Dolerite

Pending dolerite in the Neolithic quarry of Quelfennec, Brittany (see also use )

Dolerite (Greek δολερός (dolerós): cunning, treacherous) is a sub-volcanic gangue that corresponds chemically and mineralogically to the volcanic basalt or the plutonic gabbro .

Internationally, dolerite is also referred to as diabase . Because in the German-speaking area the name Diabase in older literature often denotes a geologically old, altered (i.e. modified in the mineral stock) basalt, the use of this name is problematic.

Appearance and composition

" Playground of the giants ", dolerite rocks near the Gariganus farm, Namibia

Dolerite is a dark gray-brown form of basalt and is harder than granite . It is finer-grained than a gabbro in a pluton and coarser-grained than a basalt. Most often dolerites have an ophitic , subophitic or intergranular structure.

The main constituents are the minerals pyroxene (with up to 60%), plagioclase (50%), olivine (25%) and alkali feldspar (25%), in less pronounced proportions also magnetite and clinopyroxene (as detached objects, up to 15%).

Occurrence

Weathered dolerite in Hogsback

Dolerite rocks and quiver trees near Keetmanshoop

Dolerite occur relatively shallow as intrusive sills , floors and corridors in numerous rock units. Their occurrence is particularly common in areas where the earth's crust has been subject to expansion. Dolerite dikes often occur in swarms of dikes , in which many, sometimes hundreds, of dikes are roughly parallel or extend radially from a volcanic center.

• Dolerite tunnels are widespread in the Rhenohercynian of Central Europe and England. In Germany they are widespread in association with the associated effluent rocks (diabase) in the Devonian and Carboniferous slate mountains.

• In Great Britain , dolerite dikes occur on the islands of Skye , Rum , Mull and Arran to the west of Scotland , they are part of the Hebridean gang swarm formed in the Tertiary , which extends from Ireland ( Slieve Gullion ) to northern England and Scotland.

• In the United States, the New Jersey Palisades on the Hudson River near New York City are made of dolerite. In Canada, amphibolites , possibly formed from dolerite, from the so-called Nuvvuagittuq greenstone belt near Hudson Bay in northern Quebec have been dated to an age of around 4.28 billion years - the oldest known rocks on earth.

• Parts of the igneous large province of the Cretaceous Dekkan Trapp in India are dolerites.

• The 200 km long doleritic dyke of the Norseman – Wiluna belt belongs to the Norseman and Kalgoorlie gold prospecting area , which is home to the largest Australian gold mine, the Fimiston open pit mine.

• Dolerites are most prevalent in the southern parts of Africa , South America and Antarctica , which were formerly connected and experienced a violent magma rise and volcanism when Gondwana broke up . The dolerites of the Karoo basalts in South Africa, the Ferrar group on the Ross Sea in Antarctica, the volcanic Chon Aike province in Patagonia and the dolerites of Tasmania are part of one of the largest igneous events in geological history. The dolerite deposits in Tasmania are the largest known contiguous dolerite deposits today. Here, within a geologically short period of time, doleritic magmas penetrated an area of ​​around 40,000 km². Today, dolerite takes up about a third of the surface of Tasmania and determines the landscape there. Due to the extent and the geologically comparatively rapid formation, these formerly contiguous dolerite deposits are an outstanding example of a magmatic large province.

use

Bluestone monument. In the background the Carn Menyn. At the summit quarry for the Stonehenge stones

Statue of František Polívka made of dolerite ("Schluckenauer Syenit") by Julius Pelikán (1933) in Olomouc , Czech Republic

• The stone axes of Brittany were made from fibolite , jadeite and dolerite, which u. a. in the dolerite quarry of Plussulien in the district of Quelfennec.
• The stone blocks of the inner circle of the cult site in Stonehenge are made of dolerite ( bluestone ) . The material is believed to have come from the Preseli Mountains in Pembrokeshire , Wales.
• The Egyptians used tools made from dolerite to break granite for pyramids , obelisks and sarcophagi from quarries .
• Nowadays, dolerite such as basalt and diabase is used in road construction, for tombstones or stone carving and as polished natural stone in floor coverings and facade panels.

Individual evidence

1. ↑ Le Maitre. RW, Bateman, P., Dudek, A., Keller, J., Lameyre, J. Le Bas, MJ, Sabine, PA, Schmid, R., Sorensen, H., Fahrtisen, A., Woolley, AR & Zanettin , B., 1989. A Classification of Igneous Rocks and Glossary of terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks. Blackwell Scientific Publications, Oxford, UK
2. ^ ^{A b} Hans Murawski, Wilhelm Meyer: Geological dictionary . 11th edition. Elsevier / Spektrum, Heidelberg 2004, ISBN 3-8274-1445-8 .
3. ^ Thews, J.-D .: Explanations of the geological overview map of Hesse 1: 300,000. Geol. Abhandlungen Hessen Volume 96, Hessisches Landesamt für Bodenforschung, Wiesbaden 1996, ISBN 3-89531-800-0 , p. 189 ff.
4. ^ Geology of Great Britain - Introduction , by Dr. Ian West
5. ↑ The Geology of Mull , by Rosalind Jones ( Memento of the original from July 8, 2008 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. .  
6. ↑ Jonathan O'Neil, Richard W. Carlson, Don Francis, Ross K. Stevenson: Neodymium-142 Evidence for Hadean Mafic Crust . In: Science . tape 321 , no. 5897 , September 26, 2008, p. 1828–1831 , doi : 10.1126 / science.1161925 .
7. ↑ Science News The oldest primary rock on earth found in Canada.
8. ^ Continental Flood Basalts (and Layered Intrusions) .
9. ^ RET Hill et al .: Physical volcanology of komatiites; A field guide to the komatiites of the Norseman-Wiluna Greenstone Belt, Eastern Goldfields Province, Yilgarn Block, Western Australia. Geological Society of Australia, 1990, ISBN 0-909869-55-3 .
10. ↑ O'Connor-Parsons, Tansy; Stanley, Clifford R. (2007): Downhole lithogeochemical patterns relating to chemostratigraphy and igneous fractionation processes in the Golden Mile dolerite, Western Australia. Geochemistry: Exploration, Environment, Analysis 7/2, pp. 109-127. Geological Society Publishing House, London ( abstract ).
11. ↑ Large Igneous Provinces - Database , Richard E. Ernst and Kenneth L. Buchan, website of the Geological Survey of Canada ( Memento of the original from August 20, 2007 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. .  
12. ^ Teal R. Riley, Philip T. Leat: Large volume silicic volcanism along the proto-Pacific margin of Gondwana: lithological and stratigraphical investigations from the Antarctic Peninsula. Geological Magazine 136/1, 1999, pp. 1-16 Abstract .
13. ↑ Scanned 1: 250,000 Geology Maps , sheets 5503 to 5508, Geoscience Portal of the Australian Chief Government Geologists Committee ( Memento of the original from March 14, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. .  
14. ^ Giot, Pierre-Roland (1991): Prehistory in Brittany - Menhirs and Dolmen. Edition d'Art Jos le Doaré, Chateaulin, ISBN 2-85543-076-3 , p. 54.
15. ↑ Stonehenge a "Neolithic Lourdes"? in the Internet version of the Standard dated March 31, 2008.
16. ↑ Stonehenge bluestone site revealed BBC homepage, June 2005 .
17. ↑ Rainer Lorenz: The red pyramid of King Sneferu in Dahschur-Nord .

literature

• Le Maitre (Ed.): Igneous Rocks, A Classification and Glossary of Terms . Cambridge 2004, ISBN 0-521-61948-3 .
• Roland Vinx: Rock determination in the field . Munich (Elsevier) 2005, ISBN 3-8274-1513-6 .
• Wolfhard Wimmenauer: Petrography of igneous and metamorphic rocks . Stuttgart (Enke) 1985, ISBN 3-432-94671-6 .

Web links

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