Fenite

As Fenit a is metasomatic rock denotes that with the intrusion of alkali rocks and carbonatites is associated.

etymology

The name Fenit is derived from the type locality , the Fensfeltet near Nome in Telemark ( southern Norway ).

Initial description

Fenite was first scientifically described in 1921 by Waldemar Christofer Brøgger .

education

Typical is the occurrence of fenites as concentric aureoles around intrusive bodies that are in contact with the surrounding acidic magma complexes . They can also form reaction seams around intrusive dike rocks . Carbonatites, foyaites , urtites , ijolites and melteigites as well as magmatites of nephelinitic and phonolithic composition function as intrusive bodies .

mineralogy

Characteristic of Fenite is the presence of alkali feldspar ( microcline ), sodium - amphibole ( Ferro-Eckermannit ) and sodium pyroxenes ( Aegirin and Aegirin-augite ). Typical accompanying minerals are also titanite and apatite .

Chemical composition

Due to the interaction between different types of intrusives and the most varied of surrounding rocks, fenites show a very wide range in their chemical composition.

Emergence

The formation process of fenites is called fenitization . Fenites are alkali-accentuated metasomatic alteration products - the transformation of the parent rock occurs in the solid state initially by means of hot pneumatolytic gases or in the later stage by means of hydrothermal liquids and are divided into sodium and potassium- accentuated rocks. They can develop in a variety of ways:

• contact metasomatic around igneous intrusions (very common).
• as aureoles around high-temperature ultramafic rocks , which are metamorphic as talc carbonates (rare). This creates skarn associations , amphibolite - calcite - scapolite transformations and accumulations of biotite- rich zones.
• by carbonation (conversion with the addition of carbonic acid ) of acidic to basic parent rocks (very rare).

The fenitization courtyards, which are often arranged in zones, can occupy widths in the range of meters to kilometers in the adjacent rock. Surrounding rocks particularly accessible to fenitisation are basement rocks such as granitoids , gneisses , slate and migmatites ; Corresponding transformations can also be found in sediments and volcanic rocks .

Occurrence

The following occurrences are known for fenite:

• Great Britain - Scotland :
  • Borralan complex at Loch Borralan ( Assynt ) - caused by pseudoleucite syenite . Quartzites and layers of the lower Cambrian fucoid beds were affected by the fenitization .
• Finland :
  • Sokli - um carbonatite intrusion
• India :
  • Amba Dongar , Baroda District, Gujarat - around carbonatite intrusion. Sandstones, limestone and alkali stones were fenitized. Deeper sodium fenitization and shallower potassium fenitization.
  • Mundwara , Sirohi District, Rajasthan - Sodium Fenitization
  • Sarnu-Dandali , Barmer District, Rajasthan - Sodium Fenitization
• Canada :
  • Callander Bay in Ontario - around foyaite / carbonatite intrusion
• Kenya :
  • Jombo intrusion - fenitization of sandstones
  • Sagurume - around Ijolite / urtite intrusion
  • Usaki - around microijolite
• Norway :
  • Fensfeltet near Nome in Telemark (type locality) - around Melteigit - and carbonatite intrusion
• Sweden :
  • Alnön - around carbonatite

literature

• Douglas Fettes: Metamorphic Rocks: A Classification and Glossary of Terms . Cambridge University Press, 2007, ISBN 978-0-521-33618-5 .
• Wolfhard Wimmenauer: Petrography of igneous and metamorphic rocks . Enke, 1985, ISBN 3-432-94671-6 .

Individual evidence

1. ↑ WJ Verwoerd: Fenitization of basic igneous rocks . In: OF Tuttle, J. Giffins (Ed.): Carbonatites . Interscience, New York 1966, pp. 295-306 .
2. ^ AR Woolley, inter alia: Metasomatized (fenitized) quartzites from the Borralan Complex, Scotland . In: Mineralogical Magazine . tape 38 , 1972, p. 819-836 .
3. ^ H. Vartiainen, AR Woolley: The petrography, mineralogy and chemistry of the fenites of the Sokli carbonatite intrusion, Finland . In: Geological Survey of Finland Bulletin . tape 280 , 1976, pp. 1-87 .
4. ↑ RN Sukheswala, SG Viladkar: Fenitized sandstones in Amba Dongar carbonatites, Gujarat, India . In: Journal of Geological Society of India . tape 22 , 1981, pp. 368-374 .
5. ^ KL Currie: The alkaline rocks of Canada . In: Bulletin of the Geological Survey of Canada . tape 239 , 1976, pp. 1-228 .
6. ^ BH Baker: A Chapter on hte Alkaline Igneous Complex at Jombo . In: PV Caswell, BH Baker (Ed.): Geology of the Mombasa-Kwale area, degree sheet 69 (with colored map), with a chapter on the alkaline igneous complex at Jombo. (=  Kenya geological Survey Report ). No. 24 . Government Printer, Nairobi 1953, OCLC 5866464335 , p. 32-48 ( oceandocs.org [PDF]).
7. ^ ^{A b} M. Le Bas: Carbonatite-Nephelinite Volcanism . Wiley, London 1977, pp. 318 .
8. ^ T. Andersen: Carbonatite-related contact metasomatism in the Fen Complex, Norway . In: Mineralogical Magazine . tape 53 , no. 372 , 1989, pp. 395-414 .
9. ^ H. von Eckermann: Progress in Research on the Alnö carbonatite . In: OF Tuttle, J. Giffins (Ed.): Carbonatites . Wiley, New York 1966, pp. 3-32 .