Lithology, volatile, major and trace element composition of Holes CM1A and CM2B ultramafic samples drilled in Wadi Tayin massif, SE Oman ophiolite (ICDP Oman drilling project Phase 2 Leg 3)

The database reports the results of bulk rock geochemical measurements realized on 105 ultramafic lithologies (harzburgites and dunites) samples collected from Holes CM1A (46 samples) and CM2B (59 samples) drilled in the Wadi Tayin massif in the SE of the ophiolite during Phase 2 of the ICDP OmanDP (Nov. 2017-Jan. 2018) (Kelemen et al. [2020]). The studied samples were selected following two strategies. First, a homogeneous sample was selected every 10 m downhole cores during the OmanDP Phase 2 drilling operations, onsite in Oman, in order to get a petrological and geochemical overview continuously along the cores. Second, additional samples have been selected during the daily ChikyuOman Leg 3 sampling meetings in consultation with the core description teams, to focus on more specific facies or levels. These samples are referred to as onsite samples and shipboard samples respectively. Adjacent to each onsite and shipboard sample an oriented thin section billet was taken for mineralogical and lithological characterization. Geochemical data of onsite and shipboard samples were measured both aboard the D/V Chikyu during the ChikyuOman Phase 2 Leg 3 for major element and volatile contents for part of the samples, and at Institute of Earth Science, Academia Sinica, Taiwan (IES-AS), the University of Edinburgh, Scotland (EU), Université Toulouse III - Paul Sabatier, France (TU), and Niigata University, Japan (NU) for trace element contents and additional major element and volatile contents. The purpose of the study was to obtain a high-density and high analytical quality bulk geochemical characterization along continuous cores recovered from OmanDP Holes CM1A and CM2B, from the crust to the mantle through the crust-mantle transition zone. Loss on ignition (LOI) of all onsite and shipboard samples were determined onboard the D/V Chikyu, using the OHTI (Ocean High Technology Institute, Inc., Tokyo, Japan) motion compensated balance system into a pre-weighed ceramic crucible using a spatula (that was never in contact with lithium metaborate flux). Duplicate LOI measurements were done on the onsite samples at EU, following the same steps and procedures. Major element abundances (wt.% oxides) in powdered rock samples were determined using the RIGAKU Supermini wavelength dispersive X-ray fluorescence spectrometer equipped with a 200 W Pd anode tube at 50 kV and 4 mA onboard DV Chikyu during OmanDP Phase 2 Leg 3. Major element analyses were determined to be acceptable if the sum of the anhydrous oxide concentrations totaled to between 99 and 101 wt.%. Precision and accuracy are better than 2.5 % for all oxides except for TiO2 for reference materials DTS-2B and JP-1 (better than 11%) and Na2O, P2O5 and K2O for JGb-2 (3.40, 17.60, and 7.49% respectively). Duplicates of onsite samples whole rock major element analyses were performed at EU, using the Panalytical PW2404 wavelength-dispersive sequential X-ray spectrometer. Gas chromatographic separation was undertaken on non-ignited powders to determine their volatile element contents (total carbon, CTotal and water recalculated from hydrogen) using the Thermo Finnigan™ FlashEA® 1112 elemental analyzers (EA) onboard D/V Chikyu. Whole rock trace element analyses were measured by ICP-MS using acid digestion of powder samples after ChikyuOman 2018 Leg 3. Sample powders were divided into three batches. One batch was sent to each IES-AS, TU and NU laboratory for trace element measurements. The measurements were conducted at IES-AS using an Agilent 7500s inductively coupled plasma‐mass spectrometer (ICP‐MS); at TU using a Thermo Scientific™ Element XR™ HR-ICP-MS; and at NU using Yokogawa HP4500 ICP-MS. To compare the accuracy and the precision in the three different laboratories, trace element measurements were performed on a selection of duplicate samples, and on the same reference materials (DTS-2B and JP-1a).