DISCUSSION OF SAMPLING STRATEGYCommunal and Composite Geochemical Samples
Fresh glass is important for determining the chemical composition of magmas because it is unaffected by mineral accumulation and posteruption alteration. Glass is also usually chemically homogenous so that chemical analyses made with microbeam techniques are applicable to the bulk sample. Fresh glass from flow and pillow margins and from hyaloclastites were identified under the binocular microscope during the routine description of the cores. The locations of most of the pieces that contain glass are given in Table 4. A subset of ~50 glasses was sampled on board ship for a coordinated effort to obtain a wide variety of analyses on the same samples (Table 4). Glass chips and thin sections will be analyzed first by electron microprobe for 10 major elements (Si, Al, Fe, Mg, Ca, Na, K, P, Ti, and Mn). This will determine how many different compositions are present in the cores. Based on the major element analyses, selected thin sections and chips will be distributed among the other investigators who wish to conduct laser and ion beam microanalyses and water measurements by Fourier transform infrared spectroscopy. Also, based on the major elements, samples will be distributed for mass spectroscopy for heavy isotopes, halogens, Li, and B. Some samples were distributed on board the ship for magnetic intensity measurements, and additional samples will be distributed after thin-section billets are cut from the samples. Thin sections examined for evidence of microbial activity (Fisk) will also be measured for the relative chemical and microbial alteration (Staudigel).
Analysis of Logs
An important aspect of the construction of a reference site involves integrating the geophysical and chemical logs with the core information to create a complete crustal section. In the case of the basement logging at Site 801, of particular interest is determining the relative proportions of interflow material, thick flows, and thin sheet flows or pillows. The strategy involves an integration of the FMS logs, geochemical data, and core lithology data for the Hole 801C basement. The porosity-sensitive logs (resistivity, velocity, density, and neutron porosity) will be studied for Hole 801C to characterize very old oceanic crust formed at a very fast spreading rate. In addition, a modeling study of the temperature log in Hole 801C will be undertaken to further constrain the porosity/permeability of basement.
Given the interest in the magnetic reversal history of Jurassic ocean crust, the magnetic logs will be used to establish the magnetic polarity stratigraphy of Hole 801C basement from the log data and to construct a model of the surface magnetic field using the various polarity intervals as input.
Paleomagnetic and Paleointensity Analysis
A number of the fresh glass samples from flow and pillow margins and from hyaloclastites were distributed on board the ship for magnetic intensity measurements.
The majority of the microbiology data will be generated in shore-based studies. The major efforts will be to determine community composition by DNA extraction, in situ hybridization, characterization of microbes isolated from enrichment cultures, and culturing of microbes from samples maintained at in situ pressure. Culturing at high pressure and at 1 atm will be done at different shore-based laboratories. These studies will be coordinated with additional study of igneous rocks, veins, and sediment from which biological samples were collected. Rock samples will be examined by scanning electron microscope for microbes and microbial alteration textures. The amount of microbial vs. chemical alteration will be measured in thin sections, and the types and compositions of secondary minerals will be determined by electron microprobe. The lithology of sediments used for cultures and ATP measurements will be determined from smear slides.
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