In this report, I present trace element data for samples of basement core collected during Ocean Drilling Program Leg 206 in Holes 1256C and 1256D. These samples represent a subset of a suite of samples collected and shared by a group of shipboard scientists ("pool" samples), which were powdered at Southampton Oceanography Centre and then split and distributed for analysis. The data array for the suite will consist of a wide range of geochemical analyses on the same powders, ensuring that the different analyses will be directly comparable. The samples are from the igneous basement and represent a range of alteration from background level (slightly altered) to vein-related alteration (halos) to highly altered; the single exception is Sample 206-1256D-4R-1, 13–20 cm, which is a chert from the top of the first rotary core in basement. This sample likely represents a piece of chert from within the sedimentary section immediately above the basement that fell into the hole and was sampled during initial basement coring. All of these samples have also been analyzed for lithium and oxygen isotopic composition, and these data will be discussed along with the trace element data elsewhere (K.M. Cooper et al., unpubl. data). Other geochemical data on the same sample suite are in progress, including strontium isotopes and major elements (R. Coggan and D.A.H. Teagle), chlorine isotopes (M. Bonifacie), nitrogen isotopes (Busigny et al., 2005), and sulfur isotopes and oxygen-isotope analyses of vein minerals (J.C. Alt).
The igneous stratigraphy and shipboard geochemistry of Holes 1256C and 1256D have been described in detail in the Leg 206 Initial Reports volume (Shipboard Scientific Party, 2003). Briefly, the section in Hole 1256C consists of 27 m of thin basaltic sheet flows a few tens of centimeters to ~3 m thick, which overlie a 32-m-thick massive ponded flow and an additional ~4 m of thin sheet flows. Coring in Hole 1256D began within a massive flow (Unit 1256D-1), which correlates with the massive flow in Hole 1256C but is more than twice as thick (minimum thickness of 74.2 m). The remainder of the 500 m of section cored in Hole 1256D consists mostly of thin sheet flows (tens of centimeters thick to ~3 m thick) and uncommon massive flows 3.5–16 m thick, with a few intervals of pillow basalt and hyaloclastite recovered. The threshold of 3 m between thin sheet flows and massive flows was a standard agreed to by the Leg 206 shipboard science party and is used in other publications (Shipboard Scientific Party, 2003). Igneous rocks from throughout Holes 1256C and 1256D are slightly to moderately altered, where olivine is replaced and pore spaces filled by saponite and minor pyrite, reflecting low-temperature seawater interaction at low seawater/rock ratios (Shipboard Scientific Party, 2003). One interval of basalt in Core 206-1256D-57R is intensively altered to an assemblage of blue-green phyllosilicate (celadonite?), colorless phyllosilicate, and iron oxyhydroxides and is 80%–90% altered (Shipboard Scientific Party, 2003). Shipboard chemical analyses revealed high Si, Al, Fe, Mg, K, P, Cr, and Ni and low Ca and Mn when normalized to Ti (Shipboard Scientific Party, 2003). Locations for pool samples were chosen in order to cover a range of alteration in the core; in each lithologic unit defined in the igneous basement, we chose at least one sample of the least-altered rock (background sample) for comparison with samples that represented higher degrees of alteration (e.g., halos, patchy alteration, hyaloclastites, or the intensively altered interval). I also analyzed the Leg 206 interlaboratory standard prepared on board the ship (BAS-206).