PDF《ocean in Mars》

Supplementary information C Debaille, Brandon, Yin &

Jacobsen - Coupled

142 Nd-143 Nd evidence for a protracted magma ocean in Mars Supplementary Methods Analytical techniques All meteorites were crushed by hand with an alumina mortar and pestle dedicated to Martian meteorites.

Coarse fractions of three desert meteorites (Los Angeles, SaU

008 and DaG 476) were leached in 50% acetic acid for

30 minutes in sonic bath and on hotplate at 60?C. They were then rinsed four times in ultrapure water and dried before final crushing. Powders were dissolved in teflon beakers using a mixture of ultrapure and concentrated HF-HNO3-HClO4 (10:2:1) at 160?C for

1 week. Following evaporation, concentrated HCl was added and residues were redissolved at 160?C for

1 week. In order to avoid column saturation, no more than

300 mg were dissolved in each beaker. Samples with larger weights were split into multiple beakers and then recombined into total Nd cuts following column separation. After re-dissolution in HCl, a 5% aliquot of each solution was spiked with a mixed

150 Nd-149 Sm spike. Fluorides were then expelled by successive evaporation steps using 6N HCl and HClO4. Rare-Earth elements (REE), including Ce, Nd, and Sm were purified by cation exchange chromatography using 2.5 ml of AG50-X8 resin (100-200 mesh). The REE cuts were loaded onto a column with

2 ml Eichrom LN-Spec resin (di(2-ethylhexyl) orthophosphoric acid (HDEHP) saturated on teflon beads) to separate Ce, Nd, and Sm. The LN-Spec resin quantitatively separates Sm from Nd but not Ce from Nd. The presence of Gd (which presents an isobaric interference with Sm) in the Sm cuts represents <

5% of the original amount before purification on HDEHP column. The Nd cut was then further purified of Ce using solvent extraction17 . Cerium was first oxidized in 0.5 ml of

5 mM NaBrO3-10M HNO3 solution to take advantage of the preferential partitioning of Ce4+ into organic solvent. The organic solvent consists of 3M HDEHP in n-heptane. The organic solvent was added to the solution containing REE3+ and oxidized Ce4+ resulting in Ce extraction into the solvent. After shaking and centrifuging, the organic solvent was discarded and the procedure was repeated three times. The solution was then purified for remaining traces of dissolved HDEHP and complexed Ce4+ by adding twice and then discarding pure n-heptane. Sodium from the NaBrO3 was eliminated from the Nd cuts using a small cation column of AG50-X8 resin. The Nd cut was purified one more time on the LN-Spec column. This procedure eliminates >

99.999% of Ce in the purified Nd cuts. Total procedural blanks are ≤30 pg and ≤60 pg for Nd and Sm, respectively. Chemistry yields are >

80% for Nd and >

95% for Sm. Mass Spectrometry Spiked Sm and Nd aliquots in 0.05N HNO3 have been analyzed on a multi- collector ICP-MS (MC-ICP-MS Nu Plasma) at University of California in Davis. For Nd analyses, the presence of Sm on mass

150 was monitored on mass

147 and 149, but no detectable amount of Sm was observed in the Nd cuts. Mass fractionation corrections were made using an exponential law followed by spike-stripping (see next section). Only four masses were measured for Sm: 147, 149,

152 and 154, to avoid the presence of spike Nd in the Sm cut. The presence of Gd on masses

152 and

154 in the Sm cuts were monitored with

155 Gd and corrected. Mass fractionation corrections were calculated by iteration using an exponential law on the three spiked measured ratios (149 Sm/147 Sm,

152 Sm/147 Sm and