Details
| Original language | English |
|---|---|
| Pages (from-to) | 163-177 |
| Number of pages | 15 |
| Journal | Chemical geology |
| Volume | 212 |
| Issue number | 1-2 |
| Publication status | Published - 26 Nov 2004 |
| Externally published | Yes |
Abstract
We determined the Li isotopic composition of coexisting olivine, clinopyroxene, and orthopyroxene from spinel- and garnet-bearing peridotite xenoliths from San Carlos (Arizona), Vitim (Siberia), Dreiser Weiher (Eifel, Germany), and Kapfenstein (Austria). These samples represent the upper mantle that experienced varying degrees of partial melting followed by different metamorphic and metasomatic histories. Ultrasonic cleaning of handpicked mineral separates with Milli-Q water (18 MΩ cm) removed significant amounts (10-30%) of the lithium from unwashed separates and resulted in systematically heavier lithium isotopic compositions in the washed minerals. δ7Li values for washed minerals range from +1.4‰ to +4.5‰ in olivines, from -1.0‰ to +3.9‰ in orthopyroxenes, and from -2.4‰ to +3.0‰ in clinopyroxenes, δ7Li=[(7Li/6Li)sample /(7Li/6Li)L-SVECstandard-1] ×1000. Olivines in mildly depleted lherzolites (Eifel, Vitim, San Carlos) are isotopically the heaviest (δ7Li +3.4-+4.5‰). A metasomatised, amphibole-bearing lherzolite from the Eifel gave the lightest value (+1.4‰). Olivines have similar δ7Li values to that of MORB, while the pyroxenes are isotopically lighter. In all but one sample, the δ7Li changes systematically between the minerals; olivine has the heaviest δ7Li value followed by orthopyroxene, and clinopyroxene has the lightest values. The degree of intramineral fractionation (Δδ7Li=[δ7Liol- (δ7cpx)]) correlates negatively with equilibration temperature. Δδ7Li is about 3.5 for low-temperature (∼950 °C) xenoliths and 1.5 for high-temperature (∼1150 °C) xenoliths. We therefore suggest Li isotope fractionation may occur at high, magmatic temperatures.
Keywords
- Isotope fractionation, Isotopes, Lithium, Peridotite, Upper mantle
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geology
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
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In: Chemical geology, Vol. 212, No. 1-2, 26.11.2004, p. 163-177.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Lithium isotopic signatures of peridotite xenoliths and isotopic fractionation at high temperature between olivine and pyroxenes
AU - Seitz, Hans Michael
AU - Brey, Gerhard P.
AU - Lahaye, Yann
AU - Durali, Soodabeh
AU - Weyer, Stefan
PY - 2004/11/26
Y1 - 2004/11/26
N2 - We determined the Li isotopic composition of coexisting olivine, clinopyroxene, and orthopyroxene from spinel- and garnet-bearing peridotite xenoliths from San Carlos (Arizona), Vitim (Siberia), Dreiser Weiher (Eifel, Germany), and Kapfenstein (Austria). These samples represent the upper mantle that experienced varying degrees of partial melting followed by different metamorphic and metasomatic histories. Ultrasonic cleaning of handpicked mineral separates with Milli-Q water (18 MΩ cm) removed significant amounts (10-30%) of the lithium from unwashed separates and resulted in systematically heavier lithium isotopic compositions in the washed minerals. δ7Li values for washed minerals range from +1.4‰ to +4.5‰ in olivines, from -1.0‰ to +3.9‰ in orthopyroxenes, and from -2.4‰ to +3.0‰ in clinopyroxenes, δ7Li=[(7Li/6Li)sample /(7Li/6Li)L-SVECstandard-1] ×1000. Olivines in mildly depleted lherzolites (Eifel, Vitim, San Carlos) are isotopically the heaviest (δ7Li +3.4-+4.5‰). A metasomatised, amphibole-bearing lherzolite from the Eifel gave the lightest value (+1.4‰). Olivines have similar δ7Li values to that of MORB, while the pyroxenes are isotopically lighter. In all but one sample, the δ7Li changes systematically between the minerals; olivine has the heaviest δ7Li value followed by orthopyroxene, and clinopyroxene has the lightest values. The degree of intramineral fractionation (Δδ7Li=[δ7Liol- (δ7cpx)]) correlates negatively with equilibration temperature. Δδ7Li is about 3.5 for low-temperature (∼950 °C) xenoliths and 1.5 for high-temperature (∼1150 °C) xenoliths. We therefore suggest Li isotope fractionation may occur at high, magmatic temperatures.
AB - We determined the Li isotopic composition of coexisting olivine, clinopyroxene, and orthopyroxene from spinel- and garnet-bearing peridotite xenoliths from San Carlos (Arizona), Vitim (Siberia), Dreiser Weiher (Eifel, Germany), and Kapfenstein (Austria). These samples represent the upper mantle that experienced varying degrees of partial melting followed by different metamorphic and metasomatic histories. Ultrasonic cleaning of handpicked mineral separates with Milli-Q water (18 MΩ cm) removed significant amounts (10-30%) of the lithium from unwashed separates and resulted in systematically heavier lithium isotopic compositions in the washed minerals. δ7Li values for washed minerals range from +1.4‰ to +4.5‰ in olivines, from -1.0‰ to +3.9‰ in orthopyroxenes, and from -2.4‰ to +3.0‰ in clinopyroxenes, δ7Li=[(7Li/6Li)sample /(7Li/6Li)L-SVECstandard-1] ×1000. Olivines in mildly depleted lherzolites (Eifel, Vitim, San Carlos) are isotopically the heaviest (δ7Li +3.4-+4.5‰). A metasomatised, amphibole-bearing lherzolite from the Eifel gave the lightest value (+1.4‰). Olivines have similar δ7Li values to that of MORB, while the pyroxenes are isotopically lighter. In all but one sample, the δ7Li changes systematically between the minerals; olivine has the heaviest δ7Li value followed by orthopyroxene, and clinopyroxene has the lightest values. The degree of intramineral fractionation (Δδ7Li=[δ7Liol- (δ7cpx)]) correlates negatively with equilibration temperature. Δδ7Li is about 3.5 for low-temperature (∼950 °C) xenoliths and 1.5 for high-temperature (∼1150 °C) xenoliths. We therefore suggest Li isotope fractionation may occur at high, magmatic temperatures.
KW - Isotope fractionation
KW - Isotopes
KW - Lithium
KW - Peridotite
KW - Upper mantle
UR - http://www.scopus.com/inward/record.url?scp=8344234426&partnerID=8YFLogxK
U2 - 10.1016/j.chemgeo.2004.08.009
DO - 10.1016/j.chemgeo.2004.08.009
M3 - Article
AN - SCOPUS:8344234426
VL - 212
SP - 163
EP - 177
JO - Chemical geology
JF - Chemical geology
SN - 0009-2541
IS - 1-2
ER -