Evolution of the lithosphere in the area of the Rhine Rift System

The Rhine Rift System (RRS) forms part of the European Cenozoic Rift System (ECRIS) and transects the Variscan Orogen, Permo-Carboniferous troughs and Late Permian to Mesozoic thermal sag basins. Crustal and lithospheric thicknesses range in the RRS area between 24-36km and 50-120km, respectively. We discuss processes controlling the transformation of the orogenically destabilised Variscan lithosphere into an end-Mesozoic stabilised cratonic lithosphere, as well as its renewed destabilisation during the Cenozoic development of ECRIS. By end-Westphalian times, the major sutures of the Variscan Orogen were associated with 45-60km deep crustal roots. During the Stephanian-Early Permian, regional exhumation of the Variscides was controlled by their wrench deformation, detachment of subducted lithospheric slabs, asthenospheric upwelling and thermal thinning of the mantle-lithosphere. By late Early Permian times, when asthenospheric temperatures returned to ambient levels, lithospheric thicknesses ranged between 40km and 80km, whilst the thickness of the crust was reduced to 28-35km in response to its regional erosional and local tectonic unroofing and the interaction of mantle-derived melts with its basal parts. Re-equilibration of the lithosphere-asthenosphere system governed the subsidence of Late Permian-Mesozoic thermal sag basins that covered much of the RRS area. By end-Cretaceous times, lithospheric thicknesses had increased to 100-120km. Paleocene mantle plumes caused renewed thermal weakening of the lithosphere. Starting in the late Eocene, ECRIS evolved in the Pyrenean and Alpine foreland by passive rifting under a collision-related north-directed compressional stress field. Following end-Oligocene consolidation of the Pyrenees, west- and northwest-directed stresses originating in the Alps controlled further development of ECRIS. The RRS remained active until the Present, whilst the southern branch of ECRIS aborted in the early Miocene. Extensional strain across ECRIS amounts to some 7km. Plume-related thermal thinning of the lithosphere underlies uplift of the Rhenish Massif and Massif Central. Lithospheric folding controlled uplift of the Vosges-Black Forest Arc

Refined isotopic compositions of K, Ca and a complementary comparison of the 40K-40Ca, 40K-40Ar and 87Rb-87Sr chronometers

The K-Ar geochronometer and its more sophisticated Ar-Ar version are among the most used methods in geochronology. Recently the EarthTime initiative started the attempt to calibrate the Geochronological Time Scale with a precision of 0.1% by intercalibrating orbital tuning, absolute dating and relative dating. This requires the absolute dating to be of a precision of 0.1%. Such a precision is achievable on modern mass-spectrometers for the measurements of isotope ratios; however the accuracy of the Ar-Ar dating system strongly depends on the accuracy of the constants incorporated into the age equation. Three constants are used for Ar-Ar age calculations: 1) the age of the irradiation flux monitor; 2) the 40K isotopic abundance and 3) the 40K decay constant and its branching ratio. The first one has been an object of calibrations during the last two decades; and an age of some irradiation standards is claimed to be known with a precision of 0.1%. We did not focus on this problem and just briefly discuss the issue of the age of the Fish Canyon Tuff sanidine irradiation standard in Chapter 3. Two other constants are the subject of this study. The natural K isotopic composition has been measured in 1975 with the gravimetrical method, which yielded a high precision for the 41K/39K value, but an insufficient precision for the 40K/39K ratio, which is one of the key values for K-Ar and Ar-Ar dating. The isotopic compositions of two standards NIST SRM 918a and SRM 918b have been measured in the frame of this study and compared with the bulk Earth isotopic composition. I measured K isotopic composition on a thermal ionization mass spectrometer (TIMS Triton Plus) with the application of three different amplifiers, which allowed to acquire a wide dynamic range with high precision. Three measurement techniques have been applied: total evaporation, block total evaporation and conventional block measurements. Due to a high instrumental fractionation, total evaporation measurements did not give consistent results, thus the 40K/39K ratios have been normalized to the fixed and precise 41K/39K ratio of Garner et al. (1975) [Garner E.L. et al. 1975. J. Res. Natl. Bur. Stand. 79A, 713-725]. The resulting best estimate for the 40K/39K ratio is 0.000 125 116 ± 57 (2σ), corresponding to an isotopic abundance 40K/K = (1.1668 ± 8) × 104. This value is identical with previous estimations, but the uncertainty is five times better, which brings the uncertainty of 40K isotopic abundance from 0.35% to the desired level below 0.1%. 40K decay constants are more complicated to measure. Radioactive 40K decays to 40Ca and to 40Ar; the decay to Ar presumably has three paths, two of which can be measured and one that is calculated theoretically. Therefore the uncertainty on the 40K decay constants is relatively high, which limits the accuracy of the Ar-Ar dating tool. In this work the estimation of the 40K decay constants is approached by intercalibration of K-Ca and Ar-Ar with U-Pb and Rb-Sr ages of well-characterized magmatic samples with simple geological histories. This task itself relied on two subtasks: 1) developing a high precision K-Ca dating method and 2) dating samples with a well-known geological history, using the K-Ca, Ar-Ar and Rb-Sr methods, and comparing the obtained ages with published U-Pb reference ages. High precision K-Ca dating relies upon high precision Ca measurements. A unique high precision method for the simultaneous measurements of the full range of Ca isotopes was developed, which makes use of a TIMS Triton Plus especially designed for Ca measurements. This allowed to measure 40Ca/44Ca ratios with an outstanding reproducibility of 0.06‰. The method was first used to compare the internal consistency of published Ca isotopic compositions. The isotopic compositions of two Ca standards, NIST SRM 915a and SRM 915b, were found to be identical within uncertainty and in line with published values. Small samples measured in the frame of this study (<1μg) suffered from an intense instrumental fractionation, which cannot anymore be sufficiently corrected with a simple exponential law. Therefore the use of an additional term for the exponential fractionation correction, which eliminates the offset due to an insufficient instrumental fractionation correction, is suggested and applied here. Finally K-Ca combined with Rb-Sr and Ar-Ar dating was performed on four samples. Potential samples for intercalibration should be of considerable age with a “point-like” geological history which limits the choice to well described and already dated samples. Quantitative element profiles and semi-quantitative mapping by electron microprobe were essential to ensure that our samples did not suffer from recrystallization or any other post-emplacement processes. For the Archean Siilinjärvi carbonatite Rb-Sr and low precision Ar-Ar and K-Ca dating indicate the occurrence of a post-emplacement metamorphic event at 1869 Ma. The other three samples appear to have a “point-like” geological history. A sample from the Triassic Bolgokhtokh intrusion, Kotuy, Russia, was dated with the Ar-Ar system and yielded an 225 Ma age, however microscopic investigations showed a very prominent zonation, which prevented the use of this sample for the decay constant intercalibration. The Rubikon lepidolite, Namibia, yielded an 505 Ma Rb-Sr age consistent with a previously published U-Pb age. The low precision K-Ca age we obtained did not allow us, so far, to use this sample for the 40K decay intercalibration. The fourth sample from the Phalaborwa carbonatite complex not only shows a “point-like” geological history, but also yielded high precision Rb-Sr and K-Ca ages. The Rb-Sr age for this sample is coincident with previously reported U-Pb ages for this complex and K-Ca as well as Ar-Ar ages are ca. 1% younger. Results from this last sample allowed us to assess the 40K total decay constant. Within a reported range of the 40K branching ratios the most suitable decay constant is the one published by Min at al. (2000) [Min, K., Mundil, R., Renne, P.R., Ludwig, K.R., 2000. Geochim. Cosmochim. Acta 64, 73-98]. This constant is lower than the currently recommended value and has been previously reported to be the best-fit constant also for Ar-Ar and U-Pb ages intercalibrations. Thus this work presents a newly determined 40K/K ratio with a precision of 0.07%, as well as a narrowed down range of plausible 40K decay constants, and confirms the best fit total decay constant for 40K geochronometers. It also describes high precision static Ca measurements, recommends the most consistent Ca isotopic composition, determines isotopic compositions of two widely used Ca standards and finally proposes an improved fractionation correction for small Ca samples

Tectonic and metamorphic evolution of the Central Himalayan Domain in Southeast Zanskar (Kashmir, India)

La région du Zanskar, étudiée dans le cadre de ce travail, se situe au passage entre deux domaines himalayens fortement contrastés, la Séquence Cristalline du Haut Himalaya (HHCS), composée de roches métamorphiques et l'Himalaya Tethysien (TH), composé de séries sédimentaires. La transition entre ces deux domaines est marquée par une structure tectonique majeure, la Zone de Cisaillement du Zanskar (ZSZ), au sein de laquelle on observe une augmentation extrêmement rapide, mais néanmoins graduelle, du degré du métamorphisme entre le TH et le HHCS. Il a été établi que le HHCS n'est autre que l'équivalent métamorphique des séries sédimentaires de la base du TH. C'est principalement lors d'un épisode de mise en place de nappes à vergence sudouest, entre l'Eocène moyen et l'Oligocène, que les séries sédimentaires de la base du TH ont été entraînées en profondeur où elles ont subi un métamorphisme de type barrovien. Au début du Miocène, le HHCS à été exhumé en direction du sud-ouest sous forme d'une grande nappe, délimitée a sa base par le MCT (principal chevauchement central) et à son sommet par la Zone de Cisaillement du Zanskar. L'ensemble des zones barroviennes, de la zone à biotite jusqu'à la zone à disthène, a été cisaillée par les mouvements en faille normale au sommet du HHCS et se retrouve actuellement sur une épaisseur d'environ 1 kilomètre au sein de la ZSZ. La décompression associée à l'exhumation du HHCS a provoqué la fusion partielle d'une partie du HHCS et a donné naissance à des magmas de composition leucogranitiques. Grâce à la géothermobarometrie, et connaissant la géométrie de la ZSZ, il nous a été possible de déterminer que le rejet le long de cette structure d'extension est d'au moins 35?9 kilomètres. Une série d'arguments nous permet cependant de suggérer que ce rejet aurait pu être encore bien plus important (~100km). Les données géochronologiques nous permettent de contraindre la durée des mouvements d'extension le long de la ZSZ à 2.4?0.2 Ma entre 22.2?0.2 Ma et 19.8?0.1 Ma. Ce travail apporte de nouvelles données sur les processus métamorphiques, magmatiques et tectoniques liés aux phénomènes d'extension syn-orogeniques.&lt;br/&gt;&lt;br/&gt;The southeastern part of Zanskar is located at the transition between two major Himalayan domains of contrasting metamorphic grade, the High Himalayan Crystalline Sequence (HHCS) and the Tethyan Himalaya (TH). The transition between the TH and the HHCS is marked by a very rapid, although perfectly gradual, decrease in metamorphic grade, which coincides with a major tectonic structure, the Zanskar Shear Zone (ZSZ). It is now an established fact that the relation between the HHCS and the TH is not one of basement-cover type, but that the metasedimentary series of the HHCS represent the metamorphic equivalent of the lowermost sedimentary series of the TH. This transformation of sedimentary series into metamorphic rocks, and hence the differentiation between the TH and the HHCS, is the consequence of crustal thickening associated to the formation of large scale southwest vergent nappes within the Tethyan Himalaya sedimentary series. This, Middle Eocene to Oligocene, episode of crustal thickening and associated Barrovian metamorphism is followed, shortly after, by the exhumation of the HHCS as a, large scale, south-west vergent, nappe. Foreword The exhumation of the HHCS nappe is marked by the activation of two contemporaneous structures, the Main Central Thrust at its base and the Zanskar Shear Zone at its top. Extensional movements along the ZSZ, caused the Barrovian biotite to the kyanite zones to be sheared and constricted within the ~1 km thick shear zone. Decompression associated with the exhumation of the HHCS induced the formation of leucogranitic magmas through vapour-absent partial melting of the highest-grade rocks. The combination of geothermobarometric data with a geometric model of the ZSZ allowed us to constrain the net slip at the top of the HHCS to be at least 35?9 kilometres. A set of arguments however suggests that these movements might have been much more important (~ 100 km). Geochronological data coupled with structural observations constrain the duration of ductile shearing along the ZSZ to 2.4?0.2 Ma between 22.2?0.2 Ma and 19.8?0.1 Ma. This study also addresses the consequences of synorogenic extension on the metamorphic, tectonic and magmatic evolution of the upper parts of the High Himalayan Crystalline Sequence

Natural gas of radiolytic origin: An overlooked component of shale gas.

SignificanceNatural gas is a key fossil fuel as the world transitions away from coal toward less polluting energy sources in an attempt to minimize the impact of global climate change. Historically, the origin of natural gas produced from conventional reservoirs has been determined based on gas compositional data and stable isotope fingerprints of methane, ethane, and higher n-alkanes, revealing three dominant sources of natural gas: microbial, thermogenic, and abiotic. In our detailed synthesis of published natural gas data from a variety of unconventional hydrocarbon reservoirs worldwide, we demonstrate that there is a previously overlooked source of natural gas that is generated by radiolysis of organic matter in shales

Сверхлегкие генераторные модули для КВЧ-терапии

Разработаны миниатюрные генераторные модули для КВЧ-терапии, лег-ко фиксируемые в любом месте тела пациента. Могут быть использованы не только в медицине

Geosciences Roadmap for Research Infrastructures 2025–2028 by the Swiss Geosciences Community

This community roadmap presents an integrative approach including the most urgent infrastructure requests for the future development of geosciences in Switzerland. It recommends to strengthen the multidisciplinary nature of the geosciences by putting all activities under the roof of the Integrated Swiss Geosciences supported by four specific research infrastructure pillars. The roadmap represents the view of the Swiss scientific community in the field of geosciences and is a formal element of the process to elaborate the Swiss Roadmap for Research Infrastructures 2023. This bottom-up contribution to the identification and selection of important national and international research infrastructures has been coordinated by the Swiss Academy of Sciences (SCNAT) on a mandate by the State Secretariat for Education, Research and Innovation (SERI).ISSN:2297-1564ISSN:2297-157

Chemistry and Sr–Nd isotope signature of amphiboles of the magnesio-hastingsite-pargasite-kaersutite series in Cenozoic volcanic rocks: Insight into lithospheric mantle beneath the Bohemian Massif

Amphibole phenocrysts and xenocrysts from Cenozoic volcanic rocks of the Bohemian Massif (BM) belong to the magnesio-hastingsite-pargasite-kaersutite series. Their host rocks are mostly basaltic lavas, dykes and breccia pipe fills, less commonly also felsic rocks from rift zones along lithospheric block boundaries of the BM. The calculated p–T conditions suggest that almost all amphiboles crystallized in a relatively narrow temperature range (1020–1100 °C) at depths of 20–45 km (0.7–1.2 GPa) during the magma ascent. The initial 143Nd/144Nd and 87Sr/86Sr ratios of amphiboles (0.51266–0.51281 and 0.70328–0.70407, respectively) are similar to those of their whole rocks (0.51266–0.51288 and 0.70341–0.70462, respectively). This testifies to locally elevated proportions of recycled Variscan crustal material during melting of mantle peridotites rich in clinopyroxene–amphibole veins. These veins were formed by metasomatic fluids enriched in High Field Strength Elements and are isotopically similar to EM-1 mantle type.Fenokrysty a xenokrysty amfibolů kenozoických vulkanických hornin Českého masivu (ČM) náleží svým složením do magnesiohastingsit-pargasit-kaersutitové série. Jejich hostitelské horniny jsou především bazaltické lávy, žíly nebo brekciovité výplně komínů, méně často také felsické horniny z riftových zón podél hranic litosférických bloků ČM. Vypočtené p-T podmínky ukazují, že téměř všechny amfiboly krystalizovaly v relativně úzkém teplotním rozmezí (1020–1100 °C) v hloubkách 20–45 km (0,7–1,2 GPa) během výstupu magmatu. Iniciální izotopové poměry 143Nd/144Nd a 87Sr/86Sr v amfibolech jsou v rozmezí 0,51266–0,51281 a 0,70328–0,70407. To vypovídá o lokálně zvýšeném množství recyklovaného variského korového materiálu během tavení plášťového peridotitu bohatého na klinopyroxen-amfibolové žíly. Tyto žíly vznikly z metasomatických fluid obohacených o prvky s velkým iontovým potenciálem a jsou izotopově podobné obohacenému plášti typu 1 (EM-1)

Lead isotope evolution of the Central European upper mantle: Constraints from the Bohemian Massif

This study focuses on Pb isotope data and whole-rock geochemistry of intrusive and extrusive volcanic rocks of the Bohemian Massif that sampled the upper mantle. Special attention is paid on whether Late Palaeozoic to Quaternary Central European mantle-derived rocks sampled different mantle sources on a local to regional scale and through time.Tato studie se zabývá Pb izotopovými daty a horninovou geochemií intruzivních i výlevných vulkanických hornin Českého masivu, které vzorkovaly svrchní plášť. Speciální důraz je kladen na to, zda pozdně paleozoické až kvartérní středoevropské horniny odvozené z pláště vzorkují odlišné plášťové zdroje v lokálním až regionálním měřítku a v průběhu času

Constraining long-term denudation and faulting history in intraplate regions by multisystem thermochronology: An example of the Sudetic Marginal Fault (Bohemian Massif, central Europe)

The Rychlebské hory Mountain region in the Sudetes (NE Bohemian Massif) provides a natural laboratory for studies of postorogenic landscape evolution. This work reveals both the exhumation history of the region and the paleoactivity along the Sudetic Marginal Fault (SMF) using zircon (U-Th)/He (ZHe), apatite fission track (AFT), and apatite (U-Th)/He (AHe) dating of crystalline basement and postorogenic sedimentary samples. Most significantly, and in direct contradiction of traditional paleogeographic reconstructions, this work has found evidence of a large Cretaceous sea and regional burial (to >6.5 km) of the Carboniferous-Permian basement in the Late Cretaceous (~95–80 Ma). During the burial by sediments of the Bohemian Cretaceous Basin System, the SMF acted as a normal fault as documented by offset ZHe ages across the fault. At 85–70 Ma, the basin was inverted, Cretaceous strata eroded, and basement blocks were exhumed to the near surface at a rate of ~300 m/Ma as evidenced by Late Cretaceous–Paleocene AFT ages and thermal modeling results. There is no appreciable difference in AFT and AHe ages across the fault, suggesting that the SMF acted as a reverse fault during exhumation. In the late Eocene–Oligocene, the basement was locally heated to <70°C by magmatic activity related to opening of the Eger rift system. Neogene or younger thermal activity was not recorded in the thermochronological data, confirming that late Cenozoic uplift and erosion of the basement blocks was limited to less than ∼1.5 km in the study area