Transition zone (Earth)

<h2 id="410-km-discontinuity--phase-transition">410 km discontinuity – phase transition</h2>
A peak is seen in seismological data at about 410 kilometres (250 mi) as is predicted by the transition from α- to β-Mg2SiO4 (<a href="/facts/Olivine/tLLL4rae">olivine</a> to <a href="/facts/Wadsleyite/lQPJNdfT">wadsleyite</a>). From the <a href="/facts/Clausius%E2%80%93Clapeyron_relation/Lo9SfNqM">Clapeyron slope</a>, this change is predicted to occur at shallower depths in cold regions, such as where <a href="/facts/Subduction_zone/rkasNdTo">subducting</a> slabs penetrate into the transition zone, and at greater depths in warmer regions, such as where <a href="/facts/Mantle_plume/wLXJ0Q4a">mantle plumes</a> pass through the transition zone.<a class="footnote-ref" id="fnref:2" href="#fn:2">2</a> Therefore, the exact depth of the "410 km discontinuity" can vary.

<h2 id="660-km-discontinuity--phase-transition">660 km discontinuity – phase transition</h2>
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 kilometres or 400–450 miles). The Clapeyron slope predicts a deeper discontinuity in cold regions and a shallower discontinuity in hot regions.<a class="footnote-ref" id="fnref:3" href="#fn:3">3</a> This discontinuity is generally linked to the transition from <a href="/facts/Ringwoodite/LG79eVdM">ringwoodite</a> to <a href="/facts/Bridgmanite/behIjuQ2">bridgmanite</a> and <a href="/facts/Periclase/2E5Ld50a">periclase</a>.<a class="footnote-ref" id="fnref:4" href="#fn:4">4</a> This is thermodynamically an endothermic reaction and creates a viscosity jump. Both characteristics cause this <a href="/facts/Phase_transition/eLP2BY8R">phase transition</a> to play an important role in geodynamical models. Cold downwelling material might pond on this transition.<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a>

<h2 id="other-discontinuities">Other discontinuities</h2>
There is another major phase transition predicted at 520 kilometres (320 mi) for the transition of olivine (β to γ) and <a href="/facts/Garnet/kqh2lWQI">garnet</a> in the <a href="/facts/Pyrolite/FQmNU4M7">pyrolite</a> mantle.<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a> This one has only sporadically been observed in seismological data.<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a>
Other non-global phase transitions have been suggested at a range of depths.<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a><a class="footnote-ref" id="fnref:9" href="#fn:9">9</a>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Goes, Saskia (2022). "Compositional heterogeneity in the mantle transition zone". Nature Reviews Earth & Environment. 3 (8): 533-550. Bibcode:2022NRvEE...3..533G. doi:10.1038/s43017-022-00312-w. hdl:1721.1/148207. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">Fowler, C. M. R. (2005). The Solid Earth: An Introduction to Global Geophysics (2nd ed.). Cambridge University Press. ISBN 978-0-521-89307-7.[page needed] <a href="978-0-521-89307-7" target="_blank">978-0-521-89307-7</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Fowler, C. M. R. (2005). The Solid Earth: An Introduction to Global Geophysics (2nd ed.). Cambridge University Press. ISBN 978-0-521-89307-7.[page needed] <a href="978-0-521-89307-7" target="_blank">978-0-521-89307-7</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">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. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">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. <a href="https://doi.org/10.1002%2F2013jb010466" target="_blank">https://doi.org/10.1002%2F2013jb010466</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Deuss, Arwen; Woodhouse, John (12 October 2001). "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. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">Egorkin, A. V. (1 January 1997). "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. <a href="9789048149667" target="_blank">9789048149667</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">Fowler, C. M. R. (2005). The Solid Earth: An Introduction to Global Geophysics (2nd ed.). Cambridge University Press. ISBN 978-0-521-89307-7.[page needed] <a href="978-0-521-89307-7" target="_blank">978-0-521-89307-7</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Khan, Amir; Deschamps, Frédéric (28 April 2015). The Earth's Heterogeneous Mantle: A Geophysical, Geodynamical, and Geochemical Perspective. Springer. ISBN 9783319156279. <a href="9783319156279" target="_blank">9783319156279</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
</ol>

Transition zone (Earth) open-in-new

Transition zone (Earth)