Oxygen and Strontium Isotope Compositions of Hess Deep Gabbros (Holes 894F and 894G): High-Temperature Interaction of Seawater with the Oceanic Crust Layer 3

Abstract

The Hess Deep Rift Valley exposes a young (1 Ma) section of lower oceanic crust generated at the East Pacific Rise (EPR). The drillers recovered 154 m of plutonic rocks from Hole 894G. The mineralogy and textures of these rocks suggest that they represent the roof of a magma chamber. These high-level gabbros, olivine-gabbros, and gabbronorites are slightly hydrated (average LOI = 0.75%, N = 27) and crosscut by a few olivine basaltic dikes. The dikes were altered under greenschist facies conditions, and the gabbros were amphibolitized. Most of the gabbros have Sr-isotopic ratios that range from 0.70247 to 0.70309, indicative of low water-rock ratios (