Experimental constraints on hydrogen diffusion in garnet

The incorporation mechanisms and diffusional loss of hydrogen in garnet have been experimentally investigated. A suite of gem-quality hydrous spessartine- and grossular-rich garnets were analysed by Fourier transform infrared spectroscopy (FTIR) and by ion microprobe (SHRIMP-SI) to determine the calibration coefficients for quantification of FTIR data. The excellent agreement between measured absorption and OH/O indicates that the same molar extinction coefficient can be used for spessartine and grossular. The coefficient of 14400 l mol^??1 cm^??2 proposed by Maldener et al. (Phys Chem Miner 30:337–344, 2003) seems the most appropriate for both minerals. A grossular with 6.4% andradite and 1.6% almandine containing 834 ppm H₂O, and an almost pure spessartine with 282 ppm H₂O, were selected for diffusion experiments. 1.5-mm cubes of garnets were heated between 12 h and 10 days at 1 atm under various temperature (750–1050 °C) and oxygen fugacity (\({f_{{{\text{O}}_2}}}\)) conditions, (ΔQFM +?15.2 to ??3.0). Diffusion profiles were acquired from sections through the cubes using FTIR, with a deconvolution algorithm developed to assess peak-specific behaviour. Different families of peaks have been identified based on their diffusive behaviour, representing hydrogen incorporated in different H-bearing defects. A dominant, fast, strongly \({f_{{{\text{O}}_2}}}\)-dependent oxidation-related diffusion mechanism is proposed \(\left( {\{ {{\text{M}}^{2+}}+{{\text{H}}^+}\} +\frac{1}{4}{{\text{O}}_2}={{\text{M}}^{3+}}+\frac{1}{2}{{\text{H}}_2}{\text{O}}} \right)\) (M=Fe, Mn) with a relatively low activation energy (158?±?19 kJ mol^??1). This diffusion mechanism is likely restricted by availability of ferrous iron in grossular. At low oxygen fugacity, this diffusion mechanism is shut off and the diffusivity decreased by more than three orders of magnitude. A second, slower hydrogen diffusion mechanism has been observed in minor bands, where charge balance might be maintained by diffusion of cation vacancies, with much higher activation energy (≈?200–270 kJ mol^??1). Spessartine shows clear differences in peak retentivity suggesting that up to four different H sites might exist. This opens exciting opportunities to use hydrogen diffusion in garnet as speedometer. However, it is essential to constrain the main diffusion mechanisms and the oxygen fugacity in the rocks investigated to obtain timescales for metamorphic or igneous processes.     

Laboratory experiments on three-dimensional deformable granular landslides on planar and conical slopes

Landslides of subaerial and submarine origin may generate tsunamis with locally extreme amplitudes and runup. While the landslides themselves are dangerous, the hazards are compounded by the generation of tsunamis along coastlines, in enclosed water bodies, and off continental shelves and islands. Tsunamis generated by three-dimensional deformable granular landslides were studied on planar and conical hill slopes in the three-dimensional NEES tsunami wave basin at Oregon State University based on the generalized Froude similarity. A unique pneumatic landslide tsunami generator (LTG) was deployed to control the kinematics and acceleration of the naturally rounded river gravel and cobble landslides to simulate broad ranges of landslide shapes and velocities along the slope. Lateral and overhead cameras are used to measure the landslide shapes and kinematics, while acoustic transducers provide the shape of the subaqueous deposits. The subaerial landslide shape is extracted from the camera images as the landslide propagates under gravity down the hill slope, and surface reconstruction of the landslide is conducted using the stereo particle image velocimetry (PIV) system on the conical hill slope. Subaerial landslide surface velocities are measured with a planar PIV system on the planar hill slope and stereo PIV system on the conical hill slope. The submarine deposits are characterized by the runout distances and the deposit thickness distributions. Larger cobbles are observed producing hummock type features near the maximum runout length. These unique laboratory landslide experiments serve to validate deformable landslide models as well as provide the source characteristics for tsunami generation.     

Geochemical and stable isotopic variability within two rivers rising under the same mountain,but belonging to two distant watersheds

Complementary geochemical and stable isotope investigations of the Gorski Kotar karst aquifer system in western Croatia were obtained for the first time, to answer the question whether both studied rivers drain the same aquifer system or not. The two main rivers, the Kupa and the Rje?ina, rise under the same mountain range, but belong to two different watersheds (Black Sea and Adriatic Sea). The karst aquifer of Gorski Kotar is a potentially important source of drinking water for two neighboring countries, Croatia and Slovenia (Central and South Europe), and is strongly influenced by both Mediterranean and continental weather conditions. It is a part of the Dinaric karst, which is “locus typicus” for karst worldwide and one of the most typical karst areas in the world.     

The earliest occurrence of peltasperms in the basal Permian strata of the North China Block and the radiation of this group

The peltasperm foliage Autunia naumannii (Gutbier) Kerp and possible peltasperm fructifications are for the first time described from the uppermost Taiyuan Formation of earliest Permian age near Wuda, Inner Mongolia. This is the oldest record of this group on the North China Block (Sino‐Korean Platform), indicating an early migration into this area. Data of other occurrences in China demonstrate independent radiations of the group in Cathaysia. All known records indicate that peltasperms probably originated in the tropical extrabasinal areas of Euramerica, and subsequently migrated within the tropical belt and experienced independent regional radiations in Europe, the southwestern United States and on the North China Block. The present discovery of Autunia naumannii (Gutbier) Kerp in China adds a common floral component between the Euramerican and Cathaysian floras, providing more evidence indicating mutual migration of floral elements between Cathaysia and Euramerica. Copyright © 2013 John Wiley & Sons, Ltd.     

Increased precipitation during the Little Ice Age in northern Taiwan inferred from diatoms and geochemistry in a sediment core from a subalpine lake

We studied diatoms in a 55.5-cm-long sediment core from a subalpine lake in northern Taiwan, Tsuifong Lake (TFL), to investigate environmental changes from AD 490 to present. Diatom assemblages of the last century were dominated by acidophilous species, whereas alkaliphilous taxa dominated the record between AD 1480 and 1910. Over the studied time frame, four decadal periods with high precipitation were inferred from evidence of elevated soil input from the watershed, supported by the stable isotope signatures (δ¹⁵N, δ¹³C) of organic matter and magnetic susceptibility of the sediments. We compared the inferred changes in pH of TFL to values obtained from three other Taiwanese subalpine lakes. The present study revealed that elevated precipitation was associated with increased solar irradiance over the last five centuries, with a stable dry period between AD 490 and 1450. Acidification of TFL in the last ~100 years was a consequence of deforestation and acid rain.     

Land subsidence pattern controlled by old alpine basement faults in the Kashmar Valley, northeast Iran: results from InSAR and levelling

Fluid storage systems, such as oil, gas, magma or water reservoirs, are often controlled by the host rock structure and faulted terrain. In sedimentary basins, where no direct information about underlying structure is available, the pattern of ground deformation may allow us to assess the buried fault arrangement. We provide an example in the semi-arid area of Iran, in the Kashmar Valley, a region subject to land subsidence due to water overexploitation. Geodetically determined subsidence rates in the Kashmar Valley exceed 15–30 cm yr⁻¹. The pattern of surface deformation is strongly non-uniform and displays NE–SW elongated bowls of subsidence. The trend resembles old Cretaceous-to-Tertiary faults that evolved during early alpine tectonic deformation. Although these early alpine structures are considered tectonically inactive in the present day, the observed land subsidence pattern indicates significant structural control on the geometry of the aquifer basin and its deformation during reservoir drainage.     

Soil and plant composition in the Noun river catchment basin,Western Cameroon: a contribution to the development of a biogeochemical baseline

Soils and selected edible plants of the Noun river catchment basin of western Cameroon were sampled to investigate the distribution of trace elements, based on the preliminary idea of unusual anomalies. Analytical techniques for trace elements included ICP-AES, GF-AAS, and ICP-MS. Further soil analyses comprised the mineralogy and contents of the biogenic elements carbon, nitrogen and sulphur (CNS). The trace element concentrations in the soils reflect those of the lithogeochemical background of the pluto-volcanic rocks of the region. This is consistent with the results from the mineralogical analyses and physicochemical parameters such as pH, taken in the field, which also do not suggest any geochemical anomaly. Most trace elements analyzed in the plants showed concentrations that reflect those of the soils (Al, Fe, Ti, and Rb). However, some trace elements were enriched in the plants as compared to the soils, such as Zn, Cu, Cd, Mo (excluding yam), Ni (peanut), Ba (peanut), Sr (peanut, bean), and B. Trace elements such as As, Cr, V, and Se were not bioavailable for all the analyzed plants. Besides, trace elements such as Cu, Zn, Mo, Fe, Al, Ni, B, Ti, Rb, Cs, and Ba were in the range of phytotoxicity and reached or exceeded human food tolerance level (Cu). The plants with seeds showed a higher absorption of trace elements compared to plants with tubercles.