engleski

Development of columnar jointing in albite rhyolite in a rapidly cooling volcanic environment (Rupnica, Papuk Geopark, Croatia)

The Rupnica locality became the first protected geosite in Croatia in 1948 due to a well-exposed phenomenon of columnar jointing developed in albite rhyolite. According to the geochemical signature, melt that originated from mid-crustal depths (10-15 km) reached a shallow emplacement level as a high-temperature lava. Non-destructive statistical analysis conducted at the geosite revealed that relatively narrow (29.4±6.3 cm), predominantly four- and five-sided columns, tightly packed striae (4.8±2.1 cm) and small amplitude of wavy sets of columns (wavelength of 32.5±6.7 cm) dominate the exposed part of the Rupnica. A number of features quantified through such statistical approach, together with petrography, geochemistry and the geology of the geosite surroundings, gave an idea about the rapid cooling of a (sub)surface acidic lava body and the behavior of the evolving volcanic system, developing columnar jointing under the combined influence of large scale constitutional supercooling and thermal contraction processes.

albite rhyolite; columnar jointing; constitutional supercooling; thermal contraction; Rupnica Papuk Geopark

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