GEM-Selektor geochemical modeling package: revised algorithm and GEMS3K numerical kernel for coupled simulation codes

Reactive mass transport (RMT) simulation is a powerful numerical tool to advance our understanding of complex geochemical processes and their feedbacks in relevant subsurface systems. Thermodynamic equilibrium defines the baseline for solubility, chemical kinetics, and RMT in general. Efficient RMT simulations can be based on the operator-splitting approach, where the solver of chemical equilibria is called by the mass transport part for each control volume whose composition, temperature, or pressure has changed. Modeling of complex natural systems requires consideration of multiphase–multicomponent geochemical models that include nonideal solutions (aqueous electrolytes, fluids, gases, solid solutions, and melts). Direct Gibbs energy minimization (GEM) methods have numerous advantages for the realistic geochemical modeling of such fluid–rock systems. Substantial improvements and extensions to the revised GEM interior point method algorithm based on Karpov’s convex programming approach are described, as implemented in the GEMS3K C/C+?+ code, which is also the numerical kernel of GEM-Selektor v.3 package (http://gems.web.psi.ch). GEMS3K is presented in the context of the essential criteria of chemical plausibility, robustness of results, mass balance accuracy, numerical stability, speed, and portability to high-performance computing systems. The stand-alone GEMS3K code can treat very complex chemical systems with many nonideal solution phases accurately. It is fast, delivering chemically plausible and accurate results with the same or better mass balance precision as that of conventional speciation codes. GEMS3K is already used in several coupled RMT codes (e.g., OpenGeoSys-GEMS) capable of high-performance computing.     

New Apparatus and Experimental Setup for Long-Term Swelling Tests on Sulphatic Claystones

An apparatus and experimental setup were developed to carry out a series of extremely slow and long-lasting swelling, creep or chemo-mechanics tests simultaneously. The equipment was designed specifically for investigating the behaviour of sulphatic claystones. The tests will take at least 10–15 years to complete and will provide unprecedented information about the so-called swelling law, i.e. the relationship between swelling strain and swelling stress. The swelling law is very important for designing tunnels in swelling rock. Our knowledge of the swelling law, however, is only sufficiently reliable with respect to claystones without anhydrite (e.g. marls, opalinus clay). The swelling law for sulphatic claystones remains unknown, even in qualitative terms. This is due to the underlying physico-chemical mechanisms, which are fundamentally different from those of purely argillaceous rocks. Another reason is the extremely long duration of the swelling process of clay-sulphate rocks, which makes systematic field or laboratory investigations very difficult. In order to close this knowledge gap, a series of 25 long-term simultaneous swelling tests has been started.     

Nonlinear internal waves in ideal rotating basins

Abstract

Starting from Euler's equations of motion a nonlinear model for internal waves in fluids is developed by an appropriate scaling and a vertical integration over two layers of different but constant density. The model allows the barotropic and the first baroclinic mode to be calculated. In addition to the nonlinear advective terms dispersion and Coriolis force due to the Earth's rotation are taken into account. The model equations are solved numerically by an implicit finite difference scheme. In this paper we discuss the results for ideal basins: the effects of nonlinear terms, dispersion and Coriolis force, the mechanism of wind forcing, the evolution of Kelvin waves and the corresponding transport of particles and, finally, wave propagation over variable topography. First applications to Lake Constance are shown, but a detailed analysis is deferred to a second paper [Bauer et al. (1994)].     

Development of a conceptual hydrogeological model for the evaluation of residence times of water in soil and groundwater: the state of Hesse case study, Germany

A regional conceptual hydrogeological model has been developed for evaluating residence times of both, percolate water in the unsaturated zone and groundwater in upper aquifers. The model is based on digitally geo-data bases available at the regional level and has been applied for the entire Federal State of Hesse (Germany) with a spatial resolution of 60?×?60?m. Residence times determined for unconsolidated rock areas typically ranged between 10 and 25?years, whereas residence times of <5?years were assessed for consolidated rock areas. With regard to the implementation of the EU Water Framework Directive, the determined residence times may help to assess the time periods between the introduction of well-targeted groundwater protection measures and their impact on groundwater and surface water quality, respectively.     

BaMn[CO3]2 – a previously unrecognized double carbonate in low-temperature environments: Structural,spectroscopic, and textural tools for future identification

Following a tentative evidence for the occurrence of low-temperature barium manganese(II) carbonates in brackish sediments of the Baltic Sea, a stoichiometric double carbonate, BaMn[CO₃]₂, was synthesized from aqueous solutions at ambient temperature for the first time. Here we report the results of a multi-method approach, including scanning electron microscopy (SEM–EDX) investigations, the chemical composition, and, in particular, the diagnostic powder X-ray diffraction pattern, as well as diagnostic parts of the FT infrared absorption and Raman spectra for future identification of this new carbonate in low-temperature environments, like brackish sediments.     

Volcanic arcs as archives of plate tectonic change

Processing of the oceanic lithosphere in subduction zones gives rise to arc magmatism, and strong compositional links exist between trench input and arc output. Here we address the question whether these compositional links are sufficiently strong to allow for ‘tracing’ the composition of the sedimentary and igneous oceanic crust through the chemistry of arcs. The tracing approach hinges critically on whether key characteristics of the subducted slab are transmitted to arcs. Results from forward and inverse modeling, verified by observations from modern arc settings, demonstrate that elements Sr, Pb, Nd and Hf that are associated with radiogenic isotopes may preserve chemical characteristics of the subducted slab in arc magmas. The data indicate that the much thicker igneous subducted crust dominates the recycled flux to arcs. The flux from the highly enriched, but thin sediment layer is buffered, and may be even concealed, by the concomitant contributions from igneous crust, and/or subarc mantle, despite the much better visibility of sediment components in trace element and isotope space. Arc Pb and Pb isotopes are the most promising tracers that may capture the isotopic diversity of subducted MORB-type and OIB-type crust with sufficient temporal and spatial resolution. While arc Sr is also strongly controlled by the flux from the subducted crust, arc data may allow for distinguishing among radiogenic Sr recycled from altered oceanic crust or from subducted sediment in moderately radiogenic arcs (⁸⁷Sr/⁸⁶Sr < ~ 0.7045). Co-mingling of Nd and Hf from igneous subducted crust with mantle contributions mostly hinders the isotopic identification of subducted crust through arc chemistry. However, Nd and Hf may provide complementary information about the efficiency of recycling, and recycling via subduction erosion.The tracing approach appears feasible in Cenozoic arcs where much of the original subduction context is preserved. First results from the Izu Bonin and Central American arcs show that plate tectonic events like oceanic plate formation and destruction, subduction of hotspot tracks and the closure of oceanic gateways are recorded in the chemistry of arcs. A comparative evaluation of Cenozoic global arcs may hence significantly complement the information from the modern oceanic basins, help to obtain a more complete image of the oceanic crustal composition and implicate the geochemical processes by which it formed. Possibly, the tracing approach may also be useful in ancient, inactive arcs to obtain information on the composition of oceanic crust subducted in the geological past.     

State of geoscientific research within the lorandite experiment (LOREX)

The LORandite EXperiment (acronym LOREX) is the only geochemical solar neutrino experiment still actively persued. The Tl-mineral lorandite, TlAsS₂, occurs in the ore deposit Allchar, Macedonia, close to the border of Greece. The polychronous and polygenetic Sb-As-Tl-Au Allchar deposit was formed by complex physico-chemical processes occurring in a heterogeneous geological environment and by interaction of polyphase hydrothermal fluids with the surrounding magmatic, sedimentary and metamorphic rocks. The genesis of ore mineralization is related to the products of polyphase magmatic activity of Pliocene age (~6.5 to ~1.8?Ma) and its spatial location was controlled by magmatic, structural and lithological factors. The Allchar deposit comprises several orebodies of various shapes, textural-structural characteristics and element associations. Thallium mineralization, which is of significance for the LOREX project, has been proved in two locations: (i) ore body Crven Dol in the northern part and (ii) ore body Centralni Deo in the central part of the Allchar deposit. The age of Tl-mineralization is 4.22?Ma at the Crven Dol locality and 4.31?Ma at Rudina near to the Centralni Deo locality. The present depth of ore mineralization from the present soil surface is about 30?m to 140?m, whereas the paleodepth of its formation is considerably bigger. Using the method of quantitative geomorphological analysis, and AMS- and MS-measurements of cosmogenic radionuclides ²⁶Al, ²¹Ne, and ³He, the erosion rate has been established to be ~70?m/Ma in the broader area of the Crven Dol locality and ~130?m/Ma in the Centrani Deo of the Allchar deposit. On the basis of these erosion rates and ages of Tl-mineralization, we have calculated the paleo-depth of Lorandite to be ca 180?m?±?35?m to 420?m?±?80?m. Geochemical and mineralogical investigations on lorandite in particular its trace elements (Pb, U, and Th), the quantity of lorandite in the two ore bodies, the geological age and the paleo depth of Tl-mineralization have provided encouraging results and indicate the feasibility of the LOREX project.     

The Ksar Ghilane 002 shergottite—The 100th registered Martian meteorite fragment

We report on the discovery of a new shergottite from Tunisia, Ksar Ghilane (KG) 002. This single stone, weighing 538 g, is a coarse‐grained basaltic shergottite, mainly composed of maskelynitized plagioclase (approximately 52 vol%) and pyroxene (approximately 37 vol%). It also contains Fe‐rich olivine (approximately 4.5 vol%), large Ca‐phosphates, including both merrillites and Cl‐apatites (approximately 3.4 vol%), minor amounts of silica or SiO₂‐normative K‐rich glass, pyrrhotite, Ti‐magnetite, ilmenite, and accessory baddeleyite. The largest crystals of pyroxene and plagioclase reach sizes of approximately 4 to 5 mm. Pyroxenes (Fs_26–96En_5–50Wo_2–41). They typically range from cores of about Fs₂₉En₄₁Wo₃₀ to rims of about Fs₆₈En₁₄Wo₁₇. Maskelynite is Ab_41–49An_39–58Or_1–7 in composition, but some can be as anorthitic as An₉₃. Olivine (Fa_91–96) occurs mainly within symplectitic intergrowths, in paragenesis with ilmenite, or at neighboring areas of symplectites. KG 002 is heavily shocked (S5) as indicated by mosaic extinction of pyroxenes, maskelynitized plagioclase, the occurrence of localized shock melt glass pockets, and low radiogenic He concentration. Oxygen isotopes confirm that it is a normal member of the SNC suite. KG 002 is slightly depleted in LREE and shows a positive Eu anomaly, providing evidence for complex magma genesis and mantle processes on Mars. Noble gases with a composition thought to be characteristic for Martian interior is a dominant component. Measurements of ¹⁰Be, ²⁶Al, and ⁵³Mn and comparison with Monte Carlo calculations of production rates indicate that KG 002 has been exposed to cosmic rays most likely as a single meteoroid body of 35–65 cm radius. KG 002 strongly resembles Los Angeles and NWA 2800 basaltic shergottites in element composition, petrography, and mineral chemistry, suggesting a possible launch‐pairing. The similar CRE ages of KG 002 and Los Angeles may suggest an ejection event at approximately 3.0 Ma.