Hadean)mantle)melting)recorded)by)southwest) Greenland ... · Hadean mantle melting recorded by Southwest Greenland Chromitite 186Os signatures: Supplementary Methods 1 Samples Three

Correction notice

Nature Geosci. 6, 871–874 (2013) Hadean mantle melting recorded by southwest Greenland chromitite 186Os signatures Judith A. Coggon, Ambre Luguet, Geoffrey M. Nowell & Peter W. U. Appel In the version of this Supplementary Information originally published online on 18 August 2013, Supplementary Table S1 was missing. This has been corrected on 1 October 2013.

© 2013 Macmillan Publishers Limited. All rights reserved.

SUPPLEMENTARY INFORMATIONDOI: 10.1038/NGEO1911

NATURE GEOSCIENCE | www.nature.com/naturegeoscience 1

Hadean mantle melting recorded by Southwest Greenland Chromitite 186Os signatures:

Supplementary Methods

1

Samples

Three Os-rich chromitite samples (479914, 479926 and 479930) were selected from a suite of 20

ultramafic samples from the Ujaragssuit nunât area layered body (Fig. 1). The layered body is

approximately 800 ! 100 m in outcrop and is described as a “layered ultramafic-chromitite

xenolith”, which has experienced amphibolite grade metamorphism and is entrained within

tonalitic orthogneiss13. The chromitites have been described in detail and the layered body is

dated at 3.811 Ga13. Samples weighed ~200 – 350 g each. Weathered surfaces were removed

before crushing with a hammer and powdered using an agate ring mill.

Methods

Osmium, Ir, Pt and Re (HSE) concentrations were determined by isotope dilution and

inductively coupled plasma mass spectrometry (ICP-MS) (Ir, Pt, Re) and negative thermal

ionization mass spectrometry (N-TIMS) (Os). High precision 186Os isotope measurements were

acquired by N-TIMS analysis of un-spiked sample aliquots.

HSE concentrations

Approximately 1 gram of each whole-rock powder, spiked with 190Os, 191Ir, 194Pt and 185Re, was

digested in a quartz reaction vessel with inverse aqua regia (2.5 ml 12N HCl + 5 ml 16N HNO3)

in an Anton Paar HP-Asher, at 220° C and >100 bar for 13.5 h. Triple extraction of Os was

performed using 7 ml (total) of carbon tetrachloride, followed by Os back-extraction into 4 ml of

9N HBr (described in more detail by Wittig et al.31) and purification by micro-distillation32.

Iridium, Pt and Re remain in the aqua regia cuts, which were transferred to Savilex beakers and


http://dx.doi.org/10.1038/ngeo1911

2

dried down in preparation for a second digestion in order to ensure thorough collection of Re

from silicate material33-34; 1 ml 16N HNO3 + 4 ml 24N HF was added to each sample and placed

on a hotplate at 120° C overnight. Samples were then dried, fluxed three times with 16N HNO3

and redissolved in 10 ml 0.5N HCl. HSE were separated and collected using Bio-Rad AG1X-8

(100–200#) anion exchange resin, based on the separation technique of Pearson and Woodland35

but adapted for a more efficient separation of HFSE from the HSE (in particular, Hf from Ir and

Pt).

Osmium was loaded onto Pt filaments, followed by a mixed Na(OH)-Ba(OH)2 activator30, and

isotope measurements were performed on a negative thermal ionisation Thermo Scientific Triton

mass spectrometer (N-TIMS) at Northern Centre for Isotopic and Elemental Tracing (NCIET) at

the University of Durham using the secondary electron multiplier (SEM) detector. The

measurement procedure for the determination of Os concentration and the interference correction

method have been described in detail by Dale et al.34. Iridium, Pt and Re concentrations were

measured using a Thermo Scientific ELEMENT XR ICP-MS34 at Steinmann Institut für

Endogene Prozesse, Universität Bonn. HSE concentrations of Ujaragssuit nunât chromitites are

reported in Table S2. Average procedural blanks for HSE analysis during the period May 2011 –

September 2012 were 0.74 ± 0.76 ppt Os, 2.0 ± 2.4 ppt Ir, 39 ± 43 ppt Pt, and 3.0 ± 2.5 ppt Re

(all uncertainties are 2sd). Given that the mean Os content of the samples analysed here is 56

ppb, the blank to sample Os ratio is negligible. Analyses of the UBN peridotite standard

reference material during the period June 2009 – May 2012 gave an average 3.23 ± 0.59 ppb Os,

2.73 ± 1.03 ppb Ir, 7.64 ± 0.66 ppb Pt, and 0.174 ± 0.026 ppb Re (uncertainties are 2sd), which

are consistent with published studies (e.g. most recently: 3.34 ± 0.21 ppb Os, 2.90 ± 0.16 ppb Ir,

7.20 ± 1.27 ppb Pt, and 0.179 ± 0.041 ppb Re)36.


3

186Os isotope analytical method

The chemical procedure for 186Os isotope analysis is very similar to the protocol for the analysis

of Os concentrations; differences are described here. In order to obtain sufficient Os for analysis

(>20-30 ng), ~2 g of each whole-rock powder was digested with inverse aqua regia in an Anton

Paar HP-Asher, in the absence of spike, in quartz reaction vessels that have never been exposed

to isotopic spikes. Triple solvent extraction of Os, back-extraction into HBr and purification by

Os micro-distillation were performed as described above.

Osmium was loaded onto Pt filaments, and a mixed Na(OH)-Ba(OH)2 activator solution30 was

added. Osmium isotope measurements were performed in static mode on a 7-faraday collector

Thermo Scientific Triton N-TIMS at Northern Center for Isotopic and Elemental Tracing

(NCIET) at the University of Durham. The measurement procedure and interference correction

method have been described in extensive detail by Luguet et al.30. They are briefly summarised

here. Baseline and amplifier gain calibrations were performed at the start of each day and a 30

second instrumental baseline was measured at the beginning of each analysis. Each measurement

(Routine 1, Table S3) consisted of 280 ratios divided into 28 blocks of 10 cycles. The high

number of ratios, combined with 186OsO3- and 187OsO3

- beam intensities of > 80 mV (using 1011

Ohm resistors) yields within-run precision of 10-30 ppm (2SE) on 186Os/188Os and 187Os/188Os26.

The Thermo Scientific-Triton virtual amplifier system was used to cancel out any variations in

amplifier efficiency by passing the signal from each Faraday cup through each amplifier via a

relay matrix, which switches between measurement blocks. Isobaric interferences from PtO2-,

ReO3- and WO3

- are possible on 184OsO3-, 186OsO3

- and 187OsO3-. In order to correct for these

interferences we measured masses 228 and 230 – 233 in a separate measurement routine

(Routine 2, Table S3) both immediately before and immediately after each Os isotope


4

measurement (Routine 1). Routine 2 consists of one block of 10 ratios, lasting approximately 10

minutes, with masses measured using the secondary electron multiplier detector.

Data were exported and reprocessed offline. Corrections were applied to the 280 individual

measurements of each sample in the following order: abundance sensitivity, PtO2- and ReO3

-

interference corrections; WO3- interference corrections; oxygen isotope composition interference

corrections; and mass fractionation correction.

The abundance sensitivity for Os analyses was determined by Luguet et al. (ref 30) for the

Durham Triton TIMS; although the value of 0.3 ppm is extremely low, a systematic correction

for abundance sensitivity was applied to masses 234-241 (186OsO3- to 192Os16O2

17O-).

Corrections were made to 184OsO3-, 186OsO3

- and 187OsO3- signals to account for isobaric

molecular interferences from PtO2- (from the filament) and ReO3

- (from the sample or standard

material). Secondary electron multiplier measurements of masses 228 (196Pt16O2-), 230 (198Pt16O2

-

) and 233 (185Re16O3-) before and after each faraday measurement were used to calculate a linear

evolution for each of these isobaric interferences throughout the 280-ratio measurement.

Calculated intensities for the interferences were then subtracted from each of the 280 analyte

mass measurements. Calculation of WO3- interferences on 184OsO3

- and 186OsO3- requires an

extra step in which interferences from 196Pt17O18O- and 198Pt16O17O- beams on mass 231 (183WO3-

) must be identified and subtracted. Any residual beam intensity on mass 231 is attributed to the

presence of 183WO3-, which is then used, along with the relative abundances of 183W, 184W and

186W, to calculate the contributions of W interferences on masses 232 and 234. This approach

allows us to simply yet effectively account for molecular interferences that cannot be monitored

during the 186Os isotope faraday measurement routine.


5

Oxygen isotope composition interferences were corrected using the O isotope composition

determined in-run for each standard or sample analysis, as it has been shown that the O

composition can vary significantly throughout a run in terms of its 18O/16O ratio30. The isotopic

composition of O was determined by measuring masses 239 and 241-243 (corresponding to

combinations of 16O, 17O and 18O with 190Os and 192Os) (Routine 1). Mass fractionation was

corrected relative to 192Os/188Os, using an exponential law and a 192Os/188Os ratio of 3.08330,22,37.

Finally, a 2" rejection was applied to the 280 ratios. The maximum number of ratios rejected

after this statistical test was 17 (6%).

Os isotope measurements of the DROsS reference material

The DROsS reference material was measured 21 times during the period of 186Os isotope

measurements (August 2012: n = 6; September 2012: n = 5; January 2013: n = 10). These 21

measurements generate a mean 186Os/188Os ratio of 0.1199295 ± 0.0000033 (Table S2), which is

in excellent agreement with the previously published N-TIMS DROsS value30 of 0.1199293 ±

0.0000021. Mean 184Os/188Os of 0.001304 ± 0.000004 and 187Os/188Os of 0.160922 ± 0.000003

are also in very close agreement with published N-TIMS values30 of 0.001305 ± 0.000005 and

0.160924 ± 0.000004 (n=8) and MC-ICP-MS values38 of 0.001298 ± 0.000002 and 0.160924 ±

0.000003 (n=21), respectively (all uncertainties quoted are 2SE). Additionally the average

189Os/188Os and the 190Os/188Os ratios are 1.219714 ± 0.000005 and 1.983776 ± 0.000005, in

excellent agreement with the values obtained by Luguet et al.30.

As shown by Luguet et al.30 for the UMd and DTM Os standard solutions, the interference and

mass fraction corrected 184Os/188Os, 186Os/188Os and 187Os/188Os ratios of the DROsS standard

define residual correlations. No correlation is observed between these three Os isotopic ratios


6

and 189Os/188Os or 190Os/188Os, or between 189Os/188Os and 190Os/188Os. These residual

correlations therefore likely reveal the existence of polyatomic interferences on 184Os, 186Os and

187Os, which have not yet been identified30. The absence of any residual correlation for

189Os/188Os and 190Os/188Os either results from the absence of similar polyatomic interferences on

189Os and 190Os or alternatively results from the higher natural abundances of 189Os and 190Os and

thus a much lower interference contribution of the 189Os and 190Os beams. Smaller loads of the

DROSs standard exhibit greater scatter in terms of 184Os/188Os, 186Os/188Os and 187Os/188Os (Fig.

S2). If we assume that the 184Os/188Os ratio of 0.0013, obtained during 186Os measurements of the

DROSs, UMd and DTM standard solutions on the Thermo-Scientific Neptune MC-ICP-MS38, is

close to the “true” 184Os/188Os ratio, it appears that small Os loads (30-50 ng) are more sensitive

to polyatomic interferences due to the higher “interferences/natural Os” ratios.

In addition to providing an average Os isotopic composition for the standard solution, we can

double normalise the whole DROsS dataset using the residual correlations described above. The

method for double normalisation of 186Os data has been described previously18 and employs the

same principal that has been applied to Nd isotope data39. A linear trendline was calculated using

Microsoft Excel (Fig. S3A) and double normalised 186Os/188Os ratio (186Os/188OsDN) was

calculated using Equation 1, where m = the slope of the line and a value of 0.0013 is taken as the

true 184Os/188Os ratio30.

Equation 1.

186Os/188OsDN = 186Os/188Osmeas # m (184Os/188Osmeas # 0.0013)


7

The average double normalised 186Os/188Os and 187Os/188Os ratios of the DROsS standard

solution were calculated as 0.1199267 ± 0.0000043 and 0.160920 ± 0.000005 (2SD),

respectively. These values are slightly lower than the average measured ratios given above, but

both the average and the double normalised isotope ratios are comfortably within the 2 sigma

uncertainty range of the 186Os/188Os and 187Os/188Os values previously determined for the DROsS

standard30,38. The double normalised DROsS 186Os/188Os compositions were also extremely

consistent between individual analytical sessions, with less than 8 ppm variation between the

individual sessions as well as the overall dataset, despite varying Os loads and calculated slopes

between sessions (Fig. S3B, Table S2).

Os isotope measurements of chromitite samples

Multiple aliquots of each chromitite (479914: n = 4; 479926: n = 7; 479930: n = 4) were

analysed for Os isotopes. Chromitite samples were all run with average 186Os beams > 65 mV

and as high as 206 mV for the 280 ratio measurements, with the exception of one sample aliquot;

479930-6 was measured for 190 ratios only, due to the low 186Os16O3 beam (average = 53 mV),

which decayed throughout the run. Although the 186Os16O3 beam intensity was less than the

recommended minimum of 80 mV (see above), the Os isotope data yielded by this analysis are

consistent with the other aliquots of the same sample, therefore the measurement was not

rejected.

A negative correlation is observed between Os contents and 187Os/188Os in chromitites from this

locality23, whereas no correlation is observed between Os content and 186Os/188Os ratio. This

suggests that the Pt-Os isotopic system is more robust than the Re-Os system during secondary


8

processes such as metamorphism and recrystallization of mineral phases, possibly due to the less

mobile nature of Pt relative to Re.

As described above for the DROsS standard, strong positive correlations are observed between

184Os/188Os, 186Os/188Os and 187Os/188Os for the chromitite samples, but not when 189Os/188Os or

190Os/188Os are considered. Chromitite data were treated identically to the DROsS standard data;

double normalization was performed using linear trendlines fitted to the duplicate analyses of

each individual sample (Fig. S4) and the calculated 186Os/188Os compositions are reported in

Table S1. The seven duplicate analyses of chromitite sample 479926 yield an exceptionally wide

range of measured 186Os/188Os values (0.1197989 to 0.1198852), which correspond to a similarly

relatively wide range in 184Os/188Os values (Fig. S4B). The maximum and minimum values are

defined by two aliquots that ran at relatively low average beam intensities (65 and 82 mV) (Fig.

S5) and are clearly outliers from the main group of analyses of sample 479926. However, despite

the lower beam intensities and subsequent greater deviation from the accepted 184Os/188Os,

removal of these outliers does not alter the average 186Os/188OsDN ratio (0.1198251), therefore

these analyses were not rejected. Variation in the slope of the residual correlations calculated for

each of the three chromitites might be due to varying matrix composition of the samples.

Deviation of initial 186Os/188Os composition from the mantle evolution value at 3.811 Ga is

denoted using epsilon notation20 (Equation 2). Definition of the 186Os/188Os mantle evolution line

is discussed below.

Equation 2.

$186Os3.811 = [(186Os/188Ossample 3.811 ÷ 186Os/188Osmantle 3.811) # 1] !10000


9

Model Age Calculations

Model ages were calculated using Equations 3 and 4. Constant values used are given in Table S4.

Equation 3.

TMA = (1/%) ! [ln{(186Os/188Osmantle # 186Os/188Ossample) ÷ (190Pt/188Osmantle # 190Pt/188Ossample)} +

1]

Equation 4.

TDA = (1/%) ! [ln{(186Os/188Osmantle # 186Os/188Ossample) ÷ 190Pt/188Osmantle} + 1]

Since there is no existing convention in place for the mantle reference to which Pt-Os isotope

data should be compared we considered two different published references: an estimate of the

186Os/188Os composition of the modern primitive upper mantle (PUM), based on measurements

of a range of recent samples of the mantle; and the average composition of H-chondrites22. These

are the two most recent and most precise values – defined to seven decimal places. The PUM

value is not well constrained; the samples measured are more representative of a depleted, rather

than primitive, source21, and the evolution of the mantle over the past 4.5 Gyr is complex and

poorly understood. Chondritic evolution is simpler and is likely to be more representative of

early Earth mantle conditions, as discussed in the main text. In addition, the estimated PUM

Pt/Os ratio is a major source of uncertainty when modeling the mantle evolution trend. This is

particularly significant when backward modeling as far as ~ 4 billion years, as any uncertainty is

magnified significantly. The H-chondrite Os isotope composition is better defined (Fig. 1),


10

despite a smaller sample group than PUM (n = 5 and n = 26, respectively). Furthermore, the H-

chondrite Pt/Os ratio is well constrained, whereas modern PUM is simply assumed to also have a

chondritic average Pt/Os ratio. As the Ujaragssuit nunât area chromitites are of Eoarchean age (>

3811 Ma) we consider that model ages calculated in reference to the chondrite mantle evolution

line yield the most robust model ages.

The H-chondrite reference composition was backward-modeled to give a “chondritic mantle

evolution line”. When backward modeling the 186Os/188Os composition to 4.567 Ga (Fig. 2), we

calculate a lower initial value than Brandon et al.22. This disparity results from using different

values for the atomic abundances of 190Pt and 188Os; Brandon et al.22 use values of 0.0129 % and

13.55076 %, respectively, although no reference is given for these values. We carried out our

calculations using the most up to date values available (190Pt = 0.013634 % and 188Os = 13.2434

%)40. Recalculating the TMA model ages using the same constant values as Brandon increases the

model age of each sample by ~300 Ma. This is a significant difference, hence it is of great

importance to use the most up to date and accurate constant values available. The model ages

presented in this paper are therefore the most conservative values in the sense that they are

‘minimum’ model ages.

All constant values, except %190Pt, were defined by Brandon et al.22; 186Os/188Os ratios measured

at Durham University30,18,38,41 are consistently lower relative to those of Brandon et al.22. Before

calculating model ages, the 186Os/188Os data measured in this study were offset by +36 ppm to

account for the consistent disparity between the two laboratories. The value of 36 ppm was

derived from the difference between published average 186Os/188Os measurements of the UMd

Os standard reference material by Brandon et al.22 (2006 – the study from which the various


11

constant reference values were taken) and Luguet et al.30 (2008 – the closest Durham study, in

time, to the former).

Uncertainties for TMA ages were calculated using the formulation of Albarède42, which takes into

account the uncertainty on the measured 186Os/188Os ratio and 190Pt/188Os of the sample. A

conservative value of 5 % uncertainty was assumed for all 190Pt/188Os ratios, although this

parameter has a negligible effect on the calculated TMA uncertainty, the error on the 186Os/188Os

ratio having a much greater influence. 186Os/188Os uncertainty was taken as 1se for individual

sample aliquots, and 1sd for sample averages.

Calculated TMA uncertainty ranges from 8.6 to 35 % for individual aliquots (12 samples have

uncertainty < 17 %), with the oldest model ages having the smallest uncertainties (& 10 % for

model ages > 4 Ga). The individual samples have average model age uncertainties of 9.7 %

(sample 479914, TMA = 2.912 Ga), 19 % (sample 479926, TMA = 3.465 Ga) and 2.4 % (sample

479930, TMA = 4.039 Ga) (Table S1). When these errors on the model ages are taken into

account, the least radiogenic samples still produce Hadean minimum ages of 3.95 Ga and hence

remain consistent with Hadean mantle melt depletion, particularly since the oldest ages reported

likely provide a minimum age constraint on the mantle depletion event(s). Furthermore, it should

be noted that the largest error on radiometric model ages is commonly derived from the

uncertainty on the mantle reference values with which the measured ratios are compared43.


12

O

s/

Os

186

188

Gyr BP

X

Y

Z

Os/

O

s18

6

18

8

Gyr BP

X

YZ

C = Pt gain

-ve +ve-veTMA

Os/

O

s18

6

18

8Gyr BP

X

YZ

-veTMA TMATDA

C = Pt loss C = Os gain186A B C

Figure S1. Schematic illustration of potential mechanisms for disturbance of Pt-Os model ages. In each scenario the sample begins at

the solar system initial (X) and evolves along a chondritic 186Os/188Os trend until partial melting occurs (Y). The sample continues to

evolve, now at a lower rate due to its decreased Pt/Os, until Pt-Os disturbance occurs (Z) and the 186Os evolution path is modified

again. A and B: Artificial younging of TMA ages can result from Pt loss, or 186Os gain. In the case of the Ujaragssuit nunât chromitites,

Pt loss (reduction of Pt/Os ratio) is unlikely to have caused the young TMA ages observed, as the Pt/Os ratio of the chromitite at Y

would already have been very low (based on “normal” Pt-Os fractionation observed in layered chromitites such as the Stillwater

Intrusion14), so it is difficult to envisage significant lowering of the ratio at Z. It is more probable that the disturbance that occurred at

Z took the form of 186Os gain, via metasomatic enrichment30 by a fluid derived from a relatively high Pt/Os reservoir with time-

integrated 186Os. C: Platinum gain at point Z would produce a higher present day 186Os/188Os and Pt/Os, resulting in an increase in

TMA and decrease in TDA, i.e. divergence of these model ages. Given that the Pt/Os ratios of the Ujaragssuit nunât chromitites are very

low, and TMA and TDA are within 2 % or less for all samples, it is unlikely that Pt gain has occurred. TMA model ages older than the

intrusion age are instead considered to be true ages, recording mantle depletion.


13

Os/

O

s18

4

18

8

0.00128

0.00129

0.00130

0.00131

0.00132

0 50 100 150 200 250 Os Load (ng)

Figure S2. Distribution of 184Os/188Os ratios as a function of the amount of Os loaded for analyses of the DROsS standard. Greater scatter is observed in terms of 184Os/188Os at lower Os loads.


14

Os/

O

s18

6

1

88

0.11991

0.11992

0.11993

0.11994

0.11995

0.00128 0.00129 0.00130 0.00131 0.00132 0.00133

Os/ Os184 188

Os/

O

s18

6

1

88

0.11991

0.11992

0.11993

0.11994

0.11995

0.00128 0.00129 0.00130 0.00131 0.00132 0.00133

Os/ Os184 188

A

B

Aug 2012Sep 2012Jan 2013

30 ng50 ng100 ng200 ng

Figure S3. DROsS standard solution data. A: Os loads of 30, 50, 100 and 200 ng were analysed

during the three analytical sessions. Load is denoted by colour, session is denoted by symbol. B:

A residual correlation is observed in terms of 184Os/188Os versus 186Os/188Os, as described in the

Supplementary Materials. This correlation is used to double normalise the 186Os/188Os data to a 184Os/188Os value of 0.0013. Linear trendline calculated using Microsoft Excel. Error bars are

1SE.


15

Os/

O

s18

6

1

88O

s/

Os

186

188

Os/ Os184 188

Os/ Os184 188

A

B

0.119810

0.119815

0.119820

0.119825

0.119830

0.119835

0.001285 0.001290 0.001295 0.001300 0.001305

0.11990

0.11978

0.11980

0.11982

0.11984

0.11986

0.11988

0.00126 0.00130 0.00134 0.00138

B

sample average479930

479914479926

479930

479914479926

Figure S4. Plot of 184Os/188Os versus 186Os/188Os for Ujaragssuit nunât chromitite analyses.

Residual correlations between aliquots of each sample are shown by linear trendlines, the slopes

of these were used to calculate double normalised 186Os/188Os values for these samples. Error

bars are 1SE. Trendlines were calculated using Microsoft Excel.


16

Os/ Os184 188

0.00.00126 0.00130 0.00134 0.00138

Os

O

beam

(V)

186

1

6

- 3

0.2

0.1

479930

479914479926

Figure S5. Plot of 184Os/188Os versus 186Os beam intensity for Ujaragssuit nunât chromitite

analyses. Two aliquots of sample 479926 are clear outliers, with low beam intensities and

significant deviation from the accepted 184Os/188Os value of 0.0013. However, as removal of

these two aliquots does not alter the mean 186Os/188OsDN for sample 479926, no data were

rejected. Error bars are 1SE.


17

Session Date/sequence # Os load

(ng) 184Os/188Os ±

2se 186Os/188Os ±

2se 186Os/188OsDNa 186Os/188OsDN

b 187Os/188Os ±

2se 189Os/188Os ±

2se 190Os/188Os ±

2se Aug-12 14/08/2012 1 100 0.001308 ± 1 0.1199334 ± 22 0.1199268 0.1199277 0.160924 ± 2 1.219707 ± 6 1.983757 ± 7

14/08/2012 2 50 0.001300 ± 1 0.1199283 ± 16 0.1199280 0.1199280 0.160923 ± 2 1.219714 ± 5 1.983773 ± 7

14/08/2012 3 30 0.001307 ± 3 0.1199281 ± 39 0.1199226 0.1199234 0.160923 ± 4 1.219713 ± 9 1.983773 ± 12

14/08/2012 4 50 0.001304 ± 2 0.1199273 ± 24 0.1199239 0.1199244 0.160922 ± 3 1.219732 ± 7 1.983780 ± 9

15/08/2012 5 50 0.001308 ± 3 0.1199343 ± 32 0.1199278 0.1199287 0.160929 ± 3 1.219715 ± 9 1.983771 ± 12

16/08/2012 6 30 0.001313 ± 3 0.1199357 ± 38 0.1199260 0.1199275 0.160927 ± 4 1.219712 ± 7 1.983772 ± 10

mean

0.001306 0.1199312

0.1199266 0.160924 1.219715 1.983771

2sd 0.000009 0.0000074 0.0000044 0.000005 0.000017 0.000015 Sep-12 15/09/2012 1 100 0.001294 ± 1 0.1199256 ± 17 0.1199306 0.1199265 0.160920 ± 2 1.219740 ± 6 1.983754 ± 6

15/09/2012 2 100 0.001297 ± 1 0.1199262 ± 16 0.1199283 0.1199263 0.160917 ± 2 1.219715 ± 5 1.983786 ± 7

15/09/2012 3 200 0.001295 ± 1 0.1199260 ± 18 0.1199298 0.1199265 0.160917 ± 2 1.219737 ± 6 1.983774 ± 7

16/09/2012 4 100 0.001299 ± 1 0.1199251 ± 15 0.1199258 0.1199251 0.160920 ± 2 1.219724 ± 6 1.983771 ± 7

16/09/2012 5 200 0.001301 ± 1 0.1199269 ± 11 0.1199262 0.1199269 0.160920 ± 1 1.219700 ± 5 1.983783 ± 7

mean

0.001297 0.1199260

0.1199263 0.160919 1.219723 1.983774

2sd 0.000006 0.0000013 0.0000014 0.000003 0.000033 0.000025 Jan-13 08/01/2013 1 100 0.001317 ± 2 0.1199407 ± 24 0.1199279 0.1199268 0.160936 ± 2 1.219704 ± 6 1.983777 ± 8

08/01/2013 2 50 0.001291 ± 2 0.1199201 ± 27 0.1199269 0.1199275 0.160914 ± 3 1.219711 ± 7 1.983789 ± 9

08/01/2013 3 30 0.001299 ± 1 0.1199259 ± 23 0.1199268 0.1199268 0.160919 ± 2 1.219702 ± 6 1.983776 ± 8

08/01/2013 4 200 0.001306 ± 1 0.1199269 ± 17 0.1199224 0.1199220 0.160922 ± 2 1.219705 ± 6 1.983792 ± 10

09/01/2013 5 100 0.001307 ± 1 0.1199324 ± 17 0.1199266 0.1199261 0.160924 ± 2 1.219708 ± 5 1.983779 ± 7

10/01/2013 6 50 0.001315 ± 4 0.1199386 ± 47 0.1199275 0.1199265 0.160932 ± 4 1.219699 ± 10 1.983773 ± 12

11/01/2013 7 30 0.001282 ± 2 0.1199116 ± 20 0.1199259 0.1199271 0.160905 ± 2 1.219723 ± 6 1.983807 ± 7

12/01/2013 8 30 0.001323 ± 3 0.1199471 ± 30 0.1199293 0.1199278 0.160936 ± 3 1.219712 ± 6 1.983765 ± 7

12/01/2013 9 100 0.001301 ± 1 0.1199273 ± 13 0.1199262 0.1199262 0.160918 ± 1 1.219718 ± 6 1.983777 ± 8

12/01/2013 10 50 0.001310 ± 1 0.1199319 ± 21 0.1199243 0.1199236 0.160923 ± 2 1.219696 ± 6 1.983774 ± 9

mean

0.001305 0.1199303

0.1199260 0.160922 1.219708 1.983779

2sd 0.000024 0.0000206 0.0000036 0.000019 0.000017 0.000024 All mean

0.001304 0.1199295 0.1199267 0.1199263* 0.160922 1.219714 1.983776

2sd 0.000019 0.0000149 0.0000043 0.0000006* 0.000014 0.000024 0.000023

Table S2. Os isotope compositions for the DROsS reference material determined by N-TIMS. (RM = reference material). 186Os/188OsDN

a = Double normalised ratios calculated using slope of all data 186Os/188OsDN

b = Double normalised ratio calculated using slopes from each session * = calculated from session averages only


18

Measurement routines

Mass 232 234 235 236 237 238 240

Routine 1 Sequence 1 184Os16O3- 186Os16O3

- 187Os16O3- 188Os16O3

- 189Os16O3- 190Os16O3

- 192Os16O3-

Mass 236 238 239 240 241 242

Routine 1 Sequence 2 188Os16O3- 190Os16O3

- 190Os16O217O- 192Os16O3

- 192Os16O217O- 192Os16O2

18O-

Mass 228 230 231 232 233

Routine 2 196Pt16O2- 198Pt16O2

- 183W16O3- 184Os16O3

- 185Re16O3-

Table S3. Measurement routines used for the static multi-collection high precision analysis of 186Os (Routine 1) and isobaric

interferences (Routine 2) on the Triton N-TIMS at Durham University.


19

Constant Parameter Value Source

For calculating 190Pt/188Os Atomic abundance of 190Pt 0.013634 % Böhlke et al., 200141

Atomic abundance of 188Os 13.2434 % “ Atomic mass of Pt 195.084 g/mol-1 Wieser, 200645

Atomic mass of Os 190.23 g/mol-1 “ For calculating model ages

!190Pt 1.477 x 10-12a-1 Begemann et al., 200116 Age of Earth 4567000000 a Brandon et al., 200622

Pt/Os of upper mantle 1.999 ± 0.200 “ 190Pt/188Os of upper mantle 0.00206 “ 186Os/188Os H-chondrite (average, n = 5, ± 2") 0.1198389 ± 16 “

Table S4. Constant parameter values used for calculating 190Pt/188Os from Pt and Os

concentrations, and values used for model age calculations.


20

Additional References

31. Wittig, N. et al. Formation of the North Atlantic Craton: Timing and mechanisms constrained

from Re-Os isotope and PGE data of peridotite xenoliths from S.W. Greenland. Chem. Geol.

276, 166-187 (2010).

32. Cohen, A. S. & Waters, F. G. Separation of osmium from geological materials by solvent

extraction for analysis by thermal ionization mass spectrometry. Anal. Chim. Acta 332, 269-275

(1996).

33. Bézos, A., Lorand, J.-P., Humler, E. & Gros, M. Platinum-group element systematics in Mid-

Oceanic Ridge basaltic glasses from the Pacific, Atlantic, and Indian Oceans. Geochim.

Cosmochim. Acta 69, 2613-2627 (2005).

34. Dale, C. W., Luguet, A., Macpherson, C. G., Pearson D. G. & Hickey-Vargas, R. Extreme

platinum-group element fractionation and variable isotope compositions in Phillipine Sea Plate

basalts: Tracing mantle source heterogeneity. Chem. Geol. 248, 213-238 (2008).

35. Pearson, D. G. & Woodland S. J. Solvent extraction/anion exchange separation and

determination of PGEs (Os, Ir, Pt, Pd, Ru) and Re-Os isotopes in geological samples by isotope

dilution ICP-MS. Chem. Geol. 165, 87-107 (2000).

36. Fischer-Gödde, M., Becker, H. & Wombacher, F. Rhodium, gold and other highly

siderophile element abundances in chondritic meteorites. Geochim. Cosmochim. Acta 74, 356-

379 (2010).

37. Walker, R. J. et al. 187Os-186Os systematics of Os-Ir-Ru alloy grains from southwest

Oregon. Earth Planet. Sci. Lett. 224, 399-413 (2005).


21

38. Nowell, G. M., Luguet, A., Pearson, D. G. & Horstwood, M. S. A. Precise and accurate

186Os/188Os and 187Os/188Os measurements by multi-collector plasma ionisation mass

spectrometry (MC-ICP-MS) part I: Solution analyses. Chem. Geol. 248, 363-393 (2008).

39. Thirlwall, M. F. High-precision multi collector isotopic analysis of low levels of Nd as oxide.

Chem. Geol. 94, 13-22 (1991).

40. Böhlke, J. K. et al. Isotopic Compositions of the Elements, 2001. J. Phys. Chem. Ref. Data

34, 57-67 (2005).

41. Nowell, G. M., Pearson, D. G., Parman, S. W., Luguet, A. & Hanski, E. Precise and accurate

186Os/188Os and 187Os/188Os measurements by Multi-collector Plasma Ionisation Mass

Spectrometry, part II: Laser ablation and its application to single-grain Pt–Os and Re–Os

geochronology. Chem. Geol. 248, 394-426 (2008).

42. Albarède, F. Introduction to Geochemical Modeling (Cambridge University Press,

Cambridge, 1996).

43. Ickert, R. B. Algorithms for estimating uncertainties in initial radiogenic isotope ratios and

model ages. Chem. Geol. 340, 131-138 (2013).

44. Nutman, A. P., Friend, C. L., Horie, K. & Hidaka, H. in Earth’s Oldest Rocks, M. J. Van

Kranendonk, R. H. Smithies and V. C. Bennett, Eds., (Elsevier, Amsterdam, 2007), vol. 15,

chap. 3.3.

45. Wieser, M. E. Atomic weights of the elements 2005. Pure Appl. Chem. 78, 2051-2066

(2006).


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