Chapter II. Igneous rocks in the Carpathian-Pannonian Region

Table of Contents

II.1. Ultrabasic rocks
II.2. Basic/Mafic igneous rocks
II.3. Intermediate igneous rocks
II.4. Acidic (silicic) igneous rocks
II.5. Alkali Si-undersaturated igneous rocks (Foidolites)

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.

II.1. Ultrabasic rocks

PERIDOTITE GROUP

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).

Mineral content:

Essential minerals: olivine>40%, ortho- and clinopyroxenes

Accessory minerals: spinel or garnet, rarely amphibole, phlogopite, apatite

Secondary minerals: serpentine group minerals, limonite

Rock types:

  • dunite: olivine>90%

  • harzburgite: olivine>40%, orthopyroxene, clinopyroxene < 5%

  • lherzolite: olivine>40%, clinopyroxene, orthopyroxene

  • wehrlite: olivine>40%, clinopyroxene, orthopyroxene < 5%

Figure II.1. – Peridotite xenolith with the essential minerals (Bondoró)

Figure II.2. – Thin section of a lherzolite xenolith. We can recognise the green clinopyroxenes the light brownish orthopyroxenes, the colourless olivines and the black spinels (Al Haruj, Libya)

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.

Figure II.3. – Peridotites from the Carpathian-Pannonian Region: (left) peridotite xenoliths in the pyroclastite from Szentbékkálla (right), rounded peridotite bomb from the scoria cone of Bondoró (photos: Szabolcs Harangi).

Figure II.4. – Peridotites from the Carpathian-Pannonian Region: (left) peridotite xenolith in a spindle bomb (Füzes-tó), (right) blocky peridotite xenolith in basaltic lava rock (Mátéfalva, Mateias; Persány Mts.) (photos: Szabolcs Harangi).

Figure II.5. – The cumulate originated „ore-peridotite” from Szarvaskő (southwest Bükk)

Figure II.6. – Typical microscopic photos of dunite xenolite (Fülekkovácsi/Fil’akovské Kovače, Nógrád-Gömör, Slovakia). Left with one nicol, right with crossed nicols.

Figure II.7. – Typical microscopic photos of harzburgite xenolith (Füzes-tó). Left with one nicol, right with crossed nicols.

Figure II.8. – Typical microscopic photos of protogranular lherzolite xenolith (Maskófalva/Mašková, Nógrád-Gömör, Slovakia). Left with one nicol, right with crossed nicols.

Figure II.9. – Typical microscopic photos of poikilitic lherzolite xenolith (Eresztvény). Left with one nicol, right with crossed nicols.

Figure II.10. – Typical microscopic photos of porphyroclastic lherzolite xenolith (Fülekkovácsi/Fil’akovské Kovače, Nógrád-Gömör, Slovakia). Left with one nicol, right with crossed nicols.

Figure II.11. – Typical microscopic photos of wherlite xenolith (Nádas/Trestia, Transylvania, Romania). Left with one nicol, right with crossed nicols.

Figure II.12. – Microscopic photos of the amphibole bearing ore peridotite from Szarvaskő. Left with one nicol, right with crossed nicols.

PYROXENITE GROUP

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.

Mineral content:

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

Rock types:

  • 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

Figure II.13. – Pyroxenite intrusion in Fuerteventura (left, Canary Islands) and macroscopic photo of the rock. (photos: Szabolcs Harangi)

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.).

Figure II.14. – Typical microscopic photos of olivine orthopyroxenite xenolith (Füzes-tó). Left with one nicol, right with crossed nicols.

Figure II.15. – Typical microscopic photos of a hypidiomorhic granular hornblende-bearing clinopyroxenite xenolith (Nádas/Trestia, Transylvania, Romania). Left with one nicol, right with crossed nicols.

Figure II.16. – Typical microscopic photos of hypidiomorhic granular hornblende clinopyroxenite (Nádas/Trestia, Transylvania, Romania). Left ones with one nicol, right ones with crossed nicols.

HORNBLENDITE GROUP

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.

Mineral content:

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.)

Figure II.17. – Hornblendite (Szarvaskő, southwest Bükk)

Figure II.18. – Microscopic photos of hornblendite xenolite (Nádas/Trestia, Transylvania, Romania). Left ones with one nicol, right ones with crossed nicols.

Figure II.19. – Microscopic photos of apatite bearing hornblendite (Nádas/Trestia, Transylvania, Romania). Left ones with one nicol, right ones with crossed nicols.

Figure II.20. – Microscopic photos of a lherzolite/hornblendite composite xenolith (Nádas/Trestia, Transylvania, Romania). Left ones with one nicol, right ones with crossed nicols.