Deep-seated geology of the granite intrusions at the Soultz EGS site based on data from 5 km-deep boreholes

The petrographic model for the deep-seated geology at the Soultz-sous-Forˆets Enhanced Geothermal System (EGS) site in the Rhine Graben, France, was revised on the basis of data from 5 km-deep wells. Several types of granite and sub-facies were characterized through thin-section analysis of drill cuttings. Various datalogs were studied to correlate them with petrography. The new geological model of the Soultz site is made up of a massive porphyritic granite that shows some paleo-weathering at its top, overlain by about 1400m of Mesozoic and Tertiary sediments. Between 2700 and 3200m depth, the same granite is highly fractured and hydrothermally altered. Below this zone, the granite is less fractured and is very rich in biotite and amphibole. Starting at 4700m depth is a younger, fine-grained, two-mica and amphibole-rich granite that intrudes into the porphyritic granite. © 2006 CNR. Published by Elsevier Ltd. All rights reserved.