Geochemical evidence for melting of carbonated peridotite on Santa Maria Island, Azores

The islands of the Azores archipelago emerge from an oceanic plateau built on lithosphere increasing in age with distance from the Mid-Atlantic Ridge from 10 to 45 Ma. Here, we present the first comprehensive major and trace element and Sr–Nd–Pb isotope data from Santa Maria, the easternmost island of the archipelago, along with published data from the other Azores islands situated much closer to the Mid-Atlantic Ridge axis. We can show that the distinctively more variable and more enriched trace element ratios at Santa Maria combined with a relatively small range in Sr–Nd–Pb isotope ratios are the result of low degrees of partial melting of a common Azores mantle plume source underneath thicker lithosphere. This implies that melt extraction processes and melting dynamics may be able to better preserve the trace element mantle source variability underneath thicker lithosphere. These conclusions may apply widely for oceanic melts erupted on relatively thick lithosphere. In addition, lower Ti/Sm and K/La ratios and SiO₂ contents of Santa Maria lavas imply melting of a carbonated peridotite source. Mixing of variable portions of deep small-degree carbonated peridotite melts and shallow volatile-free garnet peridotite could explain the geochemical variability underneath Santa Maria in agreement with the volatile-rich nature of the Azores mantle source. However, Santa Maria is the Azores island where the CO₂-rich nature of the mantle source is more evident, reflecting a combination of a smaller extent of partial melting and the positioning at the edge of the tilted Azores mantle plume.     

Experimental partitioning of halogens and other trace elements between olivine, pyroxenes, amphibole and aqueous fluid at 2 GPa and 900–1,300 °C

We present new partition coefficients for various trace elements including Cl between olivine, pyroxenes, amphibole and coexisting chlorine-bearing aqueous fluid in a series of high-pressure experiments at 2 GPa between 900 and 1,300 °C in natural and synthetic systems. Diamond aggregates were added to the experimental capsule set-up in order to separate the fluid from the solid residue and enable in situ analysis of the quenched solute by LA–ICP–MS. The chlorine and fluorine contents in mantle minerals were measured by electron microprobe, and the nature of OH defects was investigated by infrared spectroscopy. Furthermore, a fluorine-rich olivine from one selected sample was investigated by TEM. Results reveal average Cl concentrations in olivine and pyroxenes around 20 ppm and up to 900 ppm F in olivine, making olivine an important repository of halogens in the mantle. Chlorine is always incompatible with Cl partition coefficients D _Cl ^{olivine/fluid} varying between 10^?5 and 10^?3, whereas D _Cl ^{orthopyroxene/fluid} and D _Cl ^{clinopyroxene/fluid} are ~10^?4 and D _Cl ^{amphibole/fluid} is ~5 × 10^?3. Furthermore, partitioning results for incompatible trace element show that compatibilities of trace elements are generally ordered as D ^amph/fluid ≈ D ^cpx/fluid > D ^opx/fluid > D ^ol/fluid but that D ^{mineral/fluid} for Li and P is very similar for all observed silicate phases. Infrared spectra of olivine synthesized in a F-free Ti-bearing system show absorption bands at 3,525 and ~3,570 cm^?1. In F ± TiO₂-bearing systems, additional absorption bands appear at ~3,535, ~3,595, 3,640 and 3,670 cm^?1. Absorption bands at ~3,530 and ~3,570 cm^?1, previously assigned to humite-like point defects, profit from low synthesis temperatures and the presence of F. The presence of planar defects could not be proved by TEM investigations, but dislocations in the olivine lattice were observed and are suggested to be an important site for halogen incorporation in olivine.     

Evaluating the effect of snow and ice melt in an Alpine headwater catchment and further downstream in the River Rhine

Abstract

The runoff regime of glacierized headwater catchments in the Alps is essentially characterized by snow and ice melt. High Alpine drainage basins influence distant downstream catchments of the Rhine River basin. In particular, during the summer months, low-flow conditions are probable with strongly reduced snow and ice melt under climate change conditions. This study attempts to quantify present and future contributions from snow and ice melt to summer runoff at different spatial scales. For the small Silvretta catchment (103 km²) in the Swiss Alps, with a glacierization of 7%, the HBV model and the glacio-hydrological model GERM are applied for calculating future runoff based on different regional climate scenarios. We evaluate the importance of snow and ice melt in the runoff regime. Comparison of the models indicates that the HBV model strongly overestimates the future contribution of glacier melt to runoff, as glaciers are considered as static components. Furthermore, we provide estimates of the current meltwater contribution of glaciers for several catchments downstream on the River Rhine during the month of August. Snow and ice melt processes have a significant direct impact on summer runoff, not only for high mountain catchments, but also for large transboundary basins. A future shift in the hydrological regime and the disappearance of glaciers might favour low-flow conditions during summer along the Rhine.

Citation Junghans, N., Cullmann, J. & Huss, M. (2011) Evaluating the effect of snow and ice melt in an Alpine headwater catchment and further downstream in the River Rhine. Hydrol. Sci. J. 56(6), 981–993.     

Groundwater flow and its effect on salt dissolution in Gypsum Canyon watershed,Paradox Basin,southeast Utah,USA

Groundwater flow is an important control on subsurface evaporite (salt) dissolution. Salt dissolution can drive faulting and associated subsidence on the land surface and increase salinity in groundwater. This study aims to understand the groundwater flow system of Gypsum Canyon watershed in the Paradox Basin, Utah, USA, and whether or not groundwater-driven dissolution affects surface deformation. The work characterizes the groundwater flow and solute transport systems of the watershed using a three-dimensional (3D) finite element flow and transport model, SUTRA. Spring samples were analyzed for stable isotopes of water and total dissolved solids. Spring water and hydraulic conductivity data provide constraints for model parameters. Model results indicate that regional groundwater flow is to the northwest towards the Colorado River, and shallow flow systems are influenced by topography. The low permeability obtained from laboratory tests is inconsistent with field observed discharges, supporting the notion that fracture permeability plays a significant role in controlling groundwater flow. Model output implies that groundwater-driven dissolution is small on average, and cannot account for volume changes in the evaporite deposits that could cause surface deformation, but it is speculated that dissolution may be highly localized and/or weaken evaporite deposits, and could lead to surface deformation over time.     

Predictions on the core mass of Jupiter and of giant planets in general

More than 80 giant planets are known by mass and radius. Their interior structure in terms of core mass, number of layers, and composition however is still poorly known. An overview is presented about the core mass M _core and envelope mass of metals M _Z in Jupiter as predicted by various equations of state. It is argued that the uncertainty about the true H/He EOS in a pressure regime where the gravitational moments J ₂ and J ₄ are most sensitive, i.e. between 0.5 and 4 Mbar, is in part responsible for the broad range \(M_{\mathit{core}}=0{-}18\:M_{\oplus }\), \(M_{Z}=0{-}38\:M_{\oplus }\), and \(M_{\mathit{core}}+M_{Z}=14{-}38\:M_{\oplus }\) currently offered for Jupiter. We then compare the Jupiter models obtained when we only match J ₂ with the range of solutions for the exoplanet \(\mathrm{GJ}\:436\mathrm{b}\), when we match an assumed tidal Love number k ₂ value.     

Multi-stage emplacement of the G?temar Pluton, SE Sweden: new evidence inferred from field observations and microfabric analysis, including cathodoluminescence microscopy

The emplacement of the Mesoproterozoic G?temar Pluton into Paleoproterozoic granitoid host rocks of the Transscandinavian Igneous Belt is re-examined by microfabric analysis, including cathodoluminescence microscopy. Field data on the pluton-host rock system are used to strengthen the model. The G?temar Pluton, situated on the Baltic Shield of SE Sweden, is a horizontally zoned tabular structure that was constructed by the intrusion of successive pulses of magma with different crystal/melt ratios, at an estimated crustal depth of 4–8?km. Initial pluton formation involved magma ascent along a vertical dike, which was arrested at a mechanical discontinuity within the granitoid host rocks; this led to the formation of an initial sill. Subsequent sill stacking and their constant inflation resulted in deformation and reheating of existing magma bodies, which also raised the pluton roof. This multi-stage emplacement scenario is indicated by complex dike relationships and the occurrence of several generations of quartz (Si-metasomatism). The sills were charged by different domains of a heterogeneous magma chamber with varying crystal/melt ratios. Ascent or emplacement of magma with a high crystal/melt ratio is indicated by syn-magmatic deformation of phenocrysts. Complex crystallization fabrics (e.g. oscillatory growth zoning caused by high crystal defect density, overgrowth and replacement features, resorbed and corroded crystal cores, rapakivi structure) are mostly related to processes within the main chamber, that is repeated magma mixing or water influx.     

Approaches to stress monitoring in deep boreholes for future CCS projects

There is no monitoring technology available to observe possible changes of stress in the rock mass of a CO₂ reservoir or its cap rock formations. Any development of a stress-monitoring technique must be related to the natural regional stress conditions and must be adjusted to the possibly changing in situ stress conditions due to CCS activity. As a step towards an in situ stress-monitoring probe, a lab scale device was developed and used for investigations on the practicability of a hard-inclusion tool for stress monitoring. In situ stress conditions, as deduced from the Altmark Gas Field, were applied to evaluate the efficiency and the limits of this stress-monitoring technique. At lab-scale the applied stresses resp. stress differences with moderate amounts of 9?C15?% of the vertical stress component Sv coincide sufficiently with the resulting strain answers of the hard inclusion tool (i.e., a steel tube corresponding to the liner in the borehole). Therefore, it was possible to re-calculate the stresses and to compare them with the applied ones. The resulting coincidence, however, can be disturbed at high pressure levels due to rock failure around the borehole with extended deformations. In addition, the results are influenced by the mechanical behaviour of the surrounding rock mass type. Nevertheless, a further development of a hard inclusion probe for monitoring of stress changes in deep boreholes can be successful and may be the only possible way to detect stress changes without fracturing damages in deep boreholes.     

Quaternary coastline evolution of Lake Ohrid (Macedonia/Albania)

Lake Ohrid (between FYR of Macedonia and Albania), situated in an active tectonic region of the Balkanides, is characterized by N ?? S trending active faults. To reconstruct the Holocene shoreline evolution we investigated the coastline using sediment cores and geophysical methods to image sedimentary and tectonic structures. We revealed areas of differing sedimentation regimes. The plains north and south of the lake are dominated by clastic input related to climate variations and uplift/erosion, whereas the steep western and eastern margins are controlled by recent tectonics. Furthermore, no evidence for a much higher lake-level during the Holocene was found in the plains north and south of the lake, except rare temporary floodings. This is supported by mappings of the limestone cliffs around Lake Ohrid, which yielded no evidence for abrasional platforms or notches as indicators for past highstands.     

Using Lead Isotopes to Determine Pottery Provenance in Cyprus: Clay Source Signatures and Comparison with Late Bronze Age Cypriote Pottery

This paper presents the lead isotopic composition of potential clay sources for pottery production, collected in the four major geological zones of Cyprus (Troodos Ophiolite, Circum Troodos Sedimentary Succession, Mamonia Terrane, Kyrenia Terrane) and evaluates its usefulness in Cypriote pottery provenance studies. The clay isotopic signatures from the four zones are compared to each other and to the isotopic composition of various utilitarian pottery wares from three Late Bronze Age sites, respectively located in southern Cyprus (Alassa‐Pano Mandilaris), east Cyprus (Enkomi), and southeast Cyprus (Hala Sultan Tekke). It also explores the potential of this method to better discriminate between potential raw materials used for the production of Base‐ring ware, one of the most characteristic fine pottery of Late Bronze Age Cyprus, which was widely spread in the Eastern Mediterranean (Courtois, 1981; Vaughan, 1991, 1994). Results show that three main lead isotopic fields can be distinguished among the Cypriote clay sources and the comparison of Plain sherds with the clay sources allows discrimination between local products and imports. They also clearly indicate that all the Base‐ring sherds analyzed in this study were made of the clays from the Kathikas Formation that crops out in only limited parts of southwest Cyprus.     

A waveguide-based flexible CO2-laser heating system for diamond-anvil cell applications

Fiber-based laser heating systems offer high flexibility and are increasingly used in high-pressure/high-temperature research. Previous fiber-based laser heating systems were based on lasers delivering radiation with 1-μm wavelength that show unfavorable heating characteristics for many sample materials. We report on the development and first experiments of a waveguide (fiber)-based CO₂-laser heating system that can be used in a flexible manner for high-temperature research and for high-pressure/temperature experiments when combined with diamond-anvil cells. The waveguide-based CO₂-laser heating system allows convenient heating of optically transparent samples without the need for adding an additional laser absorber. In a pilot experiment, the flexible heating system has been installed on a Brillouin scattering system to measure high-temperature sound-wave velocities in single-crystal MgO. The waveguide-based CO₂-laser heating system offers perspectives for a variety of scientific applications, most importantly those that require the use of synchrotron facilities where space is limited and flexible solutions are required.