Amphibolite

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Amphibolite in thin section . The dark green areas probably consist of hornblende, the small red-brown spot is very likely biotite.
Garnet amphibolite from the Pflersch Valley

Amphibolite is defined as rock that is formed by the metamorphic transformation of basalt , the depth equivalent of which is gabbro or other meta-basites, under the pressure and temperature conditions of the amphibolite facies (T ≈ 550–700 ° C, P ≈ 200–1200 MPa).

Definition

Amphibolite in the real sense consists of up to 50 % vol. from representatives of the amphibole group (e.g. hornblende , pargasite or Tschermakite ) and from plagioclase (15–40%). It also contains garnet , epidote , biotite , quartz or olivine and ore minerals such as magnetite and pyrite . The relative and absolute mineral proportions depend both on the special chemical composition of the parent rock and on the degree of metamorphism. For example, epidote occurs in the lower amphibolite facies (i.e., at temperatures at the lower end of the spectrum), while garnet and clinopyroxes are formed in the upper amphibolite facies . The typical Ti phase for rocks of the amphibolite facies is the mineral ilmenite . From marls and tuffites of suitable composition a rock similar to the amphibolite can arise, which is called para-amphibolite in contrast to the ortho-amphibolite formed from igneous rocks . Transitional forms to eclogite are called eclogite amphibolite .

composition

Pressure-temperature depth diagram of metamorphic facies areas; 5 = amphibolite facies

Chemical composition

The following table summarizes the chemical composition of some amphibolite representatives (in% by mass, according to Pfeiffer, Kurz & Matthé, 1985).

chem. connection 1 2 3 4th 5
SiO 2 48.2 50.3 50.7 45.4 52.5
Ti 2 O 2 1.9 1.6 1.7 2.0 0.4
Al 2 O 3 14.5 15.7 13.0 14.4 17.2
Fe 2 O 3 3.5 3.6 2.8 2.4 4.4
FeO 10.5 7.8 8.4 7.4 5.0
MnO 0.3 0.2 0.2 0.2 0.1
MgO 6.6 7.0 10.6 8.2 6.7
CaO 10.3 9.5 6.7 8.9 8.6
Na 2 O 1.9 2.9 2.0 2.4 4.9
K 2 O 1.0 1.1 1.0 0.9 0.4
H 2 O + 1.3 0.3 2.6 2.9 0.7
CO 2 - - - 4.3 -
swell

1 = amphibolites (mean value from 7 analyzes), Emerville area ( Adirondacks , USA)
2 = amphibolites (mean
values from 200 analyzes) 3 = amphibolite with gabbroid structure relics, Claußnitz (Erzgebirge)
4 = garnet amphibolite, Hammerunterwiesenthal (Erzgebirge)
5 = epidote -Amphibolite, Sulitelma (Norway)

Mineralogical composition

The following table provides an exemplary overview of the mineral inventory of various amphibolite deposits (in% by mass, according to Pfeiffer, Kurz & Matthé, 1985).

Occurrence Hornblende Plagioclase Epidote /

Clinozoisite

Zoisite garnet Pyroxene Biotite Chlorite quartz Accessories
Emerville area ( Adirondacks , USA) 68 18th - - - 1 1 - 9 3
Kamerwald ( Spessart ) 44 49 - 1 - - - - 3 3
Claussnitz ( Ore Mountains ) 65 24 1 - 2 - - 2 2 4th
Mildenau (Ore Mountains) 60 3 15th - 10 4th - - 6th 2
Sulitelma (Norway) 42 43 1 - 12 - - - 3 - -

1) Albite

The use of the term “amphibolite” for amphibole-rich (with a proportion of up to 30% vol. Amphibole) rocks that were not formed from basalt is controversial. Alternative names, e.g. B. Amphibole gneiss can be used. According to Wimmenauer (1985), the term amphibole gneiss is recommended for feldspar contents of over 50 percent and the term amphibolic slate for amphibole contents of over 80 percent .

history

The name of the rock goes back to Alexandre Brongniart , who first described amphibolite in the Journal des Mines (vol. XXXIV) in 1827. Bernhard von Cotta lists it in this sense in his work Die Gesteinslehre from 1855 as a synonym for Hornblendefels , in the second edition (1862) as a synonym for both Hornblendefels and Hornblendeschiefer , and Franz Loewinson-Lessing explains the catchphrase amphibolite in his Petrographic Lexicon (1893 ) also entirely in the Brongniartian sense.

Properties and use

The color of amphibolite varies with the mineral inventory . Often, however, tones from black to gray to dark green or, with a high proportion of plagioclase, black and white are patterned. It is mainly used for floor and wall coverings. In the Neolithic Age they were also used to make adze blades ( shoe last wedges ). Amphibolite is also used as a road building material and railroad ballast.

Occurrence

In Canada, the protoliths of amphibolites from the so-called Nuvvuagittuq greenstone belt have been dated to an age of around 4.280 billion years. It is currently the oldest known piece of earth's crust. In Germany, amphibolite occurs in virtually all Variscan basement eruptions in which metamorphic rock complexes can be found, even if it originated from much younger parent rocks. a. in the Ruhlaer Kristallin of the Thuringian Forest , in the Münchberger Gneismasse , on the Kyffhäuser as well as in the Ore Mountains , in the Fichtel Mountains and in the Black Forest . The Dunkelstein , the eponymous mountain of the Dunkelsteinerwald (southern Bohemian Massif ) in Lower Austria , owes its name to the dark color of the amphibolite from which it is built.

literature

  • Wolfhard Wimmenauer: Petrography of igneous and metamorphic rocks . Enke, Stuttgart 1985, ISBN 3-432-94671-6 .
  • Ludwig Pfeiffer, Manfred short, Gerhard Mathé: Introduction to petrology. Akademie-Verlag, Berlin 1985

Individual evidence

  1. ↑ Amphibolite. Knowledge online: Lexicon of Geosciences
  2. ↑ AEJ Engel, Engel CG, RG Havens: Mineralogy of amphibolite interlayers in the Gneiss Complex, Northwest Adirondack Mountains, New York. In: Journal of Geology. Vol. 72, No. 2, 1964, pp. 131–156, ( JSTOR 30080947 )
  3. ↑ Arie Poldervaart: Chemistry of the Earth's Crust. In: Arie Poldervaart (Ed.): Crust of the Earth: A Symposium. Geological Society of America Special Papers. Vol. 62, 1955, pp. 119-144, doi : 10.1130 / SPE62-p119
  4. ↑ a b H. Lange: On the petrographic classification of amphibolitical and eclogitic rocks. In: Bergakademie. Vol. 15, 1965
  5. ↑ Thorolf Vogt: Sulitelmafeltets geologi og petrografi. In: Norges geologiske undersøkelse. No. 121, 1927
  6. ↑ Wimmenauer, 1985 (see literature ), p. 235
  7. ↑ Bernhard von Cotta: The rock theory. Verlag von JG Engelhardt, Freiberg (Saxony) 1855, p. 61 ( archive.org )
  8. ↑ Bernhard von Cotta: The rock theory. Second, revised edition, JG Engelhardt, Freiberg (Sachsen) 1862, p. 186, urn : nbn: de: bvb: 12-bsb10706898-0 (p. 196 in digitized version )
  9. ↑ "Granular or schisty aggregate of dark green to black hornblende or leek-green ray stone [...] Syn. Hornblende rock, hornblende slate." Franz Loewinson-Lessing: Petrographisches Lexikon. Repertory of petrographic terms and names. Jurjew (C. Mattiesen) 1893, p. 11 ( archive.org )
  10. ↑ Jonathan O'Neil, Richard W. Carlson, Don Francis, Ross K. Stevenson: Neodymium-142 Evidence for Hadean Mafic Crust . In: Science . tape 321 , no. 5897 , 2008, p. 1828–1831 , doi : 10.1126 / science.1161925 .

Web links

Commons : Amphibolite  - collection of images, videos and audio files
Wiktionary: Amphibolite  - explanations of meanings, word origins, synonyms, translations