Supplement 1.
Analytical Conditions
Samples were analyzed at four separate facilities: electron microprobe at University of Tennessee-Knoxville (UT-K) and University of Washington (UW) and FTIR at University of Oregon (UO). Table S1.1 indicates which samples were analyzed at which facilities.
At UT-K, operating conditions were: 15keV accelerating voltage, 10nA beam current with a defocussed beam, and a 10 µmbeam diameter. Count times were 20s on peak and background. Three-σ detection limits for SO2 were about 0.06 wt%. Approximate detection limits for other elements are: 0.04 wt% for Si, Al, Mg, Na, K Ca, Ti,and P and 0.06 wt% for Fe, Mn, and Cr. Standards were natural and synthetic minerals: Na–albite; K–orthoclase; Fe–hematite; Ti–rutile; Al–synthetic spinel; Si and Ca–diopside; S–anhydrite; Mg–olivine or diopside; P–apatite;Mn–spessartine;and Cr–Cr metal. Counting error is approximately 1-2% relative for concentrations over 5% and about 2-5% relative between 1 and 5%. Below 0.5% the relative error becomes larger (near 100% at detection limit—about 0.04wt% for most elements).
At UW, operating conditions were: 15keV accelerating voltage, 10nA beam current with a defocussed beam, and a 10 µm beam diameter, except for Na, K, Cl, and S, which used a 5 µm beam diameter. Count times are 20 s on peak and background for Si, Mg, Al, and Cr and 40 s on peak and 20 s on background for Ti, Mn, Fe, Ca, K, and P; and 100 s on peak and 40 s on background for S and Cl. Detection limits are 0.04% for Si, Al, Mg, Na, K, Ca, Ti, and P; 0.06 wt % for Fe, Mn, and Cr; 300 ppm for S; and 350 ppm for Cl. Standards are natural minerals: Na and Al–Tiburon albite; K–orthoclase 1; Fe–fayalite; Ti–rutile; Si, Mg, and Ca–clinopyroxene; S–celestine; Mn–Nuevo garnet (spessartine); Cl–apatite. 2σ precision for major elements is <1-2%. Reproducibility of S and Cl is ± 150 ppm.
The set of Keldunúpur KX lava glass samples (KX02-KX07) was analyzed at both UT-K and UW, although only the UW set is published here for the sake of continuity amongst lava samples. A comparison of the average composition of each sample for both analytical locations is shown in Table S1.2. Compositions acquired at UT-K differ from those acquired at UW by roughly 1–3%, with a few exceptions. MnO analyses varied by up to 21% (up to 0.06 wt%) and P2O5 analyses also showed higher than normal variation of ~2–11% (up to 0.02 wt%). UT-K analyses were generally lower than UW ones for SiO2, TiO2, Al2O3, FeO*, MnO, and K2O, while UT-K analyses of MgO and Na2O were generally higher than UW analyses. CaO and P2O5 did not show any analysis-location trends. However, these differences are not significant enough to alter the relationships noted between lava and hyaloclastite glasses within and between Rauðá and Keldunúpur in this study.
Table S1.3 shows complete FTIR analyses for Keldunúpur lava (a) and hyaloclastite (b) glasses, along with average precision per sample.
Table S1.1. Analytical techniques and locations for each sample.
UW EMP / UT-K EMP / UO FTIRSamples / Major elements / S, Cl / Major elements / S / H2O, CO2
K301 / • / •
K302 / • / •
K303 / •
K304 / • / •
KX02 / • / • / •
KX03 / • / • / •
KX04 / • / •
KX05 / •
KX06 / • / • / •
KX07 / • / •
K102 / • / •
K107 / • / •
K108 / • / •
KH01 / •
KH02r / •
KH02c / •
KH05 / •
KH06 / •
RX01 / •
RX03 / •
RX04 / •
RX05 / •
RX06 / •
RX07 / •
R104 / • / •
R106 / • / •
R107 / • / •
Table S1.2. Comparison of average compositions from KX lava glasses analyzed at UT-K and UW microprobes. All compositions are in oxide weight %.
Sample / n / Location / SiO2 / TiO2 / Al2O3 / FeO* / MnO / MgO / CaO / Na2O / K2O / P2O5KX02 / 5 / UT-K / 48.45 / 2.76 / 13.13 / 14.22 / 0.23 / 5.89 / 11.16 / 2.71 / 0.25 / 0.23
6 / UW / 49.35 / 2.84 / 13.51 / 14.37 / 0.29 / 5.77 / 10.98 / 2.64 / 0.25 / 0.24
Difference / 1.8% / 2.9% / 2.9% / 1.0% / 21.0% / 2.1% / 1.6% / 2.7% / 3.6% / 6.7%
wt.% Diff. / -0.90 / -0.08 / -0.39 / -0.14 / -0.06 / 0.12 / 0.18 / 0.07 / -0.01 / -0.02
KX03 / 5 / UT-K / 48.30 / 2.80 / 12.65 / 14.26 / 0.28 / 5.96 / 11.03 / 2.62 / 0.27 / 0.24
8 / UW / 48.72 / 2.86 / 12.89 / 14.62 / 0.27 / 5.93 / 11.08 / 2.41 / 0.27 / 0.25
Difference / 0.9% / 2.2% / 1.9% / 2.4% / 1.6% / 0.4% / 0.4% / 7.8% / 3.1% / 1.7%
wt.% Diff. / -0.42 / -0.06 / -0.24 / -0.36 / 0.00 / 0.02 / -0.05 / 0.20 / 0.01 / 0.00
KX04 / 5 / UT-K / 48.13 / 2.61 / 13.04 / 13.41 / 0.21 / 6.32 / 11.40 / 2.50 / 0.26 / 0.21
10 / UW / 49.15 / 2.59 / 13.34 / 13.45 / 0.26 / 6.25 / 11.27 / 2.44 / 0.27 / 0.22
Difference / 2.1% / 0.6% / 2.2% / 0.3% / 20.0% / 1.0% / 1.1% / 2.4% / 5.4% / 3.2%
wt.% Diff. / -1.02 / 0.01 / -0.29 / -0.04 / -0.05 / 0.06 / 0.13 / 0.06 / -0.01 / -0.01
KX06 / 5 / UT-K / 48.30 / 2.52 / 13.25 / 13.27 / 0.23 / 6.62 / 11.28 / 2.56 / 0.25 / 0.21
5 / UW / 48.78 / 2.47 / 13.49 / 13.20 / 0.25 / 6.58 / 11.02 / 2.52 / 0.25 / 0.20
Difference / 1.0% / 2.0% / 1.8% / 0.5% / 6.8% / 0.7% / 2.3% / 1.6% / 2.3% / 5.9%
wt.% Diff. / -0.48 / 0.05 / -0.24 / 0.07 / -0.02 / 0.04 / 0.26 / 0.04 / -0.01 / 0.01
KX07 / 5 / UT-K / 48.39 / 2.51 / 13.29 / 13.65 / 0.23 / 6.65 / 11.34 / 2.51 / 0.26 / 0.20
4 / UW / 49.37 / 2.56 / 13.71 / 13.71 / 0.25 / 6.67 / 11.49 / 2.40 / 0.28 / 0.22
Difference / 2.0% / 1.9% / 3.0% / 0.5% / 10.0% / 0.3% / 1.3% / 4.5% / 6.5% / 10.5%
wt.% Diff. / -0.97 / -0.05 / -0.42 / -0.06 / -0.03 / -0.02 / -0.15 / 0.11 / -0.02 / -0.02
Table S1.3a. Individual FTIR analyses for lava glass samples.
Absorbances / ConcentrationsThickness / 3570 / 1630 / Total H2O / Mol. H2O
Sample / Chip / Spot / (m) / (cm-1) / (cm-1) / (wt %) / (wt %)
K301 / 1 / 1 / 184 / 0.179 / 0 / 0.10 / 0.00
1 / 2 / 184 / 0.195 / 0 / 0.10 / 0.00
1 / 3 / 184 / 0.189 / 0 / 0.10 / 0.00
K302 / 1 / 1 / 195 / 0.074 / 0 / 0.04 / 0.00
1 / 2 / 195 / 0.122 / 0 / 0.06 / 0.00
1 / 3 / 195 / 0.081 / 0 / 0.04 / 0.00
K303 / 1 / 1 / 201 / 0.236 / 0 / 0.12 / 0.00
1 / 2 / 201 / 0.225 / 0 / 0.11 / 0.00
1 / 3 / 201 / 0.228 / 0 / 0.11 / 0.00
K304 / 1 / 1 / 165 / 0.202 / 0 / 0.12 / 0.03
1 / 2 / 165 / 0.187 / 0 / 0.11 / 0.00
1 / 3 / 165 / 0.137 / 0 / 0.08 / 0.03
KX02 / 1 / 1 / 115 / 0.100 / 0 / 0.09 / 0.00
1 / 2 / 115 / 0.132 / 0 / 0.11 / 0.00
1 / 3 / 115 / 0.156 / 0 / 0.13 / 0.00
KX03 / 1 / 1 / 212 / 0.187 / 0 / 0.09 / 0.00
1 / 2 / 212 / 0.247 / 0 / 0.12 / 0.00
1 / 3 / 212 / 0.169 / 0 / 0.08 / 0.00
KX05 / 1 / 1 / 181 / 0.926 / 0.294 / 0.51 / 0.16
1 / 2 / 181 / 0.975 / 0.417 / 0.53 / 0.14
1 / 3 / 181 / 0.161 / 0.009 / 0.09 / 0.01
KX06 / 1 / 1 / 206 / 0.422 / 0.007 / 0.20 / 0.07
1 / 2 / 206 / 0.270 / 0 / 0.13 / 0.01
1 / 3 / 206 / 0.563 / 0.027 / 0.27 / 0.06
Table S1.3b. Individual FTIR analyses for hyaloclastite samples.
Absorbances / ConcentrationsThickness / 3570 / 1630 / Total H2O / Mol. H2O
Sample / Chip / Spot / (m) / (cm-1) / (cm-1) / (wt %) / (wt %)
KH01 / 1 / 1 / 145 / 0.191 / 0 / 0.13 / 0.00
1 / 2 / 145 / 0.209 / 0 / 0.14 / 0.00
1 / 3 / 145 / 0.181 / 0 / 0.12 / 0.00
KH02r / 1 / 1 / 175 / 0.187 / 0 / 0.11 / 0.00
1 / 2 / 175 / 0.145 / 0 / 0.08 / 0.00
1 / 3 / 175 / 0.178 / 0 / 0.10 / 0.00
KH02c / 1 / 1 / 215 / 0.248 / 0 / 0.11 / 0.00
1 / 2 / 215 / 0.294 / 0.027 / 0.14 / 0.03
1 / 3 / 215 / 0.163 / 0 / 0.08 / 0.00
KH05 / 1 / 1 / 156 / 0.189 / 0 / 0.12 / 0.00
1 / 2 / 156 / 0.169 / 0 / 0.11 / 0.00
1 / 3 / 156 / 0.159 / 0 / 0.10 / 0.00
KH06 / 1 / 1 / 212 / 0.221 / 0 / 0.10 / 0.00
1 / 2 / 212 / 0.290 / 0 / 0.14 / 0.00
1 / 3 / 212 / 0.238 / 0.020 / 0.11 / 0.03
Supplement 2.
Field Observations and SDU Measurements
Fig. S2.1. Locations of samples on each outcrop.
Fig. S2.2. Standard depositional unit (as defined by Bergh 1985). Locations of field measurements taken in Iceland.
1: Thickness of lava; 2: Height of apophysis; 3: Thickness of apophysis; 4: Thickness of hyaloclastite; 5: Thickness of columnar-jointed lava; 6: Thickness of cube-jointed lava; 7: Direction of apophysis; 8: Spacing of apophyses (generally not applicable); 9: Thickness of chilled margin (not measured due to distance/height constraints); 10: Distance from top of apophysis to top of hyaloclastite unit.
Table S2.1. Measurements of SDU components. Apophysis widths were measured by photograph. Many field observations were from areas not detailed in this study (ie—not from Keldunúpur or Rauðá).
Supplement 3.
COMAGMAT Modeling of lava glass compositions
The average composition of all low-MgO Keldunúpur lava glass analyses (Table S3.2) was used as a starting liquid composition. Entering the initial parameters from Table S3.1 into the COMAGMAT 3.57 software package (Ariskin et al. 1993) and allowing ~10–20% crystallization yields liquid compositions that are more evolved and match fairly well with the average composition of the low-MgO Keldunúpur lava glass analyses. The resulting mineral assemblage, ol+plag+cpx, matches the observed assemblage in the Keldunúpur high-MgO glasses.
Table S3.1. Input parameters for COMAGMAT modeling.
Modeling process / Fractional CrystallizationPressure: / Isobaric crystallization
Total pressure (P,kbar) / 1
Maxim pressure (Pm,kbar) / 1.5
Redox conditions: / Open system (oxygen buffers)
Constant
Main oxygen buffer / QFM
Given lgfO2 - shifting / 0
Precision of calculations
Temperature convergence, C / 1
Phase compositions, mol.% / 0.25
H2O content in model system, wt % / 0.01
Crystallization increment / 1 / up to / 35
Table S3.2. Start and target compositions and model results. Shaded boxes denote where the target composition matches the model results.
% xtal / SiO2 / TiO2 / Al2O3 / FeO* / MnO / MgO / CaO / Na2O / K2O / Na2O+K2O / P2O5 / Ol / Plag / CpxStart X / 48.87 / 2.57 / 13.35 / 13.42 / 0.25 / 6.41 / 11.27 / 2.48 / 0.27 / 2.75 / 0.21
Target X / 48.99 / 2.88 / 12.59 / 14.59 / 0.28 / 5.86 / 11.00 / 2.54 / 0.26 / 2.80 / 0.25
COMAGMAT
Results / 10.00 / 49.22 / 2.84 / 12.72 / 14.49 / 0.26 / 6.26 / 11.20 / 2.47 / 0.30 / 2.77 / 0.24 / 2.50 / 41.41 / 56.10
11.00 / 49.20 / 2.86 / 12.71 / 14.58 / 0.26 / 6.22 / 11.15 / 2.48 / 0.30 / 2.78 / 0.24 / 2.22 / 40.73 / 57.05
12.00 / 49.19 / 2.88 / 12.71 / 14.67 / 0.26 / 6.17 / 11.09 / 2.49 / 0.30 / 2.79 / 0.24 / 2.92 / 40.12 / 56.97
13.00 / 49.17 / 2.90 / 12.70 / 14.76 / 0.26 / 6.13 / 11.03 / 2.49 / 0.31 / 2.80 / 0.24 / 2.77 / 39.41 / 57.83
14.00 / 49.15 / 2.92 / 12.69 / 14.86 / 0.26 / 6.09 / 10.98 / 2.50 / 0.31 / 2.81 / 0.25 / 2.57 / 39.97 / 57.47
15.00 / 49.13 / 2.94 / 12.68 / 14.96 / 0.26 / 6.05 / 10.92 / 2.51 / 0.31 / 2.82 / 0.25 / 1.26 / 41.77 / 56.98
16.00 / 49.11 / 2.96 / 12.67 / 15.05 / 0.26 / 6.01 / 10.85 / 2.51 / 0.32 / 2.83 / 0.25 / 1.66 / 41.25 / 57.09
16.99 / 49.09 / 2.99 / 12.66 / 15.15 / 0.26 / 5.96 / 10.79 / 2.52 / 0.32 / 2.84 / 0.25 / 2.18 / 40.72 / 57.10
17.99 / 49.07 / 3.01 / 12.65 / 15.25 / 0.26 / 5.92 / 10.73 / 2.53 / 0.32 / 2.85 / 0.26 / 1.82 / 41.32 / 56.86
18.99 / 49.04 / 3.03 / 12.61 / 15.37 / 0.26 / 5.89 / 10.68 / 2.53 / 0.33 / 2.85 / 0.26 / 1.34 / 48.03 / 50.63
19.99 / 49.02 / 3.06 / 12.58 / 15.48 / 0.26 / 5.85 / 10.62 / 2.53 / 0.33 / 2.86 / 0.26 / 1.77 / 47.45 / 50.78
20.99 / 48.99 / 3.09 / 12.55 / 15.60 / 0.26 / 5.82 / 10.56 / 2.54 / 0.33 / 2.87 / 0.27 / 2.33 / 46.85 / 50.82
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