ALBERT

Description: Metamorphosed oceanic gabbros provide a record of the cooling history of the lower crust near mid-ocean ridges, but the temperature range, rate, and location of subsolidus events are poorly known. We combine hornblende-plagioclase thermometry, statistical analysis, and thermal models to estimate precisely the temperature, time, distance from axis, and duration of metamorphism in East Pacific Rise gabbros from Hess Deep, ODP Hole 894G. Metamorphic hornblende and plagioclase, which formed during microfracturing and sea water penetration, equilibrated at a mean temperature of 716 +/- 8°C (90% confidence level). Comparison of the properties of the observed temperature distribution with those of model events indicates that metamorphism spanned 〈= 60°C. When combined with thermal models of fast-spreading centers, this implies that metamorphism was rapid (〈= 6000 yr) and occurred 1-4 km off axis. Application of this approach to other gabbros will allow comparison of spatial and temporal characteristics of deformation and fluid flow in the lower oceanic crust as a function of ridge setting.

Description: This database provides measurements on 87Sr/86Sr, d13C from samples of Oman Drilling Project Hole BT1B. The database includes listvenites (n=50), serpentinites (n=14), metamorphic sole rocks (n=11). The sample names and grouping by Units were determined on-board D/V Chikyu from macroscopic observations (Visual Core Description; Kelemen et al. [2020]). Rb and Sr concentrations were determined using a Quadrupole Inductively-Coupled-Plasma-Mass Spectrometer (Q-ICP-MS) at the University of Montpellier (France) and were originally reported by Godard et al. (2021). 87Sr/86Sr were analyzed for interspersed with US National Institute of Standards and Technology (NIST) SRM 987 on a Thermo Scientific Neptune multi-collector ICP-MS at Lamont Doherty Earth Observatory (United States). Total Carbon (TC) was measured from the same bulk rock powder splits as for Strontium isotopes. Total Organic Carbon (TOC, or reduced carbon) was measured from the residual rock powder after the removal of Inorganic Carbon (carbonate carbon) through reaction with dilute (3 N) HCl for at least 3 days, followed by washing with Millipore® water. Concentrations and d13C ratios of Total Carbon (TC) and Total Organic Carbon (TOC), were determined using a Costech element analyzer coupled with a Thermo Scientific Delta V plus mass spectrometer at Lamont Doherty Earth Observatory (United States). References: Reference : Kelemen, P. B., J. M. Matter, D. A. H. Teagle, J. A. Coggon, and the Oman Drilling Project Science Team (2020), Proceedings of the Oman Drilling Project, College Station, TX. and Godard, Marguerite; Carter, Elliot; Decrausaz, Thierry; Lafay, Romain; Bennett, Emma; Kourim, Fatma; de Obeso, Juan-Carlos; Michibayashi, Katsuyoshi; Harris, Michelle; Coggon, Jude; Teagle, Damon A H; Kelemen, Peter B; The Oman Drilling Project Phase 1 Science Party (2021): Lithology, major, volatile and trace element composition of Hole BT1B samples (Semail ophiolite; ICDP Oman drilling project). PANGAEA, https://doi.org/10.1594/PANGAEA.937490