Partial molar volumes of oxide components in silicate liquids

Densities of 21 silicate liquids have been determined from 1,000 ° to 1,600 ° C. The compositions studied contain from two to eight oxide components and have the following ranges in composition (mole %): SiO₂, 35–79%; TiO₂, 4–36%; Al₂O₃, 5–25%; FeO, 11–41%; MgO, 7–28%; CaO, 7–35%; Na₂O, 5–50%; and K₂O, 4–20%. The compositions thus cover the upper range observed in magmas for each oxide. Precision for each determination of liquid density is always better than ±1%.Volumes/gfw (gram formula weight) calculated from the density measurements and the chemical compositions of the analyzed liquids have been combined with data on 96 silicate liquids reported in the literature. From this data set we derive, by using multiple linear regression, partial molar volumes of the components SiO₂, TiO₂, A1₂O₃, FeO, MgO, CaO, Na₂O, and K₂O at five temperatures. The standard deviation of the multiple regression is 1.8% of the molar volumes, which is considered about equal to the total errors due to compositional and instrumental uncertainties.These derived partial molar volumes have been used to calculate volumes/gfw of natural silicate liquids which are found to agree within 1% of the measured values. No compositional dependence of the partial molar volumes can be detected within the error considered to be typical of the measurements. This is further supported by the close agreement between the calculated volumes of CaMgSi₂O₆ and Fe₂SiO₂ liquids derived from the initial slopes of their fusion curves and their heats of fusion, and the volumes obtained by summing the respective partial molar volumes. The experimental data indicate that silicate liquids mix ideally with respect to volume, over the temperature and composition range of this data set.     

Observations on the settlement patterns of Janua (Dexiospira) brasiliensis (Polychaeta: Serpulidae)

The polychaete Janua (Dexiospira) brasiliensis (Grube) is shown to exhibit gregarious settling patterns on both natural (Zostera marina) and artificial (aquarium glass) substrates. J. (D.) brasiliensis tends to be found more often on older (=longer) Zostera blades and on the upper (=older) portions of the blades on which it is found, probably as a result of requiring a diatom mat before being able to settle on the Zostera surface. On both Zostera and the aquarium glass, J. (D.) brasiliensis forms small clumps (2 cm) with the animals within the clumps distributed at random.     

Ultrafiltration of fulvic and humic acids,a comparison of stirred cell and hollow fiber techniques

The ultrafiltration of solutions of well characterized samples of fulvic and humic acids or their salts, using two different techniques, show that these materials are retained by commercial ultrafiltration membranes with molecular weight cut-off values far higher than the reported molecular weights of fulvic or humic acid. The lower molecular weight fulvic acid or its Na⁺ -salt is retained even better than the higher molecular weight Na⁺-salt of humic acid. Both stirred cell and hollow fiber techniques can be employed to concentrate or desalt solutions of these humic materials, with relatively small solute losses. Very high simple electrolyte backgrounds (above 1 M) lower the performance of a given membrane considerably, moderate concentrations of simple electrolyte do not influence the ultrafiltration efficiency.     

Constraints on the origin of alkaline and calc-alkaline magmas from the Tuxtla Volcanic Field,Veracruz, Mexico

 Lavas erupted in the Tuxtla Volcanic Field (TVF) over the last 7 Ma include primitive basanites and alkali basalts, mildly alkaline Hy-normative mugearites and benmoreites, and calc-alkaline basalts and basaltic andesites. The primitive lavas are silica-undersaturated, with high concentrations of both incompatible and compatible trace elements, variable La/Yb with constant Yb at 6 to 8 times chondritic, and low Sr and O and variable Pb and Nd isotopic ratios. The primitive magmas originated by increasing degrees of melting with pressure decreasing from greater than 30 kbar to 20 kbar, in the garnet stability field. Another group of alkali basalts and hawaiites has lower Ni and Cr concentrations and higher Fe/Mg ratios, and was derived from the primitive group by crystal fractionation at pressures of several kbar. Incompatible trace elements in these silica undersaturated lavas show depletion in high field strength elements (HFSE) relative to large ion lithophile elements, similar to subduction-related basalts. Ba/Nb ratios are nearly constant and thus the HFSE depletion cannot be the result of a residual HFSE-bearing phase in the source, but could be the result of generation from a source contaminated by fluids or melts from the subducted lithosphere. The silica-saturated mugearites and benmoreites, and the calc-alkaline basalts and basaltic andesites, were erupted only between 3.3 and 1.0 Ma. These have incompatible element concentrations generally lower than in the silica-undersaturated lavas, and thus could not have been derived by crystal fractionation from the silica-undersaturated alkaline magmas. Magmas parental to the silica-saturated magmas originated by higher degrees of melting at lower pressures than the primitive magmas. Melting may have been promoted by an influx of fluid from the subducted lithosphere. Trace element and Sr, Nd, Pb and O isotopic data suggest that three components are involved in the generation of TVF magmas: the mantle, a fluid from the subducted lithosphere, and continental crust. TVF alkaline lavas are similar to those erupted in the back-arc region of the MVB and Japan, and show characteristics similar to alkaline magmas erupted in the southern Andean volcanic arc. These low degree melts reach the surface along with calc-alkaline lavas in the TVF due to an extensional stress field that allows their passage to the surface. Received: 15 September 1994/Accepted: 14 February 1995     

Optical dating of tsunami-laid sand from an Oregon coastal lake

Optical ages for five samples of tsunami-laid sand from an Oregon coastal lake were determined using an infrared optical-dating method on K-feldspar separates and, as a test of accuracy, compared to ages determined by AMS ¹⁴C dating of detrital plant fragments found in the same beds. Two optical ages were about 20% younger than calibrated ¹⁴C ages of about 3.1 and 4.3 ka. Correction of the optical ages using measured anomalous fading rates brings them into agreement with the ¹⁴C ages. The approach used holds significant promise for improving the accuracy of infrared optical-dating methods.Luminescence data for the other three samples result in optical age limits much greater than the ¹⁴C ages. These data provide a textbook demonstration of the correlation between scatter in the luminescence intensity of individual sample aliquots and their normalization values that is expected when the samples contain sand grains not adequately exposed to daylight just prior to or during deposition and burial. Thus, the data for these three samples suggest that the tsunamis eroded young and old sand deposits before dropping the sand in the lake.     

Comparative reproductive success of winter flounder in Long Island Sound: A three-year study (biology,biochemistry, and chemistry)

In a 3-yr study, late prespawning winter flounder were collected from various stations in Long Island Sound (three of them heavily urbanized) and spawned in the laboratory. For comparative purposes, flounder from two sites in the Boston Harbor area were similarly treated in 1987 and 1988. Of the stations in Long Island Sound, New Haven Harbor alone consistently produced low percent viable hatch and small larvae. Boston Harbor produced the smallest larvae of all sites. There were no significant station-to-station differences in lipid utilization during larval development; yolk reserves at stations showing a low percent viable hatch, small larvae, and low embryonic development rate were probably used in part for stress metabolism. No significant differences in concentrations of polychlorinated biphenyls for collections from Long Island Sound were found either in livers of spawned fish, in sediments, or in eggs of winter flounder. The very low metal concentrations in winter flounder eggs showed no relation to the degree of metal contamination found at stations in Long Island Sound and Boston Harbor.     

Isotopic characteristics and petrogenesis of the lamproites and kimberlites of central west Greenland

Kimberlites which intruded the Sisimiut (formerly Holsteinsborg) region of central west Greenland during the Early Palaeozoic have initial ⁸⁷Sr/⁸⁶Sr between 0.7028 and 0.7033 and ε_Nd between + 1.3 and + 3.9. Mid-Proterozoic potassic lamproites from the same region have initial ⁸⁷Sr/⁸⁶Sr between 0.7045 and 0.7060, ε_Nd between −13 and −10 and unradiogenic initial Pb isotopic compositions. The isotopic data favour an asthenospheric mantle source for the kimberlite magmas, in common with “basaltic” kimberlites from other localities, whereas the lamproite magma sources evolved in isolation from the convecting mantle for > 1000 Ma, probably within the subcontinental lithospheric mantle of the Greenland craton, prior to emplacement of the lamproites.     

Isotopic characteristics of potassic rocks: evidence for the involvement of subducted sediments in magma genesis

The potassic igneous rock suite (with molar K₂O/Na₂O > 1) can be divided into an “orogenic” subgroup that occur in subduction-related tectonic settings and an “anorogenic” sub-group that are confined to stable continental settings. Representatives of both sub-groups possess trace element and isotopic features consistent with the contamination of their magma sources by incompatible element rich and isotopically evolved “metasomatic” components. It is argued here that these metasomatic components are principally derived from subducted lithosphere, including subducted sediments. Most examples of orogenic potassic magmatism (e.g. Italian potassic rocks, Spanish lamproites, Sunda arc leucitites) have trace-element and Sr, Nd and Pb isotopic characteristics consistent with the contamination of their mantle sources by a component derived from marine sediments. Anorogenic sub-group potassic magmas have generally similar incompatible trace element and Sr and Nd isotopic characteristics to those of orogenic potassic magmas, but many examples have unusual Pb isotopic compositions with unradiogenic ²⁰⁶Pb/²⁰⁴Pb. Modern marine sediments characteristically have low U/Pb ratios and the unradiogenic ²⁰⁶Pb/²⁰⁴Pb of anorogenic potassic magmas may have evolved during long-term storage of subducted sediments (or components derived from them) within the subcontinental lithosphere. These unusual Pb isotopic compositions require substantial time periods (> 1 Ga) to have elapsed between the fractionation events lowering the U/Pb ratio (i.e. erosion and sedimentation at the Earth's surface) and subsequent potassic magmatism and it is therefore not surprising that most examples of anorogenic potassic magmatism are not associated with recent subduction processes. Although the eruption of potassic magmas is commonly related to rifting or hotspot activity, these processes do not necessarily play an important role in the genesis of the unusual sources from which potassic magmas are derived.