Trace element diffusion in jadeite and diopside melts at high pressures and its geochemical implication

Eizou Nakamura, Ikuo Kushiro

Research output: Contribution to journalArticle

73 Citations (Scopus)

Abstract

Diffusivities of geochemically important trace elements (eleven rare earth elements (REE), Rb, Sr, Ba, and Y) in jadeite and diopside melts and those of Zr, Nb, Th, and U in jadeite melt have been measured at pressures between 7.5 and 20 kbar and at temperatures 50-200°above the liquids, using diffusion couples and ion microprobe analysis. The concentrations of these elements in the experimental charges are close to those in natural igneous rocks. In the jadeite melt which is nearly fully polymerized (NBO/T ~ 0), (1) diffusivities of REE increase with increasing ionic radii, (2) diffusivities of tri- and tetravalent elements increase with increasing pressure at constant temperature, whereas those of mono- and divalent elements do not change significantly with pressure, and (3) diffusivities of these elements decrease with increasing their ionic charge at constant pressure and temperature. In the diopside melt which is considerably less polymerized (NBO/T ~ 2), (1) diffusivities of these trace elements depend mainly on their ionic radii rather than ionic charges; the diffusivities of mono- and divalent ions decrease with increasing ionic radii at constant pressure and temperature, and (2) diffusivities of REE are nearly the same as that of Ca and decrease with increasing pressure at constant temperature. The behavior of these trace elements is correlated with that of major elements; in the jadeite melt, tri- and tetravalent elements behave similarly to network-forming cations Al and Si, whereas mono- and divalent elements behave as network-modifying cations similarly to Na. In the diopside melt, the diffusion behavior of all these trace elements is similar to that of network-modifying cations Ca and Mg. The results of the present experiments suggest that the abundance of some trace elements in igneous rocks may have been affected by diffusion process at the magmatic stage. In the case of REE, for example, if two different magmas with high and low REE concentrations become in contact one another by multiple intrusion, and a zoned magma chamber is formed, diffusion begins to take place between them, and near the interface, the REE-enriched magma will become more light REE-depleted, whereas REE-depleted magma will become more light REE-enriched, and in addition, if magmas are reduced, the former will show a negative Eu anomaly, whereas the latter will show a positive Eu anomaly.

Original languageEnglish
Pages (from-to)3151-3160
Number of pages10
JournalGeochimica et Cosmochimica Acta
Volume62
Issue number18
DOIs
Publication statusPublished - Sep 1998

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jadeite
Trace Elements
diopside
Rare earth elements
rare earth element
diffusivity
trace element
melt
Igneous rocks
Cations
cation
temperature
igneous rock
magma
Temperature
anomaly
Diffusion in liquids
Ions
ion microprobe
magma chamber

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

Trace element diffusion in jadeite and diopside melts at high pressures and its geochemical implication. / Nakamura, Eizou; Kushiro, Ikuo.

In: Geochimica et Cosmochimica Acta, Vol. 62, No. 18, 09.1998, p. 3151-3160.

Research output: Contribution to journalArticle

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