Heat flow, heat production and crustal dynamics in the Central Alps, Switzerland☆

Abstract Interrelations between temperature field, crustal structure and crustal dynamics (vertical crustal movements) have been investigated along a selected profile: the Swiss Geotraverse which cross-sects in a NW-SE direction the following tectonic units: Rhine-Graben, Jura Mountains, Molasse Basin, Helvetic Nappes, Central Massifs with autochthonous cover, Penninic units, basement and sedimentary units of the Southern Alps (total length: 220 km). The corrected heat flow is slightly elevated along or close to the traverse (≈ 75 mW/m 2 ). Thermal effects of Alpine overthrusting and metamorphism on the surface gradient are negligible today. For steady-state calculations of the temperature field heat production has been determined experimentally for surface samples; for deep crustal rocks it was inferred from an empirical relationship between heat production and seismic compressional wave velocity or density. The temperature field shows downwarped isotherms where a pronounced inversion of seismic velocity and density occurs in the upper crust. The same area of the Central Alps (Lepontine gneiss region) exhibits the strongest recent crustal movements (vertical uplift ≈ 1 mm/yr). The Mohorovicic discontinuity is clearly not an isothermal surface; its asymmetric shape found by seismic and gravimetric measurements is likely to be a result of the early Alpine subduction tectonics.