Electron Microprobe data for Hole BT1B Oman Drilling Project

Electron microprobe data for Serpentine, Spinel and carbonate (magnesite and dolomite) for 11 samples from Hole BT1B, Oman Drilling project. The discussion of the data is available in the paper "Petrological study of listvenite series drilled at OmanDP Hole BT1B: Thermodynamic constraints on metasomatic sequences in the mantle atop the basal thrust of the Semail ophiolite" submitted to the Journal of Geophysical Research, special collection "Ophiolites and Oceanic Lithosphere, with a focus on the Samail ophiolite in Oman"

Metasomatism of the off-cratonic lithospheric mantle beneath Hangay Dome, Mongolia: Constraints from trace-element modelling of lherzolite xenoliths

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Average compositions of serpentine and fuchsite from hole BT1B, Oman Drilling Project

The presented serpentine and fuchsite (Cr-muscovite) data were derived from representative carbonate-bearing serpentinite and listvenite samples from Hole BT1B, OmanDP. Electron microprobe analysis was conducted using the JEOL 8530F FE electron microprobe at Centre for Microscopy, Characterization and Analysis (CMCA), The University of Western Australia, using an acceleration voltage of 15 keV and a fully focused beam. The general analytical procedure and application of reference materials follow the method described in Beinlich et al. (2018; doi:10.1038/s41467-018-03039-9)

Carbonate stable and clumped isotope data, calculated carbonate formation temperatures and fluid equilibrium oxygen isotope composition from hole BT1B, Oman Drilling Project

Carbonate was micro-sampled from representative listvenite and serpentinite core sections of Hole BT1B for carbonate stable isotope analysis (δ13C, δ18O) and clumped isotope thermometry. This sample subset includes matrix and vein magnesite, vein dolomite from the Upper Serpentinite (BT1B 43–02 and 44–03) and listvenite. The majority of listvenite carbonate samples are from the Lower Listvenite, comprising green, light red and dark red listvenite, plus one additional light red listvenite from the Upper Listvenite. Listvenite matrix carbonate is mainly magnesite except for matrix dolomite from core sections BT1B 72–04 and BT1B 77–03. Listvenite vein dolomite was sampled from the Upper Listvenite (BT1B 32–02) and Lower Listvenite (BT1B 67–04). Carbonate was sampled by using a micro drill with 3.8 mm inner diameter and a handheld Dremel tool from thin-section billets at sites selected based on the petrography. The relatively large diameter of the drill compared to the typical grain size and vein diameter, required sampling of the most homogeneous matrix areas and veins that were macroscopically devoid of crosscutting relationships. Carbonate samples were further crushed to a fine powder using an agate mortar and pestle prior to the analysis. Stable isotope analyses were performed at the GeoLab, Utrecht University, The Netherlands. Before isotope analysis, the mineralogy of each sample powder was constrained by XRD. The duration of acid digestion was adjusted to either dolomite or magnesite according to the dominant carbonate species in the sample powder. Dolomite samples were digested in 103% phosphoric acid at 70°C for 20 minutes and the released CO2 was continuously collected in a liquid nitrogen trap using a Kiel IV carbonate device, coupled to a 253 Plus isotope ratio mass spectrometer (both instruments from Thermo Scientific) and analyzed in Long-Integration Dual-Inlet mode (Müller et al., 2017a, doi: 10.1002/rcm.7878; with 600 seconds integration time per aliquot). The weight of individual aliquots of reference materials and unknown samples ranged between 75–95 µg. Magnesite samples were digested offline, using 10–20 mg solid powder and 1–2 ml 103% phosphoric acid at 100°C for 15–16 hours in individual, sealed vials using a custom-built vacuum line containing a cold trap with liquid nitrogen acetone slush (-96°C) to remove H2O trace quantities from the CO2 gas. The analyses were conducted using the Dual Inlet of a Thermo Fisher Scientific MAT 253 in the traditional way by 8 alternating reference gas-sample gas cycles (208 seconds sample gas integration time per measurement). All analyses were carried out in sequences with intermittent analyses of the carbonate (calcite) reference materials ETH-1, ETH-2, ETH-3. Each unknown sample was analyzed 4 to 14 times. A separate dataset contains the complete summary of all individual analyses of unknown samples and reference materials (Beinlich et al., 2019; doi:10.1594/PANGAEA.908649)

Average magnesite composition from selected serpentinite and listvenite samples from hole BT1B, Oman Drilling Project

The presented carbonate electron microprobe data were derived from representative carbonate-bearing serpentinite and listvenite samples in Hole BT1B, OmanDP. The analyzed carbonate grains are chemically zoned and the data represents averages for compositionally and texturally comparable zones, e.g. matrix magnesite in 44-03 is always the core as the rim is dolomite. Electron microprobe analysis was conducted using the JEOL 8530F FE electron microprobe at Centre for Microscopy, Characterization and Analysis (CMCA), The University of Western Australia, using an acceleration voltage of 15 keV and a 5 µm defocused beam. The general analytical procedure and application of reference materials follow the method described in Beinlich et al. (2018; doi:10.1038/s41467-018-03039-9)

Clumped isotope data from hole BT1B, Oman Drilling Project

Carbonate separates from listvenite core BT1B, Oman Drilling Project, were analyzed for their stable oxygen and carbon isotope ratios and clumped isotope distribution to constrain the conditions of carbonate mineralization. This data set summarizes all individual measurement results of the reference materials used and of the unknown samples

Ship-board determination of whole-rock (ultra-)trace element concentrations by laser ablation-inductively coupled plasma mass spectrometry analysis of pressed powder pellets aboard the D/V Chikyu

The Oman Drilling Project (OmanDP), performed under the International Continental Scientific Drilling Program (ICDP), is an international scientific research project that undertook drilling at a range of sites in the Semail ophiolite (Oman) to collect core samples spanning the stratigraphy of the ophiolite, from the upper oceanic crust down to the basal thrust. The cores were logged to International Ocean Discovery Program (IODP) standards aboard the D/V Chikyu. During ChikyuOman2018 Leg 3 (July-August 2018), participants described cores from the crust-mantle transition (CM) sites. The main rock types recovered at these sites were gabbros, dunites and harzburgites, rocks typically forming the base of the oceanic crust and the shallow mantle beneath present-day spreading centres. In addition to the core description, selected samples were analysed by X-ray fluorescence spectrometry (XRF) for their chemical compositions, including major, minor and some trace elements. To complement these standard procedures, we developed new approaches to measure ultra-trace element concentrations using a procedure adapted from previous works to prepare fine-grained pressed powder pellets coupled with laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis using instrumentation aboard the D/V Chikyu. First, three (ultra)mafic reference materials were investigated to test and validate our procedure (BHVO-2, BIR-1a and JP-1), and then the procedure was applied to a selection of gabbro and dunite samples from the CM cores to explore the limitations of the method in its current stage of development. The obtained results are in good agreement with preferred values for the reference materials and with subsequent solution replicate analyses of the same samples performed in shore-based laboratories following Leg 3 for the CM samples. We describe this procedure for the determination of 37 minor and (ultra-)trace elements (transition elements and Ga, Li and Large-Ion Lithophile Elements (LILE), Rare Earth Elements (REE), High-Field-Strength Elements (HFSE), U, Th, and Pb) in mafic and ultramafic rocks. The presented method has the major advantage that it allows the determination at sea of the (ultra-)trace element concentrations in a "dry", safe way, without using acid reagents. Our new approach could be extended for other elements of interest and/or be improved to be adapted to other rock materials during future ocean drilling operations aboard the D/V Chikyu and other platforms