Alkali basalt
Alkali basalt or alkali olivine basalt is a dark-colored,
Geochemical characterization
Alkali basalt is chemically classified as a rock in region B (basalt) of the total alkali versus silica (TAS) diagram that contains nepheline in its CIPW norm. Basalts that do not contain normative nepheline are characterized as sub-alkali basalts, which include tholeiitic basalts and calc-alkaline basalts.[6]
Petrography
The groundmass of alkali basalt is mainly composed of olivine, titanium-rich augite and
Phenocrysts are ubiquitous in alkali basalt and, similarly to the groundmass, are usually made up of olivine and titanium-rich augite but can also have plagioclase and iron oxides with lower frequency.[3][4]
Geologic context
Alkali basalt can be found in areas associated with volcanic activity, such as oceanic islands (Hawaii, Madeira,[7] Saint Helena,[8] Ascension, etc.), continental rifts and volcanic fields.[3] Continental alkali basalt can be found in every continent, with prominent examples being the Rio Grande Rift (USA), the East African Rift and the Pali-Aike volcanic field.[9]
The results from the
References
- .
- ^ "Basalt | Definition, Properties, & Facts". Encyclopedia Britannica.
- ^ ISBN 9780128020418.
- ^ ISBN 0132403420.
- doi:10.1139/e71-055.
- ^ ISBN 9780521662154.
- S2CID 140549581.
- ISSN 0016-7606.
- ISBN 9780080448473.
- ISBN 9780387493268.
External links
Types of basalts | |
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| Basalts by tectonic setting | |
| Basalts by form and flow |
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| Basalts by chemistry | |
| Important minerals | |
