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doi:10.2204/iodp.proc.329.102.2011

Lithostratigraphy, igneous petrology, alteration, and structural geology

This section outlines the procedures used to document the composition, texture, and structure of geologic materials recovered during Expedition 329. These procedures included visual core description, smear slide description, digital color imaging, color spectrophotometry, X-ray diffraction (XRD), and inductively coupled plasma–atomic emission spectroscopy (ICP-AES). Because many of the geologic techniques and observations used to analyze sedimentary cores are similar to those used to analyze igneous cores, the methods by which those materials were analyzed are herein presented together. However, as necessary, descriptions of the dissimilar procedures required to characterize the sedimentary and crystalline basement rocks are also provided.

All acquired data were uploaded into the IODP-USIO Laboratory Information Management System (LIMS), and observations were entered using the DESClogik application in Tabular Data Capture mode. Additional details are provided below. A glossary of common geological terms used to describe the basaltic cores is in Table T1.

Core sections available for sedimentary and igneous observation and interpretation included both working and archive halves. Sections dominated by soft sediment were split using a thin wire held in high tension. Pieces of hard rock were split with a diamond-impregnated saw so that important compositional and structural features were preserved in both the archive and working halves. The split surface of the archive half was then assessed for quality (e.g., smearing or surface unevenness) and, if necessary, scraped lightly with a glass slide or spatula. After splitting, the archive half (sediment and basement) was imaged by the SHIL and analyzed for color reflectance and magnetic susceptibility using the SHMSL systems (see “Physical properties”). The archive section half was occasionally reimaged when visibility of sedimentary structures or fabrics improved following treatment of the split core surface.

Following imaging, the archive sections of the sediment core were described for primary features macroscopically. Lithostratigraphic units were characterized by visual inspection, and smear slide samples were used to determine microfossil and sedimentary constituents and abundance to aid in lithologic classification. Core from the basement (basalt) was also described visually and subsequently with the aid of thin sections for primary igneous features, secondary features, and structural geology. All descriptive data were entered into DESClogik (see “Data capture software” for details). Based on preliminary visual descriptions and physical property data, thin section samples and samples for XRD and ICP-AES were extracted from the working-half sections. All descriptions and sample locations were recorded using curated depths and then recorded on standard graphic report forms and documented on VCDs (Fig. F1).

Sediment visual core descriptions

Color and composition

Sediment color was determined qualitatively for core intervals using Munsell Color Charts (Munsell Color Company, Inc., 2000). Visual inspections of the archive section halves using the unaided eye and a low-power (i.e., 10×) hand lens identified compositional elements of the sediment, including concretions and nodules, porcellanites and chert, and ash.

Textures, structures, and sedimentary fabric

When visible at low magnifications, sediment grain size was determined using the Wentworth scale (Wentworth, 1922). Grain size, particle shape, and sorting were also noted; however, these textural attributes required inspection at high magnification and were only performed on smear slides and thin sections (see below).

Sedimentary structures observed in recovered cores included bedding, soft-sediment deformation, bioturbation, and displacive early diagenetic mineral authigenesis. Bed thickness was defined according to McKee and Weir (1953) and included the following units:

• Very thick bedded = >100 cm.
• Thick bedded = 30–100 cm.
• Medium bedded = 10–30 cm.
• Thin bedded = 3–10 cm.
• Very thin bedded = 1–3 cm.
• Laminae = <1 cm.

Samples were microscopically inspected for micro-graded bedding (i.e., graded bedding occurring within laminations) and indications of preferential particle orientations, including lineation and imbrication of elongated detrital and biogenic material.

Syn- to postdepositional disturbances in bedding structures, including burrowing and bioturbation, displacement of beds in the layers associated with metalliferous nodules, and soft-sediment deformation, were also noted. Of these features, the semiquantitative description of bioturbation, deemed “ichnofabrics,” warrants additional discussion. Ichnofabric description analysis included evaluation of the extent of bioturbation and notation of distinctive biogenic structures. To assess the degree of bioturbation semiquantitatively, a modified version of the Droser and Bottjer (1986) ichnofabric index (1–5) scheme was employed as follows:

• 1 = no apparent bioturbation.
• 2 = slight bioturbation (1%–30% of visible sectioned core half).
• 3 = moderate bioturbation (30%–60% of visible sectioned core half).
• 4 = heavy bioturbation (60%–90% of visible sectioned core half).
• 5 = complete bioturbation (no depositional structure remaining).

These indexes are illustrated using the numerical scale in the ichnofabric column of the core description sheets. It is important to note that the complete mixing of sediment by bioturbating organisms produces homogeneous sediment with an appearance similar to nonbioturbated sediment resulting from the deposition of material of homogeneous color and grain size. Therefore, a bioturbation scale cannot be applied to homogeneous sediment with confidence and would consequently fall into ichnofabric index 1, no apparent bioturbation.

Induration

The induration of sediment was described using a simple tripartite scale of poorly, moderately, and well-indurated classes. Each interval was assigned to one of these classes based on the ease or difficulty of inserting instruments or the ease or difficulty of obtaining samples of the material for other analyses prior to the lithologic description of the cores.

Lithologic classification scheme for sediments

The lithologic classification scheme employed during Expedition 329 conforms to the Ocean Drilling Program (ODP) sediment classification scheme of Mazzullo et al. (1988). Based on past sampling of sediments in the southern and southwestern Pacific Ocean (e.g., Shipboard Scientific Party, 1986, 1987; Graham et al., 1997), shipboard sedimentologists used only those methods listed in Mazzullo et al. (1988) that address pelagic sediments (i.e., sediments containing >60% particles finer than 63 µm). Consequently, lithologic names used during this expedition are based on (1) composition and (2) degree of consolidation of recovered sediments (Fig. F2).

Principal lithologic names used during Expedition 329 include clay, ooze, porcellanite, and chert. Although the principal name “clay” is not directly associated with pelagic sediments in Mazzullo et al.’s (1988) work, sedimentologists aboard the JOIDES Resolution use the term frequently to describe fine-grained sediments deposited in open-marine depositional environments. Our use of the term denotes the presence of clay-sized particles (i.e., <2 µm) and not specific clay-group minerals (e.g., illite, montmorillonite, or polygorskite). When calcareous or siliceous components (e.g., coccoliths or radiolarians) are dominant in sediment cores and the material is poorly consolidated, the term “ooze” was assigned to the sediment. “Porcellanite” describes fine-grained, well-indurated sediment with dull luster and bulk densities that are between clays/oozes and chert. “Chert” is used to describe compact, glassy, indurated siliceous sediments.

Principal names were modified by terms that describe compositional, textural, and structural attributes of the sediment. When sedimentary units contain a mixture of constituents, the principal name is preceded by major modifiers (in order of increasing abundance) that refer to components that make up >25% of the sediment. Examples of principal names found in the South Pacific Gyre that are modified by their compositional constituency include metalliferous pelagic clay (Shipboard Scientific Party, 1987) and siliceous microfossil ooze (Graham et al., 1997). Minor components that represent between 10% and 25% of the sediment follow the principal name in order of increasing abundance. Sedimentologists aboard Deep Sea Drilling Project (DSDP) Leg 91 demonstrated this method of adapting Mazzulo et al.’s (1988) naming schema to southwestern Pacific sediments. Their detailed sediment descriptions contain modifiers such as metalliferous clay with chert and metalliferous pelagic clay with zeolites (Shipboard Scientific Party, 1987).

Consolidation was used to further refine principal names. Oozes exist on a continuum that includes “-ites.” For example, sediments dominated by radiolarians and easily deformed by the application of light pressure are called radiolarian oozes, whereas those that are hard and compact are called radiolarites. The suffix “-stone” is used similarly and is applied to clays and silts. The names porcellanite and chert carry with them connotations that the sediment is well indurated.

Lithology, structures, and coring disturbances were recorded on standard graphic reports using a common set of symbols. A summary of the symbols and their definitions is provided in Figure F3.

Smear slide analysis

From successive sedimentary intervals with distinct color and textural characteristics, toothpick samples were taken and used to create smear slides according to the method outlined in Mazzullo et al. (1988). Individual slides were fixed by ultraviolet curing using Norland optical adhesive immersion medium. Tables summarizing data from smear slides are available (see smear slides for each site in “Core descriptions”). These tables include information about the sample location, whether the sample represents a dominant (D) or a minor (M) lithology in the core, and the visually estimated percentage ranges of all identified components. Compositional elements noted under microscopic inspection of the slides include detrital particles (i.e., clay, feldspar, quartz, lithic fragments, and vitric particles), biogenic particles (i.e., radiolarians, ichthyoliths, discoasters, foraminifers, and coccolithophorids), and authigenic or indeterminate particles (i.e., red-brown to yellow-brown semiopaque material and metalliferous micronodules). In accord with the objectives of Expedition 329, smear slides were examined closely for zeolites and Fe-Mn authigenic minerals.

As with the inspections of prepared thin sections, particle size, shape, and sorting were observed in the smear slides and documented accordingly.

Sedimentary thin sections

Thin sections were created on board to study the composition and texture of the >2 µm particles in the pelagic clays, oozes, and unusual lithologies (e.g., concretions and nodules) encountered. Thin sections were also created when intervals of interest were too well indurated to permit smear slide sampling and analysis. Thin sections generally provide less biased samples of whole rock than smear slides, and they allow for more accurate identification of the minerals present. However, the limitation of selecting samples from sorted samples and indurated sediments like concretions and nodules implies that there was some bias in the types of lithology sampled, including

• Routinely excluding >60% of the recovered sediments from study under high magnification,

• Sampling concretions in one lithology over unlithified sediments from another, and

• Recovering concreted horizons at the expense of other sediments.

Lithologies were defined according to the main lithologic classification scheme described above (Fig. F2). Additionally, a thin section sample worksheet was completed before the results were added to the database.

Hard rock visual core descriptions

During the description process, lithologic units and subunits were defined by contacts, chilled margins, variations in occurrence and abundance of primary mineralogy (e.g., phenocryst abundance), color, grain size, and structural or textural variations (e.g., Fig. F1B). Where possible, a geologic indicator was used to define a unit boundary (e.g., volcanic cooling units); however, limited recovery resulted in arbitrary boundaries placed where the unit above and below are different. Subunit classification was used in cases where mineralogy remains similar but frequent changes in texture take place. An example of such subunit classification includes frequent glassy margins within a mineralogically similar length of core. The schemes used for visual description of recovered cores are detailed below.

A VCD was created for each section of recovered core. Symbols used on the VCD are shown in Figure F4. Each form describes the following features

• Depth

• Core length scale

• Piece number

• Core image

• Orientation

• Shipboard samples taken

• Lithologic unit

• Veins

• Structure

• Structure measurement

• Phenocrysts

• Groundmass grain size

• Glass

• Alteration

Pieces orientated vertically are indicated with an upward arrow on the VCD form. All shipboard sampling is noted in terms of location and purpose (Fig. F1B). Lithologic units and subunits (increasing in number downhole) are defined by a solid and dashed horizontal line, respectively. Subunits are termed A, B, C, and so on. The structural description on the VCD contains symbols which denote the location and type of feature observed (Fig. F4). The unit summary located on the right includes

• Expedition-Hole-Core

• Unit number

• Rock name

• Summary description

• Pieces

• Contacts

• Color

• Phenocrysts

• Groundmass

• Glass

• Vesicles

• Alteration

• Veins

• Structure

• Physical properties

Igneous petrology

For each unit, the DESClogik program was used to describe groundmass, primary mineralogy, color, vesicles, and igneous contacts. Separate lithologic units within the basaltic core sections were defined by the type and abundance of phenocrysts, as well as the nature of igneous contacts and margins. The most abundant phenocryst type is named last during any written description. For example, olivine is the most abundant mineral in a plagioclase-olivine phyric basalt. Definition limits are defined as follows:

• Aphyric = <1% phenocrysts.
• Sparsely phyric = 1%–5% phenocrysts.
• Moderately phyric = 5%–10% phenocrysts.
• Highly phyric = >10% phenocrysts.

Color was determined using a Munsell color chart on a wet cut rock surface. Wetting of the rock was carried out using tap water and a sponge. Wetting was kept to a minimum because of adsorption of water onto clay minerals (particularly saponite and celadonite) that are present throughout the core.

Groundmass is characterized by grain size with the following standard notation:

• G = glassy.
• cx = cryptocrystalline (<0.1 mm).
• µx = microcrystalline (0.1–0.2 mm).
• fg = fine grained (>0.2–1 mm).
• mg = medium grained (>1–2 mm).
• cg = coarse grained (>2 mm).

Vesicles were recorded as nonvesicular (<1%), sparsely vesicular (1%–5%), moderately vesicular (>5%–20%), or highly vesicular (>20%). Vesicle data are graphically recorded on the VCD using the DESClogik core description software on a subunit level of detail. Within each subunit, relatively high zones of vesicularity (e.g., chilled margins) are described verbally within the VCD.

Breccia was described on the basis of clasts and matrix. Clasts were described in terms of size, shape, sorting, composition, and alteration, and the matrix was described in terms of volume, composition, structure, alteration, and cement by volume and composition. Breccia was defined as

• Bh (hydrothermal breccia that contains secondary matrix),

• Bm (magmatic breccia that contains glass, quench textures, and primary matrix minerals [e.g., hyaloclastites and pillow breccia]), or

• Bc (tectonic breccia in which the matrix is composed of the same material as the host rock [e.g., fault-gouge and cataclasite]).

Igneous units in the recovered basalt cores were defined as pillow basalt, basalt flows, or sheet flows based on the nature of the recovered contacts and margins. Pillow basalt was characterized by the presence of curved margins that are oblique to the vertical axis of the core or by the presence of variolitic texture, curved fractures, or micro- to cryptocrystalline groundmass grain size. Basalt flow chill margins were defined as margins with no structural similarity to pillow margins (e.g., not curved or variolitic), whereas sheet flows were defined by margins that are subhorizontal and increase in grain size toward the center of the flow.

Alteration

Alteration at all sites from which basement was recovered during Expedition 329 was manifested in terms of

• Background alteration, which is pervasive throughout basement;

• Alteration halos;

• Hydrothermal veins;

• Secondary minerals filling vesicles; or

• Hydrothermal breccia and incipient brecciation.

Areas where veining is numerous are described as a vein net, and estimated volumes of mineral contents are given. These alteration types are recorded in separate logs using the DESClogik program and are later combined into an alteration summary on the VCD.

Levels of background alteration, based on rock color and visual calibration by thin section, are defined using the following scale:

• Fresh = <2% alteration.
• Slight = 2%–10% alteration.
• Moderate = >10%–50% alteration.
• High = >50%–95% alteration.
• Complete = >95%–100% alteration.

Glass was also recorded in terms of total fresh and total altered, and the abundance and composition of infilling by secondary minerals was described. The order of infill for vesicles and veins was used, where possible, to ascertain mineral precipitation order. Halos surrounding veins and vesicles were described in terms of size, color, and most abundant secondary mineral(s) present within the halo. Any visible and obvious overprinting of earlier alteration phases was noted. Alteration patches may be spherical, irregular, or elongate; these represent domains of enhanced alteration and were recorded separately with drawings and annotations.

Veins are described using detailed vein logs in the DESClogik software package. The presence, location, width, crosscutting relationships, shape, composition percent, color, and width are recorded. Veins and halos are also recorded in DESClogik. Structural measurements of the veins were recorded in the Structures portion of the VCD and in the DESClogik program.

Hard rock thin sections

Thin sections are made because they allow more accurate description than hand specimens for grain/phenocryst size, mineralogy, abundance, and the nature of secondary mineral types and abundances. Therefore, a suite of thin sections for each site was made to calibrate and build upon our hand-specimen observations of igneous and alteration features. A thin section was made from each igneous unit and from intervals with interesting alteration or igneous features. In addition, thin section description permits us to document glomerocryst types, the presence of phenocrysts within inclusions, and the presence of minor phases that are otherwise not detectable in hand specimen (e.g., spinel, primary oxides, and sulfides). In addition, thin section descriptions are used to determine the timing and method of emplacement in terms of vesicle and void fillings, vein composition, and primary mineral replacement. Information regarding crystal size (in millimeters; minimum, maximum, and average), mineral morphology, and texture was recorded for all primary phases. Where replacement of primary phases took place, the abundance, composition, and textural features were recorded. Phenocryst abundance measurements were carried out by a combination of point counting and visual inspection.

Groundmass texture was defined as

• Heterogranular (different crystal sizes),

• Seriate (continuous range in grain size),

• Porphyritic (increasing presence of phenocrysts), or

• Glomeroporphyritic (containing clusters of phenocrysts).

Groundmass may also be defined as

• Holohyaline (100% glass),

• Hypocrystalline (100% crystals),

• Variolitic (fine, radiating fibers of plagioclase or pyroxene),

• Intergranular (olivine and pyroxene grains between plagioclase laths),

• Intersertal (groundmass fills the interstices between unoriented feldspar laths),

• Ophitic (lath-shaped euhedral crystals of plagioclase, grouped radially or in an irregular mesh, with surrounding or interstitial large anhedral crystals of pyroxene), or

• Subophitic.

Glass definitions are

• Fresh glass (amber in transmitted polarized light and isotropic in transmitted cross-polarized light),

• Dark (darkness is caused by abundant crystallites; interstitial volcanic glass of basaltic composition is termed trachylytic),

• Glass with spherulites (spheroid aggregates of acicular crystals form a nucleus), and

• Altered glass (partially or completely altered to clay minerals).

Flow texture definitions are

• Trachytic (subparallel arrangement of plagioclase laths in the groundmass),

• Pilotaxitic (aligned plagioclase microlites embedded in a matrix of granular and usually smaller clinopyroxene grains), and

• Hyalopilitic (aligned plagioclase microlites with a glassy matrix).

Plagioclase habits (as adopted from Shipboard Scientific Party, 2003b) are

• Cryptocrystalline aggregates of fibrous crystals,

• Comb-shaped or sheaflike plumose crystals,

• Granular–acicular subhedral to anhedral crystals, and

• Prismatic to stubby euhedral to subhedral crystals.

In order to maintain consistency, the same terminology is used for both macroscopic and microscopic descriptions. An example of a thin section description is provided in Figure F1B. Digital photomicrographs of each section, together with a whole-section photograph, complement the descriptions. All thin section observations were recorded into DESClogik and are available in “Core descriptions” and the IODP database.

Structural geology

Structural features were observed and recorded for the basement cores at all three sites from which basement was recovered. To maintain consistency with legacy DSDP/ODP/IODP sites during Expedition 329, we used conventions that were adopted by previous Shipboard Scientific Parties (e.g., Shipboard Scientific Party, 1989, 1992, 1993a, 1993b, 1995, 2003a, 2003b). The working and archive halves were described, with all structures and orientation measurements made on the archive half. Structural features in basement cores recovered during Expedition 329 were summarized on the VCD. Important structural features or structurally complex zones were recorded on a separate structural description form. All structural data were entered into the DESClogik program.

Structural features were defined according to brittle deformation parameters. These include joints, shear veins, faults, and breccia, which were determined according to the presence of fractures, filling phases, and evidence of shear displacement. Terminology is consistent with that of previous ODP/IODP legs and expeditions, such as ODP Leg 118 and IODP Expeditions 309 and 327 (Shipboard Science Party, 1989; Teagle, Alt, Umino, Miyashita, Banerjee, Wilson, and the Expedition 309/312 Scientists, 2006; Fisher, Tsuji, Petronotis, and the Expedition 327 Scientists, 2011). This terminology also follows that of Ramsay and Huber (1987), Twiss and Moores (1992), Davis (1984), and Passchier and Trouw (1996). Brittle deformation features recorded include the following:

• f = fracture (brittle failure ± displacement).
• J = joint (fracture with no shear displacement).
• V = vein (fracture filled with secondary minerals).
• Sv = shear vein (shear-displaced fracture filled with secondary minerals).
• F = fault (fracture with shear displacement).
• mF = microfault (fault with <1 mm of deformation).
• B = breccia (divided into Bm, Bh, and Bc as described in “Igneous petrology”).

No plastic-brittle structures were identified during Expedition 329; therefore, we do not include these features in these notes. The term “vein” is used for all fractures that have secondary mineral fill regardless of their width (note that Ramsay and Huber [1987] define veins as having >1 mm fill). Structural features that do not conform to the categories outlined above are detailed with comments and drawings.

Structural features were recorded in centimeters from the top of each section. Depth of the structure was recorded as distance from the top of the section to the top and bottom of the feature. Structures are measured according to the IODP core reference frame as used in ODP Leg 206 and Expeditions 309 and 327 (Shipboard Scientific Party, 2003b; Teagle, Alt, Umino, Miyashita, Banerjee, Wilson, and the Expedition 309/312 Scientists, 2006; Fisher, Tsuji, Petronotis, and the Expedition 327 Scientists, 2011). The plane normal to the borehole axis is given as the horizontal plane. A 360° net with a pseudosouth (180°) pointing into the archive half and a pseudonorth (0°) pointing out of the archive half and perpendicular to the cut surface of the core is used on this plane. The cut surface of the core, or cut face, is therefore a vertical plane striking 90°–270°. The dip direction of planar features measured across the cut face was measured with 0° down the vertical axis of the core, and the dip was measured using the right-hand rule (Fig. F5). Measured orientations were rotated to the IODP reference frame using MATLAB.

Drilling disturbance

Deformation and disturbance of sediment that clearly resulted from the coring process were noted and documented. The degree of drilling disturbance is described for soft and firm sediments using the categories listed below (blank regions indicate the absence of drilling disturbance):

• Slightly disturbed: bedding contacts are slightly bent or drilling biscuits are unrotated and in stratigraphic order.

• Moderately disturbed: bedding contacts are extremely bowed or sediment biscuits are rotated but likely still in stratigraphic order.

• Very disturbed: bedding is completely disturbed or sediment biscuits are likely rotated and no longer in stratigraphic order.

• Drilling slurry or flow-in: intervals are water saturated or have otherwise lost all aspects of original bedding resulting from flow-in or the presence of drilling slurry.

The degree of fracturing in indurated sediments is categorized as follows:

• Slightly fractured: core pieces are in place and contain little drilling slurry or breccia.

• Moderately fragmented: core pieces are in place or partly displaced, but the original orientation is preserved or recognizable (drilling slurry may surround fragments).

• Highly fragmented: pieces are from the cored interval and probably in the correct stratigraphic sequence (although they may not represent the entire section), but the original orientation is completely lost.

• Drilling breccia: core pieces are no longer in their original orientation or stratigraphic position and may have mixed with drilling slurry.

Data capture software

DESClogik data capture

Information from macroscopic description of each core was recorded using IODP’s DESCinfo hierarchical database and DESClogik, a software application for capturing data derived from shipboard laboratories and downhole logging operations (Expedition 320T Scientists, 2009). Geological core descriptions and interpretive information were entered into DESClogik through the customized spreadsheet application, Tabular Data Capture. Prior to core description, shipboard sedimentologists and igneous petrologists populated the Tabular Data Capture tabs and columns with terms that represent a range of sedimentary and igneous characteristics as well as drilling-related features that they expected to encounter in recovered cores. During core descriptions, scientists accessed this information through computer workstations suspended over the split core display tables and entered results into DESClogik accordingly.

Standard graphic report

The LIMS2Excel application was used to extract data in a format that could be used to plot descriptive as well as instrumental data in core graphic summaries using a commercial program (Strater, Golden Software). The Strater program was then used to produce a simplified, annotated, publication-quality VCD for each core.

Beginning with the leftmost column, each VCD displays the depth scale (meters below seafloor), core length, and section information. A fourth column displays the concatenated section half images adjacent to a graphic lithology column in which core lithologies are represented by the graphic patterns illustrated in Figure F3. Subsequent columns provide information on drilling disturbance, sedimentary structures, lithologic accessories, ichnofabric, and shipboard samples. Additional columns present age data (if possible); plots of core logging data such as magnetic susceptibility, natural gamma radiation (NGR), and color measurements (see “Physical properties”); and color determined using the Munsell soil color chart.

X-ray diffraction

XRD was used to (1) check the observations of the smear slide analysis and (2) identify small-scale compositional changes, potential authigenic minerals, principal mineral types in basalts, and the material filling fractures and vesicles in the basalt. For sediment and poorly consolidated samples, each sample was freeze-dried, ground, and mounted with a random orientation in an aluminum sample holder. For igneous samples, fragments and/or scrapings were crushed to successively finer particle sizes using shipboard crushers, mortars and pestles, and mills. For XRD measurements, a Bruker D4 Endeavor XRD with a CuKα source (40 kV and 35 mA) and Ni filter was used. The shipboard instrument also features a Vantec-1 detector. Peak intensities were converted to values appropriate for a fixed slit width. The goniometry scan was performed from 2° to 40°2θ at a scan rate of 1.2°/min (step = 0.01°; count time = 0.5 s). Common minerals were identified based on their peak position and relative intensities in the diffractogram using an interactive software package (Bruker AXS Diffrac.EVA, version 1.2).

Inductively coupled plasma–atomic emission spectrometry

During Expedition 329, a representative suite of rock samples was analyzed for major and trace elements using ICP-AES. Targets of study included distinct basaltic units as well as alteration zones in basalt. The analyses focused on assessment of major (i.e., Al, Ca, Fe, K, Mg, Mn, Na, P, Si, and Ti) and trace (i.e., Ba, Cr, Ni, Sc, Sr, V, Y, and Zr) elements.

Sample preparation

Samples were taken at each site where basement was rotary cored (Sites U1365, U1367, and U1368) to determine primary igneous chemistry and alteration characteristics, with preference to alteration phases. These samples (~8 cm³) were cut using a diamond saw blade and ground on a diamond-impregnated disk to remove contamination from cutting and drilling. The samples were placed individually into beakers containing trace metal–grade methanol and ultrasonically washed for 15 min. The methanol was decanted and the samples were washed twice in 18.2 MΩ deionized water in an ultrasonic bath for 10 min. The clean pieces were dried for 10–12 h at 110°C.

The clean, dry whole-rock samples were crushed to <1 cm chips between two disks of Delrin plastic in a hydraulic press. The chips were ground to a fine powder using tungsten carbide in a SPEX 8510 shatterbox. Once this powder was formed, the powder was prepared for ICP-AES. One gram of the resulting powder was ignited at 1025°C for 4 h. A 100 ± 0.5 mg aliquot of ignited residue was mixed with 400 ± 0.5 mg of lithium metaborate (LiBO₂) flux. The combined sample powder and flux were then fused in Pt-Au crucibles at 1050°C for 5 min in a Bead Sampler NT-2100. After cooling, the resulting glass bead was dissolved in 50 mL of 2.3 M nitric acid and shaken for 1 h. The resulting solution was filtered through 0.45 µm glass filters. A 2.5 mL subsample of this solution was isolated and diluted with 17.5 mL of 2.3 M HNO₃. Thus, the volume of solution used for analysis was 20 mL and the original rock sample was diluted by a factor of 4000.

Analyses and data correction

Concentrations of major and trace elements were determined using a Teledyne Leeman Labs Prodigy ICP-AES instrument. To facilitate steady operation, the plasma was operated for 30 min prior to analyses and a peak profile alignment was performed. During the initial setup, standard BAS-140 was used to select an emission profile for each peak to determine peak-to-background intensities and set the locations of background levels for each element. The Prodigy software uses these background locations to calculate the net intensity for each emission line. Photomultiplier voltage was optimized by automatically adjusting the gain for each element using the BAS-140 standard. ICP-AES results presented in the site chapters of this volume were attained by integrating the area under the curves for wavelength versus response plots.

Each sample was analyzed three times from the same dilute solution (i.e., in triplicate) within a given sample run. For elements measured at two wavelengths, we either used the wavelength giving the better calibration line in a given run or, if the calibration lines for both wavelengths were of similar quality, we used the data for both and reported the average concentration. A typical ICP-AES run (Table T2) included eight certified rock standards that were analyzed at the beginning of each run and again after every 20 samples. As many as 15 unknown samples were analyzed in triplicate. A 10% HNO₃ wash solution was run for 60 s before and after each analysis. A drift-correcting standard (BHVO-2) was analyzed twice each time the instrument was operated. Blank solutions were analyzed at the beginning and end of each run and at an intermediate point in runs of 12–15 samples. In addition, two “check” standards were run in triplicate as unknowns. Each standard was analyzed in triplicate at least twice during a run.

Following each sample run, the measured raw intensity values were corrected for instrument drift and procedural blank. Drift correction was applied to each element by linear interpolation between the drift-monitoring solutions run every fifth analysis. Following drift correction and blank subtraction, a calibration line for each element was calculated using the results for the certified rock standards. Element concentrations in the samples were then calculated from the relevant calibration lines. Estimates of accuracy and precision for major and trace element analyses were based on replicate analyses of international standards, the results of which are present in Table T3. Internal precision, from which error bars are derived, is reported from an unknown (Sample 329-U1367F-2R-3, 60–63 cm) that was run in triplicate (Table T4).

Digital color imaging

The SHIL captures continuous high-resolution images of section-half surfaces for analysis, description, and reporting of recovered core material. The system was custom built for the JOIDES Resolution by IODP-USIO. Adhering to the basic principles of professional photography, the SHIL creates highly detailed images by orchestrating the proper combination of good lighting, high-quality camera and lens, and appropriately positioned camera and object relative to each other. Six light-emitting diodes containing 12 separate emitters are arranged in two fanlike banks to create lighting for the SHIL. This configuration forms a homogeneous light beam at distances >75 mm from the face of the lens. At the desired target distance of 100 mm, the optimal width of illumination is 6 mm. The SHIL image capture system consists of a commercial line-scan camera fitted with a Nikon 60 mm f/2.8 microlens. The camera lens is mounted perpendicular to the section half on a firm, smooth traveling track that is motion controlled through an integrated computer interface. When held still, producing the SHIL’s maximum resolution, as much as to 20 µm of a section half can be resolved. In operation, scanning a section half at 10.5 cm/s produces an image with a resolution of 100 µm per scan line. The integrated software that operates the SHIL also promotes straightforward capture and editing of images, as well as saving and transfer of section-half images to the shipboard database.

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