Dacite
Dacite (
Dacite is relatively common, occurring in many tectonic settings. It is associated with andesite and rhyolite as part of the
Composition
Dacite consists mostly of plagioclase feldspar and quartz with biotite, hornblende, and pyroxene (augite or enstatite). The quartz appears as rounded, corroded phenocrysts, or as an element of the ground-mass.[1] The plagioclase in dacite ranges from oligoclase to andesine and labradorite. Sanidine occurs, although in small proportions, in some dacites, and when abundant gives rise to rocks that form transitions to the rhyolites.[2]
The relative proportions of
puts dacite in the O3 sector.Texture
In hand specimen, many of the hornblende and biotite dacites are grey or pale brown and yellow rocks with white feldspars, and black crystals of biotite and hornblende. Other dacites, especially pyroxene-bearing dacites, are darker colored.[2]
In thin section, dacites may have an
Geological context and formation
Dacite usually forms as an intrusive rock such as a
Dacitic magma is formed by the subduction of young oceanic crust under a thick
The formation of dacite provides a great deal of information about the connection between oceanic crust and continental crust. It provides a model for the generation of felsic, buoyant, perennial rock from a mafic, dense, short-lived one.
Dacite's role in the formation of Archean continental crust
The process by which dacite forms has been used to explain the generation of continental crust during the Archean eon. At that time, the production of dacitic magma was more ubiquitous, due to the availability of young, hot oceanic crust. Today, the colder oceanic crust that subducts under most plates is not able to melt prior to the dehydration reactions, thus inhibiting the process.[13]
Molten dacite magma at Kīlauea
Dacitic magma was encountered in a drillhole during geothermal exploration on Kīlauea in 2005. At a depth of 2488 m, the magma flowed up the wellbore. This produced several kilograms of clear, colorless vitric (glassy, non-crystalline) cuttings at the surface. The dacite magma is a residual melt of the typical basalt magma of Kīlauea.[14]
Distribution
Dacite is relatively common and occurs in various tectonic and magmatic contexts:
- In oceanic volcanic series. Examples: Iceland (Heiðarsporður ridge),[15] Juan de Fuca Ridge.[16]
- In Aleutians, the Antilles, the Sunda Arc (Mount Batur),[17] Tonga and the South Sandwich Islands. Examples of dacitic magmatism in active continental margins are the Cascade Range, Guatemala and the Andes (Ecuador, Peru and Chile).
- In continental volcanic series, often in association with tholeiitic basalts and intermediary rocks
The
Sites outside Europe include
]Dacite is found extraterrestrially at
Etymology
The word dacite comes from
The term dacite was used for the first time in the scientific literature in the book Geologie Siebenbürgens (The Geology of Transylvania) by Austrian geologists Franz Ritter von Hauer and Guido Stache.[18][24] Dacite was originally defined as a new rock type to separate calc-alkaline rocks with oligoclase phenocrysts (dacites) from rocks with orthoclase phenocrysts (rhyolites).[18]
See also
- Lassen Volcanic National Park – National park in California, United States
- Potosí – City in Bolivia
References
- S2CID 128532728.
- ^ a b public domain: Flett, John Smith (1911). "Dacite". In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 7 (11th ed.). Cambridge University Press. p. 728. One or more of the preceding sentences incorporates text from a publication now in the
- S2CID 28548230.
- ^ "Rock Classification Scheme - Vol 1 - Igneous" (PDF). British Geological Survey: Rock Classification Scheme. 1: 1–52. 1999.
- ^ "Classification of igneous rocks". Archived from the original on 30 September 2011.
- ISBN 9780521880060.
- S2CID 129314125.
- USGS. Retrieved 16 August 2015.
- .
- .
- ^ Fyfe, W.; McBirney, A. (1975). "Subduction and the structure of andesitic volcanic belts". American Journal of Science. 275-A: 285–297.
- .
- S2CID 4342740.
- ^ Puna Dacite Magma at Kilauea: Unexpected Drilling Into an Active Magma Posters, 2008 Eos Trans. AGU, 89(53), Fall Meeting
- .
- ^ Perfit, M.R.; Schmitt, A.K.; Ridley, W.I.; Rubin, K.H.; Valley, J.W. (2008). "Petrogenesis of dacites from the southern Juan de Fuca Ridge". Goldschmidt Conference Abstracts 2008. Goldschmidt Conference 2008. Retrieved 23 February 2018.
- ^ Wheller, Graeme Eric (1986). Petrogenesis of Batur caldera, Bali, and the geochemistry of Sunda-Banda arc basalts (phd). PhD thesis, University of Tasmania.
- ^ a b c d Ştefan, Avram; Szakács, Alexandru; Seghedi, loan (June 1996). Dacite from type locality: Genealogy and description (PDF). Geological Survey of Romania. Retrieved 20 February 2022.
- ^ Ellis, R. A.; et al. (1977). lnvestigation of disseminated copper mineralisation near Kilmelford, Argyllshire, Scotland (Mineral Reconnaissance Programme Report 9) (PDF). London: Institute of Geological Sciences.
- .
- ^ Thomas, Pierre (May 2016). "Dacite (Esterellite)". Observer les objets géologiques (in French). Lithothèque ENS de Lyon. Retrieved 23 February 2018.
- ^ "Dacite" (PDF). Hungarian Natural History Museum. Retrieved 23 February 2018.
- ^ "Nili Patera and Dacite Lava Flow". Mars Exploration – Multimedia. NASA. 1 April 2012. Retrieved 9 August 2017.
- ^ Ritter von Hauer, Franz; Stache, Guido (1863). Geologie Siebenbürgens (in German). Vienna: Wilhelm Brauchmüller. p. 72.
v. Richthofen's Namen gleichfalls ganz fallen zu lassen, dafür liegt wol nicht derselbe Grund vor. Dass die Oligoklasgruppe der "Quarztrachyte", dies muss der Name für die ganze Reihe bleiben, von der Orthoklasgruppe oder den "Rhyoliten" getrennt werden müsse, dafür plaidirte Roth gleichfalls schon in seiner Arbeit. Unser Nachweis der Altersverschiedenheit spricht nur um so dringender dafür. Für den Geologen genügen vielleicht die Namen "jüngerer" und "älterer" Quarztrachyt. Soll jedoch entsprechend der Sonderbezeichnung für die jüngere Gruppe, auch für die ältere Gruppe der Quarztrachyte ein besonderer Name eingeführt werden, so möchte der Name "Dacit" vielleicht entsprechend sein, da die Gruppe im alten Dacien eine besonders hervorragende Rolle zu spielen scheint).