TSK 11 Göttingen 2006 Timar-Geng et al.
 Two-dimensional finite ele-
 ment models of convective
 heat transfer in the upper
 crust — implications for the
 interpretation of fission-track
 data Poster
 Zoltan Timar-Geng1 Andreas Henk1
 Andreas Wetzel2
 Fission-track (FT) thermochronology is
 a tool routinely used for studies of sur-
 face denudation because of its sensitiv-
 ity to the low temperatures found in
 the uppermost part of the crust. FT
 ages and associated track length dis-
 tributions are regularly interpreted as-
 suming a steady-state temperature field
 and only conductive heat transfer. How-
 ever, application of the method to ther-
 mochronological studies based on such
 interpretations may lead to invalid con-
 clusions, if the temperatures at a certain
 depth had actually varied with time.
 For example, the convective transfer of
 heat by hydrothermal fluids can cause
 transient thermal events within the up-
 per crust. In particular, fluid circulation
 along fault zones can result in substan-
 tial convective heat transport and cause
 temperature anomalies in the adjacent
 rocks (Zuther & Brockamp 1988, Flem-
 ing et al. 1998, Lampe & Person 2002,
 Bächler et al 2003). As a consequence,
 any refined interpretation of FT data re-
 quires a thorough understanding of the
 upper crustal temperature field and its
 evolution through time.
 The main objective of this study is to as-
 sess quantitatively how convective heat
 transport influences the upper crustal
 1 Geologisches Institut, Universität
 Freiburg, Albertstr. 23b, D-79104 Freiburg
 2 Geol.-Paläont. Institut, Universität Basel,
 Bernoullistr. 32, CH-4056 Basel
 temperature field as well as the cooling
 ages and track length distributions ob-
 served in apatite FT data. Modelling
 utilizes Finite Element techniques and
 the software FEFLOW, respectively. In-
 depth parameter studies (including fault
 geometry, erosion rate, hydraulic po-
 tential, hydraulic and material proper-
 ties) are conducted on two-dimensional
 (cross-sectional) models of fault zones.
 After evaluating the relative importance
 of different variables relevant to fluid
 circulation in a palaeogeothermal sys-
 tem, the time-temperature (tT) histo-
 ries of particle points are tracked as
 erosion moves them closer to surface.
 These tT-paths are used in a forward
 modelling approach to determine the ex-
 pected FT age and track length distri-
 butions. For each parameter study, a
 corresponding set of FT parameters is
 produced, thus, providing a catalogue
 of FT ages and track length distribu-
 tions, which will help to interpret real
 data sets.
 One of the goals of the project is to
 investigate the regional impact of con-
 vective heat transport on the inter-
 pretation of FT data and other ther-
 mal data from the Black Forest (SW-
 Germany). The modelling techniques
 outlined above will be applied to field
 data from the Baden-Baden and Offen-
 burg troughs in the northern and central
 Black Forest.
 References
 Bächler D, Kohl T & Rybach L (2003) Im-
 pact of graben-parallel faults on hydrother-
 mal convection; Rhine Graben case study.
 Phys. Chem. Earth, 28, 431–441
 Fleming CG, Couples GD & Hazeldine RS
 (1998) Thermal effects of fluid flow in steep
 fault zones. Ű In: Jones G, Fisher QJ &
 Knipe RJ (eds) Faulting, fault sealing and
 fluid flow in hydrocarbon reservoirs. Geol
 Soc. London, Spec. Publ. 147, 217–229
 1
Timar-Geng et al. TSK 11 Göttingen 2006
 Lampe C & Person M (2000) Episodic hy-
 drothermal fluid flow in the Upper Rhine-
 graben (Germany). Journal of Geochemical
 Exploration, 69/70, 37–40
 Zuther M & Brockamp O (1988) The fos-
 sil geothermal system of the Baden-Baden
 trough (Northern Black Forest, Germany).
 Chem. Geol. 71, 337–353
 2