Large-scale organization of carbon dioxide discharge in the Nepal Himalayas

Abstract

Gaseous carbon dioxide (CO 2) and radon-222 release from the ground was investigated along the Main Central Thrust zone in the Nepal Himalayas. From 2200 CO 2 and 900 radon-222 flux measurements near 13 hot springs from western to central Nepal, we obtained total CO 2 and radon discharges varying from 10 -3 to 1.6 mol s -1 and 20 to 1600 Bq s -1, respectively. We observed a coherent organization at spatial scales of ≈ 10 km in a given region: low CO 2 and radon discharges around Pokhara (midwestern Nepal) and in the Bhote Kosi Valley (east Nepal); low CO 2 but large radon discharges in Lower Dolpo (west Nepal); and large CO 2 and radon discharges in the upper Trisuli Valley (central Nepal). A 110 km long CO 2 -producing segment, with high carbon isotopic ratios, suggesting metamorphic decarbonation, is thus evidenced from 84.5°E to 85.5°E. This spatial organization could be controlled by geological heterogeneity or large Himalayan earthquakes. Key Points CO 2 and radon fluxes were measured near 13 hot springs in the Nepal HimalayasIntegrated CO 2 discharges are heterogeneous but coherently spatially organizedA 110 km long metamorphic CO 2 -producing segment is clearly defined