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Copper and zinc isotope systematics of altered oceanic crust at IODP Site 1256 in the eastern equatorial Pacific
Author(s) -
Huang Jian,
Liu ShengAo,
Gao Yongjun,
Xiao Yilin,
Chen Sha
Publication year - 2016
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 - 10.1002/2016jb013095
Subject(s) - geology , geochemistry , basalt , oceanic crust , hydrothermal circulation , volcanic rock , crust , mineral redox buffer , igneous rock , silicic , volcano , subduction , mantle (geology) , paleontology , tectonics
This paper presents the first combined Cu and Zn isotopic study of altered oceanic crust at Integrated Ocean Drilling Program (IODP) Hole 1256D that penetrates a volcanic section, a lava‐dyke transition zone, a sheeted dyke complex, and a plutonic complex. In the volcanic section, all but one rocks have Cu and Zn isotopic compositions similar to fresh mid‐ocean ridge basalt (MORB), reflecting restricted seawater circulation and low oxygen fugacity. Rocks in the transition zone have MORB‐like δ 65 Cu and δ 66 Zn, indicating the dominant influence of basalt‐derived Cu and Zn during alteration. Rocks in the dyke complex have more variable δ 65 Cu (−0.50–0.90‰) and δ 66 Zn (0.19–0.55‰) and those in the plutonic complex have δ 65 Cu of −0.43 to 0.20‰ and δ 66 Zn of 0.21 to 0.41‰. The rocks with heavier δ 66 Zn and heavier or lighter δ 65 Cu relative to MORB are characterized by Cu‐Zn depletions, low Li/Yb (<1.0) and low δ 18 O (<5‰), suggesting that hydrothermal extraction during high temperature alteration of oceanic crust can result in significant Cu and Zn isotope fractionation. Such large Cu and Zn isotopic variations are the results of redox transformation of Cu as well as Cu and Zn isotope fractionation between altered basaltic rocks and dissolved Cu and Zn species in hydrothermal fluids (e.g., [CuCl 3 ] 1− , Zn(HS) 4 2− ). This work is the first to define the distribution of Cu and Zn isotopes in an intact oceanic crust with concentration‐weighted averages of δ 65 Cu (0.05 ± 0.03‰) and δ 66 Zn (0.27 ± 0.01‰). The potential implications of these new observations are discussed.