TY - JOUR
T1 - Extremely light Li in orogenic eclogites
T2 - The role of isotope fractionation during dehydration in subducted oceanic crust
AU - Zack, Thomas
AU - Tomascak, Paul B.
AU - Rudnick, Roberta L.
AU - Dalpé, Claude
AU - McDonough, William F.
N1 - Funding Information:
This work is supported by the NSF (Grants EAR 0106719, EAR 0004128 and OCE 9977095) and a Feodor-Lynen fellowship to T.Z. from the Alexander-von-Humboldt Foundation. Katharina Abraham, Tracey Centorbi, Maren Kahl and Lena Schilling are thanked for their assistance with preparation of mineral separates. Emily Baker assisted with Li purification for several omphacite separates. T.Z. thanks Horst Marschall and Jens Paquin for lively discussions. PBT thanks CIW-DTM for continued access to their facilities when the UMD lab was getting started. Reviews by Lui-Heung Chan, Tim Elliott and Rick Hervig helped to clarify the presentation and are greatly appreciated. [BW]
PY - 2003/3/30
Y1 - 2003/3/30
N2 - Eclogites from Trescolmen, Switzerland, derive from basaltic protoliths that experienced variable degrees of low- T seafloor alteration prior to high pressure metamorphism. δ7Li of the eclogites (-11 to +14‰) ranges to dramatically lower values than observed in fresh MORB, or altered MORB (+4.5 to +14‰ for low- T and -2 to +8‰ for high- T altered MORB). These low values cannot be explained by fluid interaction with surrounding garnet mica schist, which is generally isotopically heavier (δ7Li of +2.4 to +3.8‰). The low δ7Li values were likely produced by isotope fractionation through Rayleigh distillation during dehydration of clays and/or chlorite at early stages of metamorphism. These data are consistent with isotopically heavy Li being released into the forearc mantle wedge in subduction zones, while an isotopically light component is subducted deeply, and may form a distinct mantle reservoir that could be sampled by plume-related magmas.
AB - Eclogites from Trescolmen, Switzerland, derive from basaltic protoliths that experienced variable degrees of low- T seafloor alteration prior to high pressure metamorphism. δ7Li of the eclogites (-11 to +14‰) ranges to dramatically lower values than observed in fresh MORB, or altered MORB (+4.5 to +14‰ for low- T and -2 to +8‰ for high- T altered MORB). These low values cannot be explained by fluid interaction with surrounding garnet mica schist, which is generally isotopically heavier (δ7Li of +2.4 to +3.8‰). The low δ7Li values were likely produced by isotope fractionation through Rayleigh distillation during dehydration of clays and/or chlorite at early stages of metamorphism. These data are consistent with isotopically heavy Li being released into the forearc mantle wedge in subduction zones, while an isotopically light component is subducted deeply, and may form a distinct mantle reservoir that could be sampled by plume-related magmas.
KW - Eclogite
KW - Fractionation
KW - Isotopes
KW - Lithium
KW - Subduction
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U2 - 10.1016/S0012-821X(03)00035-9
DO - 10.1016/S0012-821X(03)00035-9
M3 - Article
AN - SCOPUS:0037473271
SN - 0012-821X
VL - 208
SP - 279
EP - 290
JO - Earth and Planetary Sciences Letters
JF - Earth and Planetary Sciences Letters
IS - 3-4
ER -