Lamprophyre

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Sample of a lamprophyre dike in granodiorite , Upper Lusatia

Lamprophyre - from the Greek λαµπρός (lamprós) = bright, shiny (in relation to the crystal surfaces of amphibole and biotite, which shine brightly when freshly whipped) and φύρω (phýro) = to mix, introduced by Carl Wilhelm von Gümbel in 1874 - are right unusual group of dark igneous rocks. They appear as intrusions that are not very powerful or as corridors and storage corridors . Due to their chemical composition, they are classed as alkaline stones . Lamprophyres are mostly used as a decorative stone and building material.

Mineral composition and chemistry

These are fine to medium-grained, sometimes very porphyry rocks made of biotite , amphiboles and pyroxenes , sometimes clinopyroxene and olivine are also mixed in. The basic mass consists of feldspar or foids . Their medium ( mesotype ) to strong ( melanocrat ) dark coloring is typical, but they are rarely ultramafic . They are characterized by a high content of lithophilic elements such as potassium , sodium , barium , cesium , rubidium and strontium and usually have high nickel and chromium contents . The silicon content is low.

Even if lamprophyres are generally ultrapotassic , they can still have variable K / Na ratios - Camptonite and Monchiquite, for example, show sodium predominance. Lamprophyre usually have very high levels of volatiles such as water , carbon dioxide , fluorine , chlorine and sulfur dioxide . Their LREE values ​​are also increased, whereas the HREE values ​​remain at the basaltic level.

The occurrence of secondary minerals such as calcite and zeolites is often found, mostly bound to ocelli - leucocrate spherical to lens-shaped inclusions, which are interpreted as immiscible foreign or residual melts.

Emergence

The origin of lamprophyres is not fully understood. According to some geologists, their formation is related to subduction processes , others see them as residual melts of plutons . Also, a coupling to Hotspot - mantle plumes or profound tectonic faults can not be excluded.

The predominance of mafic minerals indicates a great melting depth of the magma from which the lamprophyres arose. The high content of potassium-rich minerals makes it probable that the parent rock was not partially melted (partial melting), as otherwise these would have left the melt. With a few exceptions, there are hardly any signs of fractional crystallization , but there are many signs of mineral transport through gases and volatile residual solutions.

Due to their mineral inventory and their formation as late phases of intrusions, lamprophyres often show signs of hydrothermal alteration .

Types of lamprophyren

Kersantite
Thin section image of a minette

The classification of lamprophyren according to the usual methods for igneous rocks (QAPF or stretch iron diagram , TAS diagram ) is difficult, as their main components are not or only partially included in these diagrams. An official classification of lamprophyres has only existed since the late 1990s, although this is still referred to as provisional. The subdivision of the lamprophyres occurs mainly according to their dark main components amphibole, augite , biotite and olivine, plus the most important light minerals such as feldspar and foide.

The various names are mostly borrowed from the names of the sites from which they were first described. A distinction is made between the following types:

  • Kersantite , biotite-hornblende-augite-lamprophyre with a base mass in which the plagioclase component outweighs the orthoclase component
  • Minette , biotite-hornblende-augite-lamprophyr with a base mass in which the orthoclase component outweighs the plagioclase component
  • Spessartite , hornblende-augite-lamprophyr, plagioclase are more common in the matrix than orthoclase
  • Vogesite , hornblende-augite-lamprophyr, orthoclase are more common in the matrix than plagioclase
  • Sannaite , amphibole-augite-olivine-biotite-lamprophyr, orthoclase is more common in the matrix than plagioclase, foids only occur to a minor extent
  • Camptonite , amphibole-augite-olivine-biotite-lamprophyre, plagioclase is more common in the matrix than orthoclase, foids only occur to a minor extent
  • Monchiquite , amphibole-augite-olivine-biotite-lamprophyr, glassy base material or exclusively foids in the base material
  • Alnoite , is ultramafic - contains melilite .

According to the IUGS classification , alnöite , a biotite / phlogopite rock with olivine, calcite and clinopyroxene , and the ultramafic polzenite with its varieties bergalite and damkjernite are no longer included in the lamprophyres, but assigned to the melilite rocks.

The following characteristics apply to the determination of lamprophyren, which only occur in corridors or small-volume chimneys: Presence of dark rock color and only predominantly OH-containing dark minerals such as biotite , phlogopite , amphibole and dark specks, which are often very large. Both porphyry and aporphyric structures must be present and a so-called alteration, a conversion of minerals into secondary minerals, has taken place.

Groupings

In general, two larger groups can be distinguished among the lamprophyren:

  • Calcareous alkaline prophyre
  • Alkali amrophyre

The SiO 2 -rich lamprophyres can in turn be subdivided into Shoshonitic and leucitic lamprophyres.

The group of alkaline lamprophyres also includes the ultrabasic lamprophyres.

Shoshonite lamprophyres :

Leucitic lamprophyres :
extremely rare, ultrapotassic dike rocks with a glassy texture. They have the highest K 2 O content among the mafic rocks .

Alkaline lamprophyres :

Ultrabasic lamprophyres : rocks with extremely low levels of SiO 2 with a very high Ca content, which are close to carbonatites :

Occurrence

Lamprophyres occur worldwide, often in areas with granitic , granodioritic or dioritic intrusions. Important locations are:

Natural stone types

Water feature with bowl and small plaster made of Sorar lamprophyr

A selection of lamprophyren:

  • Lamprophyr Grenzland (also called Spremberger or Lausitzer Syenit incorrectly in geology ), Valtengrund in Saxony
  • Lamprophyr snowflake (also incorrectly called syenite or diabase in geology), Ottendorf
  • Lamprophyr Sora, Wilthen district of Wilthen in Saxony
  • Lamprophyr Friedersdorf (Spessartite) from Friedersdorf in Saxony
  • Śluknov-Lipova and Śluknov-Rozany (Spessartite), near Šluknov in the Czech Republic

literature

  • Roland Vinx: Rock determination in the field. Springer-Verlag, Berlin Heidelberg 2008, ISBN 3-8274-1513-6 .

See also

Individual evidence

  1. ↑ Hans Murawski: Geological Dictionary. Ferd. Enke Verlag Stuttgart, 11th edition 2004, 262 pages, ISBN 978-3-8274-1445-8
  2. ↑ Winter, JD, 2001: An introduction to igneous and metamorphic petrology , Prentice Hall, Upper Saddle River, NJ, United States (USA), United States (USA).
  3. ↑ a b c R. W. Le Maitre et al .: Igneous Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks. 252 pp., Cambridge University Press 2005. ISBN 978-0-521-61948-6
  4. ↑ McHone, JG (1978a). Lamprophyre dikes of New England, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States (USA).
  5. ^ Eby, G. Nelson (1980): Minor and trace element partitioning between immiscible ocelli-matrix pairs from lamprophyre dikes and sills, Monteregian Hills Petrographic Province, Quebec . Contributions to Mineralogy and Petrology, 75, 269-278.
  6. ↑ NMS Rock: Lamprophyres . Blackie, Glasgow, 1991.
  7. ^ RH Mitchell: Suggestions for revisions to the terminology of kimberlites and lamprophyres from a genetic viewpoint. In: HOA Meyer and OH Leonardos (eds.): Proceedings of the Fifth International Kimberlite Conference, 1: Kimberlites and Related Rocks and Mantle Xenoliths. Companhia de Pesquisa de Recursos Minerais, Special Publication 1 / A, pp. 15-26, Brasilia 1994 (Eng.).
  8. ^ Whitehead, Melissa (2008). The petrographic and geochemical analysis of lamprophyre dikes in Williston, Vermont. Thesis at Middlebury College, Vermont.
  9. ↑ Darrell Henry: A Web Browser Flow Chart for the Classification of Igneous Rocks: Classification of lamprophyres ( en ) Louisiana State University. Archived from the original on May 10, 2008. 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. Retrieved May 16, 2008. @1@ 2Template: Webachiv / IABot / www.geol.lsu.edu
  10. ^ AR Woolley et al .: Classification of lamprophyres, lamproites, kimberlites, and the kalsilitic, melilitic, and leucitic rocks . In: Journal of The Mineralogical Association of Canada . 34, April 1996, pp. 175-186.
  11. ^ Vinx: rock determination. P. 261 (see literature)
  12. ↑ Joplin, GA (1966). On lamprophyres, Journal and Proceedings of the Royal Society of New South Wales, vol. 99, pp. 37-42.
  13. ^ Rock, NMS (1977). The nature and origin of lamprophyres; some definitions, distinctions, and derivations, Earth-Science Reviews, vol. 13, no. 2, pp. 123-169.
  14. ↑ Bergman, SC (1987). Lamproites and other potassium-rich igneous rocks; a review of their occurrence, mineralogy and geochemistry; Alkaline igneous rocks, Geological Society Special Publications, vol. 30, pp. 103-190.

Web links

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