Crystal chemical control of clinopyroxene-melt partitioning in the Di-Ab-An system: Implications for elemental fractionations in the depleted mantle

Journal Article · Sat Aug 01 04:00:00 EDT 1998 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/S0016-7037(98)00197-5· OSTI ID:316235

Lundstrom, C C; Williams, Q; Gill, J ^[1]; Shaw, H F; Ryerson, F J ^[2]

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1. Univ. of California, Santa Cruz, CA (United States). Earth Sciences Board
2. Lawrence Livermore National Lab., CA (United States)

The partitioning of fifteen trace elements (Rb, Sr, Zr, Nb, Ba, La, Ce, Nd, Sm, Gd, Yb, Hf, Ta, Pb, and Th) between clinopyroxene and synthetic melt has been studied in two compositions along an isotherm in the diopside-albite-anorthite ternary at 1 bar pressure. The two compositions correspond to {approximately}Di{sub 65}An{sub 35} and {approximately}Di{sub 55}Ab{sub 45} and produce clinopyroxenes distinct in chemistry while melt compositions range from 49 wt% SiO{sub 2} to 61 wt% SiO{sub 2}. The partition coefficients of high field strength elements (HFSE) increase by factors of 2--8 in Di-An experiments relative to Di-Ab experiments while other elements show very little change ({+-}20%) between compositions. The change in HFSE partitioning correlates with increases in tetrahedral Al{sub 2}O{sub 3} ({sup IV}Al) content of clinopyroxenes in the anorthite-bearing experiments. Changes in D{sub Ta}/D{sub Nb} also correlate with {sup IV}Al based on a survey of previously published determinations. There are two important implications to the observed dependence of HFSE partition coefficients on clinopyroxene aluminum content. First, HFSE will be fractionated from their adjacent REE within ultramafic samples during melting of spinel iherzolite as clinopyroxene Al{sub 2}O{sub 3} content decreases. Second, fractionations between Nb and Ta and Zr and Hf observed in mantle-derived magmas are consistent with extraction of melt in equilibrium with spinel iherzolite having clinopyroxenes with {approximately}5 wt% Al{sub 2}O{sub 3}.

• Sponsoring Organization: USDOE, Washington, DC (United States)
• OSTI ID: 316235
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 16 Vol. 62; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ALUMINIUM OXIDES
ANORTHITE
DIOPSIDE
FELDSPARS
MAGMA
METALS
PARTITION
SILICATE MINERALS
TRACE AMOUNTS