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The Syabru-Bensi hydrothermal system in central Nepal: 1. Characterization of carbon dioxide and radon fluxes

Girault, F., Perrier, F., Crockett, R. G. M., Bhattarai, M., Koirala, B. P., France-Lanord, C., Agrinier, P., Ader, M., Fluteau, F., Gréau, C. and Moreira, M. (2014) The Syabru-Bensi hydrothermal system in central Nepal: 1. Characterization of carbon dioxide and radon fluxes. Journal of Geophysical Research: Solid Earth. 119(5), pp. 4017-4055. 2169-9313.

Item Type: Article
Abstract: The Syabru-Bensi hydrothermal system (SBHS), located at the Main Central Thrust zone in central Nepal, is characterized by hot (30–62°C) water springs and cold (<35°C) carbon dioxide (CO2) degassing areas. From 2007 to 2011, five gas zones (GZ1–GZ5) were studied, with more than 1600 CO2 and 850 radon flux measurements, with complementary self-potential data, thermal infrared imaging, and effective radium concentration of soils. Measurement uncertainties were evaluated in the field. CO2 and radon fluxes vary over 5 to 6 orders of magnitude, reaching exceptional maximum values of 236 ± 50 kg m−2 d−1 and 38.5 ± 8.0 Bq m−2 s−1, with estimated integrated discharges over all gas zones of 5.9 ± 1.6 t  d−1 and 140 ± 30 MBq d−1, respectively. Soil-gas radon concentration is 40 × 103 Bq m−3 in GZ1–GZ2 and 70 × 103 Bq m−3 in GZ3–GZ4. Strong relationships between CO2 and radon fluxes in all gas zones (correlation coefficient R = 0.86 ± 0.02) indicate related gas transport mechanisms and demonstrate that radon can be considered as a relevant proxy for CO2. CO2 carbon isotopic ratios (δ13C from −1.7 ± 0.1 to −0.5 ± 0.1‰), with the absence of mantle signature (helium isotopic ratios R/RA < 0.05), suggest metamorphic decarbonation at depth. Thus, the SBHS emerges as a unique geosystem with significant deep origin CO2 discharge located in a seismically active region, where we can test methodological issues and our understanding of transport properties and fluid circulations in the subsurface.
Uncontrolled Keywords: CO2, radon, gas fluxes, accumulation chamber, hydrothermal system, Nepal Himalayas
Subjects: G Geography. Anthropology. Recreation > GB Physical geography > GB651 Hydrology. Water > GB980 Ground and surface waters
Q Science > QE Geology > QE500 Dynamic and structural geology
Creators: Girault, Frédéric, Perrier, Frédéric, Crockett, Robin G M, Bhattarai, Mukunda, Koirala, Bharat Prasad, France-Lanord, Christian, Agrinier, Pierre, Ader, Magali, Fluteau, Frédéric, Gréau, Claire and Moreira, Manuel
Publisher: American Geophysical Union
Faculties, Divisions and Institutes: Faculties > Faculty of Arts, Science & Technology > Environmental Science
Date: 12 May 2014
Date Type: Publication
Page Range: pp. 4017-4055
Journal or Publication Title: Journal of Geophysical Research: Solid Earth
Volume: 119
Number: 5
Language: English
ISSN: 2169-9313
Status: Published / Disseminated
Refereed: Yes

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