Radiogenic trigger and driver for continental rifting and initial ocean spreading

Closure and opening of oceans on time‐scales of a few hundred million years is a fundamental tectonic process on Earth, typically referred to as a “Wilson cycle”. Subduction of oceanic and continental crust leading up to and during continent–continent collision can refertilize and enrich the orogenic continental lithospheric mantle in heat‐producing elements. The resulting thermal anomaly weakens the lithosphere and, along with structural weaknesses (e.g. sutures), make this orogenic lithosphere more prone to rifting given an extensional stress field. Thermal modelling shows that anomalously hot lithosphere can focus asthenospheric upwellings over time‐scales of a few hundred million years. Processes related to closure of oceans thus provide a mechanism for later localization of rifting and an extensional driving force.     

Congruent melting of calcium carbonate in a static experiment at 3500 K and 10–22 GPa: Its role in the genesis of ultradeep diamonds

Resulting from static experiments performed to study the phase state of CaCO₃, it was found that its melting is congruent at 20–22 GPa and 3500 K. The obtained experiment data show that the field of congruent melting of calcium carbonate is rather broad (form 2300 to 3500–3800 K at 20–22 GPa). However, the potential presence of a high-temperature phase boundary at which CaCO₃ is decomposed into CaO and CO₂ is not ruled out. The existence of a wide area of congruent melting of calcium carbonate (a common primary inclusion in diamonds of the transition zone and lower mantle of the Earth) allow one to consider deep-seated melts as potential parental media for ultradeep diamonds.     

The lunar crater Giordano Bruno as seen with optical roughness imagery

Images acquired by the LRO NAC allow 3D phase-ratio imagery of several areas in the crater Giordano Bruno. This is a new optical, remote-sensing technique that allows a determination of the optical roughness of the lunar surface. Our study confirms complicated impact melt movement on the flanks and the floor of the crater. In many cases, however, flow structures seen on the inner wall can be attributed to regolith/debris taluses rather than impact melt flows. It was found that the whirlpool-like formation seen near the western side of the crater Giordano Bruno has a small central depression that can be interpreted as either a vortex cavity or a feature which resembles such a vortex formed by viscous flows coming from the crater flanks. We discuss several features that confirm the young age of the crater, concluding, however, that it was not formed within human history; its age is, likely, on the order of 1 My.     

The deep thermal field of the Glueckstadt Graben

With this paper, we assess the present-day conductive thermal field of the Glueckstadt Graben in NW Germany that is characterized by large salt walls and diapirs structuring the graben fill. We use a finite element method to calculate the 3D steady-state conductive thermal field based on a lithosphere-scale 3D structural model that resolves the first-order structural characteristics of the graben and its underlying lithosphere. Model predictions are validated against measured temperatures in six deep wells. Our investigations show that the interaction of thickness distributions and thermal rock properties of the different geological layers is of major importance for the distribution of temperatures in the deep subsurface of the Glueckstadt Graben. However, the local temperatures may result from the superposed effects of different controlling factors. Especially, the upper sedimentary part of the model exhibits huge lateral temperature variations, which correlate spatially with the shape of the thermally highly conductive Permian salt layer. Variations in thickness and geometry of the salt cause two major effects, which provoke considerable lateral temperature variations for a given depth. (1) The “chimney effect” causes more efficient heat transport within salt diapirs. As a consequence positive thermal anomalies develop in the upper part and above salt structures, where the latter are covered by much less conductive sediments. In contrast, negative thermal anomalies are noticeable underneath salt structures. (2) The “thermal blanketing effect” is caused by thermally low conductive sediments that provoke the local storage of heat where these insulating sediments are present. The latter effect leads to both local and regional thermal anomalies. Locally, this translates to higher temperatures where salt margin synclines are filled with thick insulating clastic sediments. For the regional anomalies the cumulative insulating effects of the entire sediment fill results in a long-wavelength variation of temperatures in response to heat refraction effects caused by the contrast between insulating sediments and highly conductive crystalline crust. Finally, the longest wavelength of temperature variations is caused by the depth position of the isothermal lithosphere–asthenosphere boundary defining the regional variations of the overall geothermal gradient. We find that a conductive thermal model predicts observed temperatures reasonably well for five of the six available wells, whereas the steady-state conductive approach appears not to be valid for the sixth well.     

Fundamentals of the mantle carbonatite concept of diamond genesis

In the mantle carbonatite concept of diamond genesis, the data of a physicochemical experiment and analytical mineralogy of inclusions in diamond conform well and solutions to the following genetic problems are generalized: (1) we substantiate that upper mantle diamond-forming melts have peridotite/eclogite–carbonatite–carbon compositions, melts of the transition zone have (wadsleyite ? ringwoodite)–majorite–stishovite–carbonatite–carbon compositions, and lower mantle melts have periclase/wüstite–bridgmanite–Ca-perovskite–stishovite–carbonatite–carbon compositions; (2) we plot generalized diagrams of diamondforming media illustrating the variable compositions of growth melts of diamonds and paragenetic phases, their genetic relationships with mantle matter, and classification relationships between primary inclusions; (3) we study experimentally equilibrium diagrams of syngenesis of diamonds and primary inclusions characterizing the diamond nucleation and growth conditions and capture of paragenetic and xenogenic minerals; (4) we determine the fractional phase diagrams of syngenesis of diamonds and inclusions illustrating regularities in the ultrabasic–basic evolution and paragenetic transitions in diamond-forming systems of the upper and lower mantle. We obtain evidence for physicochemically similar melt–solution ways of diamond genesis at mantle depths with different mineral compositions.     

What Makes Nearshore Habitats Nurseries for Nekton? An Emerging View of the Nursery Role Hypothesis

Estuaries and other coastal habitats are considered essential for the survival of early life stages of commercial, recreational, and other ecologically important species. While early designations simply referred to habitats with higher densities of juveniles as nurseries, the definition was improved by arguing that contribution per unit area to the production of individuals that recruit to adult populations is greater, on average, in nursery habitats. However, this and related approaches typically consider critical habitats as individual, homogeneous entities that are static in nature and do not specifically incorporate important dynamics that determine nursery function. The latter include environmental variability, estuarine hydrodynamics, trophic coupling, ontogenetic habitat shifts, and spatially explicit usage of habitat patches and corridors within larger seascapes. Subsequent studies have identified important factors that regulate nursery value, and researchers working independently across the globe have not only supported the advances made in defining the processes underlying nursery function but, as set forth in this narrative, have advanced it while suggesting that much work still needs to be done to improve our understanding of the links between juvenile nekton survival and the estuarine-coastal seascape. We discuss the current nursery role hypothesis and the data supporting (or refuting) it along with the implications for management of estuarine habitats for the conservation or restoration of nursery function.     

Presence of fluoroquinolones and sulfonamides in urban sewage sludge and their degradation as a result of composting

The concentrations of some widely used pharmaceuticals, namely fluoroquinolones (ciprofloxacin C₁₇ H₁₈FN₃O₃, norfloxacin C₁₇ H₁₈FN₃O₃ and ofloxacin C₁₈ H₂₀FN₃O₄ and sulfonamides (sulfadimethoxine C₁₂ H₁₄N₄O₄s and sulfamethoxazole C₁₀ H₁₁N₃O₃S were determined in urban sewage sludge utilized for making compost. The levels of degradation of these pharmaceuticals resulting from sludge treatment were assessed. The concentrations of the studied pharmaceuticals sufficiently varied both in sewage sludge and in compost and due to this phenomenon the possible danger resulting from the presence of pharmaceuticals in sewage sludge, used for composting, can not be ignored. The concentrations of the studied pharmaceuticals were lower in compost, if compared to the relevant concentrations in sewage sludge. The highest pharmaceutical concentration in sewage sludge — 426 μg/kg — was detected in the case of ciprofloxacin. The highest concentrations present in compost were 22 μg/kg of norfloxacin and 20 μg/kg of ciprofloxacin. Results show that before using the sewage sludge for making compost or before using the compost a fertilizer for food plants, they should be carefully tested against the content of commonly used pharmaceuticals.     

Samovar: a thermomechanical code for modeling of geodynamic processes in the lithosphere—application to basin evolution

We present a new 2D finite difference code, Samovar, for high-resolution numerical modeling of complex geodynamic processes. Examples are collision of lithospheric plates (including mountain building and subduction) and lithosphere extension (including formation of sedimentary basins, regions of extended crust, and rift zones). The code models deformation of the lithosphere with viscoelastoplastic rheology, including erosion/sedimentation processes and formation of shear zones in areas of high stresses. It also models steady-state and transient conductive and advective thermal processes including partial melting and magma transport in the lithosphere. The thermal and mechanical parts of the code are tested for a series of physical problems with analytical solutions. We apply the code to geodynamic modeling by examining numerically the processes of lithosphere extension and basin formation. The results are directly applicable to the Basin and Range province, western USA, and demonstrate the roles of crust–mantle coupling, preexisting weakness zones, and erosion rate on the evolutionary trends of extending continental regions. Modeling of basin evolution indicates a critical role of syn-rift sedimentation on the basin depth and a governing role of Peierls deformation in cold lithospheric mantle. While the former may increase basin depth by 50%, the latter limits the depth of rift basins by preventing faulting in the subcrustal lithosphere.