In this project we developed a new geobarometer for mafic and ultramafic igneous rocks, which can be used by the scientific community for a wide range of mineralogical and petrological studies. The material here include the description of the geobarometer, guidelines for its use, software and chemical data acquired for some case studies.

We collected major element, trace element and Nd isotopes of cumulate plagioclase and clinopyroxene in lower crustal gabbros from Hess Deep oceanic crust (~2°15'N, 101°30'W) to investigate the Nd isotopic heterogeneity of melts delivered to a complete section of Hess Deep oceanic crust, accreted at the fast-spreading (133 mm/yr) East Pacific Rise (EPR). These data are presented in Cooper et al. (2025) (https://doi.org/10.1130/G52872.1). Elemental maps of 58 samples were initially obtained prior to selecting a subset of 25 samples for in-situ microanalysis. We targeted the Nd isotope record of cumulate plagioclase and clinopyroxene from lower crustal gabbro samples, representing early crystallisation products of melts delivered to the crust. These samples were collected in several expeditions: Ocean Drilling Program (ODP) Leg 147; RSS James Cook cruise JC21; Integrated Ocean Drilling Program (IODP) Expedition 345 (Site U). Combined, these studies provide the most complete composite section of fast-spreading EPR crust to date (stratigraphic depth of 4350 m to 25 m). In our study, we selected 25 samples for in situ Nd isotope microanalysis, covering the range of mineralogy and textural diversity, and over the full stratigraphic depth. For a comparison to local MORB compositions, we selected a set of 13 upper-crustal sheeted dikes collected on the RSS James Cook cruise JC21. Our data reveal that the mantle is heterogeneous at the scale of melt extraction, and the crystal record from the lower crust shows greater 143Nd/144Nd heterogeneity than the overlying MORB. Hence, Pacific MORBs do not reflect the full heterogeneity of their mantle source, and some aggregation of melts occurs within the crust. Data was collected between 2020 and 2023 by George Cooper, Johan Lissenberg and Max Jansen at Cardiff University, UK, as part of NERC Grant NE/T000317/1:HiDe: A Highly Heterogeneous Depleted Upper Mantle? Mineral isotopic analyses were performed on a Thermo Scientific TRITON Plus at the Vrije Universiteit in Amsterdam. The long-term average and reproducibility (2019–2022) for the JNdi-1 standard is 0.512094 ± 0.000011 2 SD (standard deviation; n = 28) with 1011Ω resistors (used for clinopyroxene) and 0.512105 ± 0.000044 2 SD (n = 45) with four 1013Ω resistors (used for plagioclase). Full methodology can be found within the supplemental Material of Cooper et al. (2025) at https://doi.org/10.1130/GEOL.S.28485770 The DOI is a supplement to https://doi.org/10.1130/G52872.1 Methodology: https://gsapubs.figshare.com/articles/journal_contribution/Supplemental_Material_Crustal_versus_mantle-level_aggregation_of_heterogeneous_melts_at_mid-ocean_ridges/28485770?file=52665137

Electron backscatter diffraction data for cumulates from the Skaergaard Intrusion of East Greenland. 12 samples from the Skaergaard Intrusion: 9 from the Layered Series, and 3 from the trough layering. Layered Series samples have a prefix LS; Trough layer samples have a prefix TB.

Physical properties of four serpentinite and four gabbro samples acquired respectively at the Southern Wall (IODP leg 357) and at the Central Dome (IODP leg 304-305) of the Atlantis Massif have been measured and analysed in the frame of a NERC UK-IODP moratorium research. The physical property measurements included simultaneous ultra-sonic wave velocities (compressional and shear wave velocities), attenuation, electrical resistivity and permeability under increasing and decreasing effective pressure ranging between 5 and 45 Mpa. Measurements were carried out using the experimental physical property measurement rig of the rock Physics laboratory of the National Oceanography Centre, Southampton, UK. The porosity and the density of the samples were estimated using their wet dry weight difference and the volume of the samples, under atmospheric pressure and room temperature. The aim of this research project was to learn about the physical properties of oceanic lower crustal and upper-mantle rocks and to find a geophysical method that would allow to distinguish between these rocks, remotely. The dataset has been acquired and interpreted by a science party including researchers from the University of Southampton and the National Oceanography Centre. The ultrasonic wave velocities, attenuation and the electrical resistivity for each sample and for each effective pressure (increasing from 5 to 45 with an interval of 10 MPa and decreasing from 45 to 5 with an interval of 20 MPa) are reported in this dataset. Permeability measurements could have been carried out only on 6 samples for which the permeability was high enough to be measured with the experimental rig.

Data produced from NERC Grant NE/L000059/1 - IODP Exp 335 report which is open access and includes all the observations and other data generated on the Expedition. http://publications.iodp.org/proceedings/335/335toc.htm