Visual core descriptions of metamorphic characteristics were compiled together with igneous and structural documentation of the core to provide information on the extent of alteration, alteration mineral phases, and vein characteristics. These data were recorded in the Alteration and Vein Logs (for detailed information see "Appendix," in the "Leg 176 Summary" chapter [BACKALT.XLS, VEINLOG.XLS]), respectively, and are summarized in the HRVCDs. To ensure accurate core descriptions, the petrography of representative samples was recorded in the Alteration Thin-Section Log (see "Appendix," in the "Leg 176 Summary" chapter) and integrated with the visual core descriptions. Identification of mineral phases was checked by XRD analyses according to ODP standard procedures outlined in previous Initial Reports volumes (e.g., Volume 118; Shipboard Scientific Party, 1989). For each section the following information was recorded: leg, site, hole, core number, core type, section number, piece number (consecutively downhole), and position in the section.
The metamorphic mineral assemblages and alteration intensity were recorded in the Alteration Log. Primary phases (olivine, clinopyroxene, orthopyroxene, and plagioclase) and the secondary minerals that replace them were noted and, where possible, the volume percent of each phase was estimated in hand specimen and checked by observation of representative thin sections. Vein mineralogy, vein length and width (measured on the cut face of a piece or pieces), the top and the bottom location of the vein in the piece(s), vein type, vein mineralogy and mineral abundance, associated halo widths, and wall rock alteration were recorded in the Vein Log. The length and width of each vein were used to calculate the vein area; where veins are very abundant (net veins), the percent area of the veins within a piece or interval was estimated visually. These data were used to calculate the density of veins in the core and the volume percentage of each vein type within a given interval and within the entire core.
Detailed petrographic descriptions were made aboard ship to aid in identification and characterization of metamorphic and vein mineral assemblages. Stable mineral parageneses were noted, as were textural features of minerals indicating overprinting events (e.g., coronas, overgrowths, and pseudomorphs). Mineral abundances were either estimated visually or determined by point counting. These data are recorded in the Alteration Thin Section Log and summarized in the thin-section descriptions (see the "Core Descriptions" contents list). The modal data allowed accurate characterization of the intensity of metamorphism and aided in establishing the accuracy of the macroscopic and microscopic visual estimates of the extent of alteration.