Table of Contents
The Carpathian-Pannonian region is a kind natural laboratory for the igneous rocks. Plate tectonic events in the western Tethys region during the Mesozoic led to the formation of various volcanic rocks and these formations play an important role in the reconstruction of these complex processes. The Pannonian Basin was formed during the Neogene and this was accompanied with the formation of wide range of volcanic rocks for the last 20 Ma. In this region, almost every type of igneous rocks are found from the mantle derived peridotites to the granites, from the silica-undersaturated nephelinites and leucitites to the phonolites and rhyolites. In the next sections, description of the major igneous rocks is given along many examples from the Carpathian-Pannonian region. The great selection of microscopic photos could help to recognize the often subtle differences of given rock types in different localities.
Appearance: When fresh it is green coloured, and coarse grained. Macroscopically we can recognise in the rock olive-green coloured olivines, black orthopyroxenes and grass-green clinopyroxenes. Using microscope the brown spinels can also be observed and the clinopyroxenes have light green colour. Using petrographic microscope olivines and orthopyroxenes are colorless with one nicol, their pictures with crossed nicols can help to discriminate them as orthopyroxenes have usually grey while olivines have second-third order colours (blue-red).
Essential minerals: olivine>40%, ortho- and clinopyroxenes
Accessory minerals: spinel or garnet, rarely amphibole, phlogopite, apatite
Secondary minerals: serpentine group minerals, limonite
harzburgite: olivine>40%, orthopyroxene, clinopyroxene < 5%
lherzolite: olivine>40%, clinopyroxene, orthopyroxene
wehrlite: olivine>40%, clinopyroxene, orthopyroxene < 5%
Occurrences in the Carpathian-Pannonian Region: As xenoliths in basalts from Kapfenstein, Tobaj, Gérce, Bondoró, Füzes, Szentbékkálla, Szigliget; Maskófalva-Maskova, Fülek-Filakovo-Kercsiktető, Medves-Eresztvény and Magyarbánya, Nagy-Salgó, Bagókő, Bárna-Nagykő and Kiskő; Hidegkút (Gruiu), Nádas-völgy/Trestia and Berek (Barc; Persány Mts.), and in late Cretaceous lamprophyres (e.g. Alcsútdoboz borehole, Villányi Mts.). The so called „ore-peridotite” near Szarvaskő has cumulate origin.
Appearance: The rock is usually black or dark green coloured and medium or coarse grained. Apart from the pyroxenes it can contain spinel or garnet which can only be recognised using petrographic microscope.
Essential minerals: mainly ortho- and clinopyroxenes and less than 40% olivine
Accessory minerals: spinel, garnet, Fe-Ti-oxides, plagioclase
Secondary minerals: serpentine group minerals, chlorite
clinopyroxenite: more than 90% clinopyroxene
orthopyroxenite: more than 90% orthopyroxene
websterite: more than 60% clinopyroxene and orthopyroxene, less than 10% olivine
olivine websterite: more than 60% clinopyroxene and orthopyroxene, 10-40% olivine
Occurrences in the Carpathian-Pannonian Region: Usually beside peridotite xenoliths e.g. Tobaj, Bondoró, Szentbékkálla, Maskófalva-Maskova, Fülek-Filakovo-Kercsiktető, Medves-Eresztvény and Magyarbánya, Nagy-Salgó, Bagókő, Bárna-Nagykő and Kiskő; Nádas-völgy/Trestia (Persány Mts.), and in late Cretaceous lamprophyres (e.g. Alcsútdoboz borehole, Villányi Mts.).
Appearance: The rock usually black coloured, medium or coarse grained. It contains more thn 90% amphibole (hornblende). Hornblendite is a rare igneous rock in contrast with the more aboundant amphibolite which is a metamorphic rock containing mainly amphibole (hornblende) and plagioclase.
Essential minerals: dominantly (>90%) amphibole (primarily hornblende), with less amount of pyroxene and olivine
Accessory minerals: Fe-Ti-oxides
Secondary minerals: chlorite
Occurrences in the Carpathian-Pannonian Region: Szarvaskő (southwest Bükk), Nádas-völgy/Trestia (Persány Mts.)