Subsurface granites in the Franconian Basin as the source of enhanced geothermal gradients: a key study from gravity and thermal modeling of the Bayreuth Granite

de Wall H, Schaarschmidt A, Kämmlein M, Gabriel G, Bestmann M, Scharfenberg L (2019)

Publication Type: Journal article

Publication year: 2019

Journal

DOI: 10.1007/s00531-019-01740-8

Abstract

The Franconian Basin in NE Bavaria is a region of gravity low between the Bohemian Massif in the east and the Kraichgau Terrane in the west. Borehole measurements have identified the northern part of the Franconian Basin as a regional geothermal anomaly and new heat flow calculations give values of > 100 mW/m². Distinct negative Bouguer anomalies observed in this basin are modeled as granitic intrusions in the Saxothuringian basement that underlies the Permo-Mesozoic units. The interpretation of gravity gradients, in combination with the filtering of gravity data, gives the possible depth constraints of the intrusive bodies. The resulting depths were cross-checked using microstructural studies of quartz veins in the basement rocks (at > 1341 m depth). The quartz shows structures typical for low-temperature plasticity and we infer a deformation temperature of ca. 300 °C. This indicates a considerable pre-Permian uplift of at least 7 km for parts of the Saxothuringian basement and supports depth estimates from gravity data. The heat supply of granitic intrusions by radiogenic decay is modeled considering several scenarios for the geological conditions recovered by the Obernsees borehole (model for conductive heat transfer). The 1390 m-deep drillhole is in a marginal position to the most-pronounced negative Bouguer anomaly. It could be shown that the Saxothuringian basement, including heat-producing granites (heat production rates: 4–6 μW/m³), covered by the insulating sedimentary rocks (1.35 km of Permian to Lower Jurassic units), can account for the enhanced geothermal gradient (38 °C/km) that were measured in the borehole.

Authors with CRIS profile

Involved external institutions

Leibniz-Institut für Angewandte Geophysik (LIAG) Germany (DE)

How to cite

APA:

de Wall, H., Schaarschmidt, A., Kämmlein, M., Gabriel, G., Bestmann, M., & Scharfenberg, L. (2019). Subsurface granites in the Franconian Basin as the source of enhanced geothermal gradients: a key study from gravity and thermal modeling of the Bayreuth Granite. International Journal of Earth Sciences. https://doi.org/10.1007/s00531-019-01740-8

MLA:

de Wall, Helga, et al. "Subsurface granites in the Franconian Basin as the source of enhanced geothermal gradients: a key study from gravity and thermal modeling of the Bayreuth Granite." International Journal of Earth Sciences (2019).

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