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).