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Alkali basalt

January 01, 1970

Alkali basalt or alkali olivine basalt is a dark-colored, porphyritic volcanic rock[2] usually found in oceanic and continental areas associated with volcanic activity, such as oceanic islands, continental rifts and volcanic fields.[3] Alkali basalt is characterized by relatively high alkali (Na2O and K2O) content relative to other basalts and by the presence of olivine and titanium-rich augite in its groundmass and phenocrysts, and nepheline in its CIPW norm.[4][5]

Alkali basalt is one of the rocks comprising the Pali-Aike volcanic field, in Argentina.[1]

Geochemical characterization edit

 
Depiction of the total alkali-silica diagram. Alkali basalts are generally located in the upper left corner of the basalt region (region B).[6]

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 edit

The groundmass of alkali basalt is mainly composed of olivine, titanium-rich augite and plagioclase feldspar and may have alkali feldspar or feldspathoid interstitially, but is poor in silica minerals, such as hypersthene and quartz.[4]

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 edit

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 gamma ray spectrometer on Venera 8 on Venus suggest it landed on alkali basalt.[10]

References edit

  1. ^ Skewes, Milka Alexandra; Stern, Charles R. (1979). "Petrology and geochemistry of alkali basalts and ultramafic inclusions from the palei-aike volcanic field in Southern Chile and the origin of the patagonian plateau lavas". Journal of Volcanology and Geothermal Research. 6 (1–2): 3–25. Bibcode:1979JVGR....6....3S. doi:10.1016/0377-0273(79)90044-1.
  2. ^ "Basalt | Definition, Properties, & Facts". Encyclopedia Britannica.
  3. ^ a b c Haldar, S. K. (2017). Platinum-Nickel-Chromium Deposits. Elsevier. p. 45. ISBN 9780128020418.
  4. ^ a b c Winter, John DuNann (2001). An Introduction to Igneous and Metamorphic Petrology. Upper Saddle River, New Jersey: Prentice Hall. pp. 148, 182. ISBN 0132403420.
  5. ^ Irvine, T. N.; Baragar, W. R. A. (1971). "A Guide to the Chemical Classification of the Common Volcanic Rocks". Canadian Journal of Earth Sciences. 8 (5): 523–548. Bibcode:1971CaJES...8..523I. doi:10.1139/e71-055.
  6. ^ a b Le Maitre, R. W.; Streckeisen, A.; Zanettin, B.; Le Bas, M. J.; Bonin, B.; Bateman, P., eds. (2002). Igneous Rocks: A Classification and Glossary of Terms. Cambridge University Press. pp. 36–37. ISBN 9780521662154.
  7. ^ Hughes, D. J.; Brown, G. C. (1972). "Basalts from Madeira: A petrochemical contribution to the genesis of oceanic alkali rock series". Contributions to Mineralogy and Petrology. 37 (2): 91–109. Bibcode:1972CoMP...37...91H. doi:10.1007/BF00371069. ISSN 1432-0967. S2CID 140549581.
  8. ^ Baker, Ian (1969). "Petrology of the Volcanic Rocks of Saint Helena Island, South Atlantic". GSA Bulletin. 80 (7): 1283–1310. Bibcode:1969GSAB...80.1283B. doi:10.1130/0016-7606(1969)80[1283:POTVRO]2.0.CO;2. ISSN 0016-7606.
  9. ^ Farmer, G.L. (2005). Rudnick, R.L. (ed.). Treatise on Geochemistry: The crust. Gulf Professional Publishing. p. 97. ISBN 9780080448473.
  10. ^ Ulivi, Paolo; Harland, David M (2007). Robotic Exploration of the Solar System Part I: The Golden Age 1957-1982. Springer. pp. 159–160. ISBN 9780387493268.

External links edit

  • Alkali basalt on Mindat.org

January 01, 1970
alkali, basalt, alkali, olivine, basalt, dark, colored, porphyritic, volcanic, rock, usually, found, oceanic, continental, areas, associated, with, volcanic, activity, such, oceanic, islands, continental, rifts, volcanic, fields, characterized, relatively, hig. Alkali basalt or alkali olivine basalt is a dark colored porphyritic volcanic rock 2 usually found in oceanic and continental areas associated with volcanic activity such as oceanic islands continental rifts and volcanic fields 3 Alkali basalt is characterized by relatively high alkali Na2O and K2O content relative to other basalts and by the presence of olivine and titanium rich augite in its groundmass and phenocrysts and nepheline in its CIPW norm 4 5 Alkali basalt is one of the rocks comprising the Pali Aike volcanic field in Argentina 1 Contents 1 Geochemical characterization 2 Petrography 3 Geologic context 4 References 5 External linksGeochemical characterization edit nbsp Depiction of the total alkali silica diagram Alkali basalts are generally located in the upper left corner of the basalt region region B 6 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 editThe groundmass of alkali basalt is mainly composed of olivine titanium rich augite and plagioclase feldspar and may have alkali feldspar or feldspathoid interstitially but is poor in silica minerals such as hypersthene and quartz 4 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 editAlkali 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 gamma ray spectrometer on Venera 8 on Venus suggest it landed on alkali basalt 10 References edit Skewes Milka Alexandra Stern Charles R 1979 Petrology and geochemistry of alkali basalts and ultramafic inclusions from the palei aike volcanic field in Southern Chile and the origin of the patagonian plateau lavas Journal of Volcanology and Geothermal Research 6 1 2 3 25 Bibcode 1979JVGR 6 3S doi 10 1016 0377 0273 79 90044 1 Basalt Definition Properties amp Facts Encyclopedia Britannica a b c Haldar S K 2017 Platinum Nickel Chromium Deposits Elsevier p 45 ISBN 9780128020418 a b c Winter John DuNann 2001 An Introduction to Igneous and Metamorphic Petrology Upper Saddle River New Jersey Prentice Hall pp 148 182 ISBN 0132403420 Irvine T N Baragar W R A 1971 A Guide to the Chemical Classification of the Common Volcanic Rocks Canadian Journal of Earth Sciences 8 5 523 548 Bibcode 1971CaJES 8 523I doi 10 1139 e71 055 a b Le Maitre R W Streckeisen A Zanettin B Le Bas M J Bonin B Bateman P eds 2002 Igneous Rocks A Classification and Glossary of Terms Cambridge University Press pp 36 37 ISBN 9780521662154 Hughes D J Brown G C 1972 Basalts from Madeira A petrochemical contribution to the genesis of oceanic alkali rock series Contributions to Mineralogy and Petrology 37 2 91 109 Bibcode 1972CoMP 37 91H doi 10 1007 BF00371069 ISSN 1432 0967 S2CID 140549581 Baker Ian 1969 Petrology of the Volcanic Rocks of Saint Helena Island South Atlantic GSA Bulletin 80 7 1283 1310 Bibcode 1969GSAB 80 1283B doi 10 1130 0016 7606 1969 80 1283 POTVRO 2 0 CO 2 ISSN 0016 7606 Farmer G L 2005 Rudnick R L ed Treatise on Geochemistry The crust Gulf Professional Publishing p 97 ISBN 9780080448473 Ulivi Paolo Harland David M 2007 Robotic Exploration of the Solar System Part I The Golden Age 1957 1982 Springer pp 159 160 ISBN 9780387493268 External links editAlkali basalt on Mindat org Retrieved from https en wikipedia org w index php title Alkali basalt amp oldid 1168355431, wikipedia, wiki, book, books, library,

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