismic events. In this context, the societal vulnerability of the area to seismic hazards was dramatically documented by the occurrence of the devastating earthquake of magnitude 7.2 close to the city of Van on 23 October 2011 (hereafter referred to as the VE11 earthquake). This unfortunate and tragic event offers a unique opportunity to calibrate the past seismic events recorded in the sediments of Lake Van and the related emission of fluids from the solid earth to a modern seismic analogue. Sediment and fluid transport triggered by this major seismic event need to be quantified in order to calibrate the sedimentological record, which is targeted by the follow-up field campaign proposed within this project extension. The continuation of the Swiss initiative, embedded in the overarching ICDP drilling project on Lake Van, encompasses all the 5 initial research modules (A-E) of the ongoing SNF project (200021-124981). Within this proposal extension, the extended modules (A*-E*) will focus on key issues and new developments that expand the initial topics, with a special emphasis on the recent major earthquake VE11 and its biogeochemical and sedimentological implications. At the same time, this extension will also allow the results that have already been acquired to be further analysed and written up for publication by the project team. A large number of publications is foreseen. (...)