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Table 1 Summary of the basalt samples analyzed during this study

From: Alteration and dehydration of subducting oceanic crust within subduction zones: implications for décollement step-down and plate-boundary seismogenesis

Sample name MGLB KRB MGUB OKB MKB 56R-1wa 54R-1wa
Sampling site Mugi Kure Mugi Okitsu Makimine Off the Kii Off the Kii
V.R. (Ro)b 1.0 2.1 2.5 3.1 4.5   
1 (°C) 148 225 243 266 304   
2 (°C) 158 225 240 260 293   
3 (°C) 174 243 259 279 314   
4 (°C) 160 ± 30 230 ± 30 247 ± 30 268 ± 30 304 ± 30   
Quantitative rock composition
Quartz 0.0 0.0 0.1 0.0 4.6 0.0 0.0
Plagioclase 45.1 37.1 44.0 47.0 42.4 38.0 39.3
Calcite 1.5 1.0 2.7 0.3 7.7 0.4 0.1
Pyroxene 24.1 27.5 20.2 19.1 0.0 24.4 22.9
Epidote 0.0 0.0 0.0 0.0 12.1 0.0 0.0
Fe oxide 2.1 5.9 5.7 1.9 2.4 3.7 1.5
Titanite 3.3 5.3 4.2 6.4 3.9 2.8 4.0
Total non-clays 76.1 76.8 76.8 74.8 73.1 69.2 67.9
Glass 0.0 0.0 0.0 0.0 0.0 7.1 8.1
Saponite 0.0 0.0 0.0 0.0 0.0 23.7 24.0
C/S 23.9 23.2 23.2 25.2 26.9 0.0 0.0
%Sc in C/S 14.4 9.3 8.6 6.7 0.0
Total clay + glass 23.9 23.2 23.2 25.2 26.9 30.8 32.1
Totald 100 (93.1) 100 (102.8) 100 (100.3) 100 (102.2) 100 (103.3) 100 (97.3) 100 (90.0)
Chemical composition of C/S (based on O10(OH)8)
 Ne 16 15 15 17 15   
 Si 3.08 (0.23) 2.91 (0.12) 3.02 (0.12) 2.93 (0.10) 2.80 (0.14)   
 ΣAl 2.14 (0.16) 2.45 (0.16) 2.14 (0.15) 2.44 (0.12) 2.50 (0.12)   
 IVAl 0.92 1.09 0.98 1.07 1.20   
 VIAl 1.22 1.36 1.16 1.37 1.30   
 Fef 1.60 (0.26) 2.31 (0.21) 2.47 (0.24) 2.32 (0.29) 1.44 (0.28)   
 Mg 2.73 (0.29) 2.11 (0.13) 2.05 (0.26) 2.12 (0.25) 3.11 (0.44)   
 Ti 0.10 (0.12) 0.04 (0.05) 0.11 (0.06) 0.010 (0.23) 0.05 (0.04)   
 Ca 0.12 (0.18) 0.01 (0.02) 0.02 (0.04) 0.00 0.00   
  1. Temperatures for onland samples (1–4) were determined using (1) the equation of Barker (1988), (2) the equation of Sweeney and Burnham (1990) with a heating duration of 10 Myr, (3) the equation of Sweeney and Burnham (1990) with a heating duration of 1 Myr, and (4) averaged temperatures with an uncertainty of ±30 °C. a Samples 54R-1w and 56R-1w were taken from intervals C0012-54R-1w (11–14 cm) and C0012-56R-1w (9–14 cm), respectively. b Vitrinite reflectance (V.R.) values for each sample are from Ikesawa et al. (2005) for samples MGLB and MGUB, from Mukoyoshi et al. (2006) for sample KRB, from Sakaguchi (1999) for sample OKB, and from Ohmori (1998) for sample MKB. c %S values were determined by clay-fraction XRD analysis. d Relative mineral abundances were determined using RockJock software and are normalized to 100% abundances. The total weight percentage values originally derived from the program are shown in parentheses. e N = number of analyzed grains with two standard deviations (2σ) shown in parentheses. f All Fe calculated as Fe2+