Petrographic Characteristics of Extrusive Rocks from Hruskovec, Mt. Kalnik, NW Croatia

Abstract

Spilites, altered diabases and meta-basalts from Hruskovec quarry on Mt. Kalnik form part of a complex sequence of extrusive rocks. They are the result of several successive extrusions of basaltic lava within Upper Cretaceous sediments of heterogeneous petrographic composition. The mineral composition and the numerous textural variations are the results of different cooling histories. Intense spilitization was caused by descendent (sea water) and ascendent (juvenile) solutions. Products of the hydrothermal alteration are the result of very low to low-grade metamorphism. The contacts of the extrusives with surrounding sediments suggest an Upper Cretaceous age for the volcanism. The rocks resemble the extrusives found in other parts of Mt. Kalnik, as well as the extrusives from the wider area of NW Croatia and the rocks found in ophiolitic complexes of the Internal Dinarides.