Geochemistry Onboard chemical analyses were performed on 42 altered rocks from Site 1188, mostly of homogeneous rocks but including some with anhydrite-dominated veins or breccia matrices. Some analyses of the latter display elevated contents of CaO. More generally, CaO is similar to or lower than its content in fresh dacites depending on whether relict igneous plagioclase has been preserved, and Na 2 O shows a similar behavior. Enrichment in MgO relative to likely parents is a common phenomenon, particularly in chloritic rocks. Depending on the relative abundance of illite, K 2 O varies from severely depleted to modestly enriched. On a relative basis, MnO is always extremely depleted.
Sulfur is distinctly enriched reflecting the presence of pyrite, or of pyrite and anhydrite.
Physical Properties Magnetic susceptibility varies greatly over the length of the recovered core, but generally increases downsection. The top 35 m of the cored material is characterized by high magnetic susceptibility and remanent intensity. This depth corresponds to the relatively fresh dacite-rhyodacite section at the top of the core. A sudden increase in both the susceptibility and remanent intensity is present below 135 mbsf. The cause of this change is unclear.