ANALYTICAL METHODS

Thirty-seven basalt samples containing thin (<1 mm wide) carbonate veins were chosen for analysis. Carbonate vein samples were hand-picked and prepared for compositional analysis. Stable isotope compositions (¹⁸O and ¹³C) were analyzed on a Europa GEO 20-20 spectrometer with a CAPS preparation system using Carrera marble standards that were calibrated to National Institute of Standards (NIST) reference material NIST-19. The errors for this instrument are better than ±0.1 for both C and O isotopes. The Ca, Mg, Sr, Fe, and Mn concentrations of the carbonates were measured on a PerkinElmer 4300 DV inductively coupled plasma–atomic emission spectrometer (ICP-AES) using synthetic standards prepared from ARISTAR ICP–mass spectroscopy (MS) primary standards. The precision of elemental ratios is 0.2%, whereas elemental concentration errors are 0.5%.

Strontium was isolated with 80-µL Sr-Spec columns and eluted with 3-M HNO₃. Sr samples were loaded onto out-gassed Ta filaments using a Ta activator solution and analyzed in a multidynamic mode using a VG sector 54 thermal ionization mass spectrometer. The average ⁸⁷Sr/⁸⁶Sr ratio for NIST-987 on this instrument was 0.710249 ± 0.000025 (2) for the period of the analyses (N = 83) and Sr-Spec column blanks were <0.15 ng.