Shallow sill and dyke complex in western Hungary as a possible feeding system of phreatomagmatic volcanoes in “soft-rock” environment |
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| Institution: | 1. Equipe Géomatériaux, Université Moulay Ismaïl, Faculté des Sciences, BP 11201 Zitoune, Meknès, Maroc;2. Géosciences Montpellier, Université de Montpellier 2, CNRS, Cc 60, Place Eugène Bataillon, 34095 Montpellier Cedex 05, France;3. Instituto Andaluz de Ciencias de la Tierra (IACT), CSIC and UGR, Avenida de las Palmeras 4, 18100 Armilla, Granada, Spain;1. Volcanic Risk Solutions, Institute of Agriculture and Environment, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand;2. School of Geography, Environment and Earth Sciences, Victoria University of Wellington, PO Box 600, Wellington 6140, New Zealand;3. Japan Agency for Marine Earth Science and Technology (JAMSTEC) 2-15 Natsushima-cho Yokosuka, Kanagawa 237-0061, Japan;4. Geology Department, University of Otago, PO Box 56, Dunedin 9054, New Zealand |
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| Abstract: | Neogene alkaline basaltic rocks in the western Pannonian Basin are eroded remnants of maars, tuff rings, tuff cones, scoria cones and lava fields. The erosion level of these volcanoes is deep enough to expose diatreme zones associated with the phreatomagmatic volcanoes. The erosion level is deeper yet in the west, exposing shallow dyke and sill swarms related to former intra-plate volcanoes. The basanitic sills are irregular in shape and their lateral extent is highly variable. Individual sills reach a thickness of a few tens of metres and they commonly form dome-like structures with rosette-like radial columnar joint patterns. The largest sill system identified in this region is traceable over kilometres, and forms a characteristic ridge running north-east to south-west. Elevation differences in the position of the basanitic sills within an otherwise undisturbed “layer cake-like” siliciclastic succession indicate emplacement of the basanite magma at multiple levels over kilometre-scale distances. The margins of sills in the system are irregular at a dm-to-mm-scale. Undulating contacts of the sills together with gentle thermal alteration in the host sediment over cm-to-dm distances indicate the soft, but not necessarily wet state of the host deposits at the time sills were intruded. Parts of the sill complex show a complicated relationship with the host sediment in form of peperitic zones and irregularly shaped, disrupted, peperite textures. This is interpreted to reflect inhomogenities in water content and rheology of the siliciclastic deposits during intrusion. The current summit of the longest continuous ridge preserves a small diatreme that seems to cut through an otherwise disk-like sill indicating of relationship between sill emplacement and phreatomagmatic explosive eruptions. |
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