Ekati xenoliths geochemical data and thin section images

Full description

The dataset comprises thin section and mount micrographs and geochemical data on forty-one eclogitic and pyroxenitic xenoliths brought to the surface by the Ekati kimberlite 52 Myrs ago. Thin sections images were taken using a Zeiss polarized light microscope equipped with a digital camera. Micro X-ray fluorescence analysis (μXRF) element maps (Si, Ca, Mg, Fe, Al, Ti, Ni, Na, K, P, Cr) of polished surfaces of xenoliths embedded in epoxy resin and of thin sections were generated with a Bruker M4 Tornado Micro-XRF equipped with a Rh anode operating at 50 kV and 200 μA. The chamber was at a 0.5–0.6 mbar vacuum, pixel resolution was 40 μm, with a dwell time 10 ms/pixel. Major element concentrations were determined with a CAMECA SX-50 electron microprobe at C.F. Mineral Research following standard analytical methods. Microprobe calibration procedures were employed using a variety of natural and synthetic oxides and silicates. Analyzing crystals used in the analyses were LiF, PET and TAP. The operating accelerating voltage was 15 kV, with a beam current of 30nA and the beam size maintained at 2 microns. Counting intervals for each element ranged from 10 seconds for major elements and 30-50 seconds for minor elements. The detection limits for K, P and Ni were 0.01 wt%. Trace elements in garnets, clinopyroxenes and ilmenites were analysed in situ by Laser Ablation ICP-MS with an Agilent 7500cs quadrupole ICP-MS coupled with a New Wave Research UP213 Laser at the Department of Geosciences, University of Greifswald, Germany (Jacob, 2006). Ablation was carried out at 10 J/cm2 and 10 Hz, using He as carrier gas. The commercial software GLITTER 4.0 (Griffin et al., 2008) was used for data reduction with NIST SRM 612 as external standard and 43Ca as internal standard using values for CaO from the electron microprobe analyses for the silicates and 47Ti determined as TiO2 for the ilmenites. Optically pure mineral separates of clinopyroxene and garnet for Nd, Sr and O isotope measurements were prepared following methods described in (Jacob et al., 1994). Chemical separation and measurements of the isotopic compositions of Nd and Sr as well as of element concentration of Sr, Nd and Sm by isotope dilution were carried out at the Max-Planck Institut für Chemie using a modified Finnigan MAT 261 mass spectrometer following methods described in (Jacob et al., 1994). Blank contributions were 300 pg for Sr, and 30 pg for Nd and Sm. Neodymium was measured as NdO+ and normalized to 146Nd/144Nd = 0.7219. Values obtained for the La Jolla and the Eimer and Amend standards were 0.51185 ± 3 and 0.70800 ± 4, respectively. Apatite-containing mineral separates of clinopyroxene and garnet from sample GE1 were leached to test for isotopic equilibrium between inclusions and host minerals. The pre-leached mineral separates were finely ground in a thoroughly cleaned boron-carbide mortar (measured blank contribution 15 pg for Nd and Sm) in the clean-lab and the resulting powder was then leached in a Teflon beaker with ultrapure 2.5N HCl at 60°C for 35 min. The residues were washed twice with distilled water, dried down and subjected to the routine dissolution and column separation procedure. Sm and Nd concentrations measured by isotope dilution generally agree within 15% with the Laser ablation ICP-MS data except for garnets from samples LE7 and PGE1. Oxygen isotope ratios were measured at Royal Holloway, University of London (RHUL), using a laser-assisted fluorination technique (Mattey and MacPherson, 1993). Optically clean mineral separates were prepared for analysis, with sample weights for each analysis ranging between 1.0 and 1.8 mg. The grains were rinsed with water and ethanol, but no acid leaching was applied. Values were duplicated and are reported relative to SMOW. Limitations of the dataset are connected to the small sample sizes, which precluded radiogenic isotope analyses for more than four of the samples.

Notes

119 MB.

Significance statement

A large dataset on barren eclogite and pyroxenite xenoliths from the Ekati diamond mine in Canada