In geology ultrahigh-temperature metamorphism (UHT) is extreme crustal metamorphism with metamorphic temperatures exceeding 900 °C.[1][2][3][4] Granulite-facies rocks metamorphosed at very high temperatures were identified in the early 1980s, although it took another decade for the geoscience community to recognize UHT metamorphism as a common regional phenomenon. Petrological evidence based on characteristic mineral assemblages backed by experimental and thermodynamic relations demonstrated that Earth's crust can attain and withstand very high temperatures (900–1000 °C) with or without partial melting.
Metamorphism of crustal rocks in which peak temperature exceeds 900 °C, recognized either by robust thermobarometry or by the presence of a diagnostic mineral assemblage in an appropriate bulk composition and oxidation state, such as assemblages with orthopyroxene + sillimanite + quartz, sapphirine + quartz or spinel + quartz, generally at pressure conditions of sillimanite stability in metapelites [after Brown (2007)[2] following proposal by Harley (1998)[1]].
Petrological indicators of UHT metamorphism are usually preserved in extremely Mg-Al-rich rocks which are usually dry and restitic in nature. Mineral assemblages such as sapphirine + quartz, orthopyroxene + sillimanite ± quartz, osumilite and spinel + quartz provide straight away evidence for such extreme conditions. Occasionally widespread assemblages like garnet + orthopyroxene, ternary feldspars, (F-Ti) pargasite or metamorphic inverted pigeonite are taken as typical indicators of UHT metamorphism.
UHT rocks are now identified in all major continents and span different geological ages ranging from c. 3178 to 35 million years associated with major geological events. More than 46 localities/terranes with diagnostic UHT indicators have been reported over the globe, related to both extensional and collisional tectonic environments; the two fundamental types of Earth orogenic systems.[3][5] The major Archean UHT rocks are distributed in East-Antarctica, South Africa, Russia and Canada.[6][7][8][9][10] Paleoproterozoic UHT granulites were reported from the North China Craton (during the accretion of the supercontinent Columbia),[11][12][13] Taltson magmatic zone, northwestern Canada[14] and South Harris, Lewisian complex, Scotland.[15][16][17][18] UHT rocks from the Neoproterozoic Grenville orogeny are distributed in the Eastern Ghats Province, India.[19] Neoproterozoic-Cambrian (Pan-African) UHT occurrences are mainly distributed in Lutzow-Holm Bay, East Antarctica,[20] southern Madagascar,[21] Sri Lanka[22][23][24] and southern India.[11][25][26][27][28][29][30][31][32][33] UHT rocks are also reported from younger terranes like the Triassic Kontum Massif, Vietnam,[34] Cretaceous Higo belt, Japan[35][36] and Paleogene Gruf Complex, central Alps.[37] Three-million-year-old xenoliths erupted in Qiangtang imply that UHT metamorphism is ongoing beneath central Tibet.[38]
A correlation was proposed between the episodic formation of UHT metamorphic rocks and the episodic assembly of supercontinents in the Precambrian.[39] However, inspection of extreme metamorphism at convergent plate margins indicates that supercontinental assembly is associated with regional HP to UHP eclogite-facies metamorphism at low thermal gradients of less than 10 °C/km, whereas continental rifting plays a crucial role in causing regional HT to UHT granulite-facies metamorphism at high thermal gradients of greater than 30 °C/km.[40] In this regard, the episodic formation of HT to UHT granulite-facies metamorphic rocks is temporally and spatially coupled with the breakup or attempting rupture of supercontinents in the plate tectonics context.
Because UHT rocks are generally characterized by low water contents, this led to an illusion for the involvement of CO2-rich fluids in generating diagnostic UHT assemblages according to the finding of abundant pure CO2 fluid inclusions in these rocks.[13] However, the extraction of liquid phases such as aqueous solutions and hydrous melts from anatectic systems during UHT metamorphism is so efficient that the common occurrence of pure CO2 fluid inclusions looks as if the incoming CO2 could have buffered the water activity and stabilized the anhydrous mineralogy of UHT rocks. Anatectic melts were variably extracted from anatectic systems, leading to granulite-migmatite-granite associations in accretionary and collisional orogens.[41] Metamorphic core complexes were emplaced due to the buoyant entrainment of granitic melts. The abundant water was liberated by heating dehydration of the lowest orogenic crust, contributing aqueous solutions to amphibolite-facies retrogression of the overlying crust.
Brown, M., 2007, Metamorphic conditions in orogenic belts: a record of secular change. International Geology Review 49, 193-234
Kelsey, D.E., 2008, On ultrahigh-temperature crustal metamorphism. Gondwana Research 13, 1-29
Santosh, M., Omori, S., 2008a, CO2 flushing: a plate tectonic perspective. Gondwana Research 13, 86-102
Santosh, M., Omori, S., 2008b, CO2 windows from mantle to atmosphere: Models on ultrahigh- temperature metamorphism and speculations on the link with melting of snowball Earth. Gondwana Research 14, in press, doi:10.1016/j.gr.2007.11.001 Arima, M., and Barnett, R. L., 1984, Sapphirine bearing granulites from the Sipiwesk Lake area of the late Archean Pikwitonei granulite terrain, Manitoba, Canada: Contributions to Mineralogy and Petrology, v. 88, p. 102-112.
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Harley, S. L., and Motoyoshi, Y., 2000, Al zoning in orthopyroxene in a sapphirine quartzite: Evidence for >1120°C UHT metamorphism in the Napier complex, Antarctica, and implications for the entropy of sapphirine: Contributions to Mineralogy and Petrology, v.138, p. 293–307.
Fonarev, V. I., Pilugin, S. M., Savko, K. A., and Novikova, M. A., 2006, Exsolution textures of ortho-and clinopyroxene in high-grade BIF of the Voronezh Crystalline Massif: Evidence of ultrahigh-temperature metamorphism: Journal of Metamorphic Geology, v. 24, p. 135-151.
Santosh, M. Sajeev K. and J. Li 2006, Extreme crustal metamorphism during Columbia supercontinent assembly: Evidence from North China Craton. Gondwana Research, v. 10, p. 256-266.
Santosh, M., Tsunogae, T., Li, J.H., and Liu, S.J., 2007, Discovery of sapphirine- bearing Mg-Al granulites in the North China Craton: Implications for Paleoproterozoic ultrahigh- temperature metamorphism. Gondwana Research 11, 263-285.
Santosh, M., Tsunogae, T., Ohyama, H. Sato, K., Li, J.H., and Liu, S.J., 2008, Carbonic metamorphism at ultrahigh-temperatures. Earth and Planetary Science Letters 266, 149-165.
Farquhar; Chacko, Thomas; Ellis, David J.; et al. (1996). "Preservation of oxygen isotope compositions in granulites from Northwestern Canada and Enderby Land, Antarctica: implications for high-temperature isotopic thermometry". Contributions to Mineralogy and Petrology. 125 (2–3): 213–224. Bibcode:1996CoMP..125..213F. doi:10.1007/s004100050217. Baba, S., 1998, Proterozoic anticlockwise P-T path of the Lewisian complex of South Harris, outer Hebrides, NW Scotland: Journal of Metamorphic of Geology, v. 16, p. 819–841.
Baba, S., 1999, Sapphirine-bearing orthopyroxene-kyanite/sillimanite granulites from South Harris, NW Scotland: Evidence for Proterozoic UHT metamorphism in the Lewisian: Contributions to Mineralogy and Petrology, v. 136, p. 33–47.
Baba, S., 2003, Two stages of sapphirine formation during prograde and retrograde metamorphism in the Paleoproterozoic Lewisian complex in South Harris, NW Scotland: Journal of Petrology, v. 44, p. 329–354.
Hollis, J. A., Harley, S. L., White, R. W., and Clarke, G. L., 2006, Preservation of evidence for prograde metamorphism in UHT HP granulites, South Harris, Scotland: Journal of Metamorphic Geology, v. 24, p. 263–279.
Dasgupta, S., Sanyal, S., Sengupta, P., and Fukuoka, M.,1994, Petrology of granulites from Anakapalle-evidence for Proterozoic decompression in the Eastern Ghats, India: Journal of Petrology, v. 35, p. 433–459.
Motoyoshi, Y., and Ishikawa, M., 1997, Metamorphic and structural evolution of granulites from Rundvågshetta,Lützow-Holm Bay, east Antarctica, in Ricci, C. A., ed., The Antarctic region: Geological evolution and processes: Proceedings of the VII International Symposium on the Antarctic Earth Sciences, Siena, Terra Antarctica, p. 65–72.
Sajeev, K. and Osanai, Y. 2004a, Ultrahigh-temperature Metamorphism (1150°C and 12 kbar) and Multi-stage Evolution of Mg-Al Granulites from Central Highland Complex, Sri Lanka, Journal of Petrology, v. 45, p. 1821-1844.
Sajeev, K.; Osanai, Y.; Connolly, J.A.D.; Suzuki, S. Ishioka; Kagami, H.; Rino, S. (2007). "Extreme Crustal Metamorphism during a Neoproterozoic Event in Sri Lanka: A Study of Dry Mafic Granulites". Journal of Geology. 115 (5): 563–582. Bibcode:2007JG....115..563S. doi:10.1086/519778. Brown, M., and Raith, M., 1996, First evidence of ultrahigh-temperature decompression from the granulite province of Southern India: Journal of the Geological Society, London, v. 153, p. 819–822.
Morimoto, T., Santosh, M., Tsunogae, T., and Yoshimura, Y., 2004, Spinel + quartz association from the Kerala khondalites, southern India: Evidence for ultrahightemperature metamorphism: Journal of Mineralogical and Petrological Sciences, v. 99, p. 257–278.
Tateishi, K., Tsunogae, T., Santosh, M. and Janardhan, A.S., 2004, First report of sapphirine+ quartz assemblage from southern India: Implications for ultrahigh- temperature metamorphism. Gondwana Research 7, 899-912.
Sajeev, K., Osanai, Y. and Santosh, M. 2004, Ultrahigh-temperature metamorphism followed by two-stage decompression of garnet-orthopyroxene-sillimanite granulites from Ganguvarpatti, Madurai block, southern India. Contributions to Mineralogy and Petrology, v. 148, p. 29-46.
Sajeev, K., Santosh, M. and Kim, H.S. 2006, Partial melting and P-T evolution of the Kodaikanal Metapelite Belt, southern India. Lithos v. 92, p. 465-483. Santosh, M., Sajeev, K., 2006. Anticlockwise evolution of ultrahigh-temperature granulites within continental collision zone in southern India. Lithos 92, 447–464.
Shimpo, M., Tsunogae, T., Santosh, M., 2006. First report of garnet–corundum rocks from southern India: implications for prograde high-pressure (eclogite-facies?)metamorphism. Earth and Planetary Science Letters 242, 111–129.
Prakash,D., Arima, M.and Mohan, A.2006, UHT metamorphism in the Palni Hills, South India: Insights from feldspar thermometry and phase equilibria. International Geology Review, v. 48, pp. 619-638.
Osanai, Y., Nakano, N., Owada, M., Nam, T. N., Toyoshima, T., Tsunogae, T., and Binh, P., 2004, Permo-Triassic ultrahigh-temperature metamorphism in the Kontum Massif, central Viet Nam: Journal of Mineralogical and Petrological Sciences, v. 99, p. 225–241.
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note-Brown2007-2 note-Santosh%26Omori2008a-4 (malformed ref)
Zheng, Y.-F., Chen, R.-X., 2017. Regional metamorphism at extreme conditions: Implications for orogeny at convergent plate margins. Journal of Asian Earth Sciences, v. 145, p. 46-73.
Zheng, Y.-F., Chen, R.-X., 2017. Regional metamorphism at extreme conditions: Implications for orogeny at convergent plate margins. Journal of Asian Earth Sciences, v. 145, p. 46-73.
- Clark, C., I.C.W. Fitzsimons, D. Healy, and S.L. Harley, 2011, How does the continental crust get really hot?, Elements, 7 (4), 235-240.
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- Sajeev, K. and Santosh, M. 2006, Extreme crustal metamorphism and related crust-mantle processes. Lithos v. 92 n. 3-4, p. 321-624.
- Santosh, M., Osanai, Y. and Tsunogae, T. 2004, Ultrahigh temperature metamorphism and deep crustal processes Journal of Mineralogical and Petrological Sciences v. 99 (part 1 & 2), n. 4-5, 137-365.
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- Zheng, Y.-F., Chen, R.-X., 2017. Regional metamorphism at extreme conditions: Implications for orogeny at convergent plate margins. Journal of Asian Earth Sciences, v. 145, p. 46-73.
