We used VCD forms to document each section of the igneous rock cores. The left column on the form, adjacent to the core photograph, is a graphical representation of the archive half. A horizontal line across the entire width of the column denotes a plastic spacer. Oriented pieces are indicated on the form by an upward-pointing arrow in the column to the right. Locations of samples selected for shipboard studies are indicated in the column headed "Shipboard studies" with the following notations:
Textural and other features documented in the right-hand column use the following notations:
Terminology for describing vesicle abundance is defined below (see "Rock Names").
After making lithologic descriptions, we subdivided the core into consecutively numbered lithologic units on the basis of changes in structure, brecciation, grain size, vesicle abundance, mineral occurrence and abundance, the presence of sedimentary interbeds, color, and, in some cases, significant changes in drilling rate. Abrupt changes in degree and type of alteration also helped to define some units in massive basalt near the bottom of Hole 1185B. Intercalated sediment horizons were designated as "A" subunits and the underlying volcanic rock as "B" subunits within the same unit. Basaltic breccias or hyaloclastites cemented with carbonate were particularly useful for determining unit boundaries. However, brecciated zones within units were not designated as subunits but simply noted as "brecciated." Although every effort was made to have unit boundaries reflect individual lava packages, the term "unit" should not necessarily be considered synonymous with "lava flow" in this volume.
We assigned provisional rock names based on hand-specimen observations (hand lens and binocular microscope) and later checked them with studies of thin sections. Porphyritic rocks were named by phenocryst type. The term "phenocryst" was used for a crystal that was significantly (typically five times) larger than the average size of the groundmass crystals and generally euhedral in shape. This usage is sensitive to changes in the groundmass grain size (e.g., a single cooling unit could have a moderately phyric aphanitic margin and an aphyric fine-grained interior without any change in the distribution or size of the early-formed crystals). To avoid the problem of describing pillow margins as phyric and cogenetic pillow interiors as aphyric, we based our terminology on the aphanitic margins of cooling units. If aphanitic pillow margins were sparsely olivine-phyric basalt, we described the fine-grained interiors using the same name even though the euhedral olivine phenocrysts in the pillow interiors were similar in size to groundmass plagioclase laths. Many porphyritic basalts recovered during Leg 192 exhibited a range of groundmass crystal sizes, making estimation of phenocryst populations approximate. We used the following descriptors:
We modified these descriptors by including the names of phenocryst phases, in order of decreasing abundance. Thus, a "highly olivine-plagioclase-phyric basalt" contains >10% (by volume) phenocrysts, the dominant phenocryst being olivine, with lesser amounts of plagioclase. The minerals named include all of the phenocryst phases in the rock, as long as the total content >1%. In addition to phenocryst abundance (in volume percent) and size range (in millimeters), we described shape, type and amount of alteration, and made further comments, if appropriate.
Groundmass texture and grain size. Textures are glassy or aphanitic. Grain sizes are fine grained (<1 mm), medium grained (1-5 mm), or coarse grained (>5 mm). We also noted grain size changes within units.
Vesicles. We described vesicles by their abundance, size, and shape (sphericity and angularity). Abundance categories are sparsely vesicular (1-5 vol%), moderately vesicular (>5-20 vol%), and highly vesicular (>20 vol%). Visual estimates of the volume fraction of vesicles were supplemented by observations using a binocular microscope.
Miarolitic cavities. We noted the presence, size, and shape of miarolitic cavities in pillow interiors.
Color name and code. For the dry rock surface, we described color using the Munsell color charts.
Rock structure. Structure is determined by whether the rock is massive, pillowed, hyaloclastic, banded, brecciated, scoriaceous, or tuffaceous. We sought to produce an integrated picture of the style of volcanism and environmental setting of each drill site by identifying features that are diagnostic of specific physical processes. Pillowed sequences were inferred from the presence of glassy margins, groundmass grain-size variations, and vesicle-rich bands. An interval was described as massive if there was no evidence for pillows, even though it may be part of a pillowed sequence. Every effort was made to distinguish brecciated lava from volcaniclastic rocks.
Volcaniclastic rocks contain >60 vol% volcaniclastic grains and <40 vol% biogenic material. This class includes epiclastic rocks (detritus produced by erosion of volcanic rocks by wind or water), pyroclastic deposits (products of explosive magmatism), and hydroclastic rocks (products of granulation by steam [phreatic] explosions and quenching [hyaloclastite and peperite]). For rocks composed of abundant glassy pyroclasts, we followed the classification of Fisher and Schmincke (1984), which uses the names volcanic breccia (clasts >64 mm), lapillistone (>75 vol% lapilli; 2-64 mm), tuff (>75 vol% ash; <2 mm), and lapilli tuff (25-75 vol% lapilli and 25-75 vol% ash). The relative proportions and types of clasts within the volcaniclastic rocks were recorded and clasts were assigned to the following groups: lithic clasts, vitric clasts, discrete crystal fragments, and matrix (<0.1 mm) or cement. The lithic- to vitric-clast proportions were then used to further classify the rocks (e.g., lithic vitric tuff or vitric lithic tuff). In each case, the second qualifier denotes the more abundant component.
Eruptive style. The features observed were tied to physical processes (e.g., explosive eruption or lava flow), the emplacement style of individual units was inferred (e.g., dominantly pillowed or massive), and the environmental setting for the whole sequence at a site was assessed (e.g., subaerial or submarine).
Alteration. We graded the degree of alteration as unaltered (<2 vol% of alteration products), slight (2-10 vol%), moderate (10-40 vol%), high (40-80 vol%), very high (80-95 vol%), or complete (>95 vol%). We also noted changes of alteration through a section or a unit and briefly described vein abundance, width, mineral linings, and fillings. More detailed descriptions of alteration and weathering of igneous units and of veins and fractures can be found in the "Alteration" and "Structural Geology" sections of each site chapter (see also "Alteration" and "Structural Geology").
We examined thin sections from the core intervals noted on the VCD forms to complement and refine our hand-specimen observations. In general, we used the same terminology for thin section descriptions as for the VCDs. Percentages of individual phases were estimated visually, and textural descriptions were reported (see the "Core Descriptions" contents list). The textural terms used are defined by MacKenzie et al. (1982). For some porphyritic basalts, the thin section descriptions and VCDs differ slightly, typically because small plagioclase laths in a rock with seriate texture are visible only in thin section. For example, a rock described in the VCD as olivine-plagioclase-phyric may be plagioclase-olivine-phyric in the thin section description. Similarly, vitric and lithic components may have been estimated incorrectly in volcaniclastic hand samples, and the name assigned may have been different than that determined from a thin section. Where possible, we described at least one thin section per unit.
We selected representative samples of major lithologic units for shipboard ICP-AES analysis. Large whole-rock pieces were cut with a diamond-impregnated saw and ground on a diamond wheel to remove surface contamination. We then washed the samples in an ultrasonic bath containing methanol for ~10 min, followed by three consecutive ~10-min washes in an ultrasonic bath containing deionized water. The samples were dried for ~12 hr in an oven at 110°C, after which ~20 cm3 of each sample was crushed to fragments <1 cm in diameter between two disks of Delrin plastic in a hydraulic press. The chips were ground for ~5 min in a Spex 8510 shatterbox with a tungsten carbide barrel. We weighed the resulting powders on a Scientech balance and ignited them in a furnace at 1100°C for an hour to determine weight loss on ignition (LOI).
We weighed 0.100 ± 0.002-g aliquots of the ignited whole-rock powders and mixed them with 0.4000 ± 0.0004 g of Li metaborate (LiBO2) flux that had been preweighed onshore. We included standard rock powders and full procedural blanks with the unknowns for each sample run.
Mixtures of flux and rock powders were fused in Pt-Au crucibles at 1050°C for 10-12 min in a Bead Sampler NT-2100. Ten microliters of 0.172-mM aqueous lithium bromide (LiBr) solution was added to the mixture before fusion, as an antiwetting agent to prevent the cooled bead from sticking to the crucible. We transferred the cooled beads to 125-mL polypropylene bottles and dissolved them in 50 mL of 2.3-M HNO3 by shaking with a Burrell Wrist Action bottle-shaker for an hour. After digestion of the glass bead, all of the solution was filtered to 0.45 µm into a clean 60-mL wide-mouth polypropylene bottle. Next, 2.5 mL of this solution was transferred to a plastic vial and diluted with 17.5 mL of 2.3-M HNO3 to bring the total volume to 20 mL. The solution-to-sample dilution factor for this procedure is ~4000.
We determined major (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, and P) and trace (Zr, Y, Sr, Ba, Ni, Cr, Sc, and V) element concentrations with the JY2000 ULTRACE ICP-AES. The JY2000 sequentially measures characteristic emission intensities (with wavelengths between ~100 and ~800 nm). ICP-AES protocols for shipboard dissolution and analysis of rock powders were developed by Murray et al. (2000) (see also the "Explanatory Notes" chapter of the Leg 187 Initial Reports volume [Shipboard Scientific Party, 2001]). We refined the analytical procedure for igneous rocks during Leg 192. All major elements were analyzed in Mode 2 instead of Mode 5 (see below for description). The elements analyzed, emission lines used, and specific analytical conditions used during Leg 192 are provided in Table T2. Because of initially poor silica determinations, Si was quantified using three peaks instead of one (for internal verification).
The JY2000 plasma was ignited 30 min before each run to allow the instrument to warm up and stabilize. After the warm-up period, a zero-order search was performed to check the mechanical zero of the diffraction grating. After the zero-order search, the mechanical step positions of emission lines were tuned by automatically searching with a 0.002-nm window across each emission peak using the University of Massachusetts Kilauea basalt laboratory standard K-1919, prepared in 2.3-M HNO3. The only exception is P, which was automatically located by using a single element standard. During the initial setup, we collected an emission profile for each peak, using K-1919, to determine peak-to-background intensities and to set the locations of background points for each element. The JY2000 software uses these background locations to calculate the net intensity for each emission line. We optimized the photomultiplier voltage by automatically adjusting the gain for each element using the standard (BHVO-2, BCR-2, BIR-1, or K-1919) with the highest concentration for that element. During the later part of the leg, the Si peaks were autoattenuated on BHVO-2, even though BCR-2 has a higher Si content, to modify the gain on the Si peaks to increase their intensities. Before each run, we collected a profile of K-1919 to assess the performance of the machine from day to day. A typical sample run lasted ~12-14 hr, depending on the number of samples and replicate analyses.
The parameters for each run are given in Table T2. All ICP-AES data presented in the site chapter reports were acquired using Mode 2 of the JY2000 software, except for Fe, Mg, Mn, Ba, Cr, Sc, V, and Y data, which were acquired in Mode 5. In Mode 5, the intensity at the peak of an emission line is measured and averaged over a given counting interval repeated three times sequentially. Mode 2 fits a Gaussian curve to a variable number of points across a peak and then integrates to determine the area under the curve. We ran each unknown sample at least twice, nonsequentially, in all sample runs.
A typical ICP-AES run includes
Following each sample run, we transferred the raw intensities to a data file; data reduction was completed using a spreadsheet to ensure proper control over standardization and drift correction. Once transferred, we corrected the intensities for all samples for the full procedural blank. Drift correction was then accomplished by linear interpolation between each consecutively run drift-correcting solution, and corrections to the intensities of the samples run between those drift-correcting solutions were made. We calculated the interpolation using the lever rule. Following blank subtraction and drift correction, we calculated concentrations for each sample from the average intensity per unit concentration for the USGS standard BHVO-2, which was analyzed twice during the run. The resulting major element data were used to calculate the CIPW normative composition (Cross et al., 1903) for each sample.
Estimates of accuracy and precision for major and trace element analyses are based on replicate analyses of BHVO-2, BIR-1, and BCR-2, the results of which are presented in Table T3. In general, run-to-run relative precision by ICP-AES was <2% for the major elements. Run-to-run relative precision for trace elements was generally <5%.