Volcanic evolution and stratigraphy of the Miocene Borzony Mountains, Hungary: An integrated study

The Middle Miocene volcanic evolution of the Borzsony Mountains, North Hung ary, is presented, correlating new volcanological, petrological, geochemica l, geophysical and paleontological data and establishing a detailed stratig raphy on the basis of additional K/Ar radiometric and paleomagnetic measure ments. For the earliest volcanic activity, previous biostratigraphy showing an Early Badenian age has been confirmed and precisely defined by paleomag netic investigations. The first-stage volcanic formations (16.5-16.0 Ma), d eposited in a shallow marine environment, include resedimented, syn-eruptiv e, garnet-bearing dacitic volcaniclastics (originating mostly from small-sc ale ignimbrite eruptions) and coeval, garnet-bearing dacitic lava domes, so metimes with their volcaniclastic aprons. As the eruptions filled the marin e basin, subaerial dacitic-andesitic volcaniclastics, comprising minor igni mbrites 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 m edium-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 degrees CCW rotation occurred. The thir d stage produced the most voluminous, moderately explosive, andesitic - bas altic andesitic High Borzsony subaerial lava dome complex erupting up to th e Badenian/Sarmatian boundary (ca. 13.7 Ma). Correlation of K/Ar geochronol ogical and volcanological data shows that lava dome activity of the second and third stage may have been coeval with marine sedimentation in the south ern Borzsony.