The procedures and methods for igneous rock core descriptions used during Leg 187 generally follow those adopted during Leg 183 (Coffin, Frey, Wallace, et al., 2000), and much of the discussion presented here comes from that source. Observations on hard-rock petrology and petrography were stored in ODP written and electronic media according to the definitions given below. Macroscopic observations on igneous rocks were recorded on HRVCD forms by the igneous petrologists.
HRVCD forms were used to document each section of the igneous rock cores. The left column on the form, adjacent to the core photograph, graphically represents the archive half. A horizontal line across the width of this column denotes a plastic spacer. Oriented pieces are indicated on the form by an upward-pointing arrow to the right of the piece. Locations of samples selected for shipboard studies are indicated in the column headed "Shipboard Studies" with notation as described in "Introduction" in "Geochemistry."
Written descriptions accompanying the schematic representation of the core sections include the following information for each unit:
Volcanic rocks were classified according to the nature and abundance of phenocryst assemblages. The rocks were described as aphyric when 1% phenocrysts were visible with a hand lens or under a binocular microscope. Porphyritic volcanic rocks were further classified by phenocryst type using mineral name modifiers given in the order of decreasing abundance. Given the predominance of cryptocrystalline to microcrystalline quench crystal morphologies in the groundmass of most rocks recovered during Leg 187, the term "phenocryst" was used for a crystal that was significantly larger than the average size of the groundmass crystals; in practice, these were generally >~1 mm. Thus, a "highly olivine-plagioclase phyric basalt" contains >10% phenocrysts, the dominant phenocryst being olivine, with lesser amounts of plagioclase. The prefix includes all of the phenocryst phases that occur in the rock, as long as the total content >1%. Rock names were assigned initially on the basis of hand-specimen observations and later were checked with the thin sections. The term "glass" was reserved for a homogeneous, isotropic material free of quench crystals, with <2% alteration. Altered or hydrated glass was designated palagonite. In chilled margins, glass containing discrete spherulitic quench growth was distinguished from clear glass free of these textures.
The core was subdivided into consecutively numbered lithologic units. Lithologic unit boundaries were generally defined on the basis of major changes in lithology (i.e., changes in phenocryst type or content and/or texture). Boundaries were placed at the lowest piece of the upper interval. Generally, boundaries were not defined on the basis of type or degree of alteration or deformation. Lithologic units defined as rubble, breccia, or talus may consist of more than one rock type; such units were generally identified by the random mixture of lithologic types in the core, a predominance of weathered rounded surfaces and/or cementing sediments (i.e., breccias).
Thin sections from most igneous-rock units recovered during Leg 187 were examined to complement the hand-specimen observations. Specifically, thin sections were used to (1) confirm the rock name assigned from macroscopic description of the core and (2) determine alteration mineralogy. Features of the thin sections described included
Modal data were visually estimated by reference to standard charts. Crystal sizes were measured using a micrometer scale; generally, these measurements are more precise than hand-specimen estimates. Groundmass textural terms used are listed in Table T1. All data are summarized in ODP format thin-section description forms (see the "Core Descriptions" contents list, for thin-section information for each site).