Research ArticleGEOPHYSICS

Metamorphic records of multiple seismic cycles during subduction

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Science Advances  21 Mar 2018:
Vol. 4, no. 3, eaaq0234
DOI: 10.1126/sciadv.aaq0234
  • Fig. 1 Garnet compositional maps and profiles.

    Color-enhanced wavelength-dispersive spectrometer (WDS) x-ray count maps for Mg (top row) and Mn (middle row) in garnets from Ring Mountain. Decreasing Mg and Mn content are indicated by yellow-green-blue-black color progression. Spots give location of Raman quartz analyses and are colored according to peak position (±1.5 cm−1 about 470.9 cm−1 for CA13-01; ±1.5 cm−1 about 470.2 cm−1 for CA13-05A; see data in Fig. 3D). Transparent spots correspond to partially transparent analyses in Fig. 3D. Spot size indicated is larger than the actual ~1-μm spot. White rectangles show notable zones with varying Raman response associated with compositional zoning boundaries (blowups provided in the Supplementary Materials). Dashed white ellipses highlight examples of zoning embayments/incursions. Gray backscattered electron (BSE) images indicate locations of quantitative (WDS) electron microprobe traverses at the bottom of the figure. Regions with steep compositional gradients in the traverses are indicated by vertical gray bands (with length scale indicated).

  • Fig. 2 Model for garnet zoning in response to pressure pulses.

    Conceptual models for development of rim-side (top row of garnets with Mn back diffusion during resorption) and core-side zoning (bottom row of garnets with no Mn back diffusion during resorption) by fluctuating garnet stability (growth-resorption cycles) in response to pressure pulses. Blue stars mark the onset of undrained conditions at the start of a phase of fluid overpressure development and garnet growth. Orange stars mark full overpressure conditions at the end of a growth phase (immediately before an earthquake event and fracturing due to dynamic stresses and relief of overpressure). Grt, garnet.

  • Fig. 3 Quartz-in-garnet Raman microspectroscopy results.

    (A to C) Transmitted-light photomicrographs of some analyzed quartz inclusions in garnet. (D) Positions for the nominally 464 cm−1 A1g Raman peak for quartz inclusions in garnet from Ring Mountain, analyzed in triplicate. Inclusion circled in pink displays an abnormally low peak position despite lack of evidence that it was exposed during polishing or associated with visible cracks in garnet. Yellow-to-red background coloring is shown for reference to spot colors on garnet x-ray count maps in Fig. 1.

  • Fig. 4 Synchrotron FTIR microspectroscopy results.

    X-ray count maps for Mn in garnet and synchrotron FTIR analysis for one-dimensional (1D) traverses (bottom of each Mn map) and two-dimensional (2D) maps (right of each Mn map) for OH and H2O. Dashed white lines on Mn maps indicate the position of garnet growth unconformities and correspond to the white lines on the 1D FTIR traverses and 2D FTIR maps. Vertical axis on 1D traverse plots and colors of the 2D FTIR maps correspond to integrated intensity in the 3520 to 3620 cm−1 region for OH (a dimensionless measure of OH abundance) and in the 3350 to 3450 cm−1 region for H2O (a dimensionless measure of H2O abundance). Pink arrows on 1D traverse plots indicate regions of decreasing OH in the vicinity of garnet growth unconformities.

  • Fig. 5 Time scale comparisons.

    Time scales for individual cycles relating to (i) megathrust earthquake (EQ) events from tsunami and turbidite deposits and subsidence/uplift histories, (ii) garnet dissolution-growth cycles and associated P pulses as recorded in the garnets of this study, and (iii) physical burial-exhumation cycles relating to “yo-yo” tectonics, exhumation-erosion-deposition-subduction cycles, or convection within a putative subduction channel. Note that time scales for (ii) are maximum values due to bias toward overestimation in the approach used and the possibility that P pulses were significantly more numerous than recorded in the garnets (see text).

  • Fig. 6 Cross-polarized-light photomicrographs of samples CA13-01 and CA13-05A.

    For each rock, some of the garnets mapped for major elements are circled in red.

  • Fig. 7 Mineral composition plots.

    Plots showing solid solution for (A) amphibole, (B) clinopyroxene, (C) chlorite, and (D) white mica. Green data are for CA13-01, and blue data are for CA13-05A. Circled points are those whose geochemistry is given in Tables 1 and 2. p.f.u., per formula unit.

  • Fig. 8 Zoisite zoning and composition.

    (A and B) Color overlay BSE maps for zoisite in CA13-01 and CA13-05A, highlighting fine-scale oscillatory zoning. (C) Discrimination plot showing positive correlation between Fe/(Fe + Al) and MnO in zoisite. (D) Discrimination plot showing one analysis distinct from others on the basis of lower oxide totals: an allanite that contains a high proportion of trace elements not analyzed for. Green data are for CA13-01, and blue data are for CA13-05A. Yellow, red, and maroon groupings match the color of analysis spots and low to high BSE response, respectively, in the maps. Spots on maps are three times larger than actual analyses.

  • Fig. 9 Results of thermodynamic modeling.

    MnNCKFMASHT metamorphic assemblage diagrams for (A and C) CA13-01 and (B and D) CA13-05A. Phase assemblage fields and labels redrafted from the Perple_X output. White dashed box indicates approximate equilibrium P-T range of the peak-metamorphic assemblage in each rock. Green and pink contours in (A) and (B) are for modal zoisite and garnet, respectively; contour intervals of 0.5 volume % are used for zoisite, and contour intervals of 1 and 2 volume % are used for garnet in CA13-01 and CA13-05A, respectively. Note the significant congruence between zoisite and garnet contours, suggesting a metamorphic relationship between the phases (that is, the dissolution of one partially accommodates the growth of the other). The yellow arrow shows a 250-MPa isothermal P increase (starting at T = 570°C and P = 1.55 GPa), associated with an absolute gain of 5 volume % garnet and loss of 1.25 volume % zoisite for CA13-01 and an absolute gain of 9 volume % garnet and loss of 4 volume % zoisite for CA13-05A. Blue and red contours in (C) and (D) are for proportion of Mg garnet (pyrope) and Mn garnet (spessartine), respectively; contour intervals of 1 mol % are used for pyrope, and contour intervals of 0.25 mol % are used for spessartine.

  • Table 1 Stoichiometric mineral compositions for CA13-01, based on assumed number of oxygen atoms shown.

    Stoichiometric mineral compositions for CA13-01, based on assumed number of oxygen atoms shown.. Note that Fe in zoisite was assumed to be 100% Fe3+ and Fe in all other minerals was assumed to be 100% Fe2+. Gln, glaucophane; Omph, omphacite; Phe, phengite; Zo, zoisite.

    CA13-01
    GlnOmphPheZo 1Zo 2
    Si7.992.023.492.912.92
    Ti0.010.01
    Al1.690.361.972.412.25
    Cr
    Fe1.150.220.190.500.62
    Mn0.01
    Mg2.210.440.390.01
    Ca0.150.511.791.72
    Na1.870.460.03
    K0.87
    O2361112.512.5
    Al/(Al + Si)0.170.150.360.450.44
    Fe/(Fe + Al)0.410.380.090.170.21
    Fe/(Fe + Mg)0.340.340.33
    Na/(Na + Ca)0.930.48
    Na/(Na + K)0.04
    Total oxides (wt %)97.5100.694.596.397.6
  • Table 2 Stoichiometric mineral compositions for CA13-05A, based on assumed number of oxygen atoms shown.

    Stoichiometric mineral compositions for CA13-05A, based on assumed number of oxygen atoms shown.. Note that Fe in zoisite was assumed to be 100% Fe3+ and Fe in all other minerals was assumed to be 100% Fe2+. Hbl, hornblende; Gln, glaucophane; Chl, chlorite; Aln, allanite.

    CA13-05A
    Hbl 1Hbl 2GlnChlZo 1Zo 2Aln
    Si7.296.927.852.972.912.852.94
    Ti0.020.030.010.010.010.060.01
    Al1.241.911.772.322.412.092.01
    Cr
    Fe1.561.571.301.840.510.730.87
    Mn0.020.010.010.020.010.020.02
    Mg3.002.672.212.68
    Ca1.501.470.121.771.701.40
    Na0.820.931.98
    K0.040.080.01
    O2323231412.512.512.5
    Al/(Al + Si)0.150.220.180.440.450.420.41
    Fe/(Fe + Al)0.560.450.420.440.170.260.30
    Fe/(Fe + Mg)0.340.370.370.41
    Na/(Na + Ca)0.350.390.94
    Na/(Na + K)0.950.92
    Total oxides (wt %)97.198.997.186.196.797.281.0
  • Table 3 Whole-rock geochemistry determined by XRF (values in wt %).

    Whole-rock geochemistry determined by XRF (values in wt %).. LOI, loss on ignition.

    SiO2TiO2Al2O3Fe2O3MnOMgOCaONa2OK2OP2O5SO3LOITotal
    CA13-0148.091.5315.789.900.195.3810.743.491.540.12<0.0021.2698.02
    CA13-05A40.852.8416.4317.230.356.3612.531.110.130.100.1121.2899.32

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/3/eaaq0234/DC1

    fig. S1. Color overlay x-ray count maps for major divalent elements in Garnet 1.1 from CA13-01.

    fig. S2. Color overlay x-ray count maps for major divalent elements in Garnet 1.4 from CA13-01.

    fig. S3. Color overlay x-ray count maps for major divalent elements in Garnet 1.5 from CA13-01.

    fig. S4. Color overlay x-ray count maps for major divalent elements in Garnet 1.6 from CA13-01.

    fig. S5. Color overlay x-ray count maps for major divalent elements in Garnet 2.1 from CA13-01.

    fig. S6. Color overlay x-ray count maps for major divalent elements in Garnet 2.2 from CA13-01.

    fig. S7. Color overlay x-ray count maps for major divalent elements in Garnet 2.3 from CA13-01.

    fig. S8. Color overlay x-ray count maps for major divalent elements in Garnet 1.2 from CA13-05A.

    fig. S9. Color overlay x-ray count maps for major divalent elements in Garnet 1.4 from CA13-05A.

    fig. S10. Color overlay x-ray count maps for major divalent elements in Garnet 1.7 from CA13-05A.

    fig. S11. Color overlay x-ray count maps for major divalent elements in Garnet 1.8 from CA13-05A.

    fig. S12. Color overlay x-ray count maps for major divalent elements in Garnet 2.1 from CA13-05A.

    fig. S13. Color overlay x-ray count maps for major divalent elements in Garnet 2.2 from CA13-05A.

    fig. S14. Color overlay x-ray count maps for Mg in garnets from CA13-01 and CA13-05A.

    fig. S15. Color overlay x-ray count maps for Mn in garnets from CA13-01 and CA13-05A.

    fig. S16. Blowups of regions indicated by white rectangles in (top row) fig. S14 and (bottom row) fig. S15.

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    References (7183)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Color overlay x-ray count maps for major divalent elements in Garnet 1.1 from CA13-01.
    • fig. S2. Color overlay x-ray count maps for major divalent elements in Garnet 1.4 from CA13-01.
    • fig. S3. Color overlay x-ray count maps for major divalent elements in Garnet 1.5 from CA13-01.
    • fig. S4. Color overlay x-ray count maps for major divalent elements in Garnet 1.6 from CA13-01.
    • fig. S5. Color overlay x-ray count maps for major divalent elements in Garnet 2.1 from CA13-01.
    • fig. S6. Color overlay x-ray count maps for major divalent elements in Garnet 2.2 from CA13-01.
    • fig. S7. Color overlay x-ray count maps for major divalent elements in Garnet 2.3 from CA13-01.
    • fig. S8. Color overlay x-ray count maps for major divalent elements in Garnet 1.2 from CA13-05A.
    • fig. S9. Color overlay x-ray count maps for major divalent elements in Garnet 1.4 from CA13-05A.
    • fig. S10. Color overlay x-ray count maps for major divalent elements in Garnet 1.7 from CA13-05A.
    • fig. S11. Color overlay x-ray count maps for major divalent elements in Garnet 1.8 from CA13-05A.
    • fig. S12. Color overlay x-ray count maps for major divalent elements in Garnet 2.1 from CA13-05A.
    • fig. S13. Color overlay x-ray count maps for major divalent elements in Garnet 2.2 from CA13-05A.
    • fig. S14. Color overlay x-ray count maps for Mg in garnets from CA13-01 and CA13-05A.
    • fig. S15. Color overlay x-ray count maps for Mn in garnets from CA13-01 and CA13-05A.
    • fig. S16. Blowups of regions indicated by white rectangles in (top row) fig. S14 and (bottom row) fig. S15.
    • References (71–83)

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