TSK 11 Göttingen 2006 Scholz et al.
 Figure 1: Stretched crystals of quartz and
 chlorite. Note how the quartz crystal from
 the matrix gets involved in the vein build
 up and indicates a distinct direction of
 grain growth. The dark spotted areas in the
 vein itself are fluid inclusion trails. What
 do they tell us about the vein growth?
 Sample from 1447.5mTVD.
 Microstructural analysis of
 the RWTH-1 cores in thin-
 sections Vortrag
 Katerina Scholz1 Janos L. Urai1 Ute
 Trautwein2 Peter A. Kukla2
 Introduction
 The Aachen RWTH-1 well was drilled
 to 2544mTVD for geothermal purposes
 and gives substance to extensive geosci-
 entific research. It is located in a hy-
 drothermally and seismically active area
 of the Aachen Anticline, 500m NW of
 the Aachen Overthrust and 420m ENE
 of the Laurensberg Fault. The main fo-
 cus of this PhD work is the structural
 and microtectonic analysis of the cores
 sampled.
 For 94% of the total well length the col-
 lected cuttings give information of the
 lithology and stratigraphy of the sub-
 surface. A total of 145.5m was cored in
 1 Geologie-Endogene Dynamik, RWTH
 Aachen, Germany 2 RWTH Aachen,
 Department of Geology, Germany
 Figure 2: This vein gives an example of a
 vein on which the ‘crack seal’ models given
 so far can be critically tested on. How did
 the various minerals quartz, chlorite and
 calcite get deposited in one vein? Sample
 from 1392.5mTVD.
 three different intervals. A complete set
 of wireline measurements including high
 resolution borehole image allow map-
 ping of fractures and folds, and linking
 the core to the logs. About 100 core
 samples were selected for detailed mi-
 crostructural analysis.
 First results
 Microstructural analysis of veins formed
 in Mode I and II fractures shows a wide
 range of structures, depending on host
 rock lithology, fluid composition and
 opening history. Four different vein gen-
 erations have been interpreted based on
 overprinting relationships (Fig. 1).
 The first of these is interpreted to have
 formed during burial, under conditions
 of increasing pore pressure. The subse-
 quent generations are interpreted to be-
 long to the Variscan compression event.
 Microstructures vary considerably, be-
 tween fibrous antitaxial calcite veins in
 siltstone, unitaxial streched crystals in
 siltstone, blocky calcite veins in car-
 bonate, and multiphase chlorite-quartz-
 calcite veins with spectacular syntax-
 1
Scholz et al. TSK 11 Göttingen 2006
 ial fibrous microstructures. This last
 type of veins which was formed at lower
 greenschist facies conditions allow a crit-
 ical test of the available models of crack-
 seal vein evolution (Fig. 2). We present
 computer models of syntaxial crystal
 growth during delocalized cracking in a
 polyphase vein which may explain the
 observed microstructures. In a later
 event part of the veins were deformed
 into cataclasites under conditions of
 high shear stress.
 2