Fingerprinting a multistage metamorphic fluid–rock history: Evidence from grain scale Sr,O and C isotopic and trace element variations in high-grade marbles from East Antarctica

Granulite grade marble layers interlayered with metapelitic granulites from Lützow Holm Bay, East Antarctica, provide insight into fluid–rock interactions during burial to and exhumation from lower crustal levels. Sub-millimeter scale strontium, oxygen and carbon isotope variations along with LA-ICPMS trace element geochemistry and mineral chemistry of texturally characterized carbonates and associated minerals helped to reconstruct the multistage metamorphic fluid history.Fluid–rock interaction dating back to prograde metamorphism are still preserved in consistently low oxygen and high strontium isotope compositions (δ¹⁸O = 12‰; ⁸⁷Sr/⁸⁶Sr_(550Ma) = 0.7248) within a massif dolomitic marble layer that escaped significant later metasomatism. In most marbles, total re-crystallization and isotopic resetting occurred in the presence of “externally derived” hyper-saline fluids that circulated along the carbonate layers during the early stages of prograde metamorphism. This leads to a trend of increased radiogenic Sr in marbles towards the value of associated metapelitic rocks that have ⁸⁷Sr/⁸⁶Sr_(550Ma) of 0.764.LA-ICPMS studies on trace elements in carbonate and associated silicate minerals at different textural settings, distinguished using cathodoluminescence microscopy, revealed multiple metasomatic events during retrograde metamorphism. Trace element contents of Ba, Sr, Pb and U gave compelling evidence for metasomatic alteration that postdate the exsolution of carbonate at ~ 600 ºC, which can be correlated with the fluids released from the crystallization of anatectic melts and pegmatites. Subsequently, meteoric fluid infiltration occurred at a shallower level of the crust and caused extreme oxygen isotopic heterogeneity (δ¹⁸O = 14.7 ~ ? 4.9‰) and imprinted high concentration of fluid mobile elements. Taken together our results emphasize the importance of integrating textural and chemical heterogeneities to reveal the multiple episodes of fluid–rock interaction processes in a dynamic continental crust, which has major implications on migration of fluids and material and help in formulating models on the geodynamic evolution of crust.     

Spatio-temporal variability in debris-flow activity: a tree-ring study at Geisstriftbach (Swiss Alps) extending back to AD 1736

Past debris-flow activity on the forested cone of the Geisstriftbach torrent (St. Niklaus, Valais, Swiss Alps) was assessed from growth disturbances in old conifer trees, providing a much improved record of past events. The study of 633 tree-ring sequences sampled from 252 European larch (Larix decidua Mill.), Norway spruce (Picea abies (L.) Karst.) and Silver birch (Betula pendula Roth.) trees allowed reconstruction of 53 debris-flow events since AD 1736. The spatial analysis of trees affected during particular events on the geomorphic map allowed for a spatial representation of individual events and a reconstruction of four flow patterns. Based on our results and Siegfried maps, we believe that before the formation of a dogleg near the cone apex in the late 1890s, debris flows preferentially used the channels located in the west-southwestern part of the Geisstriftbach cone. This study contributes to our understanding of debris-flow processes on cones and provides an example of how dendrogeomorphic techniques may help in the reconstruction and understanding of debris flows in Alpine areas.     

Using chloride and other ions to trace sewage and road salt in the Illinois Waterway

Chloride concentrations in waterways of northern USA are increasing at alarming rates and road salt is commonly assumed to be the cause. However, there are additional sources of Cl⁻ in metropolitan areas, such as treated wastewater (TWW) and water conditioning salts, which may be contributing to Cl⁻ loads entering surface waters. In this study, the potential sources of Cl⁻ and Cl⁻ loads in the Illinois River Basin from the Chicago area to the Illinois River’s confluence with the Mississippi River were investigated using halide data in stream samples and published Cl⁻ and river discharge data. The investigation showed that road salt runoff and TWW from the Chicago region dominate Cl⁻ loads in the Illinois Waterway, defined as the navigable sections of the Illinois River and two major tributaries in the Chicago region. Treated wastewater discharges at a relatively constant rate throughout the year and is the primary source of Cl⁻ and other elements such as F⁻ and B. Chloride loads are highest in the winter and early spring as a result of road salt runoff which can increase Cl⁻ concentrations by up to several hundred mg/L. Chloride concentrations decrease downstream in the Illinois Waterway due to dilution, but are always elevated relative to tributaries downriver from Chicago. The TWW component is especially noticeable downstream under low discharge conditions during summer and early autumn when surface drainage is at a minimum and agricultural drain tiles are not flowing.     

Geology of the Niederlausitz Lignite district, Germany

One of the largest brown coal producing districts in the world is the Miocene of Niederlausitz Lignite area in the southeastern part of Germany. Production is in a range of 320 million t/yr. The resources of the first (shallowest) Miocene seam have nearly been exhausted and it is now mainly the second seam which is being mined. A fourth is being explored. The third Miocene and the Oligocene seam, Calau, are unminable. All brown coal is mined in open pits. The rank of brown coal of the second Miocene seam ranges from fuel coal to coking coal. Its heat value (dry) from 22.2 to 23.5 MJ, its ash content (dry) from 6% to 13%, its moisture from 57% to 59%, and its seam thickness from 10 to 12 m. Due to the close relationship between swamp facies and the main coal quality parameters, the coal quality can be directly determined from the drill log.The Oligocene and Miocene brown coal formation was synchronous with the alpine orogenesis and the seafloor spreading of the North Atlantic Ocean, which both caused north and east oriented migrations of the labile basement of central Europe. Periods of compression alternated with longer periods of isostatic subsidence and sedimentation. Additionally, the trends of thickness and facies of sediments were controlled by a block system in the basement of the brown coal district of Niederlausitz, uplifting, subsiding, collapsing, rotating or spreading.The second Lower Miocene seam is situated at sea level in the north of the Niederlausitz area and rises to the south to +150 to +180 m above sea level, due to considerable widespread subsidence and uplifting since the Lower Miocene. Horizontal tectonic movements were caused by the collapse of asymmetric grabens with slight tendency to rotation. Regional shear movements led to block faulting followed by volcanism. Counter-clockwise rotation of the basement blocks is assumed, a hypothesis supported by recent tension measurements and seismic observations. Ice cover in the Pleistocene caused wide destruction zones, narrow and deep channels and intensively folded or imbricated seam structures. Some gravity-induced plastic structures were also formed.     

500-yr. precipitation variability in Southern Taihang Mountains,China, and its linkages to ENSO and PDO

An annually resolved and absolutely dated ring-width chronology spanning 657 yrs. is constructed with Whitebark pine (Pinus bungeana Zucc.) samples from the southern Taihang Mountains, Eastern China. On the basis of a significant correlation between the tree-ring width index and observed instrumental data, precipitation in current May is reconstructed for the region since AD 1510, with predictor variables accounting for 37.9 % of the variance in precipitation data. In agreement with other drought reconstructions, notable dry spells occur in the 1630s–1650s, 1680s–1700s, and 1770s–1800s, whereas wet periods prevail in the 1530s–1570s, 1840s–1870s, and 1950s-present. Wavelet analysis reveals clear 2–8, 20–40, and 80–130 yrs cycles at the 95 % confidence level for the reconstructed series over the past 500 yrs, suggesting possible linkages with the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Correlation analysis between the tree-ring series, ENSO, and PDO index further demonstrates that precipitation is negatively correlated with PDO and ENSO in the long term.     

OH-bearing planar defects in olivine produced by the breakdown of Ti-rich humite minerals from Dabie Shan (China)

The partial breakdown of Ti-chondrodite and Ti-clinohumite during exhumation from ultra-high pressure to amphibolite facies conditions in garnet-pyroxenites from Dabie Shan (China) produces coronas of olivine coexisting with ilmenite blebs. Fourier transform infrared (FTIR) spectra of this newly formed olivine exhibit absorption bands in the hydroxyl-stretching region. Two intense peaks were observed at 3,564 and 3,394 cm⁻¹, identical in energy to peaks in Ti-clinohumite. Transmission electron microscopy (TEM) of the same olivine domains revealed the presence of a complex (001) planar intergrowth. These interlayers have a 1.35 nm repeat distance, which is characteristic of clinohumite. Such interlayers are also enriched in Ti with respect to the adjacent olivine as shown by energy dispersive spectrometry. The combined evidence from FTIR spectroscopy and TEM indicates that OH is incorporated along Ti-clinohumite planar defects. This study provides evidence that the nominally anhydrous phase olivine may contain OH as a humite-type defect beyond the breakdown of the hydrous humite minerals and confirms earlier suggestions that Ti plays a key role in OH incorporation in mantle olivine. We suggest that olivine containing Ti-clinohumite defects is an important phase for water transport in subduction zones and for the storage of water in cold subcontinental mantle. However, these defects are unlikely to be stable in hotter parts of the oceanic mantle such as where basaltic magmas are generated.     

Illite mineral synthesis at surface temperatures

The synthesis of illite mixed-layer minerals at surface conditions is possible through precipitation of Al hydroxides from Si-, Mg- and K-containing solutions. It has been shown that amorphous hydroxides of Al, Fe, etc. are capable of coprecipitating silica even from very dilute solutions. By aging of these X-ray amorphous hydroxide—silica precipitates under certain conditions, clay minerals can be synthesized at low temperatures. The presence of Mg particularly favors the formation of three-layer clay minerals. Mg-rich Al hydroxide—silica precipitates permit formation of tri- and di-octahedral smectite, illite and chlorite. The formation of three-layer clay minerals is only possible when the precipitates contain at least 6% MgO. The precipitates stay amorphous if the Mg content is lower. The adsorption of Mg and K on the hydroxide—silica precipitate controls the illite or montmorillonite portion in the mixture of the three-layer silicates. There is a competition for K and Mg adsorption on the hydroxide—silica precipitates. Higher K concentration inhibits the three-layer mineral formation through the lowering of the Mg content in the precipitates. Illite mineral formation is favored under certain K/Mg ratios. Higher NaCl contents do not favor the three-layer mineral formation.The enrichment of Mg and K in the precipitates is not as large as the enrichment of Si in the hydroxides. This means that the illite mineral formation is only possible from solutions with a high-salt content like seawater.     

Degradation of chlorinated ethylenes by Fe0: inhibition processes and mineral precipitation

. Granular zero-valent iron was used for the treatment of groundwater pollution caused by chlorinated ethylenes, mainly TCE, cis-DCE and VC at an industrial site. The rapidly decreasing rates of de-chlorination in the initial phase were attributed to the precipitation of carbonates and the development of hydrogen by anaerobic corrosion. After 70 pore volumes, sulphate was reduced by bacteria. From this point in time, the degradation of TCE was slightly accelerated whereas the de-chlorination rates of the other chlorinated ethylenes decreased only slowly. This relative improvement was assumed to be caused by the uptake of electron-transfer-blocking hydrogen by bacteria. Because the overall trend of the degradation rates is negative we conclude that the inhibitive effect of carbonate precipitation and hydrogen formation cannot be compensated for by the positive influence of the activity of sulphate-reducing bacteria.