Geophysical signature of the transition zone between the sedimentary cover and the basement: an analogue approach to help de-risking geothermal prospects

TL;DR

This study investigates the physical properties of a transition zone between sedimentary cover and basement in the Vosges Mountains to improve geothermal prospecting methods, using an analogue approach on exhumed rocks.

Contribution

It provides new insights into the electrical and acoustic properties of the transition zone, aiding in de-risking geothermal exploration.

Findings

Electrical properties vary across the transition zone.

Acoustic properties reveal fracture and alteration patterns.

Results help interpret geophysical data in geothermal exploration.

Abstract

Within the frame of the ANR-funded CANTARE-Alsace project, we have undertaken a multi-scale and multidisciplinary approach to increase our knowledge of the transition zone between the sedimentary cover and the basement and provide fundamental knowledge for the assessment of its geothermal potential. In this paper, we report out the results of a study performed on an exhumed transition zone in the Ringelbach area in the Vosges Mountains, on the flank of the Rhine graben. In this analogue of a deeply buried transition zone of the Rhine Graben, a thin layer of Triassic sandstones is still present on the top of the fractured and altered granitic basement providing the opportunity to study in-situ the physical properties of this transition zone. In this paper, we focused on electrical and acoustic properties of the transition zone as they are the main physical parameters usually assessed with the help of geophysical methods during the exploration phase of a geothermal project.