Lithofacies characteristics of the Smrekovec volcaniclastics, northern Slovenia
The Smrekovec mountains are characterised by a widespread occurrence of volcanic rocks of the Upper Oligocene age. Their development is closely related to volcanic activity which resulted in the formation of a submarine stratovolcano complex, emplaced onto pre-Tertiary carbonate basement and locally, on Upper Oligocene marine marls and silts. Magma composition varied with time during volcanic activity. The original tholeiitic magmas very likely underwent a differentiation due to low pressure crystal fractionation, resulting in the development of andesitic and finally rhyodacitic magmas. The early stage of volcanic activity was dominantly non-explosive; the main style of fragmentation was autoclastic, related to chill and quench processes that affected lavas and high-level intrusive bodies. During the late-stage of volcanic activity, explosive volcanism was also present, being most probably related to magmatic and combined magmatic-hydrovolcanic activity. Explosions also seem to have generated or triggered volcaniclastic debris flows and turbidity ash flows. Shallow intrusive bodies (syn-volcanic sills and feeder dykes) were a local source of heat that generated hydrothermal/geothermal conditions in the enclosing, water-saturated volcaniclastic sediments. Consequently laumontite, analcime, clinoptilolite, heulandite, thomsonite, yugawaralite, prehnite, pumpellyite, albite, apophyllite, epidote, sphene, chlorite and mixed-layered clay minerals developed as replacements of the primary constituents, interstitial fillings and vein minerals.