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Mantle Zn Isotopic Heterogeneity Caused by Melt‐Rock Reaction: Evidence From Fe‐Rich Peridotites and Pyroxenites From the Bohemian Massif, Central Europe
Author(s) -
Huang Jian,
Ackerman Lukáš,
Zhang XingChao,
Huang Fang
Publication year - 2019
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2018jb017125
Subject(s) - metasomatism , geochemistry , geology , radiogenic nuclide , massif , mantle (geology) , basalt , isotope fractionation , fractional crystallization (geology) , partial melting , fractionation , incompatible element , chemistry , organic chemistry
To investigate the effect of melt‐rock reaction on Zn isotope fractionation and mantle Zn isotopic heterogeneity, we analyzed Zn isotopic compositions of peridotites, pyroxenites, and mineral separates from the Bohemian Massif, Central Europe. The Mg‐lherzolites (Mg# = 90.9 to 89.1, FeO T = 7.9 to 9.0 wt %) are melting residues with only moderate metasomatism and have δ 66 Zn from 0.11 to 0.20‰. In contrast, the Fe‐rich peridotites (Mg# = 88.2 to 80.3, FeO T = 10.0 to 14.5 wt %) and pyroxenites have larger ranges of δ 66 Zn from 0.11 to 0.31‰ and −0.33 to 0.42‰, respectively. Large disequilibrium intermineral Zn isotope fractionation occurs in the Fe‐rich peridotites and pyroxenites with Δ 66 Zn Opx‐Ol = −0.50‰, Δ 66 Zn Grt‐Ol = −0.55 to −0.39‰, Δ 66 Zn Grt‐Opx = −0.28 to −0.05‰, and Δ 66 Zn Grt‐Cpx = −0.50 to 0.12‰. Combined with their low SiO 2 contents and radiogenic Sr‐Nd‐Os isotopic compositions, the high δ 66 Zn of the Fe‐rich peridotites is attributed to reaction between Mg‐lherzolites and percolating SiO 2 ‐undersaturated basaltic melts that incorporated isotopically heavy crustal components. Crystallization of the isotopically heavy percolating melts migrating through the lithospheric mantle yield the high‐δ 66 Zn pyroxenites. The low δ 66 Zn of the pyroxenites and large intermineral Zn isotopic disequilibrium may result from kinetic Zn isotope fractionation during melt‐rock reaction. Collectively, these observations indicate that melt‐rock reaction can cause intermineral Zn isotopic disequilibrium and significant Zn isotopic heterogeneity in the mantle. This study thus highlights the potential use of Zn isotopes to trace melt‐rock reaction events in the mantle.