Publication

Journal	Geology
Title of proceedings	Geology
DOI	10.1130/g45394.1

URL	https://watermark.silverchair.com/g45394.pdf?token=AQECAHi208BE49Ooan9kkhW_Ercy7Dm3ZL_9Cf3qfKAc485ysgAAAgQwggIABgkqhkiG9w0BBwagggHxMIIB7QIBADCCAeYGCSqGSIb3DQEHATAeBglghkgBZQMEAS4wEQQMRXS-kipMh03YM_OYAgEQgIIBt6buQXwzRxNImwt57QjgzAa-DCHIlbsYFrQSbuA3Jo-0YIBG6eAF9eIuPlg_IrE91jXE-lHK26Sg369njuiwtC2FEvOWH
Type of Open Access	Publisher (Gold Open Access)

Warm springs emanating from deep-reaching faults in orogenic belts with high topography and orographic precipitation attest to circulation of meteoric water through crystalline bed- rock. The depth to which this circulation occurs is unclear, yet it is important for the cooling history of exhuming orogens, for the exploitation potential of orogenic geothermal systems, and for the seismicity of regional faults. The orogenic geothermal system at Grimsel Pass, Swiss Alps, is manifested by warm springs with a clear isotopic ngerprint of high-altitude meteoric recharge. Their water composition and their occurrence within a 3 Ma fossil up ow zone render them particularly favorable for estimating the temperature along the deep ow path via geochemical modeling. Because the background geotherm has remained stable at 25 °C/km and other heat sources are unavailable, the penetration depth can be derived from the deep-water temperature. We thus estimated the base of the Grimsel system to be at 230–250 °C and 9–10 km depth. We propose that deep temperatures in such systems, par- ticularly those with normal background geotherms (<30 °C/km), have been systematically underestimated. Consequently, far more enthalpy may be accessible for geothermal energy exploitation around the up ow zones than previously thought. Further, the prevalence of recent earthquake foci at Grimsel at ≤10 km suggests that meteoric water is involved in the seismicity of the host faults. Our results therefore call for reappraisal of the heat budget and the role of meteoric water in seismogenesis in uplifting orogens.