Solubilities of some hydrous REE phosphates with implications for diagenesis and sea water concentrations

Solubility product determinations suggest that the hydrous phosphates of the rare earths, REPO₄ · $\text{xH}{}_2\text{O}$, are important in controlling the sea water REE concentrations. Two of these solids, rhabdophane, (P6₂22) and “hydrous xenotime”, (14₁/amd), have been synthesized at 100°C via the acid hydrolysis of the respective REE pyrophosphate. The solubility products at infinite dilution were determined to be $\text{pK}{}^0\text{= 24.5}$, (La at 25°C); 26.0, (Pr at 100°C); 25.7, (Nd at 100°C): and 25.5, (Er at 100°C). On the basis of calculations involving the reaction of RE³⁺ with apatite to form the hydrous phosphate, the lanthanum concentration in sea water is predicted to be about 140 pmol/L. Laboratory experiments support the hypothesis that apatite is a substrate for reactions with dissolved REE.     

Two-step deglaciation: 14C-Dated high-resolution δ18O records from the tropical Atlantic Ocean

Eight box cores from the tropical Atlantic were studied in detail with regard to foraminiferal oxygen isotopes, radiocarbon, and Globorotalia menardii abundance. A standard Atlantic oxygen-isotope signal was reconstructed for the last 20,000 yr. It is quite similar to the west-equatorial Pacific signal published previously. Deglaciation is seen to occur in two steps which are separated by a pause. Onset of deglaciation is after 15,000 yr B.P. The pause is centered between 11,000 and 12,000 yr B.P., but may be correlative with the Younger Dryas (10,500 yr B.P.) if allowance is made for a scale shift due to mixing processes on the sea floor. Step 2 is centered near 10,000 yr B.P. and is followed by a brief excursion toward light oxygen values. This excursion (the M event) may correlate with the Gulf of Mexico meltwater spike.     

Petrology of the Northern East Greenland Tertiary Flood Basalts: Evidence from Hold with Hope and Wollaston Forland

Predominantly silica-oversaturated tholeiitic basalts spreadwidely across the northern East Greenland continental margin(73–76° N) at the onset of Tertiary magmatism. Thesehave been studied in two of the principal outcrop areas: Holdwith Hope and Wollaston Forland. In Hold with Hope very minoreruption of nephelinitic magma preceded the tholeiitic phase.The early tholeiites of northern East Greenland tend to be moresiliceous and aluminous and less iron and titanium rich thantheir more voluminous counterparts in the main East Greenlandprovince south of 70° N. Some, notably those of WollastonForland, approach ‘enriched MORB’ compositions.The early flood basalts (distinguished in the Hold with Hoperegion as the Lower Plateau Lava Series, LPLS) show limitedcompositional range. Such variation as is shown is attributedto low-pressure plagioclase—olivine—augite fractionation.Intrusion of quartz dolerite sills within and beneath the LPLSmay have constituted a separate but closely allied magmaticevent. The sills are slightly more enriched in incompatibleelements, have higher initial Sr isotopic ratios and show morepronounced Fe-enrichment trends. Conformably overlying the LPLS in the Hold with Hope area isa succession of incompatible element enriched basalts composingthe Upper Plateau Lava Series (UPLS). The more extremely enrichedlavas (anomalous UPLS) tend to define the base of the UPLS andrange from olivine tholeiites to analcime basanites. Togetherwith the more normal UPLS, these range from nearly aphyric tostrongly porphyritic varieties; the latter include highly magnesianoceanites and ankaramites. The normal UPLS ranges from picriticolivine tholeiites to quartz tholeiites. While orthopyroxenephenocrysts occur among the more differentiated basalts, pigeoniteappears wholly absent from the UPLS. Compositional variationamong the normal UPLS is ascribed to olivine + spinel fractionationjoined by clinopyroxene in compositions with less than 8 percent MgO. The UPLS basalts have incompatible element levelsand elemental ratios (e.g. Zr/Nb, Zr/Y, La/Y and Ti/V) thatdistinguish them from the earlier, more depleted tholeiites.Initial Sr isotope ratios vary widely, with high values indicativeof crustal interaction. A genetic model is proposed whereby the more depleted tholeiites,as exemplified by those of Wollaston Forland and the earliervolcanic products on Hold with Hope, arose from large-scalemelting of relatively infertile asthenosphere prior to the initiationof the Mohn's Ridge and continental separation, while the UPLSof the Hold with Hope region and isolated inland occurrencesof nephelinitic and basanitic magmatism were produced by meltingof K–Ti–P enriched facies of the heterogeneous mantlepresumed to have formed the lower part of the sub-Greenlandcontinental lithosphere. Basalts of the Vøring Plateauon the Norwegian continental shelf, may represent analoguesof the UPLS on the eastern Atlantic margins.     

Normalized 87Sr86Sr by multiple collection and comparison to a standard

A system for precisely determining normalized ${}^{87}\text{Sr}{}^{86}\text{Sr}$ by comparing unknown to standard in a solid-source quadruple-collector mass spectrometer is outlined. This is made possible by a mathematical approximation in the data-reduction process.