TY - JOUR
T1 - The composition of peridotites and their minerals
T2 - A laser-ablation ICP-MS study
AU - Eggins, S. M.
AU - Rudnick, R. L.
AU - McDonough, W. F.
N1 - Funding Information:
This work has been made possible by the assistance and technical expertise of Mike Shelley, Les Kinsley, Nick Ware, Graeme Mortimer and Richard Rudowski. We thank Kim Patrick for performing some of the electron probe analyses. Dimitri Ionov kindly shared some of his unpublished data. Heinz-Günter Stosch, Fred Frey, Gilles Chazot and two anonymous reviewers are thanked for their thorough and critical evaluation of the manuscript. Finally, we thank Steve Richardson for his paleogeotechnical skills in coming up with unpublished major-element data for some samples. RLR and WFM acknowledge the support of the ANU in the initial stages of this research and the NSF (grant numbers EAR 95-06510 to RLR and EAR 95-06517 to WFM) in the later stages of the work. SME has undertaken this work through support from an ARC Postdoctoral Fellowship and an ARC Research Fellowship. [CH]
PY - 1998/1
Y1 - 1998/1
N2 - We have analyzed the major- and trace-element contents of minerals and whole rocks for two peridotite xenoliths from SE Australia (one fertile, the other infertile) using both solution chemistry (ICP-MS) and microbeam techniques (EMP, LA-ICP-MS). The incompatible lithophile trace elements are contained mainly in solid mineral phases at upper-mantle conditions, with no significant concentrations occurring on grain boundaries or in fluid inclusions. No exotic accessory minerals are required hosts for elements such as Nb and Ta. Mass balance is achieved for the highly incompatible trace elements only with inclusion of data for precursor amphibole, now present as pockets of alkali-, alumina- and silica-rich glass containing euhedral olivine, clinopyroxene, and spinel daughter crystals. The glass in these pockets is enriched in incompatible trace elements, particularly Ba, Nb and Ta, reflecting the preferential partitioning of these elements into amphibole at upper-mantle conditions. Orthopyroxene-clinopyroxene partition coefficients are similar for most incompatible elements (except Ti) between the two peridotites, suggesting that compositional differences do not significantly affect subsolidus partitioning for these elements. Comparison of our data with those from the literature reveals large variations in Dopx/cpx for all incompatible trace elements. For the REE, Zr (Hf) and Sr, these variations correlate with reciprocal equilibration temperature, reflecting the substitution of these elements for Ca in the M2 site. In contrast, poor correlation exists for V and no correlations exist for Ti and Nb between Dopx/cpx and temperature, which may reflect their substitution into multiple sites in the pyroxene structure and the influence of mineral composition on their partitioning. These features highlight the need for caution in inferring crystal-liquid D-values from subsolidus partitioning relations.
AB - We have analyzed the major- and trace-element contents of minerals and whole rocks for two peridotite xenoliths from SE Australia (one fertile, the other infertile) using both solution chemistry (ICP-MS) and microbeam techniques (EMP, LA-ICP-MS). The incompatible lithophile trace elements are contained mainly in solid mineral phases at upper-mantle conditions, with no significant concentrations occurring on grain boundaries or in fluid inclusions. No exotic accessory minerals are required hosts for elements such as Nb and Ta. Mass balance is achieved for the highly incompatible trace elements only with inclusion of data for precursor amphibole, now present as pockets of alkali-, alumina- and silica-rich glass containing euhedral olivine, clinopyroxene, and spinel daughter crystals. The glass in these pockets is enriched in incompatible trace elements, particularly Ba, Nb and Ta, reflecting the preferential partitioning of these elements into amphibole at upper-mantle conditions. Orthopyroxene-clinopyroxene partition coefficients are similar for most incompatible elements (except Ti) between the two peridotites, suggesting that compositional differences do not significantly affect subsolidus partitioning for these elements. Comparison of our data with those from the literature reveals large variations in Dopx/cpx for all incompatible trace elements. For the REE, Zr (Hf) and Sr, these variations correlate with reciprocal equilibration temperature, reflecting the substitution of these elements for Ca in the M2 site. In contrast, poor correlation exists for V and no correlations exist for Ti and Nb between Dopx/cpx and temperature, which may reflect their substitution into multiple sites in the pyroxene structure and the influence of mineral composition on their partitioning. These features highlight the need for caution in inferring crystal-liquid D-values from subsolidus partitioning relations.
KW - Inductively coupled plasma methods
KW - Partition coefficient
KW - Peridotites
KW - Trace-element analyses
UR - http://www.scopus.com/inward/record.url?scp=0031851527&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0031851527&partnerID=8YFLogxK
U2 - 10.1016/s0012-821x(97)00195-7
DO - 10.1016/s0012-821x(97)00195-7
M3 - Article
AN - SCOPUS:0031851527
VL - 154
SP - 53
EP - 71
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
SN - 0012-821X
IS - 1-4
ER -