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'''Pyrolite''' is a term used to characterize a model composition of the Earth's [[Upper mantle (Earth)|mantle]]. This model is based on that a pyrolite source can produce [[mid-ocean ridge]] [[basalts]] (MORB) by partial melting.<ref name=":32">{{Cite book|last=Anderson|first=Don L.|url=https://resolver.caltech.edu/CaltechBOOK:1989.001|title=Theory of the Earth|date=1989-01-01|publisher=Blackwell Scientific Publications|isbn=978-0-86542-335-0|location=Boston, MA}}</ref><ref name=":12">{{Cite journal|last1=Xu|first1=Wenbo|last2=Lithgow-Bertelloni|first2=Carolina|author-link2=Carolina Lithgow-Bertelloni|last3=Stixrude|first3=Lars|last4=Ritsema|first4=Jeroen|date=October 2008|title=The effect of bulk composition and temperature on mantle seismic structure|url=http://dx.doi.org/10.1016/j.epsl.2008.08.012|journal=Earth and Planetary Science Letters|volume=275|issue=1–2|pages=70–79|doi=10.1016/j.epsl.2008.08.012|bibcode=2008E&PSL.275...70X |issn=0012-821X|url-access=subscription}}</ref> It was first proposed by [[Ted Ringwood]] (1962)<ref>{{Cite journal|last=Ringwood|first=A. E.|date=Feb 1962|title=A model for the upper mantle|url=http://dx.doi.org/10.1029/jz067i002p00857|journal=Journal of Geophysical Research|volume=67|issue=2|pages=857–867|doi=10.1029/jz067i002p00857|bibcode=1962JGR....67..857R |issn=0148-0227|url-access=subscription}}</ref> as being 1 part basalt and 4 parts [[harzburgite]], but later was revised to being 1 part [[tholeiitic basalt]] and 3 parts [[dunite]].<ref name=":32" /><ref>{{Cite journal|last1=Ringwood|first1=A.E.|last2=Major|first2=Alan|date=Sep 1966|title=High-pressure transformations in pyroxenes|url=http://dx.doi.org/10.1016/0012-821x(66)90023-9|journal=Earth and Planetary Science Letters|volume=1|issue=5|pages=351–357|doi=10.1016/0012-821x(66)90023-9|bibcode=1966E&PSL...1..351R |issn=0012-821X|url-access=subscription}}</ref> The term is derived from the mineral names [[Pyroxene|PYR-oxene]] and [[Olivine|OL-ivine]].<ref>D.H. Green. Pyrolite. In: Petrology. Encyclopedia of Earth Science. Springer, 1989</ref> However, whether pyrolite is entirely representative of the Earth's mantle remains debated.<ref name=":22">{{Cite journal|last1=Katsura|first1=Tomoo|last2=Shatskiy|first2=Anton|last3=Manthilake|first3=M. A. Geeth M.|last4=Zhai|first4=Shuangmeng|last5=Yamazaki|first5=Daisuke|last6=Matsuzaki|first6=Takuya|last7=Yoshino|first7=Takashi|last8=Yoneda|first8=Akira|last9=Ito|first9=Eiji|last10=Sugita|first10=Mitsuhiro|last11=Tomioka|first11=Natotaka|date=2009-06-12|title=P-V-Trelations of wadsleyite determined by in situ X-ray diffraction in a large-volume high-pressure apparatus|journal=Geophysical Research Letters|volume=36|issue=11|doi=10.1029/2009gl038107|bibcode=2009GeoRL..3611307K |issn=0094-8276|doi-access=free}}</ref>

== Chemical composition and [[phase transition]] ==
[[File:Phase_diagram_of_pyrolite_.jpg|left|thumb|376x376px|Fig.1 The mineral volume fraction in a pyrolitic mantle up to 1000 km depth.<ref name=":02">{{Cite journal|last=Frost|first=Daniel J.|date=2008-06-01|title=The Upper Mantle and Transition Zone|url=https://pubs.geoscienceworld.org/msa/elements/article/4/3/171/137766/The-Upper-Mantle-and-Transition-Zone|journal=Elements|language=en|volume=4|issue=3|pages=171–176|doi=10.2113/GSELEMENTS.4.3.171|bibcode=2008Eleme...4..171F |s2cid=129527426 |issn=1811-5209|url-access=subscription}}</ref><ref>{{Cite journal|last1=Stixrude|first1=Lars|last2=Lithgow-Bertelloni|first2=Carolina|date=2005|title=Mineralogy and elasticity of the oceanic upper mantle: Origin of the low-velocity zone|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=110|issue=B3|doi=10.1029/2004JB002965|bibcode=2005JGRB..110.3204S |issn=2156-2202|doi-access=free|hdl=2027.42/94924|hdl-access=free}}</ref> Ol: olivine; Opx: orthopyroxene; Cpx: clinopyroxene; Gt: garnet; Wad: wadsleyite; Ring: ringwoodite; Pv: perovskite; Fp: ferropericlase; Ca-Pv: calcium perovskite.]]

The major elements composition of pyrolite is about 44.71 [[molar percent]] (mol%) SiO2, 3.98 % Al2O3, 8.18 % FeO, 3.17 % CaO, 38.73 % MgO, 0.13 % Na2O.<ref>{{Cite journal|last1=Workman|first1=Rhea K.|last2=Hart|first2=Stanley R.|date=Feb 2005|title=Major and trace element composition of the depleted MORB mantle (DMM)|url=http://dx.doi.org/10.1016/j.epsl.2004.12.005|journal=Earth and Planetary Science Letters|volume=231|issue=1–2|pages=53–72|doi=10.1016/j.epsl.2004.12.005|bibcode=2005E&PSL.231...53W |issn=0012-821X|url-access=subscription}}</ref>

1) A pyrolitic [[Upper mantle (Earth)|Upper Mantle]] is mainly composed of olivine (~60 [[volume percent]] (vol%)), [[clinopyroxene]], [[orthopyroxene]], and [[garnet]].<ref name=":02" /> Pyroxene would gradually dissolved into [[garnet]] and form [[Majorite|majoritic]] garnet.<ref>{{Cite journal|last=Irifune|first=Tetsuo|date=May 1987|title=An experimental investigation of the pyroxene-garnet transformation in a pyrolite composition and its bearing on the constitution of the mantle|url=http://dx.doi.org/10.1016/0031-9201(87)90040-9|journal=Physics of the Earth and Planetary Interiors|volume=45|issue=4|pages=324–336|doi=10.1016/0031-9201(87)90040-9|bibcode=1987PEPI...45..324I |issn=0031-9201|url-access=subscription}}</ref>

2) A pyrolitic [[Transition zone (Earth)|Mantle Transition Zone]] is mainly composed of 60 vol% olivine-polymorphs ([[wadsleyite]], [[ringwoodite]]) and ~40 vol% majoritic garnet. The top and bottom boundary of the Mantle Transition zone are mainly marked by olivine-wadsleyite transition and ringwoodite-perovskite transition, respectively.

3) A pyrolitic [[Lower mantle (Earth)|Lower Mantle]] is mainly composed of magnesium perovskite (~80 vol%), [[Ferropericlase|ferroperclase]] (~13 vol%), and calcium perovskite (~7%). In addition, [[post-perovskite]] may present at the bottom of the Lower Mantle.

== Seismic velocity and density properties ==
[[File:Seismic_velocities_of_pyrolite_along_the_1600_K_adiabatic_geotherm_.jpg|thumb|262x262px|Fig. 2 Vp and Vs profiles of pyrolite along the 1600 K adiabatic geotherm<ref name=":12" />]]
[[File:Densities_of_pyrolite.jpg|thumb|262x262px|Fig. 3 Density profile of pyrolite along the 1600 K adiabatic geotherm<ref name=":12" />]]
The [[P-wave]] and [[S-wave]] velocities (Vp and Vs) of pyrolite along the 1600 K adiabatic [[Geothermal gradient|geotherm]] are shown in Fig. 2,<ref name=":12" /> and its density profile is shown in Fig. 3.<ref name=":12" />

At the boundary between the Upper Mantle and the Mantle Transition Zone (~410 km), Vp, Vs, and density jump by ~6%, ~6%, and ~4% in a pyrolite model,<ref name=":12" /> respectively, which are mainly attributed to the olivine-wadsleyite [[phase transition]].<ref>{{Cite journal|last1=SAWAMOTO|first1=H.|last2=WEIDNER|first2=D. J.|last3=SASAKI|first3=S.|last4=KUMAZAWA|first4=M.|date=1984-05-18|title=Single-Crystal Elastic Properties of the Modified Spinel (Beta) Phase of Magnesium Orthosilicate|url=http://dx.doi.org/10.1126/science.224.4650.749|journal=Science|volume=224|issue=4650|pages=749–751|doi=10.1126/science.224.4650.749|pmid=17780624|bibcode=1984Sci...224..749S |s2cid=6602306 |issn=0036-8075|url-access=subscription}}</ref>

At the boundary between the Mantle Transition Zone and the Lower Mantle, Vp, Vs, and density jump by ~3%, ~6%, and ~6% in a pyrolite model, respectively.<ref name=":12" /> With more elasticity parameters available, the Vp, Vs, and density profiles of pyrolite would be updated.

== Shortcomings ==
Whether pyrolite could represent the ambient mantle remains debated.

In the geochemical aspect, it does not satisfy trace elements or isotopic data of Mid-Ocean Ridge Basalts because the pyrolite hypothesis is based on major elements and some arbitrary assumptions (e.g. amounts of basalt and melting in the source).<ref name=":32" /> It may also violate mantle heterogeneity.<ref>Don L. Anderson, ''New Theory of the Earth'', Cambridge University Press, 2nd ed. 2007, p. 193 {{ISBN|978-0-521-84959-3}}</ref>

In the geophysical aspect, some studies suggest that seismic velocities of pyrolite do not match well with the observed global seismic models (such as [[Preliminary reference Earth model|PREM]]) in the Earth's interior,<ref name=":22" /> whereas some studies support the pyrolite model.<ref>{{Cite journal|last1=Irifune|first1=T.|last2=Higo|first2=Y.|last3=Inoue|first3=T.|last4=Kono|first4=Y.|last5=Ohfuji|first5=H.|last6=Funakoshi|first6=K.|date=2008|title=Sound velocities of majorite garnet and the composition of the mantle transition region|url=http://dx.doi.org/10.1038/nature06551|journal=Nature|volume=451|issue=7180|pages=814–817|doi=10.1038/nature06551|pmid=18273016|bibcode=2008Natur.451..814I |s2cid=205212051 |issn=0028-0836|url-access=subscription}}</ref>

== Other Mantle Rock models ==
[[File:Eclogite_phase_proportion.jpg|thumb|346x346px|Fig. 4. Mineral proportion of a MORB-transformed eclogite at 250-500 km depth<ref name=":42">{{Cite journal|last1=Hao|first1=Ming|last2=Zhang|first2=Jin S.|last3=Pierotti|first3=Caroline E.|last4=Zhou|first4=Wen-Yi|last5=Zhang|first5=Dongzhou|last6=Dera|first6=Przemyslaw|date=Aug 2020|title=The seismically fastest chemical heterogeneity in the Earth's deep upper mantle—implications from the single-crystal thermoelastic properties of jadeite|journal=Earth and Planetary Science Letters|volume=543|pages=116345|doi=10.1016/j.epsl.2020.116345|bibcode=2020E&PSL.54316345H |issn=0012-821X|doi-access=free}}</ref>]]
There are other rock models for the Earth's mantle:

(1) Piclogite: by contrast to the olivine-enriched pyrolite, piclogite is an olivine-poor model (~20% olivine) proposed to provide a better match to the seismic velocity observations in the transition zone.<ref>{{Cite journal|last1=Bass|first1=Jay D.|last2=Anderson|first2=Don L.|date=Mar 1984|title=Composition of the upper mantle: Geophysical tests of two petrological models|url=http://dx.doi.org/10.1029/gl011i003p00229|journal=Geophysical Research Letters|volume=11|issue=3|pages=229–232|doi=10.1029/gl011i003p00229|bibcode=1984GeoRL..11..229B |issn=0094-8276}}</ref><ref>{{Citation|last1=Bass|first1=Jay D.|title=Composition of the upper mantle: Geophysical tests of two petrological models|date=1988|url=http://dx.doi.org/10.1029/sp026p0513|work=Elastic Properties and Equations of State|pages=513–516|place=Washington, D. C.|publisher=American Geophysical Union|isbn=0-87590-240-5|access-date=2020-10-03|last2=Anderson|first2=Don L.|doi=10.1029/sp026p0513|url-access=subscription}}</ref> The piclogite phase composition is similar as 20% olivine + 80% eclogite.<ref>{{Citation|last1=Irifunea|first1=T.|title=Phase transformations in primitive MORB and pyrolite compositions to 25 GPa and some geophysical implications|date=1987|url=http://dx.doi.org/10.1029/gm039p0231|work=High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto|pages=231–242|place=Washington, D. C.|publisher=American Geophysical Union|isbn=0-87590-066-6|access-date=2020-10-03|last2=Ringwood|first2=A. E.|volume=39 |doi=10.1029/gm039p0231|bibcode=1987GMS....39..231I |url-access=subscription}}</ref>

(2) [[Eclogite]], it is transformed from the Mid-Ocean Ridge Basalt at a depth of ~60 km,{{Cn|date=April 2023}} exists in the Earth's mantle mainly within the subducted slabs. It is mainly composed of garnet and clinopyroxene (mainly [[omphacite]]) up to ~500 km depth (Fig. 4).

(3) Harzburgite, it mainly exists under the Mid-Ocean Ridge basalt layer of the oceanic [[lithosphere]], and can enter into the deep mantle along with the subducted oceanic lithosphere. Its phase composition is similar as pyrolite, but shows higher olivine proportion (~70 vol%) than pyrolite.<ref>{{Cite journal|last1=Ishii|first1=Takayuki|last2=Kojitani|first2=Hiroshi|last3=Akaogi|first3=Masaki|date=Apr 2019|title=Phase Relations of Harzburgite and MORB up to the Uppermost Lower Mantle Conditions: Precise Comparison With Pyrolite by Multisample Cell High-Pressure Experiments With Implication to Dynamics of Subducted Slabs|url=http://dx.doi.org/10.1029/2018jb016749|journal=Journal of Geophysical Research: Solid Earth|volume=124|issue=4|pages=3491–3507|doi=10.1029/2018jb016749|bibcode=2019JGRB..124.3491I |s2cid=146787786 |issn=2169-9313|url-access=subscription}}</ref>

Overall, pyrolite and piclogite are both rock models for the ambient mantle, eclogite and harzburgite are rock models for [[Subduction|subducted]] [[oceanic lithosphere]]. Formed from partial melting of pyrolite, the oceanic lithosphere is mainly composed of the basalt layer, harzburgite layer, and depleted pyrolite from top to bottom.<ref>{{Cite journal|last1=Ringwood|first1=A. E.|last2=Irifune|first2=T.|date=Jan 1988|title=Nature of the 650–km seismic discontinuity: implications for mantle dynamics and differentiation|url=https://www.nature.com/articles/331131a0|journal=Nature|language=en|volume=331|issue=6152|pages=131–136|doi=10.1038/331131a0|bibcode=1988Natur.331..131R |s2cid=4323081 |issn=1476-4687|url-access=subscription}}</ref> The subducted oceanic lithospheres contribute to the heterogeneity in the Earth's mantle because they have different composition (eclogite and harzburgite) from the ambient mantle (pyrolite).<ref name=":12" /><ref name=":42" />

== See also ==

* [[Peridotite]]

== References ==
{{Reflist}}

[[Category:Igneous rocks]]
[[Category:Petrology]]
[[Category:Geologic modelling]]

Pyrolite - Revision history

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