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Subduction zone metamorphism

Melt production and accretion of melt onto continental crust in a subduction zone[1]

A subduction zone is a region of the Earth's crust where one tectonic plate moves under another tectonic plate; oceanic crust gets recycled back into the mantle and continental crust gets produced by the formation of arc magmas. Arc magmas account for more than 20% of terrestrially produced magmas[2] and are produced by the dehydration of minerals within the subducting slab as it descends into the mantle and are accreted onto the base of the overriding continental plate.[3] Subduction zones host a unique variety of rock types formed by the high-pressure, low-temperature conditions a subducting slab encounters during its descent.[4] The metamorphic conditions the slab passes through in this process generates and alters water bearing (hydrous) mineral phases, releasing water into the mantle. This water lowers the melting point of mantle rock, initiating melting.[5] Understanding the timing and conditions in which these dehydration reactions occur, is key to interpreting mantle melting, volcanic arc magmatism, and the formation of continental crust.[6]

Pressure-temperature pathway for subducted crust

A metamorphic facies is characterized by a stable mineral assemblage specific to a pressure-temperature range and specific starting material. Subduction zone metamorphism is characterized by a low temperature, high-ultrahigh pressure metamorphic path through the zeolite, prehnite-pumpellyite, blueschist, and eclogite facies stability zones of subducted oceanic crust.[7] Zeolite and prehnite-pumpellyite facies assemblages may or may not be present, thus the onset of metamorphism may only be marked by blueschist facies conditions.[8] Subducting slabs are composed of basaltic crust topped with pelagic sediments;[9] however, the pelagic sediments may be accreted onto the forearc-hanging wall and not subducted.[10] Most metamorphic phase transitions that occur within the subducting slab are prompted by the dehydration of hydrous mineral phases. The breakdown of hydrous mineral phases typically occurs at depths greater than 10 km.[11] Each of these metamorphic facies is marked by the presence of a specific stable mineral assemblage, recording the metamorphic conditions undergone by the subducting slab. Transitions between facies cause hydrous minerals to dehydrate at certain pressure-temperature conditions and can therefore be tracked to melting events in the mantle beneath a volcanic arc.

  1. ^ Cite error: The named reference Winter 344-345 was invoked but never defined (see the help page).
  2. ^ Tatsumi, Yoshiyuki (2005). "The subduction factory: How it operates in the evolving Earth" (PDF). GSA Today. 15 (7): 4. doi:10.1130/1052-5173(2005)015[4:TSFHIO]2.0.CO;2. Retrieved December 3, 2014.
  3. ^ Spandler, Carl; et al. (2003). "Redistribution of trace elements during prograde metamorphism from lawsonite blueschist to eclogite facies; implications for deep subduction-zone processes". Contributions to Mineralogy and Petrology. 146 (2): 205–222. Bibcode:2003CoMP..146..205S. doi:10.1007/s00410-003-0495-5. S2CID 140693326.
  4. ^ Zheng, Y.-F., Chen, Y.-X., 2016. Continental versus oceanic subduction zones. National Science Review 3, 495-519.
  5. ^ "How Volcanoes work – Subduction Zone Volcanism". San Diego State University Department of Geological Science. Archived from the original on 2018-12-29. Retrieved 2015-01-11.
  6. ^ Mibe, Kenji; et al. (2011). "Slab melting versus slab dehydration in subduction zones". Proceedings of the National Academy of Sciences. 108 (20): 8177–8182. doi:10.1073/pnas.1010968108. PMC 3100975. PMID 21536910.
  7. ^ Zheng, Y.-F., Chen, R.-X., 2017. Regional metamorphism at extreme conditions: Implications for orogeny at convergent plate margins. Journal of Asian Earth Sciences 145, 46-73.
  8. ^ Winter, John D. (2010). Principles of Igneous and Metamorphic Petrology. Prentice Hall. pp. 541–548. ISBN 978-0-321-59257-6.
  9. ^ Reynolds, Stephen (2012-01-09). Exploring Geology. McGraw-Hill. p. 124. ISBN 978-0073524122.
  10. ^ Bebout, Grey E. (May 31, 2007). "Metamorphic Chemical Geodynamics of Subduction". Earth and Planetary Science Letters. 260 (3–4): 375. Bibcode:2007E&PSL.260..373B. doi:10.1016/j.epsl.2007.05.050.
  11. ^ Peacock, Simon M. (1 January 2004). "Thermal Structure and Metamorphic Evolution of Subducting Slabs". In Eiler, John (ed.). Inside the subduction factory. Geophysical Monograph Series. Vol. 138. American Geophysical Union. pp. 12–15. ISBN 9781118668573.

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অধোগামী অঞ্চল রূপান্তরণ Bengali/Bangla Metamorfismo de zona de subducción Spanish Métamorphisme de zone de subduction French 俯衝帶變質作用 Chinese

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