Rare earth element composition and mass accumulation rates at DSDP Hole 92-598

Site 598 sediments were analyzed to determine the factors controlling the rare earth element (REE) geochemistry of the hydrothermal component. Site 598 provides an ideal sample suite for this purpose. Samples are lithologically "simple," primarily consisting of a hydrothermal component and biogenous carbonates. Also, the composition of the hydrothermal component appears unchanged through time or space, and the site appears to have undergone minimal diagenetic alteration. The shale-normalized REE patterns are similar to the pattern of seawater, varying only in absolute REE content. The REE content increases with distance from the paleorise crest and exhibits a pronounced increase in sediments deposited below the paleolysocline. Results presented are consistent with the following model: the source mechanism for the REE content of hydrothermal sediments is scavenging by Fe oxyhydroxides from seawater. With prolonged exposure to seawater resulting from transport far from the injection point and/or long residence at the seawatersediment interface, the absolute REE content of hydrothermal sediments increases and becomes more like seawater.

Major and rare earth element contents and their speciations in ferruginous nodules and host sediments from the Barents Sea

Contents of Fe, Mn, Al, P, and rare earth elements (REE) in ferruginous nodules and host sediments of the eastern Barents Sea were studied. A direct Fe-P correlation in reactive components of the sediments and nodules was found. The nodules were shown to be formed through Fe(II) oxidation in the surface layer of sediments and cementation of terrigenous fraction of sediments by Fe(III) oxyhydroxides. The latter accumulate phosphorus due to processes of sorption - co-precipitation, by forming Fe(III) hydrophosphates. REE composition in the sediments and nodules normalized to NASC contents is characterized by increased proportion of light REE that may be caused by regional features of their sources. Due to significant share of terrigenous matter in the Fe nodules (up to 65% for Nd), REE composition of bulk samples is similar to that of host sediments. A negative cerium anomaly in composition of reactive REE may result from REE sorption from seawater. REE bulk composition of a ferruginous crust is closer to that of seawater than one of the ferruginous nodules from the sediments because of essentially lower content of diluent terrigenous matter.

Major, trace and rare earth element concentration of ODP Site 210-1277 basalts, Newfoundland margin

Drilling of the distal Newfoundland margin at Ocean Drilling Program Site 1277 recovered part of the transition between exhumed sub-continental mantle lithosphere and normal mid-ocean-ridge basalt (N-MORB) volcanism perhaps related to the initiation of seafloor spreading, which may have occurred near the Aptian/Albian boundary, coincident with the final separation of subcontinental mantle lithosphere. Subcontinental mantle lithosphere was recovered near the crest of a basement high, the Mauzy Ridge. This ridge lies near magnetic Anomaly M1 and is inferred to be of Barremian age. The recovered section is dominated by serpentinized spinel harzburgite, with subordinate dunite and minor gabbroic intrusives, and it includes inferred high-temperature ductile shear zones. The serpentinite is capped by foliated gabbro cataclasite that is interpreted as the product of a major seafloor extensional detachment. The serpentinized harzburgite beneath is highly depleted subcontinental mantle lithosphere that was exhumed to create new seafloor within the ocean-continent transition zone. After inferred removal of overlying brittle crust, the detachment was eroded, producing multiple mass flows that were dominated by clasts of serpentinite and gabbro in a lithoclastic and calcareous matrix. Basaltic lavas were erupted spasmodically, mainly as sheet flows, with subordinate lava breccia, hyaloclastite, and possible pillow lava. The sedimentary-volcanic succession and the exhumed mantle lithosphere experienced later high-angle extensional fracturing and probably faulting. Extensional fissures opened incrementally and were filled with silt-sized carbonate, basalt-derived clastic sediment, and hyaloclastite, forming neptunian dykes and geopetal structures. Chemical analysis of representative basalts for major elements and trace elements were made using a high-precision, high-accuracy X-ray fluorescence method (utilizing increased count times) and by whole-rock inductively coupled plasma-mass spectrometry that yielded additional evidence for rare earth elements. The analyses indicate N-MORB to slightly enriched compositions. The MORB was produced by relatively high degree melting of a fertile mantle source that differed strongly from the cored serpentinized peridotites. The basalts exhibit a distinct negative Nb anomaly on MORB-normalized plots that can be explained by prior extraction of melt from upper mantle that had previously been affected by subduction, possibly during closure of the Iapetus or Rheic oceans. In the proposed interpretation, mantle lithosphere was exhumed to the seafloor and experienced mass wasting to form serpentinite-rich mass flows. The interbedded MORB records the beginning of a transition to "normal" seafloor spreading. This interpretation takes into account drilling results from the Iberia-Galicia margin and the Jurassic Alps-Apennines.