Trachyandesite

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Auvergne, France, used as building stone, forming part of the walls of Clermont-Ferrand Cathedral
, France
Trachyandesite is field S3 in the TAS diagram

Trachyandesite is an

silica.[1][2]

The term trachyandesite had begun to fall into disfavor by 1985[1] but was revived to describe extrusive igneous rocks falling into the S3 field of the TAS classification. These are divided into sodium-rich benmoreite and potassium-rich latite.[3]

Trachyandesitic magma can produce explosive Plinian eruptions, such as happened at Tambora in 1815.[4] The Eyjafjallajökull 2010 eruption (VEI-4[5]), which disrupted European and transatlantic air travel from 14–18 October 2010,[6] for some time was dominated by trachyandesite.[7]

Petrology

Trachyandesite is characterized by a silica content near 58% and a total alkali oxide content near 9%. This places trachyandesite in the S3 field of the TAS diagram.

accessory minerals are amphibole, biotite or pyroxene. Small amounts of nepheline may be present and apatite is a common accessory mineral.[2] Trachyandesite is not a recognized rock type in the QAPF classification, which is based on the actual mineral content. However, latite is recognized in this classification, while benmoreite would likely fall into either the latite or the andesite fields.[8]

Trachyandesite magmas can have a relatively high

phenocrysts in the magma.[10] The 1982 El Chichón eruption produced trachyandesite pumice rich in anhydrite, and released 2.2 × 107 metric tons of sulfur.[11]

Varieties

Sodium-rich trachyandesite (with %Na2O > %K2O + 2) is called benmoreite, while the more potassic form is called latite. Feldspathoid-bearing latite is sometimes referred to as tristanite.[12] Basaltic trachyandesite is transitional to basalt and likewise comes in two varieties, mugearite (sodium-rich) and shoshonite (potassium-rich).[8]

Occurrence

Trachyandesite is a member of the

oceanic islands[16][14] and in continental rift valleys and mantle plumes.[17]

Trachyandesite is found in the Yellowstone area as part of the

arc volcanism in Mesoamerica[11] and at Mount Tambora.[19]

References

  1. ^
    ISBN 0198578105
    .
  2. ^
    ISBN 9781680151787
    .
  3. ^
    S2CID 28548230
    .
  4. S2CID 56290102
    .
  5. ^ Eyjafjallajokull. Eruptive history. Global Volcanism Program. Retrieved 26 August 2020.
  6. doi:10.1029/2012JB009592
    .
  7. doi:10.1111/j.1475-4959.2010.00379.x
    .
  8. ^ a b c Philpotts and Ague 2009
  9. ISBN 9783642189524
    .
  10. doi:10.1093/petrology/28.5.781
    .
  11. ^
    doi:10.1016/S0016-7037(02)00931-6
    .
  12. ISBN 9780521880060
    .
  13. ISBN 0824808320
    .
  14. ^ a b Philpotts and Ague 2009, pp. 369-370
  15. doi:10.1016/j.crte.2019.07.003
    .
  16. ^ MacDonald 1983, pp. 51-52
  17. ^ Philpotts and Ague 2009, pp. 390–394
  18. doi:10.3133/b1254H
    .
  19. doi:10.1130/0091-7613(1984)12<659:VSOTGT>2.0.CO;2
    .

External links
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