Surface geochemical and geophysical studies for geothermal exploration at the southern volcanic rift zone of Tenerife, Canary Islands, Spain

A joint geochemistry and magnetotellurics survey was carried out in the southern volcanic rift zone of Tenerife (Canary Islands, Spain) covering an area ∼100 km2 for geothermal exploration purposes. Soil CO2 and H2S diffuse effluxes, 222Rn and 220Rn activities, soil He, H2, N2, CO2, O2 and H2S concentrations and isotopic composition of CO2 were measured in 557 selected sampling sites. Magnetotelluric survey (MT) was carried out in the northern part of the study area. A total of 47 MT sites were surveyed and a new 3-D resistivity model was obtained. The observed geochemical anomalies at the soil surface have allowed the detection of areas of deep-seated gas emanations as well as the identification of high vertical permeability volcano-tectonic features in the study area. The resistivity distribution model shows a prominent low-resistivity structure interpreted as a clay alteration cap of variable thickness that might play a role on the mechanism of upward motion of deep-seated gases from the volcano-geothermal system. This is supported by positive correlation between thickness of clay alteration cap and helium emission.