Hard rock petrographic observations made during Leg 209 are stored in both written and electronic media. All igneous descriptions and measurements were made on the archive halves of the cores, except where otherwise noted. The igneous team worked together during the same shift to minimize measurement inconsistencies. Each member of the team was responsible for making a specific set of observations throughout the entire core. Some of the igneous observations obtained during shipboard analyses of core are summarized in the visual core description (VCD) forms (Fig. F2). Complete macroscopic descriptions are available for each site in igneous petrology spreadsheets (see the "Supplementary Material" contents list). The depth of a given feature was defined as the point where the center of a given structure intersects the center of the cut face of the archive half of the core or, if the feature does not appear in the center of the core, the depth of the centroid of the feature in the archive half of the core. All descriptive parameters are converted to numerical equivalents and are detailed fully in the spreadsheets. In the case of the rock name (e.g., dunite) the numbers are simply shorthand. For more quantitative descriptions (e.g., crystal shape), the numerical system defines progressive sequences (e.g., equant to elongate) and intermediate values (e.g., 1.5) are used to characterize intermediate stages (see the "Supplementary Material" contents list). Complete microscopic descriptions on petrographic thin sections are available for each site in the "Thin Sections" (see the "Core Descriptions" contents list).
Characterization of igneous rocks is based on abundance of primary minerals, grain size, and texture. When modal analyses can be reliably obtained, igneous rocks are classified according to the Streckeisen (1974) classification, as shown in Figure F3. A sample that contains >10% chromian spinel is called "chromitite."
Rock names are assigned based on the primary phases present prior to alteration. For severely altered rocks, the term "primary assemblage" is used to refer to the estimated pre-alteration mineral assemblage. Where alteration in ultramafic rocks is so extensive that estimation of the primary phase assemblages is not possible, the protolith is called "serpentinite." If primary assemblages, their pseudomorphs, and textures can be recognized in ultramafic samples, even though they were partially or completely replaced, the rock name used is based on the reconstructed primary assemblage and is termed either "serpentinized" or "altered" (i.e., serpentinized dunite, altered lherzolite, etc.).
The primary rock-forming minerals recovered are olivine, orthopyroxene, clinopyroxene, spinel, Fe-Ti oxide, plagioclase, and amphibole. For each, the following data are available for each site on the VCDs (see the "Core Descriptions" contents list):
In addition, accessory phases such as mica, other oxide minerals, sulfide minerals, or others (e.g., zircon) are also noted and the above three classes of observations collected. The modal percentage of the mineral includes both the fresh and altered parts of the rocks interpreted to represent that mineral. Grain size refers to the average long dimension of the minerals and is given in millimeters, as are the minimum and maximum crystal sizes. The shape describes the aspect ratio of the grains and is used when deformation has modified the original crystal morphology. The aspect ratio is the ratio of the short to the long dimension of the crystal. The terms euhedral, subhedral, anhedral, and interstitial are used to describe the shapes of crystals interpreted to preserve their igneous morphology. The shapes are divided into four classes:
Spinel occurs in various shapes that can be divided into three categories:
The presence of linear arrays of spinel grains, termed trains, that sometimes form in peridotite is denoted simply by yes (1) or no (0), and their character is described more fully in the comments. In general, these descriptions and estimates are based on hand-sample inspection; however, a limited sample suite was also studied in petrographic thin sections, and these observations were used to refine the hand-sample descriptions. This is indicated in the Shipboard Studies column of the VCD forms.
Five major classes of rocks (peridotite, pyroxenite, gabbro, diabase, and basalt) are delineated for their igneous texture. For peridotites and pyroxenites, descriptors include the following:
For diabase and gabbroic rocks the texture is defined by the grain size and the extent of igneous foliation that is developed. Diabases have grain sizes that range from too small to be discerned by the unaided eye to fine grained; microgabbros are fine grained; gabbros are medium grained or coarser. The textural distinction between diabases and microgabbros is based on the modal homogeneity of the sample. Diabases are defined as having a felty texture with randomly distributed plagioclase laths throughout and are modally homogeneous. Microgabbros can have felty textured plagioclase or be more massive, but those with a felty texture have distinctive modal segregations of plagioclase laths into a framework in the sample. For basaltic rocks, the proportions and characters of phenocrysts and vesicles define the following textures:
We use the term "dike" to refer to any later crosscutting feature that formed by injection of magma and/or juvenile fluids and reserve the word "vein" for describing features formed by precipitation from nonmagmatic fluids. Veins are described in "Metamorphic Petrology".
Thin sections of igneous rocks complement hand-specimen observations. In general, the same type of data was collected from thin sections as from visual descriptions but the microscopic analyses provide a more complete and accurate description of the rock. Modal data were collected from representative thin sections by visual estimates. All data for each site are available in "Thin Sections" (see the "Core Descriptions" contents list). Rigorous reconstruction of peridotite primary assemblages was not possible on board ship because they require additional information such as the bulk rock and mineral chemistry for each sample. Therefore, we reported only the abundance of serpentine after olivine and pyroxene. Additional textural features recorded include crystal sizes (measured using a micrometer scale); the presence of inclusions, overgrowths, and zonation; and the presence of accessory minerals.