Hawaiite

Hawaii t is a basalt -like volcanic rock. It is the sodium- leading variety of Trachybasalts and contains olivine. His normative plagioclase is oligoclase or andesine either. Hawaii tables magmas are slightly alkaline, nepheline - normative and undersaturated to SiO2.

Etymology and history

The name Hawaii t is derived from the Hawaiian Islands. The rock was first described and named in 1913 by Joseph Paxson Iddings. Its type locality are the Hawaiian Islands.

Classification

Hawaii t is defined chemically in TAS field S1. When sodium- rich trachybasalt he fulfills the condition Na2O - K2O ≥ 2. The weight content of SiO 2 is between 45 and 52%, the weight proportion of the sum of Na2O and K2O 5 to 7.3 %. To further distinguish it from other volcanic rocks of the MgO content can be used, which is at Hawaii t 4-8 weight percent.

Composition

Hawaiite lead 40-70 volume percent mafic minerals, usually augite ( clinopyroxene ) and olivine. Another main part mixture occurs plagioclase added, mostly andesine or labradorite. Foide may also be present.

Mineral constituents

Phenocrysts in Hawaiiten are usually:

  • Plagioclase ( andesine / labradorite )
  • Augite (usually rich in titanium)
  • Olivine
  • Lodestone

The Mesostasis contains:

  • Augite
  • Plagioclase ( anorthite - rich )
  • Lodestone
  • Ilmenite
  • Titanomagnetite
  • Apatite
  • Alkali feldspar
  • Amphibole
  • Olivine (magnesium - rich )

The base may be formed partly glassy.

Chemical composition

As an example of the chemical composition of Hawaii t let out of the high Eifel serve ( Rappoldsley, Breidscheid at Adenau ):

Quartz and hypersthene missing as standard minerals, instead nepheline occurs.

External appearance

Hawaiite are fine-grained volcanic rocks whose grain sizes are on average less than 0.25 mm. They are mostly of light gray to dark gray color. Your color number varies between 40 and 70

Formation and association

Hawaii tables magmas produced by fractional crystallization of olivine and clinopyroxene from alkali basalts. They occur at temperatures between 1080 ° C ( Etna ) and 1250 ° C ( Auvergne ) as a relatively thin liquid and sometimes bubble -rich lavas at the surface from. So far, relatively shallow magma chambers were as origin of Hawaiiten assumed, ie low pressure conditions. This is contradicted by an occurrence in New South Wales, has the inclusions of lherzolite and Pyroxenfremdkristallen and thus similar to basalts of the upper mantle suggests as the source.

Hawaiite belong to the following sodium - stressed Magmenassoziationen:

  • Ankaramit - alkali basalt - Hawaii t - Differentiationsserie
  • Alkali basalt - Hawaii t - Mugearit - Benmoreit - trachyte ( - rhyolite ) Differentiationsserie

Occurrence and Locations

As a member of the basalt group Hawaiite are encountered very often and in most tectonic contexts:

  • In the oceanic area: Within oceanic islands along with OIB 's. Examples include the Azores, the Canary Islands, the Comoros, Kerguelen and the Marquesas Islands
  • In oceanic hotspots such as Galapagos, Hawaii (type locality), Iceland and Réunion
  • In Seamounts and guyots, as an example, the Hawaii - Emperor seamount chain of islands
  • In subsea back, as an example of Keli - back ( Line Islands ) in the Pacific
  • In continental hotspots - Eifel, French Massif Central, Cameroon line
  • Within volcanic series of grave fractures - Large African grave breach in Ethiopia
  • In continental flood basalts (CFB 's) as an example of the Ferrar Supergroup in Antarctica
  • In intraplate volcanism ( Plateaulaven Patagonia ) and
  • In complex volcanic contexts - Etna and Hybleisches plateau.

Locations of Hawaii t in Europe are Germany ( High Eifel and Vogelsberg ), France ( Morvan and Chaîne des Puys ), Iceland ( Heimaey ), Italy ( Etna, Pantelleria, Vulcano ) and Scotland ( Skye and Mull ). In the Atlantic region also finds himself at Ascension, Madeira, the Gough Island and Tristan da Cunha. The Hawaiian islands as type locality lead Hawaiite in Hawaii on Mauna Kea, and the Kohala Hualālai on and on Molokai. Hawaii tables lavas were also promoted in America in the southwestern Basin and Range Province ( Nevada) and with the basalts of the eastern Snake River for days. Continue to lead are Mexico, and the Pacific Islands, the Austral ( Tubuai ).

Footnotes

Swell

  • Volcanic rocks
TAS classification Fractional crystallization (geology) Hawaiian–Emperor seamount chain New Zealand Ascension Island Kohala (mountain) Tuha'a Pae
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