Pages: 325 - 343
Abstract: The Middle Miocene volcanic evolution of the Börzsöny Mountains, North Hungary, is presented, correlating new volcanological, petrological, geochemical, geophysical and paleontological data and establishing a detailed stratigraphy on the basis of additional K/Ar radiometric and paleomagnetic measurements. For the earliest volcanic activity, previous biostratigraphy showing an Early Badenian age has been confirmed and precisely defined by paleomagnetic investigations. The first-stage volcanic formations (16.5–16.0 Ma), deposited in a shallow marine environment, include resedimented, syn-eruptive, garnet-bearing dacitic volcaniclastics (originating mostly from small-scale ignimbrite eruptions) and coeval, garnet-bearing dacitic lava domes, sometimes with their volcaniclastic aprons. As the eruptions filled the marine basin, subaerial dacitic-andesitic volcaniclastics, comprising minor ignimbrites and different types of debris-flow deposits were also deposited. A part of the latter may have been related to the formation of two or three medium-sized calderas. The second stage (16.0–14.5 Ma) was characterized by andesitic lava dome activity terminated by a hydrothermal event. During the first half of this stage, a ca. 30° CCW rotation occurred. The third stage produced the most voluminous, moderately explosive, andesitic — basaltic andesitic High Börzsöny subaerial lava dome complex erupting up to the Badenian/Sarmatian boundary (ca. 13.7 Ma). Correlation of K/Ar geochronological and volcanological data shows that lava dome activity of the second and third stage may have been coeval with marine sedimentation in the southern Börzsöny.
Keywords: Miocene calc-alkaline volcanism, Borzsony Mountains, volcanology, geochemistry, paleomagnetism, K/Ar geochronologyDownload PDF document Show Text Version