Oxygen isotope concentrations of minerals from the upper kilometer of the ocean crust, DSDP Hole 504B@en

DSDP Hole 504B is the deepest basement hole in the oceanic crust, penetrating through a 571.5 m pillow section, a 209 m lithologic transition zone, and 295 m into a sheeted dike complex. An oxygen isotopic profile through the upper crust at Site 504 is similar to that in many ophiolite complexes, where the extrusive section is enriched in 18O relative to unaltered basalts, and the dike section is variably depleted and enriched. Basalts in the pillow section at Site 504 have delta 18O values generally ranging from +6.1 to +8.5 per mil SMOW (mean= +7.0 per mil ), although minor zeolite-rich samples range up to 12.7 per mil . Rocks depleted in 18O appear abruptly at 624 m sub-basement in the lithologic transition from 100% pillows to 100% dikes, coinciding with the appearance of greenschist facies minerals in the rocks. Whole-rock values range to as low as +3.6 per mil , but the mean values for the lithologic transition zone and dike section are +5.8 and +5.4 per mil , respectively. […]