Experimental determination of partition coefficients for rare earth and high-field-strength elements between clinopyroxene,garnet, and basaltic melt at high pressures

Clinopyroxene/melt and garnet/melt partition coefficients have been determined for Ti, Sr, Y, Zr, Nb, Hf, and rare earth elements from 19 doped experiments on 1921 Kilauea basalt. The experiments were carried out from 2.0 to 3.0 GPa and 1310° to 1470 °C. The purpose was to derive a set of partition coefficients for high-field-strength elements (HFSE) and rare earth elements (REE) in a systematic, linked set of experiments at P and T conditions relevant to basalt petrogenesis. These data are used in melting models to understand the development of negative HFSE anomalies observed in many abyssal peridotite clinopyroxenes. It is shown that melting can account for the observed trace element patterns in some residual peridotites, but that other processes may also be needed to account for most residual mantle compositions in mid-ocean ridge systems. It is also shown that REE are more strongly fractionated by garnet at these P-T conditions than previously thought. Received: 1 July 1997 / Accepted: 11 May 1998     

Extensive carbonate cementation of fluvial sandstones: An integrated outcrop and petrographic analysis from the Upper Cretaceous, Book Cliffs, Utah

Extensive, large-scale pervasive cementation in the form of cement bodies within fluvial strata has rarely been documented although fluvial strata commonly act as important hydrocarbon reservoirs, as well as groundwater aquifers. Here, we present outcrop, petrographic and geochemical data for pervasive ferroan dolomite cement bodies up to 250 m in size from Upper Cretaceous Desert Member and Castlegate Sandstone fluvial strata exposed in the Book Cliffs in Utah. These cement bodies are present with coastal plain fluvial strata within both the Desert and Castlegate lowstand sandstones and are most abundant in the thin, distal fluvial strata. Cement bodies are almost entirely absent in updip, thicker, fluvial strata. Petrographic observations suggest a predominantly early diagenetic timing to the mildly ferroan dolomite, with a component of later burial origin. δ¹³C values for the cement (+4.8 to −5.7‰ V-PDB) suggest a marine-derived source for the earliest phase with a burial organic matter source for later cement. δ¹⁸O data (−6.3 to −11.8‰ V-PDB) suggest precipitation from freshwater dominated fluids. It is proposed here that dolomite was derived from leaching of detrital dolomite under lowstand coals and cementation took place in coastal aquifers experiencing mixed meteoric-marine fluids as a result of base-level fluctuations. This data presented here shows that large cement bodies can be an important component within fluvial sandstones with a potentially significant impact upon both reservoir quality and fluid flow within reservoirs, especially at the marine-non-marine interface.     

U-Pb sphene dating of metamorphism: the importance of sphene growth in the contact aureole of the Red Mountain pluton,Laramie Mountains,Wyoming

 The relative importance of thermal diffusion versus new growth or recrystallization on U-Pb isotopic data from sphene is assessed through a study of amphibolites and granite gneisses within the contact aureole of the Red Mountain pluton, Laramie anorthosite complex, Wyoming. Samples were collected along a traverse approximately perpendicular to the margin of the intrusion over a distance of 0.13 to 2.65 km from the contact. The ²⁰⁷Pb/²⁰⁶Pb ages of sphene from amphibolite samples range between 1.43 Ga, the intrusive age of the Red Mountain pluton, to 1.78 Ga, the age of regional metamorphism. The ²⁰⁷Pb/²⁰⁶Pb ages of sphene in rocks metamorphosed above 700° C are within error of the intrusive age of the pluton, and appear to have resulted from diffusional resetting of preexisting sphene and the metamorphic growth of additional sphene at 1.43 Ga. At greater distance from the contact the ²⁰⁷Pb/²⁰⁶Pb ages range from 1.45 to 1.72 Ga. This 300 million year spread in ages is interpreted to result from two periods of sphene growth, one produced during regional metamorphism at 1.78 Ga and another generation of newly grown or recrystallized sphene that formed during contact metamorphism at 1.43 Ga. These two age populations may be identified on the basis of petrographic textures, the morphologies and color differences of grain separates as well as by the U-Pb systematics. In rocks metamorphosed to temperatures less than 700° C, sphene growth was the dominant process controlling the response of the U-Pb isotope system to contact metamorphism. Sphene grew well outside the zone of obvious contact metamorphism. The U-Pb sphene ages were reset by diffusion only at high temperatures, supporting the experimentally determined closure temperature estimates for the U-Pb system in sphene of around 650° C (Cherniak 1993). This study demonstrates that U-Pb ages of sphene can be used to date metamorphism not only in areas with a simple geologic history, such as igneous intrusion or single metamorphic or deformational events, but also to date multiple events so long as different generations of sphene can be identified and separated. Received: 22 August 1995 / Accepted: 17 April 1996     

Structure, charge distribution, and electron hopping dynamics in magnetite (Fe3O4) (1 0 0) surfaces from first principles

For the purpose of improving fundamental understanding of the redox reactivity of magnetite, quantum-mechanical calculations were applied to predict Fe²⁺ availability and electron hopping rates at magnetite (1 0 0) surfaces, with and without the presence of adsorbed water. Using a low free energy surface reconstruction (½-Fe_tet layer relaxed into the Fe_oct (1 0 0) plane), the relaxed outermost layer of both the hydrated and vacuum-terminated surfaces were found to be predominantly enriched in Fe²⁺ within the octahedral sublattice, irrespective of the presence of adsorbed water. At room temperature, mobile electrons move through the octahedral sublattice by Fe²⁺-Fe³⁺ valence interchange small polaron hopping, calculated at 10¹⁰-10¹² hops/s for bulk and bulk-like (i.e., near-surface) environments. This process is envisioned to control sustainable overall rates of interfacial redox reactions. These rates decrease by up to three orders of magnitude (10⁹ hops/s) at the (1 0 0) surface, and no significant difference is observed for vacuum-terminated versus hydrated cases. Slower hopping rates at the surface appear to arise primarily from larger reorganization energies associated with octahedral Fe²⁺-Fe³⁺ valence interchange in relaxed surface configurations, and secondarily on local charge distribution patterns surrounding Fe²⁺-Fe³⁺ valence interchange pairs. These results suggest that, with respect to the possibility that the rate and extent of surface redox reactions depend on Fe²⁺ availability and its replenishment rate, bulk electron hopping mobility is an upper-limit for magnetite and slower surface rates may need to be considered as potentially rate-limiting. They also suggest that slower hopping mobilities calculated for surface environments may be amenable to Fe²⁺-Fe³⁺ site discrimination by conventional spectroscopic probes.     

Photosynthetic community responses to upwelling in mesoscale eddies in the subtropical North Atlantic and Pacific Oceans

In this paper we summarise the photo-physiological responses of phytoplankton to upwelling of macronutrients in mesoscale eddies in the subtropical North Atlantic (EDDIES project, Sargasso Sea) and subtropical North Pacific (E-FLUX project, Hawaii). The observations, obtained on two sets of cruises over 2 years, occupied six cyclonic eddies and two mode-water eddies. The photosynthetic physiological parameters were measured using a bench-top fluorescence induction and relaxation (FIRe) system and a submersible in situ fast repetition rate fluorometer (FRRF) deployed on an undulating towed vehicle. Both of these instruments were used to provide highly sensitive and well-resolved data on community responses. The responses are dependent on both the type of eddy and its stage of development. Our results indicate that, while cyclonic eddies in the Atlantic and Pacific can increase primary photosynthetic production early in their development, mode-water eddies in the subtropical North Atlantic can support patchy blooms of large diatoms for long periods of time (more than 3 months).     

Ag, Te and Pd in 17 Geochemical Reference Materials by Mass Spectrometric Isotope Dilution Analysis

Seventeen geochemical reference samples have been analysed for Ag, Te, Pd using mass spectrometric isotope dilution analysis. For most samples, analytical data on these elements were lacking. The concentration range encountered was generally in the nanogram levels.     

Regional patterns of postwildfire streamflow response in the Western United States: The importance of scale‐specific connectivity

Wildfires can impact streamflow by modifying net precipitation, infiltration, evapotranspiration, snowmelt, and hillslope run‐off pathways. Regional differences in fire trends and postwildfire streamflow responses across the conterminous United States have spurred concerns about the impact on streamflow in forests that serve as water resource areas. This is notably the case for the Western United States, where fire activity and burn severity have increased in conjunction with climate change and increased forest density due to human fire suppression. In this review, we discuss the effects of wildfire on hydrological processes with a special focus on regional differences in postwildfire streamflow responses in forests. Postwildfire peak flows and annual water yields are generally higher in regions with a Mediterranean or semi‐arid climate (Southern California and the Southwest) compared to the highlands (Rocky Mountains and the Pacific Northwest), where fire‐induced changes in hydraulic connectivity along the hillslope results in the delivery of more water, more rapidly to streams. No clear streamflow response patterns have been identified in the humid subtropical Southeastern United States, where most fires are prescribed fires with a low burn severity, and more research is needed in that region. Improved assessment of postwildfire streamflow relies on quantitative spatial knowledge of landscape variables such as prestorm soil moisture, burn severity and correlations with soil surface sealing, water repellency, and ash deposition. The latest studies furthermore emphasize that understanding the effects of hydrological processes on postwildfire dynamic hydraulic connectivity, notably at the hillslope and watershed scales, and the relationship between overlapping disturbances including those other than wildfire is necessary for the development of risk assessment tools.     

The Meteoritical Bulletin,No. 93, 2008 March

Abstract— In this edition of the Meteoritical Bulletin, 1443 approved meteorite names with their relevant data are reported, one from a specific location within Africa, 211 from Northwest Africa, 5 from KOREAMET, 598 from the Chinese Antarctic Expedition, 23 from the Americas, 151 from Asia, three from Australia, two from Europe, two from NOVA, and 447 from ANSMET that were not reported in the Meteoritical Bulletin no. 87. Also reported are 4 falls from the Americas. Some highlights of approved meteorites are 10 lunar (including NWA 5000, an 11.528 kg sample), 3 Martian, 4 irons (one from Indonesia), 2 ureilites, 5 mesosiderites, 1 pallasite, 6 brachinites, 3 CV3s, 4 CO3s, 8 CMs, 12 CK3s, and many more. Finally, the Committee on Nomenclature of the Meteoritical Society announces two new names series in North America.     

The alpine geomorphology of the Mt Anne Massif,south‐western Tasmania

The Mt Anne massif is characterised by spectacular erosional landforms of glacial origin. Evidence of at least two separate Pleistocene glaciations is preserved in valleys that extend east and south of the massif, and also on nearby Schnells Ridge. There is evidence of a much older glaciation beneath the western slopes of the Mt Anne massif. Dense vegetation in the eastern valleys has inhibited mapping of the Quaternary geology there. These glaciations have influenced postglacial evolution of the landscape, including the advent of prominent karst features and Holocene landslip activity.