This section describes the technologies used for defining the lithologic units and subunits in the cores. In addition to these units, a further series of sequences were defined. These include groups of units that correspond to major lithologic changes. They are commonly coupled with changes in the physical properties of the rocks, as defined in the logs, and/or geochemical changes determined by significant shifts in geochemistry from X-ray fluorescence (XRF) or ICP analyses. In addition to the 60 lithologic units and ~250 subunits defined in Hole 801C basement, 18 geochemical units and 8 sequences were identified.
To preserve important features and structures, core sections containing igneous rocks were examined before the core was split. Contacts were examined for evidence of chilling, baking, and alteration. Each piece was numbered sequentially from the top of each core section and labeled on the outside surface. Broken core pieces that could be fitted together were assigned the same number and were lettered consecutively from the top down (e.g., 1A, 1B, 1C). Composite pieces sometimes occupied more than one section. Plastic spacers were placed between pieces with different numbers. The presence of a spacer may represent a substantial interval without recovery. If it was evident that an individual piece had not rotated about a horizontal axis during drilling, an arrow was added to the label pointing to the top of the section. The pieces were split with a diamond-impregnated saw so that important compositional and structural features were preserved in both the archive and working halves.
Nondestructive physical properties measurements, such as magnetic susceptibility and natural gamma-ray emission, were made on the core before it was split (see "Physical Properties"). After splitting, the archive half was described on VCD forms and photographed. Digital images of the core were taken using the AMST. To minimize contamination of the core with Pt-group elements and Au, the describers removed jewelry from their hands and wrists before handling. After the core was split and described, the working half was sampled for shipboard physical properties, magnetic studies (see "Paleomagnetism"), thin sections, XRD, XRF, and shore-based studies.
VCD forms (Fig. F6) were used to document each section of the igneous rock cores. From left to right on the VCD the following were displayed: (1) a photograph of the archive half of the core, (2) a scale from 0 to 150 cm, (3) the piece numbers, (4) a graphical representation of the rock with structural details, (5) the piece orientation, (6) the location of samples selected for shipboard studies, (7) the boundaries of lithologic units, and (8) structure. In the graphical representation, fractures, veins, breccia, glassy contacts, and vesicles were indicated by using the symbols shown in Figure F7. A horizontal line across the entire width of this column denotes a plastic spacer. Vertically oriented pieces are indicated on the form by an upward-pointing arrow to the right of the appropriate piece. The location of samples selected for shipboard studies is indicated in the column headed "Shipboard studies," using the following notation: XRD = X-ray diffraction analysis; XRF = X-ray fluorescence analysis; TS = petrographic thin section; PP = physical properties analysis; and PM = paleomagnetic analysis. Column 7 displays the number of the lithologic unit and the location of the boundaries between units. Column 8 displays the graphical representations of structural types from the key in Figure F7.
Each section of core was examined separately by two teams of describers, igneous characteristics (discussed here) and alteration (see "Alteration"). Lithologic units and subunits (the latter representing single cooling units, breccia, or interflow sediment) were identified on the basis of the presence of contacts, chill margins (Fig. F7), changes in primary mineralogy (occurrence and abundance), color, grain size, and structural or textural variations. The boundaries of the lithologic units were drawn on the VCD, and for Hole 801C the units were numbered continuously from the end of Leg 129, starting with Unit 33. Some units were divided into subunits (-1,-2, etc.) for each cooling unit. For Site 1149 the igneous unit numbers start at 1 in Core 185-1149B-29R-1 at 407.74 mbsf. VCDs also contain a text description of each section of core that includes the (1) leg, site, hole, core number, core type, section number; (2) depth of the top of the section in mbsf; (3) unit number (consecutive downhole), number of pieces in the unit in the section, and the rock name; (4) groundmass, grain size, the Munsell color, vesicle abundance and size, structure, the nature of the alteration, information about abundance and filling of fractures, and additional comments.
The lithology spreadsheet (Table T1) lists for each unit and subunit the core number, section number, piece numbers, locations of the top and bottom of the unit in mbsf and in centimeters from the top of the section, length of each unit in centimeters, unit number, rock name, texture, structure, color, comments, and whether the unit has top and/or bottom contacts. Units were defined based on major changes in lithology, texture, structure, and mineralogy. Subunits were defined by contacts and changes in lithology within the units. Types of contacts are indicated in Table T1. When a contact was unrecovered, changes in lithology were used to define units. In the spreadsheet the first subunit of each unit is highlighted in blue. The units and subunits were named on the basis of the structure and abundance of primary minerals. In the lithology column, basalts were described as aphyric (<1% phenocrysts), sparsely phyric (1%-2% phenocrysts), moderately phyric (2%-10% phenocrysts), or highly phyric (>10% phenocrysts). They were further classified by the types of phenocrysts or megascopic crystals present (e.g., sparsely plagioclase-olivine phyric in which the amount of plagioclase exceeds the amount of olivine). Sedimentary, interpillow, and rubble units were also present in the upper levels of the hole. These are indicated in yellow in the spreadsheet. Rock color was determined on a wet, cut surface of the rock using the Munsell color chart.
Pillow basalts were identified by their chilled margins or, when these margins were absent, by variolitic texture, curved fractures, and microcrystalline grain size. In some cases when the margins were not recovered, pillows could not be distinguished from thin flows, and these were called pillow and flow units. Massive units were identified by continuous sections of similar lithology that increased in grain size toward their center. In the lithology spreadsheet, structures of the basalts were subdivided into pillows, flows, breccias, and massive units; these structures were included in the barrel sheet using the key in Figure F7.
Mineralogy spreadsheets contain the core, section, piece number, depth interval (cm), depth in mbsf, lithologic unit number, groundmass grain size, and mineralogy of the rocks. At least one sample from each section and unit was examined with the binocular microscope to determine phenocryst size, abundance, morphology, and vesicle abundance and size. In addition, for Cores 185-801C-13R through 30R, the spreadsheet (Table T2) contains cells for recording the groundmass mineral abundance and grain size, and the spinel, oxide, and sulfide abundance. However, because basalts from Hole 801 were consistently fine grained and microcrystalline, this information could not be determined in hand specimen.
Groundmass character was identified as medium grained (MG) if the average grain size was 1 mm or greater, fine grained (FG) if the grains could be identified and were <1 mm, microcrystalline (M) if the groundmass crystals could be seen but were too fine to identify, cryptocrystalline (C) if crystals could not be distinguished, hypocrystalline (HY) if glass was present with crystals and crystal abundance exceeded glass abundance, and hypohyaline (HH) if glass abundance exceeded crystals. Mineral morphology was indicated as anhedral (an), subhedral (su), or euhedral (eu). A hyphen indicates the absence of a phase. Maximum, minimum, and average crystal size were also estimated. An estimate of the percentage of vesicles and their average sizes was made. Mineral abundance was used in determining the rock name. The igneous lithology and mineralogy logs are included (see the "Supplementary Materials" contents list.
Thin sections of igneous rocks were studied to complete and refine the hand-specimen observations. This included textural features that were not identified in hand specimen; precise determination of grain size of phenocrysts and groundmass; the mineralogy, abundance, and kind of glomerocrysts; the presence of inclusions within phenocrysts; and the presence of spinel, oxides, and sulfides. Crystal sizes of all primary phases were measured. In addition, mineral morphologies, grain sizes, and textural features were described. The terms heterogranular (different crystal sizes), seriate (continuous range in grain size), porphyritic (indicating presence of phenocrysts), glomerophyric (containing clusters of crystals), hypocrystalline (100% crystals) to hypohyaline (100% glass), and intergranular (olivine and pyroxene grains between plagioclase laths) were used to describe the textures of the mesostasis. The same terminology was used for thin-section descriptions and the megascopic descriptions. Thin-section descriptions are included (see the "Core Descriptions" contents list) and are also available from the ODP Janus database.
All igneous rocks recovered during Leg 185 have undergone alteration. On the hard-rock VCD forms, rocks were graded according to whether they are fresh (<2% by volume alteration products) or have slight (2%-10%), moderate (10%-40%), high (40%-80%), very high (80%-95%), or complete (95%-100%) alteration. Alteration and vein core description logs on a piece-by-piece scale were tabulated to provide a consistent characterization of the rocks and to quantify the different alteration types (see the "Core Descriptions" contents list). Descriptions are based mostly on hand-specimen observations, and specific secondary minerals are not generally distinguished, except where crystal morphology allows unequivocal identification. Where additional mineralogical evidence is available from either thin-section descriptions and/or X-ray diffractograms, these identifications were integrated into the alteration and vein logs and the VCDs. Table T3 provides a list of abbreviations used in the alteration and vein logs.
We recorded the following information in the logs:
1. The alteration log (e.g., Table T4) was used to record the bulk-rock alteration. Each entry records the igneous unit; identifiers for the core, section, piece, subpiece; the length of each piece; and the depth below seafloor of the top of each piece. Visual estimates of the alteration type (as represented by wet rock color and calibrated by thin-section observations), the abundance (in percent), size (in millimeters), mineral fillings of vesicles, and the proportion of altered groundmass and phenocrysts with the primary and secondary minerals are documented for each piece. A column for comments is included.
2. The igneous core description log (e.g., Table T1) was used to record the presence, location, width, and mineral content of veins observed on the cut surface of the cores. Each entry records the igneous unit and the identifiers for the core, section, piece, and subpiece. For each vein the location of the top and bottom of the feature is recorded, and the mineral fillings, vein width (in millimeters), presence or absence of a related alteration halo, and the half width (in millimeters) of the halo are recorded. Data recorded for breccias include percentages of cement and clasts, and the percentages of secondary minerals and sediments present. A column for comments is included, where crosscutting relationships between veins are recorded.