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GSA Data Repository 2018013 Cruz-Uribe et al., 2018, Generation of alkaline magmas in subduction zones by partial melting of mélange diapirs An experimental study: Geology, https://doi.org/10.

25 t mel ent dim se al rti pa 20 0.5128 bulk sediment % +b ulk sed ime nt 0.20 0.15 0.10 sediment mixi ng mantle Ma ntl e+ 1.0 Nd/Sr 0.4 0.5130 0.05 20% 1% AOC fluid 0.5120 0.702 0.704 0.706 0.708 0.

1 GSA Data Repository Cruz-Uribe et al., 2018, Generation of alkaline magmas in subduction zones by partial melting of mélange diapirs An experimental study: Geology, Cruz-Uribe et al. [1] Supplemental Material A mantle B % Nd/ 144 Nd 2.0 alkaline arc lavas (n=1184) M an tle t mel ent dim se al rti pa bulk sediment % +b ulk sed ime nt sediment mixi ng mantle Ma ntl e+ 1.0 Nd/Sr % 1% AOC fluid Sr/ 86 Sr forbidden AOC fluid/ sediment melt field Sr/ 86 Sr Fig. DR 1 87 Sr/86 Sr versus 143 Nd/144 Nd (A) and 87 Sr/86 Sr versus Nd/Sr (B) for alkaline arc lava compilation (grey contours) from GEOROC, as in Figure 1. Mantle, sediment, and altered ocean crust (AOC) compositions used can be found in Table S5. Yellow triangular field in (B) represents the "forbidden" field, which is impossible to produce by either sediment partial melting or bulk sediment mixing. After Nielsen and Marschall (2017). ol glass glass phl amp grt cpx ilm SY400-AC µm 1.5 GPa, 1110 C rt cpx SY400-AC GPa, 1110 C 40 µm Fig. DR 2 Backscattered electron images of experimental run products at 1110 C. a, 1.5 GPa. b, 2.5 GPa. Cpx, clinopyroxene; amp, amphibole; ol, olivine; ilm, ilmenite; grt, garnet; phl, phlogopite; rt, rutile

2 Cruz-Uribe et al. [2] partial melting Mantle 143 Nd/ 144 Nd mixing Sed Hf/Nd Campi Flegrei Astroni Averno Campanian Ignimbrite Ischia Roccamonfina Ariccia Latera Monte Cimino Fig. DR 3 Plot of Hf/Nd versus 143 Nd/ 144 Nd for alkaline lavas (<62 wt % SiO 2 ) from nine volcanic centers in the Campanian and Roman provinces, Italy. Isotopic composition of Italian offshore sediment from Weldeab et al. (2002). After Nielsen and Marschall (2017). Data were compiled from the GEOROC database and are a subset of the alkaline lava compilation used throughout the paper. A GPa 2.5 GPa B 0.10 Nd/Sr T ( C) T ( C) Fig. DR 4 Plot of experimental run temperature ( C) versus Nd/Sr ratio. A, 1.5 GPa experiments. B, 2.5 GPa experiments.

3 Cruz-Uribe et al. [3] H 2 O/Ce T ( C) :1 1.5 GPa corrected (after Cooper et al ) 4 GPa (original Plank et al., 2009 calibration) Experimental run T ( C) Fig. DR 5 Plot of experimental run temperature ( C) versus H2O/Ce temperature ( C) for 1.5 GPa experimental glasses at C. The solid black line shows the 1:1 relationship. 6 5 H 2 O (wt %) Experimental Run T ( C) Fig. DR 6 Plot of experimental run temperature ( C) versus H2O (wt %) from microprobe totals.

4 Cruz-Uribe et al. [4] 300 NMORB 2.5 GPa 1.5 GPa alkaline arc lavas 200 Zr/Sm 100 NMORB Nb/La Fig. DR 7 Plot of Nb/La versus Zr/Sm for experimental glasses at 2.5 GPa (orange inverted triangles) and 1.5 GPa (blue squares). Alkaline arc lava compilation from GEOROC, as in Figure 1, shown by grey contours. Values for N-MORB from Hofmann (1988). The HFSE contents compared to the REE of similar incompatibility of the experimental melts are in the same range as observed in natural alkaline arc magmas Experiment T ( C) P (GPa) Table DR 1 Experimental run conditions and products. Capsule Material Duration (hr) Run Products SY400-AC Au 72 G, Amp, Cpx, Rt, Ilm SY400-AC Au 72 G, Amp, Cpx, Rt, Ilm, Zrn, Pl, Chev SY400-AC Au 72 G, Amp, Cpx, Rt, Ilm SY400-AC Au 80 Pd G, Amp, Cpx, Rt, Ilm SY400-AC Au 80 Pd G, Amp, Cpx, Rt, Ilm, Ttn, Ol SY400-VL Au 80 Pd G, Cpx, Ol MEL graphite 5 G, Cpx, Ol SY400-VL Au 80 Pd G, Cpx, Ol MEL graphite 5 G, Ol MEL graphite <1 G SY400-AC Au 72 G, Grt, Cpx, Amp, Phl, Rt SY400-AC Au 72 G, Grt, Cpx, Amp, Phl, Rt SY400-AC Au 72 G, Grt, Cpx, Amp, Phl, Rt SY400-AC Au 80 Pd G, Grt, Cpx, Amp, Phl, Rt SY400-AC Au 80 Pd G, Grt, Cpx, Rt SY400-AC Au 80 Pd G, Grt, Cpx SY400-AC / Au 80 Pd 20 24/72 G, Grt, cpx SY400-AC Au 80 Pd G, Grt, cpx SY400-AC Au 80 Pd G, Grt, cpx SY400-AC Au 80 Pd G, Grt, cpx G, glass; amp, amphibole; cpx, clinopyroxene; rt, rutile; ilm, ilmenite; zrn, zircon; ol, olivine; ttn, titanite; grt, garnet; phl, phlogopite; pl, plagioclase; chev, chevkinite.

5 Cruz-Uribe et al. [5] Table DR 2 Major element chemistry of experimental glasses determined by EPMA. Values expressed as weight percent oxides. Each reported value represents the mean of 10 individual analyses. Units in parentheses represent one standard deviation on the basis of replicate analyses in terms of least unit cited. Experiment SiO 2 TiO 2 Al 2 O 3 FeO MnO MgO CaO Na 2 O K 2 O P 2 O 5 Total SY400-AC (3) 0.26(2) 19.86(9) 2.57(4) 0.06(1) 1.44(4) 2.58(6) 7.6(1) 3.44(5) 0.15(3) SY400-AC (3) 0.24(3) 19.8(1) 2.87(5) 0.08(1) 1.58(3) 2.88(4) 6.9(1) 3.14(2) 0.19(2) SY400-AC (2) 0.33(2) 19.9(1) 2.92(8) 0.10(1) 1.61(3) 2.51(3) 7.38(8) 3.44(6) 0.17(2) SY400-AC (1) 0.50(3) 19.63(9) 4.02(8) 0.07(1) 2.20(3) 2.69(6) 7.4(2) 3.44(4) 0.16(3) SY400-AC (1) 0.75(3) 19.59(8) 5.69(7) 0.11(1) 3.91(3) 4.32(2) 6.9(1) 2.91(2) 0.15(2) SY400-VL (2) 1.23(4) 19.5(1) 6.02(7) 0.10(1) 4.74(8) 5.47(6) 6.5(1) 2.81(3) 0.12(2) MEL3 49.2(6) 1.17(4) 18.5(1) 5.7(2) 0.13(2) 6.4(2) 6.6(3) 6.1(1) 2.41(9) 0.12(2) SY400-VL (7) 1.19(3) 18.50(9) 6.10(9) 0.11(1) 5.92(6) 6.34(4) 6.3(1) 2.59(3) 0.12(2) MEL4 48.9(3) 1.10(2) 16.8(2) 5.44(7) 0.10(1) 8.69(8) 8.2(1) 5.11(9) 2.11(4) 0.11(2) MEL5 48.8(7) 1.2(2) 16.2(2) 5.6(2) 0.13(1) 8.8(2) 8.3(2) 5.3(1) 1.96(5) 0.1(2) SY400-AC (4) 0.67(3) 19.45(7) 1.94(3) 0.02(1) 1.14(2) 1.57(3) 7.0(1) 3.94(4) 0.24(3) SY400-AC (2) 0.59(4) 19.36(5) 2.03(5) 0.02(1) 1.15(4) 1.55(3) 7.04(8) 4.15(5) 0.23(2) SY400-AC (3) 0.77(3) 19.31(9) 2.45(6) 0.05(1) 1.52(6) 1.66(5) 7.2(1) 4.28(5) 0.25(3) SY400-AC (2) 1.00(4) 19.16(7) 4.1(1) 0.05(1) 1.76(7) 2.06(5) 7.8(1) 4.34(4) 0.19(1) SY400-AC (2) 1.18(3) 18.69(8) 4.89(9) 0.06(1) 2.52(6) 2.43(4) 8.0(2) 4.20(9) 0.19(2) SY400-AC (4) 1.36(3) 18.9(2) 5.18(5) 0.04(1) 2.74(8) 2.52(5) 7.5(2) 4.25(8) 0.15(2) SY400-AC (2) 1.36(3) 18.90(8) 5.29(6) 0.07(1) 2.86(4) 2.72(5) 7.4(1) 4.11(5) 0.17(3) SY400-AC (2) 1.37(3) 18.7(1) 5.45(6) 0.05(1) 3.67(3) 3.37(5) 7.0(1) 3.62(3) 0.14(3) SY400-AC (4) 1.39(2) 18.4(1) 6.3(1) 0.08(1) 4.7(1) 4.1(1) 6.82(8) 3.3(1) 0.15(2) SY400-AC (3) 1.29(2) 18.2(1) 6.54(9) 0.09(2) 5.7(1) 4.9(1) 6.31(7) 2.93(5) 0.13(2) 95.71

6 Cruz-Uribe et al. [6] Table DR 3 Table S3: Trace element chemistry of experimental glasses determined by LA-ICP-MS. Values expressed as µg/g. Average 2s analytical uncertainties for each element expressed as percentages. Experiment Ti Rb Sr Y Zr Nb Cs Ba La Ce Pr Nd Sm Eu Gd Dy Tm Yb Hf Ta Pb Th U SY400-AC SY400-AC SY400-AC SY400-AC SY400-AC SY400-VL MEL SY400-VL MEL MEL SY400-AC SY400-AC SY400-AC SY400-AC SY400-AC SY400-AC SY400-AC SY400-AC SY400-AC SY400-AC Avgerage 2σ Uncertainty (%)

7 Cruz-Uribe et al. [7] Table DR 4 Values used for H2O/Ce thermometry. Experiment Exp T ( C) H 2O* (wt %) Ce (µg/g) H 2 O/Ce H 2 O/Ce T ( C), 4 GPa H 2 O/Ce T ( C), 1.5 GPa SY400-AC SY400-AC SY400-AC SY400-AC SY400-AC *Based on microprobe totals (Table S2). Table DR 5 Values used in Sr and Nd mixing models. From Nielsen and Marschall (2017) and references therein. Sr Nd Hf/Nd 87 Sr/ 86 Sr 143 Nd/ 144 Nd mantle sediment sediment (Italy) AOC

8 Cruz-Uribe et al. [8] Table DR 6 Major element chemistry of experimental minerals (clinopyroxene, amphibole, phlogopite, plagioclase) determined by EPMA. Values expressed as weight percent oxides. Each reported value represents the mean of 6-10 individual analyses. Units in parentheses represent one standard deviation on the basis of replicate analyses in terms of least unit cited. Experiment SiO 2 Al 2 O 3 FeO MgO CaO MnO TiO 2 Na 2 O K 2 O Cr 2 O 3 Total Clinopyroxene SY400-AC (7) 6.2 (8) 6.7 (3) 14.4 (5) 20.7 (3) 0.16 (2) 0.4 (1) 1.4 (1) 0.02 (1) 0.08 (3) SY400-AC (2) 6.7 (6) 6.55 (9) 14.6 (3) 19.8 (5) 0.20 (2) 0.36 (3) 1.5 (1) 0.02 (1) 0.09 (3) SY400-AC (1) 10 (1) 6.4 (5) 12 (1) 17 (2) 0.18 (3) 0.51 (1) 2.7 (7) 0.4 (5) 0.09 (4) SY400-AC (5) 9.8 (7) 7.3 (3) 12.7 (5) 16.7 (2) 0.20 (1) 0.51 (5) 2.6 (1) 0.08 (8) 0.06 (2) SY400-AC (4) 7.5 (3) 6.0 (1) 14.9 (2) 19.5 (4) 0.15 (2) 0.8 (1) 1.26 (8) 0.01 (1) 0.12 (5) MEL (9) 6.30 (1) 3.9 (9) (7) (1) 0.1 (2) 0.6 (9) 1.1 (2) 0.1 (5) 0.3 (7) SY400-AC (4) 13.3 (5) 5.9 (1) 9.5 (3) 13.7 (5) 0.12 (3) 0.8 (1) 5.3 (4) 0.04 (2) 0.07 (1) SY400-AC (1) 12.6 (7) 6.2 (2) 10.3 (3) 13.9 (5) 0.13 (3) 0.9 (3) 4.9 (6) 0.2 (4) 0.07 (2) SY400-AC (6) 11.6 (4) 6.4 (2) 10.7 (3) 14.8 (3) 0.16 (2) 0.9 (1) 4.6 (3) (5) 0.05 (5) SY400-AC (4) 11.1 (6) 6.4 (2) 11.4 (3) 15.0 (4) 0.14 (2) 0.9 (2) 4.3 (3) 0.04 (5) 0.10 (2) SY400-AC (4) 10.8 (3) 6.3 (2) 11.8 (3) 15.3 (2) 0.11 (2) 0.9 (2) 3.9 (3) 0.02 (1) 0.06 (2) SY400-AC (5) 11.1 (2) 6.2 (2) 11.7 (4) 15.1 (3) 0.09 (1) 1.0 (1) 4.1 (3) 0.02 (1) 0.06 (3) SY400-AC (3) 11.2 (4) 6.0 (2) 12.0 (3) 15.0 (3) 0.09 (2) 0.91 (9) 4.1 (2) 0.05 (9) 0.11 (3) SY400-AC (3) 10.7 (3) 6.1 (1) 12.8 (4) 15.6 (5) 0.10 (1) 0.8 (1) 3.4 (1) 0.1 (1) 0.13 (5) SY400-AC (3) 10.6 (4) 5.9 (2) 13.2 (4) 15.7 (5) 0.11 (2) 0.7 (1) 3.2 (1) 0.05 (12) 0.12 (2) SY400-AC (6) 10.6 (5) 5.6 (2) 14.2 (3) 15.7 (5) 0.13 (2) 0.7 (2) 2.7 (2) 0.01 (1) 0.15 (4) Amphibole SY400-AC (7) 14.5 (5) 7.9 (4) 16.6 (2) 11.1 (2) 0.11 (1) 2.3 (6) 3.21 (9) 0.86 (6) 0.05 (5) 97.7 SY400-AC (8) 15.1 (4) 8.3 (2) 16.3 (4) 10.7 (1) 0.12 (2) 1.8 (7) 3.23 (4) 0.93 (5) 0.07 (4) 97.9 SY400-AC (6) 15.0 (9) 8.2 (5) 17 (2) 10.0 (7) 0.14 (2) 1 (1) 3.2 (3) 1.0 (1) 0.03 (3) 97.9 SY400-AC (3) 14.8 (4) 8.1 (1) 16.3 (2) 10.4 (1) 0.12 (2) 2.2 (2) 3.15 (4) 1.07 (5) 0.2 (1) 97.8 SY400-AC (5) 15.2 (3) 7.3 (3) (8) 10.7 (2) (5) 3.3 (7) 2.99 (9) 1.10 (3) 0.11 (2) 97.9 SY400-AC (2) 17.4 (4) 7.3 (8) 13 (1) 8 (1) 0.09 (2) 1.4 (9) 4.3 (4) 1.7 (5) 0.07 (5) 97.1 SY400-AC-6 42 (1) 17.9 (8) 7.6 (3) 14.5 (8) 8.6 (4) 0.13 (3) 1.4 (5) 3.9 (2) 1.7 (2) 0.02 (2) 97.7 SY400-AC (3) 17.2 (1) 8.0 (3) 14.7 (2) 9.32 (4) 0.10 (1) 2.0 (2) 3.77 (7) 1.59 (1) 0.13 (4) 98.0 Phlogopite SY400-AC (2) 19.1 (8) 7.68 (9) 17.8 (3) 0.05 (2) 0.03 (2) 2.9 (7) 0.91 (5) 8.53 (8) 0.04 (2) 95.0 SY400-AC (6) 18.4 (7) 7.9 (1) 18.1 (4) 0.06 (5) 0.04 (2) 3.3 (5) 0.95 (6) 8.53 (7) 0.06 (4) 94.9 SY400-AC (4) 17.6 (3) 9.7 (1) 17.3 (3) 0.1 (2) 0.04 (1) 3.8 (1) 0.91 (6) 8.4 (1) 0.06 (1) 95.5 Plagioclase SY400-AC (9) 24.5 (6) 0.32 (1) 0.01 (1) 5.7 (1) 0.01 (1) 0.0 (1) 8.00 (6) 0.8 (3) 0.01 (1) 100.4

9 Cruz-Uribe et al. [9] Table DR 7 Major element chemistry of experimental garnet (cores and rims) determined by EPMA. Values expressed as weight percent oxides. Each reported value represents the mean of 1-6 individual analyses. Units in parentheses represent one standard deviation on the basis of replicate analyses in terms of least unit cited. Experiment SiO 2 Al 2 O 3 FeO MgO CaO MnO TiO 2 Na 2 O K 2 O Cr 2 O 3 Total SY400-AC-13 core (5) 24.8 (1) 12.1 (1) 19.3 (4) 3.4 (3) 0.44 (6) (4) 0.07 (3) 0.03 (1) 0.04 (2) SY400-AC-13 rim 42 (1) 23.7 (6) (7) 15.8 (3) 6.8 (4) 0.47 (6) 0.53 (7) 0.19 (4) 0.04 (1) 0.06 (2) SY400-AC-10 core 41.6 (4) 23.3 (4) 10.6 (6) 20 (1) 4 (2) 0.31 (5) 0.4 (3) 0.04 (4) (4) SY400-AC-10 rim 42.1 (4) 23.6 (5) 12.3 (1) 16.5 (3) 6.1 (2) 0.53 (3) 0.35 (4) 0.2 (1) 0.08 (3) 0.04 (3) SY400-AC-6 core SY400-AC-6 rim 41.8 (3) 23.6 (1) 12.3 (1) 17.1 (1) 6.04 (7) 0.55 (1) 0.39 (5) 0.10 (2) 0.03 (1) 0.06 (6) SY400-AC-7 core SY400-AC-7 rim (6) (8) 14.8 (6) 15.4 (2) 6.2 (3) 0.39 (2) 0.40 (4) 0.07 (3) 0.01 (1) 0.06 (2) SY400-AC-8 core b.d. b.d SY400-AC-8 rim (6) (4) 14.5 (3) 15.5 (4) 6.39 (5) 0.42 (2) 0.46 (7) 0.09 (5) 0.03 (2) 0.04 (1) SY400-AC-9 core 40.9 (7) 22.7 (4) 10 (1) 18.0 (8) 6.7 (5) 0.37 (5) 0.9 (3) 0.10 (4) 0.01 (1) 0.08 (3) SY400-AC-9 rim 42 (2) 23.1 (5) 13 (1) 15 (2) 6.5 (7) 0.38 (2) 0.7 (3) 0.3 (5) 0.1 (2) 0.07 (4) SY400-AC-14 core 41 (1) (2) 10.7 (3) 20.2 (1) 3.1 (5) 0.14 (1) 0.2 (1) 0.08 (2) (1) SY400-AC-14 rim 40.7 (2) 23.0 (2) 13.8 (8) 15 (1) 6.7 (8) 0.6 (3) 0.5 (1) 0.10 (2) 0.03 (2) 0.15 (9) SY400-AC-15 core 41.3 (8) 23.8 (6) 11 (6) 19 (3) 4 (2) 0.3 (2) 0.3 (3) 0.07 (3) 0.01 (1) 0.03 (2) SY400-AC-15 rim 42 (2) (8) 12.3 (2) 16.3 (9) 6.5 (4) 0.36 (2) 0.6 (4) 0.3 (3) 0.1 (1) 0.06 (3) SY400-AC-16 core 41.7 (1) 22.9 (9) 8.72 (2) 20.0 (2) 6.28 (4) 0.33 (1) 0.56 (1) (4) SY400-AC-16 rim 41.4 (2) 23.5 (1) 11.9 (2) 17.1 (1) 6.12 (3) 0.36 (2) 0.35 (2) (3) 0.02 (1) 0.03 (2) SY400-AC-17 core 41.6 (5) 22.8 (1) 7.8 (2) 20.3 (5) 6.7 (4) 0.31 (1) 0.8 (4) 0.09 (3) (7) SY400-AC-17 rim 42.1 (4) 23.8 (3) 10.3 (1) (9) 6.18 (7) 0.38 (3) 0.38 (4) 0.07 (6) 0.02 (1) 0.11 (5) Table DR 8 Major element chemistry of experimental chevkinite determined by EPMA. Values expressed as weight percent oxides. Each reported value represents the mean of 6 individual analyses. Units in parentheses represent one standard deviation on the basis of replicate analyses in terms of least unit cited. Experiment SiO 2 TiO 2 ThO 2 Al 2 O 3 FeO La 2 O 3 Ce 2 O 3 Pr 2 O 3 Nd 2 O 3 CaO MgO K 2 O P 2 O 5 Total SY400-AC (4) 16.1 (8) 0.39 (3) 5.6 (3) 5.71 (9) 9.30 (4) 20.9 (8) n.a. 6.7 (3) 4.8 (3) 2.3 (3) 0.12 (5) 0.07 (3) 94.2

10 Cruz-Uribe et al. [10] H 2 O/Ce Values used for H 2 O/Ce thermometry are shown in Table S4. Values for H 2 O are based on microprobe totals (Table S4). Temperatures were calculated based on H 2 O/Ce ratios at 4 GPa (the original calibration from Plank et al., 2009). Pressure-corrected temperatures were calculated at 1.5 GPa using the pressure correction: T d = T 4PGa (d 124) (1) where T d is the temperature at the depth d, and 124 is the depth in km at 4 GPa (Cooper et al., 2012). Experimental Methods The starting material for our experiments is powdered natural mélange rock sample SY400B of (Marschall and Schumacher, 2012). Sample SY400B is a chlorite-omphacite fels containing phengite, epidote, rutile, titanite, apatite, and tourmaline. It formed at low temperature/high pressure conditions ( 430 C, up to 2.0 GPa) during Eocene subduction. The bulk composition of this rock is represented by experiment MEL5, which is 100% melt (Tables DR2 and DR3). These types of rocks show a variety of compositions from Mg-Al-rich to Na-Al-rich to Si-rich compositions that are dominated by chlorite, omphacite or amphibole/talc, respectively. Future experiments will also investigate the melting behavior of more extreme compositions in the global mélange range.for an extensive review of mélange processes the reader is referred to Marschall and Schumacher (2012). Experiments investigating peridotite mélange melt interaction are underway as part of a parallel study by our group. However, this paper represents the first step in our efforts to understand mélange melting, and it cannot address all aspects of subduction magmatism. Partial melting experiments were performed using an end-loaded piston cylinder device (Boyd and England, 1960) with 1.27 cm diameter assemblies using the cold-piston-in technique (Johannes et al., 1971). The friction correction was determined at 1.2 to 1.4 GPa and 1300 C using the breakdown of Ca- Tschermakite to the assemblage anorthite, gehlenite, and corundum (Hays, 1966) and is within the pressure uncertainty (± 50 MPa). Therefore, no friction correction was applied to reported pressures. The temperature was measured and controlled using W97Re3 W75Re25 thermocouples with no correction for the effect of pressure on thermocouple EMF. The accuracy for pressure is within ± 50 MPa and for temperature is within ± 10 C. Experiments were terminated by turning off the power. The majority of our experiments were conducted in either Au (lower temperatures) or Au 80 Pd 20 (higher temperatures) capsules. All Au 80 Pd 20 capsules were preconditioned with basaltic melt (AII ) in a vertical gas mixing furnace at 1200 C for 48 h, in order to minimize Fe loss during experiments (Gaetani and Grove, 1998). Oxygen fugacity was maintained at 1 log unit below the fayalite-magnetite-quartz oxygen by mixing CO 2 and CO gases. After conditioning, glass was removed from the capsules using a diamond-tipped dremel tool bit, followed by soaking in an HF-HNO 3 solution for 24 h. Capsules were cleaned with ethanol and dried before starting materials were added. Three experiments were performed in graphite capsules, one of which was repeated in an Au 80 Pd 20 capsule to verify the consistency of the results. Experiments were conducted by first packing mg of rock powder into an Au or Au 80 Pd 20 capsule, or 40 mg of powder into a graphite capsule. Metal capsules were then crimped and welded shut; graphite capsules were closed by placing graphite lid on top. All capsules were placed into an alumina sleeve and positioned in a graphite furnace using crushable MgO spacers, which was then inserted into a CaF 2 sleeve (the pressure medium for all experiments). Temperature was measured and

11 Cruz-Uribe et al. [11] controlled using W97Re3 W75Re25 thermocouples. To minimize thermocouple oxidation, N 2 gas was flowed over the top of the thermocouple throughout the experiments. Experiments were terminated by shutting off power to the furnace. Experiments were sectioned longitudinally using a low speed diamond saw, mounted in epoxy, and polished using a diamond suspension. Analytical methods Melt proportions in the experimental run products were estimated using BSE images of each capsule, which were processed using GeoPixelCounter v. 1.0 (Mock et al., 2012). Melt proportions range from 40% in experiment SY400-AC-13 (1050 C, 2.5 GPa) to 100 % melt in experiment MEL5 (1280 C, 1.5 GPa). In lower temperature experiments ( C), we estimate that the melt proportion calculation is within 5 % because melt is evenly distributed within the capsule. Most of our experiments done above 1070 C exhibit melt pooling at the edges of the capsule, and thus estimates of the melt proportion are more difficult because of the 3D nature of the capsule and 2D nature of the BSE images. However, the range of % melt reflects the range of melt proportions in the experiments. Major element concentrations (Table DR2) in experimental glasses were determined by electron probe microanalysis (EPMA) using the JEOL-JXA-8200 Superprobe at the Massachusetts Institute of Technology. Glass analyses were performed using a defocused beam (10 µm) with an accelerating voltage of 15 kv and a beam current of 10 na. To minimize Na migration during analyses of these hydrous glasses, Na was analyzed at the beginning of each analysis for 5 s (background) and 10 s (peak). Counting times for other major elements were 20 s (background) and 40 s (peak). Trace element concentrations (Table DR3) in experimental glasses were determined by laser ablation (LA)-ICP-MS using a Photon Machines Analyte G2 193 nm excimer laser ablation system coupled to a Thermo Scientific X-Series II quadrupole ICP-MS at Brown University. Glasses were analyzed using a laser beam diameter of 50 µm with a beam energy density of 3.78 J/cm 2 and a repetition rate of 20 Hz, using helium as the carrier gas. Each analysis was acquired over 65 s, which consisted of 25 s of background collection during laser warm-up, 30 s of dwell time during ablation, and 10 s of washout. Trace element concentrations in glasses were determined by analyzing the isotopes 29 Si, 39 K, 43 Ca, 49 Ti, 85 Rb, 88 Sr, 89 Y, 90 Zr, 93 Nb, 133 Cs, 137 Ba, 139 La, 140 Ce, 141 Pr, 146 Nd, 147 Sm, 153 Eu, 159 Tb, 160 Gd, 163 Dy, 165 Ho, 166 Er, 169 Tm, 172 Yb, 176 Lu, 180 Hf, 181 Ta, 208 Pb, 232 Th, and 238 U. Between 10 and 20 unknown glass analyses were performed between standard blocks. Each standard block consisted of two analyses each of the USGS glass reference materials BHVO-2G, BCR-2G, and BIR-1G, and the NIST SRM612 glass. Trace element concentrations in experimental glasses were determined relative to the USGS glass reference material BCR-2G using Iolite (Paton et al. 2011) with 43 Ca as the normalizing mass (Ca composition based on EPMA analyses). Approach to Equilibrium The approach to equilibrium attained in our experiments was assessed by approaching the final equilibrium state for one of the experiments from different starting conditions to demonstrate that it is independent of path. This was done by initially performing a 24 h synthesis experiment at 2.5 GPa and 1000 C. The temperature was then increased to 1150 C and held there for 72 h. This experiment was compared to an experiment done at 1150 C and 2.5 GPa for 72 h, without the initial 24 h synthesis experiment. These two experiments yielded identical phase assemblages with major element major element compositions that are within analytical uncertainties.

12 REFERENCES Cruz-Uribe et al. [12] References Boyd, F.R., and England, J.L., 1960, Apparatus for phase-equilibrium measurements at pressures up to 50 kilobars and temperatures up to 1750 C: Journal of Geophysical Research, v. 65, no. 2, p Cooper, L.B., Ruscitto, D.M., Plank, T., Wallace, P.J., Syracuse, E.M., and Manning, C.E., 2012, Global variations in H2O/Ce: 1. Slab surface temperatures beneath volcanic arcs: Geochemistry Geophysics Geosystems, v. 13, no. 3. Gaetani, G.A., and Grove, T.L., 1998, The influence of water on melting of mantle peridotite: Contributions to Mineralogy and Petrology, v. 131, no. 4, p Hays, J.F., 1966, Lime-alumina-silica: Carnegie Institution of Washington Yearbook, v. 65, p Johannes, W., Bell, P.M., Mao, H.K., Boettcher, A.L., Chipman, D.W., Hays, J.F., Newton, R.C., and Seifert, F., 1971, An interlaboratory comparison of piston-cylinder pressure calibration using the albite-breakdown reaction: Contributions to Mineralogy and Petrology, v. 32, no. 1, p Marschall, H.R., and Schumacher, J.C., 2012, Arc magmas sourced from mélange diapirs in subduction zones: Nature Geoscience, v. 5, no. 11, p Mock, K., Amato, J., and Bertmaring, J., 2012, GeoPixelCounter (Version 1.0) [software] Eafkjm/GeoPixelCounter/:. Plank, T., Cooper, L.B., and Manning, C.E., 2009, Emerging geothermometers for estimating slab surface temperatures: Nature Geoscience, v. 2, no. 9, p Weldeab, S., Emeis, K.C., Hemleben, C., and Siebel, W., 2002, Provenance of lithogenic surface sediments and pathways of riverine suspended matter in the Eastern Mediterranean Sea: evidence from 143 Nd/ 144 Nd and 87 Sr/ 86 Sr ratios: Chemical Geology, v. 186, no. 1-2, p

EMMR25 Mineralogy: Ol + opx + chlorite + cpx + amphibole + serpentine + opaque

EMMR25 Mineralogy: Ol + opx + chlorite + cpx + amphibole + serpentine + opaque GSA Data Repository 2017365 Marshall et al., 2017, The role of serpentinite derived fluids in metasomatism of the Colorado Plateau (USA) lithospheric mantle: Geology, https://doi.org/10.1130/g39444.1 Appendix