IMPACT OF METEORIC FLUID FLOW ON THE THERMAL EVOLUTION OF THE GOTTHARD MASSIF; INSIGHTS FROM ALPINE RAILWAY TUNNELS
Apatite (AHe) and zircon (ZHe) (U-Th)/He ages will be measured for 30 samples collected from the length of the tunnel through the Piora Zone, as well as corresponding surface transects, in order to trace the extent to which meteoric fluid has depressed the underlying isotherms throughout the exhumation history of the complex. Samples adjacent to the Piora Zone have been analyzed and show AHe ages of ~2.0 Ma, which represent cooling of the massif through 70°C, unperturbed by the Piora Zone aquifer. Ages within the Piora Zone that are significantly older will indicate that meteoric fluid has depressed isotherms substantially enough to affect the closure of apatite and zircon during exhumational cooling. The resulting data will reveal the topologic evolution of the AHe and ZHe closure temperature isotherms through times t1 (tunnel samples) and t2, (surface samples) shaped by the coupled effect of meteoric fluid-flow and topography.