How much time is needed for laccolith formation? A new approach based on a case study from Csódi-hegy, Dunabogdány, Hungary

The Csodi-hegy laccolith belongs to the Middle Miocene Borzsony and Visegrad Andesite Formation, and is built up by fluidal amphibole biotite dacite. This is a small, typical laccolith as shown by its size (Dl = 11000-1200 m, D2 = 900-1000 m, A ~ 150 m), shape, areal extent of 1 km2 and aspect ratio of 0.08 to 0.14. The fluidal structure of the laccolith is the result of alternation of dark and light bands. The thickness of the bands is in cm-dm scale. This structure and the feeding channels are very well exposed here thanks to quarrying activity. The time span-calculation was performed by counting of the individual bands, by volume estimations and by detailed magnetostratigraphic study. For the calculation of magma transport and growing-time the following assumptions were made: 6-8 km depth of the magma chamber, pressure of 8-10 kbars, temperature of 850-900 °C, a rate of ascent 1 mm/20-36 hours, 15 cm as the average width of a single band, a relative depth for emplacement about 450 m and the volume of t...