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A geochemical link between plume head and tail volcanism

B.J. Peters1,#,

1Geosciences Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA
#Now at Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, DC 20015, USA

J.M.D. Day1

1Geosciences Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA

Affiliations  |  Corresponding Author  |  Cite as  |  Funding information

Peters, B.J., Day, J.M.D. (2017) A geochemical link between plume head and tail volcanism. Geochem. Persp. Let. 5, 29–34.

National Geographic Society (NGS 8330-07); U.S. National Science Foundation (EAR 1116089, EAR 1447130); Devendra & Aruna Lal Fellowship.

Geochemical Perspectives Letters v5  |  doi: 10.7185/geochemlet.1742
Received 05 April 2017  |  Accepted 28 September 2017  |  Published 3 November 2017
Copyright © 2017 European Association of Geochemistry



Figure 1 Satellite bathymetry map of the western Indian Ocean basin. Approximate aerial extent of Deccan Traps lava flows are shown by the gray fields on the Indian subcontinent. Numbers in the shaded region correspond to sampling regions: 1 – Kutch (samples 1-5), 2 – Saurashtra (samples 6-46), 3 – Pavagadh, Kalsubai, Amba Dongar and surrounds (samples 48-54, 63-78), 4 – Dhule and surrounds (samples 55-62), 5 – Mumbai, Western Ghats and coastal Maharashtra (samples 79-115, MMF7). Approximate trace of the Réunion hotspot is shown by the transparent black arrow, approximate plate motion vectors are shown by solid black arrows over land areas and are proportional to plate motions. Base map reproduced from the GEBCO world map 2014, www.gebco.net.
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Figure 2 (a) 187Os/188Os versus [Os] for Deccan lavas (red circles), with inferred compositions of the Réunion primary magma (green circle) (Peters et al., 2016

Peters, B.J., Day, J.M.D., Taylor, L.A. (2016) Early mantle heterogeneities in the Réunion hotspot source inferred from highly siderophile elements in cumulate xenoliths. Earth and Planetary Science Letters 448, 150–160.

), crust (CC: continental crust) and lithosphere (DMM: depleted mid-ocean ridge basalt mantle, CLM: continental lithospheric mantle) and mixing lines. Initial 187Os/188Os reported in literature data (Allegre et al., 1999

Allegre, C.J., Birck, J.L., Campas, F., Courtillot, V. (1999) Age of the Deccan traps using 187Re-187Os systematics. Earth and Planetary Science Letters 170, 197–204.

) shown as blue. (b) Small scale view of (a) showing end member compositions and uncertainties with initial 187Os/188Os calculated in this study (transparent red box with range indicated by bidirectional arrow) and in Allegre et al. (1999)

Allegre, C.J., Birck, J.L., Campas, F., Courtillot, V. (1999) Age of the Deccan traps using 187Re-187Os systematics. Earth and Planetary Science Letters 170, 197–204.

(blue box with outline). (c) Rhenium-osmium isotopes for Deccan lavas in this study (red circles) and from Allegre et al. (1999)

Allegre, C.J., Birck, J.L., Campas, F., Courtillot, V. (1999) Age of the Deccan traps using 187Re-187Os systematics. Earth and Planetary Science Letters 170, 197–204.

(blue squares), with inset for low Re samples. For reference, a 65 Ma isochron with initial 187Os/188Os = 0.1336 ± 0.0031, as determined from our samples, is shown. Uncertainty on the isochron is thinner than line thickness in panel (c) and is represented by the shaded region in the inset. A 65 Ma isochron corresponding to the initial 187Os/188Os determined by Allegre et al. (1999)

Allegre, C.J., Birck, J.L., Campas, F., Courtillot, V. (1999) Age of the Deccan traps using 187Re-187Os systematics. Earth and Planetary Science Letters 170, 197–204.

is approximately equivalent to a line following the lower bound of the shaded region, given the precision noted in that study. Model end members are given in Table S-4.
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Figure 3 (a,b) Strontium-osmium, (c,d) Nd-Os and (e,f) Sr-Nd isotopic variations for Deccan basalts plotted with a Réunion end member, crustal (LCC: lower continental crust, UCC: upper continental crust) and lithospheric assimilants as in Figure 2. Small ‘x’ marks denote 10 % mass intervals of mixing unless otherwise marked. In (e,f), a secondary mixing curve between a 20 % Réunion-80 % lower continental crust end member and an upper continental crust end member is shown to illustrate the effects of two stage crustal assimilation. For clarity, not all possible mixing arrays or end member compositions are shown in every panel. Model end members are given in Table S-4.
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Supplementary Figures and Tables


Figure S-1 Map of northwestern India showing sampling locations included expanded views of sample locations with major geographic indicators (roads, mountain tops – Insets A to C).
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Figure S-2 Chemostratigraphic subgroups and formations of the Deccan Traps volcanic province (Cox and Hawkesworth, 1985) with relative unit thicknesses (Jay and Widdowson, 2008) represented along the vertical axis (total eruptive thickness of ca. 3 km) and relative unit volumes (Richards et al., 2015) along the horizontal axis of the right-most panel. Dashed lines represent minimum volume estimates (DiMuro et al., 2014) and diagonal wavy lines represent range of possible total volumes up to the volume of the next upward formation with a well constrained estimated volume.
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Figure S-3 Comparison of trace element abundances obtained from XRF (x-axis) and ICPMS (y-axis) plotted with unity lines. Elements are selected to represent several types of relationships: (a) Ni, which shows a robust correlation near unity; (b) Ba, which shows a robust relationship slightly offset from unity; (c) Y, which shows a moderately robust relationship offset from unity; and (d) La and Ce, which show a poor relationship offset from unity. Only rare earth elements and U, Th and Pb, the latter three of which are often below detection limits, fall into the last category. We use only the higher precision and accurate ICPMS REE, U, Th and Pb data in our discussion.
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Figure S-4 Total alkali versus silica plot for new bulk rock major element data for Deccan lavas.
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Figure S-5 MgO versus major and minor elements for new whole rock geochemical data with approximate fractionation pathways relative to an assumed melt composition. Symbols as in Figure S-4.
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Figure S-6 Trace element variation diagrams for Deccan lavas, normalised to primitive mantle (McDonough and Sun, 1995). Gray field represent range of Réunion lava compositions (Table S-3; Peters et al., 2016). Symbols as in Figure S-4.
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Figure S-7 Primitive upper mantle (PUM) (Becker et al., 2006) normalised highly siderophile element patterns for Deccan lavas. Range of compositions for Saurashtra low Ti basalts (b) shown as gray region in other panels. Nearly all samples show evidence for sulphide fractionation of HSE evidenced by elevated (Pt + Pd + Re) / (Os + Ir + Ru), as evidenced by Figure S-10. Symbols as in Figure S-4.
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Figure S-8 (a) PUM-normalised (Becker et al., 2006) HSE patterns for host lavas and (b) mineral separates. Crossed symbols in (b) are recycled powders from crushing in a WC crusher. Gray fields represent range of all measured Deccan samples.
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Figure S-9 (a) Plots of 87Sr/86Sr versus Sr abundance and (b) 143Nd/144Nd versus Nd abundance. Similar to Figure 2a and Figure 3, inferred compositions of Réunion primary magmas are shown by dark circles. Mantle and crustal reservoirs that may act as assimilants to ascending Deccan primary magmas are shown by other large symbols. Small x symbols demarcate 10 % intervals of mixing. In (b), a number of alkalic and ultra-alkalic rocks show enrichment in Nd that moves them away from the Réunion-LCC join; no known crustal or upper mantle reservoir has Nd greater than about 20 ppm. Data sources are listed in Table S-4.
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Figure S-10 (a) Plot of Pd versus Cu to discriminate S-undersaturated and S-saturated lavas (Keays and Lightfoot, 2007). Although many Deccan lava samples lie above the qualitative line denoting the boundary between the S-saturated and S-undersaturated fields, most overlap the field of S-saturated (“contaminated”) West Greenland (WG) lavas (Keays and Lightfoot, 2007) which we take to imply that these lavas are also S-saturated. WG/EG: S-undersaturated (“uncontaminated) West and East Greenland lavas (Keays and Lightfoot, 2007). Symbols as in Figure S-4. (b) Assimilation-fractional crystallisation model for a hypothesised Deccan parental magma, equal to the calculated Réunion parental HSE composition of Peters et al. (2016), using partition coefficients of Jamais et al. (2008) and Day (2013) and an upper continental crust HSE composition of Peucker-Ehrenbrink and Jahn (2001). Shown for comparison are composition ranges of Mahabaleshwar main sequence basalts (light gray), Saurashtra low Ti basalts (medium gray) and the field in which these ranges overlap (dark gray). Question mark denotes unknown minimum Ir composition after several analyses for which measured Ir contents were less than the Ir contents of associated total analytical blanks.
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Table S-1 Unspiked Sr-Nd digestion and column procedure.
Digestion

Precisely weigh 0.100 grams homogenised rock powders into labelled 15 mL or 20 mL PFTE beakers. Adjust powder mass to achieve a target load of ca. 1 µL Sr and 500 ng Nd, but do not load more than 0.200 grams into a 15 mL beaker or 0.300 mL into a 20 mL beaker.

Add 1 mL teflon distilled HNO3 per 0.100 grams rock powder to each beaker.

Add 4 mL Optima HF per 0.100 grams rock powder to each beaker.

Place tightly capped beakers on vented hotplate at 150 °C. Monitor for reaction between powder and acid; this should produce a yellowish, gaseous substance above the liquid in the beaker. Allow to flux for at least 72 hours.

Carefully uncap beakers and evaporate to incipient dryness on a vented hotplate at a maximum temperature of 100 °C. Expect this drydown to take 10-12 hours for 5 mL acid at 100 °C.

Add 2 mL teflon distilled HNO3 per 0.100 grams rock powder to each beaker.

Place tightly capped beakers on vented hotplate at 120 °C. Allow to flux for at least 24 hours.

Carefully uncap beakers and evaporate to incipient dryness on a vented hotplate at a maximum temperature of 100 °C. Expect this drydown to take 4-6 hours for 2 mL acid at 100 °C.

Add 5 mL teflon distilled HCl per 0.100 grams rock powder to each beaker.

Place tightly capped beakers on vented hotplate at 120 °C. Allow to flux for at least 24 hours.

Carefully uncap beakers and evaporate to incipient dryness on a vented hotplate at a maximum temperature of 100 °C. Expect this drydown to take 10-12 hours for 5 mL acid at 100 °C.

Add 2 mL 4 M HCl to each beaker.

Place tightly capped beakers on vented hotplate at a maximum temperature of 100 °C for at least three hours to equilibrate sample with dilute acid.

If desired, extract a ca. 20 uL aliquot for trace element analysis on the ICP-MS.

Preliminary cation exchange column

Prepare new columns with 1.5 mL AG50W-X8 resin, or take used columns from storage. With proper cleaning procedures, each column can be used about 10 times with no loss in functionality.

Elute 1 column volume mQ H2O and discard.

Elute 1 column volume 4 M HF and discard into HF-bearing waste container.

Elute 1 column volume mQ H2O and discard.

Elute 1 column volume 6 M HCl and discard into acid waste container.

Elute 1 column volume mQ H2O and discard.

Elute 5 mL 4 N HCl and discard into acid waste container.

Load sample in 2 mL 4 M HCl and collect in 7 mL beaker (Hf-Pb cut)

Elute 2 mL 2.5 N HCl-1 N HF and collect in same 7 mL beaker (Hf-Pb cut)

Elute 20 mL 2.5 N HCl-1 N HF and collect in 20 mL beaker (Sr cut)

Elute 1 column volume 2 N HNO3 and discard into acid waste container (LILE, including Ba).

Elute 15 mL 6 N HCl and collect in 15 mL beaker (REE cut)

Elute 1 column volume mQ H2O and discard.

Elute 5 mL 4 N HCl and discard into acid waste container.

Fill column with 4 N HCl so that liquid level in the column is higher than liquid level in the storage container, and return used column to storage. If the column has been used >10 times, discard the column.

Place uncapped Hf-Pb, Sr and REE beakers on a vented hotplate and evaporate to incipient dryness at a maximum temperature of 100 °C.

Take up Sr cut in 1 mL 4 N HNO3 and allow to equilibrate for at least three hours at a maximum temperature of 70 °C.

Leave REE cut at incipient dryness for now; do not take up in any liquid.

Sr column

Prepare new columns with ca. 200 mg Sr-spec resin in a 1 mL pipette tip (ask for direction), or take used columns from storage. With proper cleaning procedures, each column can be reused with no loss in functionality.

Elute 1 column volume mQ H2O and discard.

Elute 1 column volume 4 N HNO3 and discard.

Elute 1 column volume mQ H2O and discard.

Elute 1 column volume 4 N HNO3 and discard.

Elute 1 column volume mQ H2O and discard.

Elute 1 column volume 4 N HNO3 and discard.

Load sample in 1 mL 4N HNO3 and collect onto dry REE cut.

Elute a further 1 mL 4 N HNO3 and collect into REE cut. Evaporate replenished REE cut to incipient dryness at a maximum temperature of 100 °C. Expect this drydown to take 2-4 hours. Then, take up REE cut in 1 mL 0.2 5N HCl and allow to equilibrate for at least three hours at a maximum temperature of 70 °C.

Elute 1 mL 4 N HNO3 and collect into Sr beaker. Repeat 5 further times for a cumulative collection of 6 mL 4 N HNO3 into the Sr beaker.

Elute 1 mL 0.05 N HNO3 and collect into Sr beaker. Repeat 2 further times for a cumulative collection of 3 mL 0.05 N HNO3 into the Sr beaker. Place uncapped Sr beaker on vented hotplate at a maximum of 100 °C and evaporate to incipient dryness. It is now ready for analysis on the Triton.

Elute 1 mL 0.05 N HNO3 and discard. Repeat 2 further times for a cumulative 3 mL of discarded 0.05 N HNO3.

Elute 1 column volume mQ H2O and discard.

Elute 1 column volume 4 N HNO3 and discard.

Fill column with 4 N HNO3 so that liquid level in the column is higher than liquid level in the storage container, and return used column to storage in 4N HNO3.

Nd column

Prepare new columns with ca. 200 mg LN-spec resin in a 1 mL pipette tip (ask for direction), or take used columns from storage. With proper cleaning procedures, each column can be reused with no loss in functionality.

Elute 1 column volume mQ H2O and discard.

Elute 1 column volume 4 N HNO3 and discard.

Elute 1 column volume mQ H2O and discard.

Elute 1 column volume 6 N HCl and discard.

Elute 1 column volume mQ H2O and discard.

Elute 1 column volume 0.25 N HCl and discard.

Load sample in 1 mL 0.25 N HCl and discard.

Elute 1 mL 0.25 N HCl and collect into Nd beaker. Repeat 2 further times for a cumulative collection of 3 mL 0.25 N HCl into the Nd beaker. Place uncapped Nd beaker on vented hotplate at a maximum of 100 °C and evaporate to incipient dryness.

Elute 1 mL 0.25 N HCl and discard. Repeat 2 further times for a cumulative 3 mL of discarded 0.25 N HCl (Sm).

Elute 1 mL 0.75 N HCl and discard. Repeat 3 further times for a cumulative 4 mL of discarded 0.75 N HCl (HREE).

Elute 1 column volume mQ H2O and discard.

Elute 1 column volume 0.2 5N HCl and discard.

Fill column with 0.2 5N HCl so that liquid level in the column is higher than liquid level in the storage container, and return used column to storage in 0.25 N HCl.
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Table S-2 Tabulated HSE blank concentrations and percent blank contributions to samples.

Os (ng)Ir (ng)Ru (ng)Pt (ng)Pd (ng)Re (ng)187Os/188Os
B6-4
0.1310.0810.0290.0490.054

B6-8
0.1250.0720.0240.0550.100

B8-4
0.0900.0280.0100.065


B9-4
0.0770.0260.0120.0580.033

B9-8
0.0880.0290.0070.038


B10-4
0.0750.0860.0110.0830.046

B12-1
0.0970.0390.0140.0940.049

B12-20.0030.0920.0150.0120.0630.021

B12-3
0.0990.0180.0160.0570.020

B12-40.0040.1370.0140.0110.0730.021

B12-50.0040.1500.0200.0150.0630.0220.683
B14-40.0010.1680.0400.0310.0220.0250.231
B15-40.0010.1640.3820.0460.0140.0350.310
B16-40.0010.2020.0370.0190.0130.0150.255
B17-40.0010.1770.0520.0340.0220.0220.325
B18-40.0030.1640.5250.0240.0230.0180.137

*Many Os blanks reflected inefficient spike equilibration and were consequently discarded

Os (ng)Ir (ng)Ru (ng)Pt (ng)Pd (ng)Re (ng)187Os/188Os1 St.Dev.
Average blank0.0020.1270.0920.0200.0500.0340.320.19
Sample:Os (%)Ir (%)Ru (%)Pt (%)Pd (%)Re (%)

DC14-01F

55.314.720.05.2

DC14-020.828.923.53.58.523.6

DC14-050.38.56.32.79.211.8

DC14-090.39.615.20.41.3


DC14-10A0.311.715.90.52.13.4

DC14-10B0.410.219.20.51.73.7

DC14-10B0.310.317.00.52.72.3

DC14-10B0.311.519.80.52.22.3

DC14-10B0.28.315.40.41.30.7

DC14-10B
11.019.70.52.52.7

DC14-1510.7
65.90.30.45.3

DC14-156.2
48.30.30.42.9

DC14-190.728.626.30.51.44.0

DC14-200.714.812.70.30.89.6

DC14-212.652.937.80.42.14.5

DC14-2833.7
41.625.19.919.9

DC14-300.814.133.40.31.06.6

DC14-31A0.39.512.70.20.47.9

DC14-361.421.618.10.42.06.1

DC14-381.118.417.30.41.37.8

DC14-381.021.316.10.41.87.0

DC14-3933.1
53.784.218.94.3

DC14-3937.7


48.05.4

DC14-46A1.733.642.41.712.12.9

DC14-46A1.638.446.71.612.92.5

DC14-46B1.957.158.01.814.03.3

DC14-46C0.343.454.81.811.810.4

DC14-47B1.237.248.62.27.420.8

DC14-47B0.647.284.42.95.616.4

DC14-47A7.945.179.02.16.32.1

DC14-532.131.959.50.63.624.4

DC14-5922.4

7.811.22.5

DC14-6333.5

26.423.34.9

DC14-689.6
48.80.81.13.3

DC14-690.410.018.00.42.08.0

DC14-711.042.533.40.71.94.0

DC14-720.927.944.80.52.25.6

DC14-751.9
92.37.635.95.6

DC14-770.317.619.60.43.14.8

DC14-770.514.920.30.41.41.1

DC14-770.415.121.10.41.75.9

DC14-780.612.916.70.41.77.5

DC14-796.370.688.01.33.30.9

DC14-801.826.465.01.74.10.0

DC14-820.25.617.10.41.13.9

DC14-83B0.518.927.81.62.84.2

DC14-83B1.120.932.41.64.41.0

DC14-83B0.720.032.81.73.14.2

DC14-84A1.420.445.50.41.13.3

DC14-851.313.734.50.31.03.7

DC14-960.217.933.00.82.93.9

DC14-960.936.633.10.82.13.2

DC14-970.852.235.50.72.44.1

DC14-9912.9
39.90.81.34.6

DC14-1034.7
36.80.80.97.0

DC14-1088.6
37.91.00.82.5

DC14-1100.925.144.30.60.95.7

DC14-11114.8
44.01.00.53.0

MMF7
86.648.821.532.17.8

MMF72.3

42.321.77.9

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Table S-3 Geochemical and isotopic data (Table S-3 is available for download as an Excel file below).
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Table S-4 Modelling parameters.

87Sr/86SrRange[Sr]143Nd/144NdRange[Nd]187Os/188OsRange[Os]References
Réunion0.70418910.704-0.7042557.240.51285310.5128-0.5129350.13240.1310-0.13381.01Peters et al. (2016). GEOROC (accessed 13 January 2017)
Upper Continental Crust0.727150.725-0.7352840.5105560.51035-0.51114.61.20.196-1.20.001 - 0.004Ray et al. (2008). Peucat et al. (1989. 2013). Asmerom and Walker (1998)
Lower Continental Crust0.702640.702-0.7129890.51060.51035-0.511713.70.833350.196-1.20.001 - 0.004Peucat et al. (1989. 2013). Asmerom and Walker (1998)
Continental Lithospheric Mantle0.702550.702-0.704532520.5127770.5133-0.51241.2520.1130.105-0.1203.4Aulbach et al. (2016); McBride et al. (1996)
Depleted MORB Mantle


0.513210.5125-0.513580.1250.1218-0.12743Snow and Reisberg (1995); Roy-Barman et al. (1998)

Notes:
1 Elemental concentrations projected from MgO versus element plots assembled from listed references; isotopic ratios projected from element versus isotope ratio plots assembled from listed references.
2 Estimated concentrations to match appropriate R values as discussed in the literature.
3 Representing Archean-aged CLM.

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Table S-5 Data used for initial 187Os/188Os calculation filtered from Table S-3 (second tab in the Excel version of Table S-5, available for download below).
Filter parameters

Filtering ranges can be adjusted to test effect on initial

MgOwt. %LOIwt. %187Re/188Os187Os/188Os

min.6min.0min.0min.0.125

max.15max.2.5max.100max.1.000
Remarks:Avoids highly differentiated and olivine-accumulative samplesAvoids highly altered samplesAvoids samples that experienced significant crustal assimilationAvoids samples that experienced significant lithospheric or crustal assimilation
Initial calculation

Filtered samples





nsamples15





nmeasurements21





Isochron method (least-squares)Weighted initial (t = 65 Ma)


187Os/188Os (i)0.1337187Os/188Os (i)0.1332


Max0.1365Max0.1333


Min0.1308Min0.1331


95 % c.i.0.002895 % c.i.0.0001


Isochron method (Isoplot / York)





187Os/188Os (i)0.1336This result is static and will not automatically update. It is based on initial filtering conditions: 6 < MgO wt. % < 14, LOI < 2.5 wt. %. 187Re/188Os < 100, 0.125 < 187Os/188Os < 1.

Max0.1367

Min0.1305

2σ s.d.0.0031
Filtered samples
Sample nameMgO (wt. %)LOI (wt. %)187Re/188Os187Os/188Os187Os/188Os (T = 65 Ma)
DC14-213.962.161.040.050.132710.000140.131580.00020
DC14-98.681.94.470.220.134020.000090.129180.00033
DC14-10A8.912.094.270.210.135110.000130.130480.00036
DC14-10B8.932.034.130.210.136500.000070.132020.00030
DC14-10B8.932.035.130.260.135530.000070.129970.00035
DC14-10B8.932.036.190.310.138110.000100.131400.00044
DC14-10B8.932.030.720.040.139100.000100.138320.00014
DC14-156.761.7991.434.570.235460.000850.136350.00581
DC14-156.761.7994.854.740.244800.000430.141980.00557
DC14-156.761.797.800.390.141040.000340.132580.00076
DC14-209.371.172.800.140.132600.000100.129570.00025
DC14-309.362.345.020.250.134590.000460.129140.00074
DC14-31A11.221.441.560.080.128700.000080.127010.00016
DC14-46A8.522.0424.841.240.161990.000190.135060.00154
DC14-46A8.522.0427.701.390.166520.000180.136490.00168
DC14-46B8.422.4923.321.170.165580.000350.140300.00161
DC14-538.371.182.850.140.150660.000790.147570.00094
DC14-716.962.4310.300.520.140460.000140.129300.00070
DC14-8212.91.912.270.110.140640.000060.138180.00018
DC14-84A7.551.8217.830.890.162970.000140.143640.00111
DC14-858.381.914.760.740.159070.000150.143070.00095
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