1 3 Int J Earth Sci (Geol Rundsch) DOI 10.1007/s00531-014-1085-7 ORIGINAL PAPER Geometry of laccolith margins: 2D and 3D models of the Late Paleozoic Halle Volcanic Complex (Germany) T. Schmiedel · C. Breitkreuz · I. Görz · B.-C. Ehling Received: 3 February 2014 / Accepted: 13 October 2014 © Springer-Verlag Berlin Heidelberg 2014 was essential. A major finding of the 3D modelling is the presence of prolate sediment rafts, up to 1,400 m in length and up to 500 m in thickness, surrounded by Landsberg rhyolite. The sedimentary rafts dip away from the lacco- lith centre. The engulfing laccolith sheets reach thickness of 100–300 m. For other HVC laccolith units (Löbejün, Petersberg, Brachstedt), well data reveal vertical rhyolite/ sediment contacts or magma lobes fingering into the host sediments. HVC laccolith contact textures include small- scale shearing of the intruding magma and of the host sedi- ment. In addition, internal shear zones have been detected inside the rhyolite bodies. The present study suggests that the emplacement of successive magma sheets was an important process during laccolith growth in the HVC. Keywords GOCAD© · Well data · Magma sheet emplacement · Porphyritic rhyolite Introduction Traditionally, subvolcanic complexes have been in the focus of geological interest either as important factor in geological basin development or for their genetic link with economic resources/deposits. For the understanding of both, the geometry and dimensions of these complexes are the key elements. Three-dimensional modelling of basaltic sill complexes has been carried out based on seismic data of hydrocarbon plays, e.g. in the North Atlantic (Thom- son and Schofield 2008). The geometry of sills and lacco- liths, among others their aspect ratio (height by length), is strongly controlled by composition and thus by viscosity, and by magma volume (Bunger and Cruden 2011). The emplacement of laccoliths and the mode of vertical inflation are still a matter of debate. As one end member, Abstract Well data and core samples from the Late Paleozoic Halle Volcanic Complex (HVC) have been used to describe the geometry of the rhyolitic porphyritic lac- coliths and their margins. The HVC formed between 301 and 292 Ma in the intramontane Saale basin, and it com- prises mainly rhyolitic subvolcanic bodies (~300 km 3 ) as well as minor lava flows and volcaniclastic deposits. The major HVC laccolith units display aspect ratios ranging between 0.04 and 0.07, and they are separated by tilted and deformed Carboniferous–Permian host sediments. For the margin of the Landsberg laccolith, a major coarsely porphyritic unit of the HVC, an exceptional data set of 63 wells concentrated in an area of 10 km 2 reaching to depth of 710 m exists. It was used to explore the 3D geometry and textures, and to deduce an intrusion model. For a 3D visualization of the Landsberg laccolith margin, Geologi- cal Object Computer Aided Design; Paradigm ® software (GOCAD) was used. Curve objects have been derived from the intrusion–host contacts. Automated GOCAD ® methods for 3D modelling failed. As a result, manual refinement Electronic supplementary material The online version of this article (doi:10.1007/s00531-014-1085-7) contains supplementary material, which is available to authorized users. T. Schmiedel (*) · C. Breitkreuz Geology Department, TU Bergakademie Freiberg, Freiberg, Germany e-mail: tobiasschmiedel@web.de I. Görz Geophysics and Geoinformatics Department, TU Bergakademie Freiberg, Freiberg, Germany B.-C. Ehling Sachsen-Anhalt State Survey for Geology and Mining, Halle, Germany