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| Titel |
Perovskite inclusions in deep mantle diamonds and the fate of subducted lithosphere |
| VerfasserIn |
Michael Walter, Lora Armstrong |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250040264
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| Zusammenfassung |
| Sublithospheric diamonds are typically Type II, frequently exhibit complex zoning,
and sometimes contain mineral inclusions that can potentially reveal deep mantle
lithologies and petrologic processes. A considerable number of these diamonds contain
inclusions with elemental stoichiometries consistent with transition zone (e.g. majoritic
garnet, Ca-perovskite) and lower mantle phases (e.g. Mg-perovskite, Ca-perovskite,
(Mg,Fe)-periclase) [1]. Ca-rich perovskites, some containing considerable CaTiO3
component, almost invariably have very low Mg contents, unlike what would be expected in
solid lower mantle peridotitic or basaltic lithologies, but have elevated incompatible elements
abundances that almost certainly indicate crystallization from a low-degree Ca-rich partial
melt [2,3]. High-Ca majoritic garnets also have both major and trace element characteristics
indicating the role of low-degree, Ca-rich partial melts [3,4], and in some cases calculated
melts likely formed in subducted oceanic crust or lithosphere [3]. Given that diamond
crystallized syngenetically with the inclusions, crystallization from carbonated melts is
implicated. The reducing conditions expected in the ambient transition zone and lower
mantle [5] could promote reduction of the carbonate component in slab-derived,
carbonated (oxidized), partial melts. Reduction can lead to diamond and perovskite
crystallization from the melt, possibly with H2O as a by-product through a reaction such
as:
CaCO3 (melt) + SiO2(melt-solid) + CH4(fluid-melt)= CaSiO3(melt-solid)) + 2H2O(melt)
+ 2Cdiamond
Mg-perovskite could crystallize via a similar reaction involving the MgCO3 component
of the melt. We speculate that when subducted slabs stall at the base of the transition zone,
they may heat up and release low-degree carbonated melts [6]. Such melts may migrate,
crystallize and metasomatize the ambient mantle. Trace element abundances in some
kimberlites are remarkably similar to liquids that could have coexisted with majoritic garnet
and Ca—perovskite inclusions in diamonds [2,4,7]. This implies a link between carbonated
melts released from subducted materials in the deep mantle or transition zone and
protokimberlite melt generation.
1. Harte, B., et al., In Mantle Petrology: Field observations and high pressure
experimentation. Geochemical Society Special Publications, 1999: 125-153.
2. Wang, W., T. Gasparik, and R. Rapp, Earth Planet. Sci. Lett., 2000. 181:
291-300.
3. Walter, M., et al., Nature, 2008. 454: 622-625.
4. Keshav, S., G. Gudfinnsson, and D. Presnall, 11th EMPG Abstracts, 2006:
36.
5. Frost, D.J. and C.A. McCammon, Ann. Rev. Earth Planet. Sci., 2008. 36:
389-420.
6. Dasgupta, R., M.M. Hirschmann, and A.C. Withers, Earth Planet. Sci. Lett., 2006. 227:
73-85.
7. Moore, R.O., E. J. Mineral., 1991. 3. |
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