A Kovászna területén feláramló CO2 eredetének meghatározása

Determining the origin of the CO2 gases in the Covasna area

Abstract

Global CO₂ emanation in relation with global climate change helps us to better understand the global CO₂ cycle. In the southeastern part of the Carpathian-Pannonian region one of the most intensive locality concerning CO₂ emanation is the city Covasna and surroundings. The geological setting of Covasna (i.e., lying triple boundary of the Audia and Tarcau nappe and the deep normal fault at the eastern boundary of the Kézdi basin) assumes that CO₂ emanation is highly controlled by the connection of the tectonic structures and thus a forming a continuous channel between surface and mantle. Previous studied, based on the stable isotopic composition of the outgassing CO₂ (δ¹³C, δ¹⁸O), suggested that the gas originated from a deep crustal, partially mantle source. In our study, we further studied the issue, regarding the origin of the gas and water, and for this we sampled springs from the Covasna city centre and from springs located in the Hankó valley that lies in northeastern part of the city. Additionally, we also measured the stable isotopic composition of the noble gases that, like CO₂, are dissolved in water as these gases are inert in the Earth crust and mantle. Our results strengthen the dominantly deep lithospheric origin for CO₂ and even H₂O. In contrast to previous models, we propose that the crustal component of the fluids originates from the lower crustal region of the crust and not from the sinking Vrancea slab. The release of the fluids can be owed to a suspected heat anomaly located at the crust-mantle boundary.

Kivonat

A globális szén-dioxid (CO₂) természetes kigázosodásának tanulmányozása jelentősen hozzájárul a globális klímaváltozás megértéséhez. A Kárpát-Pannon régió délkeleti részén fekvő Kovászna térségében jelentős mennyiségű nem vulkáni CO₂ kigázosodás figyelhető meg. Kutatásunk során a Kovászna központjának (Fő tér), az Erdészeti Hivatal (Vajna) és a várostól délkeletre fekvő Hankó-völgy forrásainak víz (δ²H, δ¹⁸O) és a vízben oldott gáz stabilizotóp arányát (δ³He, δ¹³C, δ¹⁸O) vizsgáltuk meg.