1
Supplementary Material Appendix A: Litlavíti Description and data.
2
Litlavíti is ~200 m across and ~60-70 m deep. Rubble fills the bottom of the
3
crater, but ~40 m of the crater wall exposes 10 distinct lava flows. The topmost flow
4
exposed in the Litlavíti crater can be traced back to the Stóravíti summit caldera. Using
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technical climbing methods, a sequence of 13 lavas was collected from the vertical to
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overhanging wall of the crater. This ~40 m vertical sequence samples the 10 flows
7
exposed along the crater wall. Except for a small 1-2 m section about halfway down the
8
wall of the crater, the flow contacts are fresh with no indication of weathered surfaces,
9
soil, or charcoal. The locations of the samples collected along the crater wall are shown in
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Figure A1.
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12
Figure A1. (a) Sample locations, flow contacts, and sample names collected from a
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vertical cross section by technical methods in Litlavíti crater shown as a function of depth
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measured from the crater rim. (b) Vertical profiles of Mg # and LaN/SmN, SmN/YbN, and
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SrN/NdN from the Litlavíti lava section. Trace element normalization values are C1
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chondrite: [La]=0.235 ppm, [Sm]=0.147 ppm, [Yb]=0.163 ppm. Over the 40 m vertical
17
sequence the Litlavíti lavas are nearly constant in composition, both for major and trace
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elements (Table A1), except for LTLV-2, which has slightly lower MgO, Al2O3, and CaO
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and has slightly higher concentrations of other major elements, as well as incompatible
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trace elements, suggesting that this particular lava is slightly more differentiated. There
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are no obvious systematic variations in trace elements with depth in the crater, which is in
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sharp contrast to samples from the flanks of Stóravíti, the majority of which were
1
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collected at distances of 5-25 km from the main caldera (Slater, 1996). The Litlavíti lavas
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are generally more fractionated (i.e. lower Mg#s) and have less compositional variability
25
than the Stóravíti samples. Concentrations of FeO, incompatible trace elements, and
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SmN/YbN and LaN/SmN are higher in Litlavíti compared to the rest of Stóravíti.
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Table A1. Major and trace element data for Litlaviti and Krafla samples. Major and
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trace element concentrations were measured at the GeoAnalytic Laboratory of
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Washington State University (WSU) using XRF and ICP-MS, respectively. Detailed
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descriptions of the XRF and ICP-MS techniques, including estimates of accuracy based
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on measurement of international standards, are given in Johnson et al. (1999) and Knaack
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et al. (1994), respectively. The precision (1σ) for major elements in basalts measured by
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XRF is 0.11-0.33% for SiO2, Al2O3, TiO2, and P2O5 and 0.38-0.77% for other elements
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(Johnson et al., 1999; Hart and Blusztajn, 2006). The precision (1σ) for trace elements in
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basalts analyzed by ICP-MS is 0.77-3.2% for all elements except Th (9.5%) and U
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(9.3%) (Knaack et al., 1994; Hart and Blusztajn, 2006). To establish the reproducibility
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of the major and trace element measurements, repeated analyses were done of LTLV-
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09B, the standard BHVO-1, and Hawaiian sample HK-10-KWWS-92 and the results
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compared with accepted literature values (Gladney et al., 1988, and Sims et al., 1999,
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respectively). These repeat analyses show that the reproducibility of major and trace
42
element data varies from element to element but in most cases varies <10%.
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2
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Supplementary Material Appendix B: Nd, Sr, Pb and Hf Isotopic Compositions-
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Measurement Results and Analytical Details.
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Sr, Nd and Pb isotopic compositions were measured at Woods Hole Oceanographic
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Institution (WHOI) and hafnium isotopic compositions were measured at the Ecole
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Normale Supérieure in Lyon, France. Measurement results are reported in Table B1. Our
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analytical methods are detailed below.
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Sr, Nd and Pb isotopic compositions were measured at Woods Hole
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Oceanographic Institution (WHOI) using a Thermo Finnigan Neptune multi-collector
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inductively-coupled plasma mass spectrometer (MC-ICP-MS). The analyses were done
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on powders leached for ~1 hour in hot 6.2 N HCl, then repeatedly rinsed with pure water.
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This leaching is essential, particularly for Sr and Pb, as shown by a comparison of Nd, Sr
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and Pb isotopic analyses for the Litlavíti samples on both leached and unleached samples
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(Appendix Figure B1 and Table B2).
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For the Sr and Nd separation chemistries, powders were dissolved in a concentrated
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HF:HClO4 mixture, followed by conversion of fluorides to chlorides by drying down
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three times with 6.2 N HCl. Strontium and Nd separation were done by conventional ion-
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exchange chromatography using DOWEX 50 cation-exchange resin, followed by
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HDEHP-coated Teflon powder (Taras and Hart, 1987). The total procedural blank for
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Sr was <400 pg and that for Nd <100 pg.
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3
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Neodymium isotopic ratios were normalized for instrumental mass fractionation relative
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to 146Nd/144Nd = 0.7219 using an exponential law. Strontium isotopic ratios were
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normalized for instrumental mass fractionation relative to 86Sr/88Sr = 0.1194 also using an
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exponential law. For Sr and Nd isotopic measurements, the internal precision was 5–
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10 ppm (2σ). The external precision, after adjusting to 0.710240 and 0.511847 for the
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NBS987 Sr and La Jolla Nd standards, respectively, was <30 ppm (2σ) for Sr and <30
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ppm (2σ) for Nd (Jackson and Hart, 2006; Sims et al., 2008). εNd was calculated using
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(143Nd/144Nd)CHUR(0)=0.512638 (Jacobsen, and Wasserburg, 1980).
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Lead separation chemistry followed the HBr-HNO3 procedure of Abouchami et al. (1999)
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using a single column pass. Lead isotope compositions were normalized for instrumental
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mass bias relative to NBS/SRM 997 203Tl/205Tl = 0.41891. Additionally, NBS981 was
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analyzed as a bracketing standard every few samples (White et al., 2000) and then
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normalized against NBS981 using 206Pb/204Pb = 16.9356, 207Pb/204Pb = 15.4891, and
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208
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keep all WHOI data self-consistent. Internal precisions for 206Pb/204Pb, 207Pb/204Pb, and
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208
Pb/204Pb were 15–60 ppm. Analyses of USGS standards AGV-1 gave
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206
Pb/204Pb=18.9414, 207Pb/204Pb=15.6548, and 208Pb/204Pb=38.5615 and for BCR-1
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206
Pb/204Pb=18.8215, 207Pb/204Pb=15.6356, and 208Pb/204Pb-38.7309, in good agreement
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with Weis et al. (2006). External reproducibility for analyses of these standards ranges
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from 75 ppm (2σ) for 207Pb/206Pb to 200 ppm (2σ) for 208Pb/204Pb. The total procedural Pb
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blank was 120-150 pg. Further details can be found in Hart et al. (2004, open file reports
87
10 and 12) and Hart and Blusztajn (2006).
4
Pb/204Pb = 36.7006 (Todt et al., 1996). The Todt et al. (1996) normalization is used to
88
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Hafnium isotopic compositions were measured at the Ecole Normale Supérieure in Lyon,
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France, using a Nu Plasma HR MC-ICP-MS. Hafnium separation and isotope
91
measurement protocols are given in Blichert-Toft et al. (1997) and Blichert-Toft (2001)
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with the only difference being the use here of a second-generation Nu Plasma instead of
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the first-generation Plasma 54. Hafnium isotopic ratios were normalized for instrumental
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mass fractionation relative to 179Hf/177Hf = 0.7325 using an exponential law. Accuracy
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and external analytical uncertainties of < ±30 ppm for Hf isotopic measurements were
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estimated from repeated runs of the JMC-475 Hf standard (Blichert-Toft et al., 1997),
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which gave 0.28216±0.00001 (2σ) during the course of this study. Since this is identical
98
within error bars to the accepted value of 0.282163 ± 0.000009 (Blichert-Toft et al.,
99
1997) for JMC-475, no corrections were applied to the data. Internal run errors for all
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samples are less than half or one third of the external reproducibility. The hafnium total
101
procedural blank was <20 pg. εHf values were calculated using (176Hf/177Hf)Chur(0) =
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0.282772 (Blichert-Toft and Albarède, 1997).
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The observation that the Litlavíti samples are compositionally similar places a potential
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upper limit on the measure of external reproducibility of the data. Assuming that all of
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the Litlavíti crater flows are uniform in their isotopic compositions, the reproducibility
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(2
108
ppm for 87Sr/86Sr, ~700 ppm for 208Pb/204Pb and 207Pb/204Pb, and 1350 ppm for
109
206
5
) of the isotopic data is 22 ppm for 176Hf/177Hf, 42 ppm for 143Nd/144Nd, 40
Pb/204Pb (Table B2). Both leached and unleached Litlavíti samples were analyzed for
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Nd, Sr and Pb isotopes. The effect of this leaching step was negligible for Nd, but
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significant and variable for Sr and Pb isotopes (Figures B1 and B2, Table B2)
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demonstrating the necessity of leaching for Sr and Pb isotopic analyses consistent with
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previous studies (e.g. Hart et al., open file report 10; Nobre Silva et al., 2009, 2010).
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115
Whether the much larger variability in Pb isotopes is due to analytical uncertainties or
116
greater sample variance in Pb isotopes will require further studies. As pointed out by Hart
117
et al. (2004), given the large improvement in precision provided by MC-ICP-MS and
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double/triple spike methods, sample heterogeneity may now be the limiting influence in
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Pb isotope studies; other local and global studies have shown that for a given set of lavas
120
there is often a larger variance in the isotopes of Pb than in those of Nd, Sr and Hf (e.g.
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Sims et al., 2002; Sims and Hart, 2006; Waters et al., 2011). The fact that the
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reproducibility of Pb isotopes in rock standards such as BCR-1 and AGV-1 is better than
123
observed within the Litlavíti sample suite itself suggests that the variability is due, in
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large part, to real sample variance and not to mass spectrometric instabilities. It is also
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possible that more aggressive leaching would bring the Pb isotopes into even tighter
126
agreement/uniformity (Figures B1 and B2, Table B2).
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In this regard, another useful analytical comparison for examining intra-laboratory and
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inter-laboratory reproducibility for Pb isotope measurements is the Mývatnseldar 1729
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flow, which was analyzed twice in this study from two adjacent localities (Krafla 3 and
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Krafla 4) and once (I646) by Thirlwall et al. (2004). In this comparison (Figure B3), we
6
132
again assume that all three measurements are from the same homogeneous flow. The
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intra-laboratory difference for Krafla 3 and Krafla 4 is 91 ppm, 97 ppm, and 131ppm for
134
206
135
WHOI values with those of Thirlwall (2004), the difference is 324 ppm, 318 ppm, and
136
418 ppm for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, respectively. This difference is
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similar in both direction and magnitude as the offset between the Todt et al. (1996) NBS
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981 values used in this study and the more recent triple and double-spike NBS 981 values
139
measured by Galer and Abouchami, (1998), Thirlwall et al. (2002), and Baker et al.
140
(2004). The NBS 981 values in these later studies are all similar to each other (< 60 ppm
141
for 206Pb/204Pb, < 185 ppm for 207Pb/204Pb, and < 105 ppm for 208Pb/204Pb), but all
142
significantly higher (300-360 ppm for 206Pb/204Pb, 515-700 ppm for 207Pb/204Pb, and 638-
143
697 ppm for 208Pb/204Pb) than the values measured by Todt et al. (1996). See Baker et al.
144
(2004) for a compilation of double and triple spike TIMS and MC-ICP-MS
145
measurements of NBS 981. (Again we note that the Todt et al., 1996 value is used in this
146
study because this is the WHOI lab tradition and we feel it is important to maintain
147
consistency among all data produced from the same laboratory).
Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, respectively. When comparing the average of the
148
149
With this difference in the NBS 981 normalization being noted, there is good agreement
150
between our data and the recent high-precision studies of Krafla and Theisturekyir of
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Thirlwall et al. (2004), Baker et al. (2004), and Peate et al. (2010) (Figure B3). Our data
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lie on an array between the glacial Gaesafjoll data (Peate et al., 2010; this study) and the
153
Arnahvammurhraun data (Baker et al., 2004; Peate et al., 2010); and as discussed above,
154
there is a reasonable match between our data and those of Thirwall et al. (2004) for the
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155
1729 Mývatnseldar flow of Krafla, with much of the difference being an effect of the
156
different NBS981 values used for data normalization. However, as has been noted before
157
in other studies (Thirlwall et al., 2004; Baker et al., 2004; Peate et al. 2010) (Figure B3),
158
there is a significant off-set in the Stracke et al. (2003b) data from the ever evolving
159
Icelandic Pb isotope arrays, and this off-set is probably analytical.
160
161
That being said, for Nd, Sr and Hf isotopes there is a good agreement between our new
162
data and those of Stracke et al. (2003b). The Stracke et al. (2003b) study and this study
163
are the only two studies measuring Hf and Nd isotopes in samples from northern Iceland
164
(Figure B4). For these isotope systems these two data sets are well correlated within their
165
respective uncertainties and are consistent with the global basaltic array (Figure B4).
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These two data sets are also complementary as the present study includes the
167
measurements of several glacial age lavas, while Stracke et al. (2003b) analyzed several
168
early postglacial lavas, in this way defining each end-member.
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Table B1: 143Nd/144Nd, 87Sr/86Sr, 208Pb/204Pb, 207Pb/204Pb and 206Pb/204Pb of basaltic lava
170
samples from Krafla and Theistareykir.
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Table B2: 143Nd/144Nd, 87Sr/86Sr, 208Pb/204Pb, 207Pb/204Pb and 206Pb/204Pb for leached and
172
unleached Litlavíti samples.
173
Figure B1: 143Nd/144Nd versus 87Sr/86Sr for leached and unleached Litlavíti samples.
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Referential error bars represent 25 ppm uncertainties.
8
175
Figure B2: 208Pb/204Pb versus 206Pb/204Pb for leached and unleached Litlavíti samples.
176
Referential error bars represent 200 ppm uncertainties.
177
Figure B3. Comparison of A) 208Pb/204Pb and B) 207Pb/204Pb versus 206Pb/204Pb for Krafla
178
and Theisteraykyir samples measured by MC-ICPMS and internal Tl normalization and
179
external sample-standard bracketing using NBS 981 and MC-ICP-MS double spike data
180
for the same volcanic centers (Stracke et al., 2003b; Thirwall et al., 2004; Baker et al.,
181
2004; Peate, 2010; this study). The double spike data are shown with filled symbols,
182
while the Tl-doped data are shown with open symbols.
183
Figure B4: Hf versus Nd for glacial, early postglacial and late postglacial/recent lavas
184
show a comparison between the data of this study (filled symbols) and data from Stracke
185
et al. (2003b) (open symbols).
186
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Supplementary Material Appendix C: Table C1. Compilation of ages, locations and
188
isotopic and major and trace element data for the entire suite of glacial (n =39), early
189
postglacial (n= 76) and late postglacial (n =16) lavas from Krafla and Theistareykir used
190
in this study.
191
192
10