Chemical composition and fluxes of deep sea suspended matter within and over the 9°50'N hydrothermal field, EPR

Results of geochemical studies of suspended matter from the water mass over the hydrothermal field at 9°50'N on the East Pacific Rise are reported. The suspended matter was sampled in background waters, in the buoyant plume, and in the near-bottom waters. Contents of Si, Al, P, Corg, Fe, Mn, Cu, Zn, Ni, Co, As, Cr, Cd, Pb, Ag, and Hg were determined. No definite correlations were found between the elements in the background waters. Many of the chemical elements correlated with Fe and associated with its oxyhydroxides in the buoyant plume. In the near-bottom waters trace elements are associated with Fe, Zn, and Cu (probably, with their sulfides formed during mixing of hydrothermal fluids with seawater). Chemical composition of sediment matter precipitated in a sediment trap was similar to the near-bottom suspended matter.

Contents of radioactive elements, main chemical composition, and sedimentation rates of bottom sediments from some stations in the Southeast Pacific

Gamma-spectrometric analysis was used for six sediment cores from the area occupied by metalliferous sediments in the Southeast Pacific. In five of these cores vertical distribution curves of 230Th enabled positions of equilibrium points to be determined and sediments to be dated. The ionium curve was normalized for one core. Vertical distribution of 230Th in metalliferous sediments resembles its distribution in normal ocean-floor sediments beyond the area of influence of active ridges. Sedimentation rates lay within the range 0.7-12.3 mm/ky.

Mineral composition, major element oxides and trace element concentration of sediments from ODP Leg 180 sites

Middle Miocene to Holocene fine-grained argillaceous sediments (clays, claystones/muds, and mudstones), which volumetrically dominated the sediment recovery in the Woodlark Basin during Leg 180, were chemically analyzed for major elements, trace elements, and some rare earth elements by X-ray fluorescence. Selected samples also underwent X-ray diffraction (XRD) analysis for mineral determination. The results shed light on sediment provenance when combined with shipboard sediment descriptions, smear slide study, and XRD. The oldest sediments recovered (Site 1108) of middle-late Miocene age include volcanogenic muds with distinctive high MgO and K2O, indicative of a relatively basic calc-alkaline source related to an inferred Miocene forearc succession. The forearc basement, composed of diabase and basalt, was locally exposed (Site 1109) and eroded in the late Miocene (<5.4-9.93 Ma), giving rise to fluvial conglomerates (Sites 1109, 1115, and 1118). Chemically distinctive fine-grained claystones and siltstones (with relatively high Ti, low K) are compatible with derivation from tropically weathered basic igneous rocks, correlated with the Paleogene Papuan ophiolite. Overlying latest Miocene-Pleistocene fine-grained sediments throughout the Woodlark Basin were partly derived from calc-alkaline volcanic sources. However, relatively high abundances of Al2O3 and related element oxides (K2O and Na2O) and trace elements (e.g., Rb and Y) reflect an additional terrigenous input throughout the basin, correlated with pelitic metamorphic rocks exposed on Papua New Guinea and adjacent areas. In addition, sporadic high abundances of Cr and Ni, some other trace metals, and related minerals (talc, crysotile, and chlorite) reflect input from an ophiolitic terrain dominated by ultramafic rocks, correlated with the Paleogene Papuan ophiolite. The source areas possibly included serpentinized ultramafic ophiolitic rocks exposed in the Papua New Guinea interior highlands. Chemical evidence further indicates that fine-grained terrigenous sediment reached the Woodlark Basin throughout its entire late Miocene-Holocene history. Distinctive high-K volcanogenic muds rich in tephra and volcanic ash layers that appear at <2.3 Ma (Sites 1109 and 1115) are indicative of high-K calc-alkaline volcanic centers, possibly located in the Dawson Strait, Moresby Strait, or Dobu Seamount area. Chemical diagenesis of fine-grained sediments within the Woodlark Basin is reflected in clay neomorphism and localized formation of minerals including dolomite, ankerite, and zeolite but has had little effect on the bulk chemical composition of most samples.

Chemical composition of manganese nodules from the Southern Pacific

Deep sea manganese nodules from the Southern Ocean have been studied using chemical analysis, X-ray diffraction, optical mineragraphic and electron probe microanalysis techniques. The nodules were lower in manganese, iron and associated elements than the average grade of manganese nodules from other localities. A number of chemical relationships have been observed. Nickel, copper, cobalt, barium, zinc, molybdenum, strontium, sulphur and phosphorus are associated with the manganese rich phases and titanium with the iron rich phases. X-ray diffraction analysis and electron probe microanalysis results indicate that the manganese phases are similar to the disordered delta-MnO2 and "manganite" phases reported by other workers.

Chemical composition of hydrogarnet and celadonite from ODP Hole 206-1256D

Mid-ocean-ridge basalts recovered from Hole 1256D during Ocean Drilling Program Leg 206 exhibit the effects of various low-temperature (<100°C) alteration processes, including the formation of black or dark green alteration halos adjacent to celadonite-bearing veins. In several samples from the deepest basalts, a Ti-rich hydrogarnet occurs. To our knowledge, such a mineral has never been reported in the oceanic crust. This report presents a brief description and microprobe analyses of this hydrogarnet and associated celadonite. More detailed characterizations of this mineral and a description of its relationship to other secondary minerals will be undertaken in a future study, in an attempt to determine the mineral's formation conditions and its place in the general alteration history of the Hole 1256D basalts.