Research ArticleGEOCHEMISTRY

Postmelting hydrogen enrichment in the oceanic lithosphere

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Science Advances  09 Jun 2021:
Vol. 7, no. 24, eabf6071
DOI: 10.1126/sciadv.abf6071
  • Fig. 1 Core-to-rim variations of H2O and F (μg g−1) in pyroxenes.

    H2O in (A) cpx rims versus cores (R2 = 0.66) and (B) opx rims versus cores (R2 = 0.88), and F in (C) cpx rims versus cores (R2 = 0.99) and (D) opx rims versus cores (R2 = 0.97). Color code refers to associated crustal ages. Each point represents one analysis. Error bars are typical propagated 2 SE of individual analyses (internal error and propagated error from calibration curve; see the Supplementary Materials) and smaller than symbols when not apparent. F-rich cpx (>10 μg g−1) and F-rich opx (>4 μg g−1) appear as triangles.

  • Fig. 2 Covariations of H2O and F (μg g−1) in pyroxenes.

    (A) H2O in opx versus cpx from this study (R2 = 0.80) compared to experimental studies (11, 25, 39), xenoliths (7), and other oceanic peridotites (13, 14). (B) F in opx versus cpx from this study (R2 = 0.95) compared to experimental studies (11, 69) and peridotitic pyroxenes from various tectonic environments (26). Error bars are omitted for clarity. Color code refers to associated crustal ages. Each point represents the average of all grains in one sample. F-rich cpx (>10 μg g−1) and F-rich opx (>4 μg g−1) appear as triangles.

  • Fig. 3 H2O and F (μg g−1) in pyroxenes over 23-Ma time series.

    (A) H2O in cpx and (B) in opx versus crustal ages (R2 = 0.52 and 0.43, respectively). Note that the x axis is reversed to reflect older rocks in the West compared to the East. Error bars are omitted for clarity for a previous FTIR study (14). (C) F in cpx and (D) in opx versus crustal ages. F-rich cpx (>10 μg g−1) and F-rich opx (>4 μg g−1) appear as triangles. In (C), R2 values for F-poor and F-rich samples are 0.1 and 0.51, respectively. In (D), R2 values for F-poor and F-rich samples are 0.2 and 0.61, respectively. Error bars for volatiles are 2 SE of sample averages and smaller than symbols when not apparent; each point represents the average of all grains in one sample. Color code refers to associated crustal ages.

  • Fig. 4 H2O and F (μg g−1) in pyroxenes versus degree of melting of peridotites.

    (A) H2O in cpx and (B) in opx versus melting degree. R2 values are 0.19 and 0.21, respectively. (C) F in cpx and (D) in opx versus melting degree. In (C), R2 values for F-poor and F-rich samples are 0.32 and 0.27, respectively. In (D), R2 values for F-poor and F-rich samples are 0.26 and 0.42, respectively. Error bars for volatiles are 2 SE of sample averages and smaller than symbols when not apparent; each point represents the average of all grains in one sample. Color code refers to associated crustal ages. F-rich cpx (>10 μg g−1) and F-rich opx (>4 μg g−1) appear as triangles.

  • Fig. 5 H2O and F (μg g−1) versus minor and trace elements in pyroxenes.

    H2O versus (A) Ti in atoms per formula unit (a.p.f.u.) (R2 = 0.36) and (B) Na a.p.f.u. in opx (R2 = 0.39), (C) H2O versus Ti a.p.f.u. (R2 = 0.25), and (D) Na a.p.f.u. in cpx (R2 = 0.52). (E) H2O versus Gd/YbN (30) in cpx (R2 = 0.37) and (F) F versus Gd/YbN in cpx (R2 values for F-poor and F-rich samples are 0.50 and 0.62, respectively). Error bars for volatiles are 2 SE of sample averages and smaller than symbols when not apparent; each point represents the average of all grains in one sample. Color code refers to associated crustal ages. F-rich cpx (>10 μg g−1) and F-rich opx (>4 μg g−1) appear as triangles.

  • Fig. 6 Volatile and trace element variations compared to fractional melting model of DMM (31).

    (A) Sm/YbN in cpx versus YbN in cpx (30) compared to spinel-field melting (thick light green) and projected garnet-field melting (22) (brown trend) followed by spinel-field melting (dark green). Small colored numbers next to cross symbols indicate the degree of melting. The source is assumed to have 16 μg g−1 F and 142 μg g−1 H2O (32). (B) F in cpx (μg g−1) versus Yb in cpx (μg g−1), compared to the melting models. R2 values for F-poor and F-rich samples are 0.16 and 0.50, respectively. (C) H2O versus Gd (μg g−1) in cpx (R2 = 0.34) compared to the melting models. Mid-REEs display the best inverse correlations with H2O. (D) H2O versus F (μg g−1) in cpx compared to the melting models. R2 values for F-poor and F-rich samples are 0.02 and 0.51, respectively. Error bars for volatiles are 2 SE of sample averages and smaller than symbols when not apparent; each point represents the average of all grains in one sample. Color code refers to associated crustal ages. F-rich cpx (>10 μg g−1) and F-rich opx (>4 μg g−1) appear as triangles.

Supplementary Materials

  • Supplementary Materials

    Postmelting hydrogen enrichment in the oceanic lithosphere

    Veronique Le Roux, Benjamin M. Urann, Daniele Brunelli, Enrico Bonatti, Anna Cipriani, Sylvie Demouchy, Brian D. Monteleone

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