The mantle was divided into the upper mantle, transition zone, and lower mantle as a result of sudden seismic-velocity discontinuities at depths of 410 and 660 km (250 to 400 mi). This is thought to occur as a result of rearrangement of grains in olivine (which constitutes a large portion of peridotite) at a depth of 410 km, to form a denser crystal structure as a result of the increase in pressure with increasing depth. Below a depth of 660 km, evidence suggests due to pressure changes ringwoodite minerals change into two new denser phases, bridgmanite and periclase. This can be seen using body waves from earthquakes, which are converted, reflected or refracted at the boundary, and predicted from mineral physics, as the phase changes are temperature and density-dependent and hence depth dependent.
A peak is seen in seismological data at about 410 km as is predicted by the transition from α- to β-Mg2SiO4 (olivine to wadsleyite). From the Clapeyron slope, this change is predicted to occur at shallower depths in cold regions, such as where subducting slabs penetrate into the transition zone, and at greater depths in warmer regions, such as where mantle plumes pass through the transition zone.[1] Therefore, the exact depth of the "410 km discontinuity" can vary.
660 km discontinuity – phase transitionedit
The 660 km discontinuity appears in PP precursors (a wave which reflects off the discontinuity once) only in certain regions but is always apparent in SS precursors. It is seen as single and double reflections in receiver functions for P to S conversions over a broad range of depths (640–720 km, or 397–447 mi). The Clapeyron slope predicts a deeper discontinuity in cold regions and a shallower discontinuity in hot regions.[1] This discontinuity is generally linked to the transition from ringwoodite to bridgmanite and periclase.[2] This is thermodynamically an endothermic reaction and creates a viscosity jump. Both characteristics cause this phase transition to play an important role in geodynamical models. Cold downwelling material might pond on this transition.[3]
Other discontinuitiesedit
There is another major phase transition predicted at 520 km for the transition of olivine (β to γ) and garnet in the pyrolite mantle.[4] This one has only sporadically been observed in seismological data.[5]
Other non-global phase transitions have been suggested at a range of depths.[1][6]
Referencesedit
^ abcC.M.R. Fowler, The Solid Earth (2nd Edition), Cambridge University Press 2005.
^Ito, E; Takahashi, E (1989). "Postspinel transformations in the system Mg2SiO4–Fe2SiO4 and some geophysical implications". Journal of Geophysical Research: Solid Earth. 94 (B8): 10637–10646. Bibcode:1989JGR....9410637I. doi:10.1029/jb094ib08p10637.
^Fukao, Y.; Obayashi, M. (2013). "Subducted slabs stagnant above, penetrating through, and trapped below the 660 km discontinuity". Journal of Geophysical Research: Solid Earth. 118 (11): 5920–5938. Bibcode:2013JGRB..118.5920F. doi:10.1002/2013jb010466. S2CID 129872709.
^Deuss, Arwen; Woodhouse, John (2001-10-12). "Seismic Observations of Splitting of the Mid-Transition Zone Discontinuity in Earth's Mantle". Science. 294 (5541): 354–357. Bibcode:2001Sci...294..354D. doi:10.1126/science.1063524. ISSN 0036-8075. PMID 11598296. S2CID 28563140.
^Egorkin, A. V. (1997-01-01). "Evidence for 520-Km Discontinuity". In Fuchs, Karl (ed.). Upper Mantle Heterogeneities from Active and Passive Seismology. NATO ASI Series. Springer Netherlands. pp. 51–61. doi:10.1007/978-94-015-8979-6_4. ISBN9789048149667.
^Khan, Amir; Deschamps, Frédéric (2015-04-28). The Earth's Heterogeneous Mantle: A Geophysical, Geodynamical, and Geochemical Perspective. Springer. ISBN9783319156279.
February 15, 2024
transition, zone, earth, transition, zone, part, earth, mantle, located, between, lower, mantle, upper, mantle, between, depth, earth, mantle, including, transition, zone, consists, primarily, peridotite, ultramafic, igneous, rock, mantle, divided, into, upper. The transition zone is part of the Earth s mantle and is located between the lower mantle and the upper mantle between a depth of 410 and 660 km 250 to 400 mi The Earth s mantle including the transition zone consists primarily of peridotite an ultramafic igneous rock The mantle was divided into the upper mantle transition zone and lower mantle as a result of sudden seismic velocity discontinuities at depths of 410 and 660 km 250 to 400 mi This is thought to occur as a result of rearrangement of grains in olivine which constitutes a large portion of peridotite at a depth of 410 km to form a denser crystal structure as a result of the increase in pressure with increasing depth Below a depth of 660 km evidence suggests due to pressure changes ringwoodite minerals change into two new denser phases bridgmanite and periclase This can be seen using body waves from earthquakes which are converted reflected or refracted at the boundary and predicted from mineral physics as the phase changes are temperature and density dependent and hence depth dependent Contents 1 410 km discontinuity phase transition 2 660 km discontinuity phase transition 3 Other discontinuities 4 References410 km discontinuity phase transition editA peak is seen in seismological data at about 410 km as is predicted by the transition from a to b Mg2SiO4 olivine to wadsleyite From the Clapeyron slope this change is predicted to occur at shallower depths in cold regions such as where subducting slabs penetrate into the transition zone and at greater depths in warmer regions such as where mantle plumes pass through the transition zone 1 Therefore the exact depth of the 410 km discontinuity can vary 660 km discontinuity phase transition editThe 660 km discontinuity appears in PP precursors a wave which reflects off the discontinuity once only in certain regions but is always apparent in SS precursors It is seen as single and double reflections in receiver functions for P to S conversions over a broad range of depths 640 720 km or 397 447 mi The Clapeyron slope predicts a deeper discontinuity in cold regions and a shallower discontinuity in hot regions 1 This discontinuity is generally linked to the transition from ringwoodite to bridgmanite and periclase 2 This is thermodynamically an endothermic reaction and creates a viscosity jump Both characteristics cause this phase transition to play an important role in geodynamical models Cold downwelling material might pond on this transition 3 Other discontinuities editThere is another major phase transition predicted at 520 km for the transition of olivine b to g and garnet in the pyrolite mantle 4 This one has only sporadically been observed in seismological data 5 Other non global phase transitions have been suggested at a range of depths 1 6 References edit a b c C M R Fowler The Solid Earth 2nd Edition Cambridge University Press 2005 Ito E Takahashi E 1989 Postspinel transformations in the system Mg2SiO4 Fe2SiO4 and some geophysical implications Journal of Geophysical Research Solid Earth 94 B8 10637 10646 Bibcode 1989JGR 9410637I doi 10 1029 jb094ib08p10637 Fukao Y Obayashi M 2013 Subducted slabs stagnant above penetrating through and trapped below the 660 km discontinuity Journal of Geophysical Research Solid Earth 118 11 5920 5938 Bibcode 2013JGRB 118 5920F doi 10 1002 2013jb010466 S2CID 129872709 Deuss Arwen Woodhouse John 2001 10 12 Seismic Observations of Splitting of the Mid Transition Zone Discontinuity in Earth s Mantle Science 294 5541 354 357 Bibcode 2001Sci 294 354D doi 10 1126 science 1063524 ISSN 0036 8075 PMID 11598296 S2CID 28563140 Egorkin A V 1997 01 01 Evidence for 520 Km Discontinuity In Fuchs Karl ed Upper Mantle Heterogeneities from Active and Passive Seismology NATO ASI Series Springer Netherlands pp 51 61 doi 10 1007 978 94 015 8979 6 4 ISBN 9789048149667 Khan Amir Deschamps Frederic 2015 04 28 The Earth s Heterogeneous Mantle A Geophysical Geodynamical and Geochemical Perspective Springer ISBN 9783319156279 Retrieved from https en wikipedia org w index php title Transition zone Earth amp oldid 1169972962, wikipedia, wiki, book, books, library,
