Search

The Vinschgau Shear Zone (VSZ) is one of the largest and most significant shear zones developed under plastic conditions within the Austroalpine domain, juxtaposing the Ötztal and the Texel units to the Campo, Scharl and Sesvenna units during the building of the Eo-Alpine Orogen. The VSZ dominates the structural setting of a large portion of the central Austroalpine Late Cretaceous thrust stack. In order to fully assess the evolution of the VSZ, a multi-faceted approach based on detailed multiscale structural and petrochronological analyses has been carried out across representative transects of the shear zone in the Vinschgau Valley. The research has been performed with a view to characterizing kinematics, P-T conditions and timing of motion of the VSZ. Our fieldwork-based analyses suggest that the dip angle of mylonitic foliation increases from west to east with an E-W-trending stretching lineation which dips alternatively to the west and to the east, due to later folding related to the Cenozoic crustal shortening. The dominant top-to-W shear sense of the mylonites recognized in the field and confirmed by microstructural analyses led to exhumation of the upper Austroalpine nappes in the hanging wall of the shear zone; the Texel unit with Late Cretaceous eclogites and the Schneeberg and Ötztal units were all affected by Eo-Alpine amphibolite-facies metamorphism. Chemical and microstructural analyses suggest deformation temperatures of ca. 350-400C during shearing. Timing of deformation along the VSZ has been constrained for the first time through 40Ar/39Ar dating of syn-shearing micas, which reveal a Late Cretaceous age of the VSZ mylonites with ages ranging between 80 and 97Ma. A systematic younging age of deformation occurs towards the central part of the shear zone in the studied transects. Vorticity analysis shows a clear decrease in the simple shear component correlated to the younging of mica ages towards the core of the shear zone. This evolution is consis

Radiogenic strontium isotopes (87Sr/86Sr) of vein carbonates play a central role in the tectonometamorphic study of fold-and-thrust belts and accretionary wedges and have been used to document fluid sources and fluxes, for example, along major fault zones. In addition, the 87Sr/86Sr ratios of vein carbonates can trace the diagenetic to metamorphic evolution of pore fluids in accreted sediments. Here we present 87Sr/86Sr ratios of vein carbonates from the Infrahelvetic flysch units of the central European Alps (Glarus Alps, Switzerland), which were accreted to the North Alpine fold-and-thrust belt during the early stages of continental collision. We show that the vein carbonates trace the Sr isotopic evolution of pore fluids from an initial seawater-like signature towards the Sr isotopic composition of the host rock with increasing metamorphic grade. This relationship reflects the progressive equilibration of the pore fluid with the host rock and allows us to constrain the diagenetic to low-grade metamorphic conditions of deformation events, including bedding-parallel shearing, imbricate thrusting, folding, cleavage development, tectonic mélange formation and extension. The strontium isotope systematics of vein carbonates provides new insights into the prograde to early retrograde tectonic evolution of the Alpine fold-and-thrust belt and helps to understand the relative timing of deformation events. © The Author(s), 2022. Published by Cambridge University Press.

Vorticity estimates based on porphyroclasts analysis are limited by the extrapolation to three dimensions of two-dimensional data. We describe a 3D approach based on the use of X-ray micro-computed tomography that better reflects the real 3D geometry of the porphyroclasts population. This new approach for kinematic vorticity analysis in the Munsiari Thrust mylonites, the lower boundary of the Main Central Thrust zone (MCTz) in Indian Himalaya, indicates a large pure shear component during non-coaxial shearing. 40Ar/39Ar ages of micas along the mylonitic foliation of the Munsiari and Vaikrita thrusts (the upper boundary of the MCTz) constrain thrust activity to 5–4 and 8–9 Ma, respectively. Available kinematic vorticity analyses of the Vaikrita mylonites suggest the dominance of a simple shear component. Combining these data, we suggest that the southward and structurally downward shift of deformation along the MCTz was accompanied by a progressive increase in the pure shear component in a general shear flow.

Tephra layers are a unique tool for stratigraphy. Their geologically instantaneous deposition across wide areas makes them a powerful instrument for dating and correlating distant localities. In this paper, we apply tephra fingerprinting for high-resolution stratigraphic purposes in the upper Miocene portion of the Pisco Formation, which crops out along the southern Peruvian coast. The Pisco Formation diatomaceous strata host an important marine vertebrate Fossil-Lagerstätte, whose palaeontological relevance has entailed the necessity of reconstructing a detailed chronostratigraphic framework using 39 Ar– 40 Ar dating and tephra correlations. Distal ashes from the Central Andes volcanoes are frequent in the Pisco Formation, but their similar glass composition and mineral assemblage, together with the shallow marine environment limiting tephra preservation, could be unpromising for tephra-based correlations. In this study, tephra layers from measured stratigraphic sections were fingerprinted with a combined petrographic and microanalytical approach, including glass shard morphology and granulometric analyses. Based on the obtained results, we correlated sections several kilometres apart, greatly increasing the chronostratigraphic detail. Major element composition of biotite proved a valuable tool to discriminate the Central Andes metaluminous to peraluminous tephra deposited in the Peruvian forearc basins. This study highlights the applicability of tephra fingerprinting in unfavourable shallow marine environments.

The South Asian river dolphin (Platanista gangetica) is the only extant survivor of the large clade Platanistoidea, having a well-diversified fossil record from the Late Oligocene to the Middle Miocene. Based on a partial skeleton collected from the Chilcatay Formation (Chilcatay Fm; southern coast of Peru), we report here a new squalodelphinid genus and species, Macrosqualodelphis ukupachai. A volcanic ash layer, sampled near the fossil, yielded the 40Ar/39Ar age of 18.78±0.08Ma (Burdigalian, EarlyMiocene). The phylogenetic analysis places Macrosqualodelphis as the earliest branching squalodelphinid. Combined with several cranial and dental features, the large body size (estimated body length of 3.5 m) of this odontocete suggests that it consumed larger prey than the other members of its family. Together with Huaridelphis raimondii and Notocetus vanbenedeni, both also found in the Chilcatay Fm, this new squalodelphinid further demonstrates the peculiar local diversity of the family along the southeastern Pacific coast, possibly related to their partition into different dietary niches. At a wider geographical scale, the morphological and ecological diversity of squalodelphinids confirms the major role played by platanistoids during the EarlyMiocene radiation of crown odontocetes.

The Jurassic clay-rich aquitard sequence underlying the Swiss Molasse Basin is locally penetrated by unusually frequent veins consisting of calcite ± celestite, in particular in the Schlattingen-1 and Oftringen drill cores. The veins are linked to extensional brittle structures, with shear senses ranging between dip-slip and strike-slip. Deformation triggered transient and localised events of fluid flow within the aquitard followed by sealing of the structures by the vein minerals. Vein calcite was dated by LA-ICP-MS analysis using the U/Pb method. While this was a demanding undertaking, given the low U and high common Pb contents of calcite, 9 significant ages could be obtained. Two groups of ages can be distinguished, namely 31–39 and 11–18 Ma. Both age groups are consistent with the known regional tectonic evolution. The older age group corresponds to the main phase of rifting in the Upper Rhine Graben, a major crustal discontinuity, whose effects were not limited to the graben proper but affected large parts of the Molasse Basin. The younger age group is linked to crustal tilting and related extensional deformation. Isotopic compositions of O and C in vein calcite from the Schlattingen-1 core show substantial variability but do not discriminate between veins of the two age groups. In contrast,87Sr/86Sr ratios in veins show different signatures. The depth trend of87Sr/86Sr ratios in veins fits well with that in pore water obtained by rock squeezing. The two data sets define a trend of values increasing with depth, connecting the current values in the embedding Malm and Keuper aquifer waters. This trend is best explained as a near-steady-state diffusion profile. While advective mixing of waters originating from the embedding aquifers to produce the veins, implying structures that cross cut the whole low-permeability sequence, cannot be discarded on the basis of existing data, it is considered more likely that the veins have local fluid sources. These are mixtures

Many morphological elements in Cuba's landscape (e.g. marine terraces, tidal notches) demonstrate that coastal uplift has taken place, but the rate at which this occurs is not known. Carbonate phreatic overgrowths on speleothems have been found in a cave in Central North Cuba, ~1 km from the present coastline at 16 m asl. They form exceptional and unique mushroom-shaped speleothems and balconies decorating the walls of the rooms. These phreatic overgrowths on speleothems (POS) formed at the oscillating air–water interface in sea-level controlled anchialine lakes. U/Th dating of these overgrowths suggests ages that are compatible with the Marine Isotope Stage 5e (i.e. 130–115 ka). These POS have fixed this sea-level highstand and demonstrate that this part of Cuba has been subjected to a much lower uplift rate than previously reported, that is, less than 0.1 mm/year since the last interglacial.

The units of time (both absolute time and duration) most practical to use when dealing with very long times, for example, in nuclear chemistry and earth and planetary sciences, are multiples of the year, or annus (a). Its proposed definition in terms of the SI base unit for time, the second (s), for the epoch 2000.0 is 1 a = 3.1556925445×107 s. Adoption of this definition, and abandonment of the use of distinct units for time differences, will bring the earth and planetary sciences into compliance with quantity calculus for SI and non-SI units of time

Multichronometric analyses were performed on samples from a transect in the French-Italian Western Alps crossing nappes derived from the Briançonnais terrane and the Piemonte-Liguria Ocean, in an endeavour to date both high-pressure (HP) metamorphism and retrogression history. Twelve samples of white mica were analysed by 39Ar-40Ar stepwise heating, complemented by two samples from the Monte Rosa nappe 100 km to the NE and also attributed to the Briançonnais terrane. One Sm-Nd and three Lu-Hf garnet ages from eclogites were also obtained. White mica ages decrease from c. 300 Ma in the westernmost samples (Zone Houillère), reaching c. 300°C during Alpine metamorphism, to <48 Ma in the internal units to the east, which reached c. 500°C during the Alpine orogeny. The spatial pattern of Eocene K-Ar ages demonstrates that Si-rich HP white mica records the age of crystallization at 47-48 Ma and retains Ar at temperatures of around 500°C. Paleocene-early Eocene Lu-Hf and Sm-Nd ages, recording prograde garnet growth before the HP peak, confirm eclogitization in Eocene times. Petrological and microstructural features reveal important mineralogical differences along the transect. All samples contain mixtures of detrital, syn-D1 and syn-D2 mica, and retrogression phases (D3) in greatly varying proportions according to local variations in the evolution of pressure-temperature-fluid activity-deformation (P-T-a-D) conditions. Samples from the Zone Houillère mostly contain detrital mica. The abundance of white mica with Si > 6·45 atoms per formula unit increases eastward. Across the whole traverse, phengitic mica grown during HP metamorphism defines the D1 foliation. Syn-D2 mica is more Si-poor and associated with nappe stacking, exhumation, and hydrous retrogression under greenschist-facies conditions. Syn-D1 phengite is very often corroded, overgrown by, or intergrown with, syn-D2 muscovite. Most importantly, syn-D2 recrystallization is not limited to S2 schistosity domains; mic

Zircons were studied from high-pressure/low-temperature metamorphosed meta-igneous lithologies from Syros. These rocks carry several zircon generations related to each other by dissolution-reprecipitation processes. One generation is pristine zircon that shows growth zoning, relatively elevated contents of trivalent cations and high Th/U ratios. The other end-member is a skeletal zircon generation with negligible trivalent cation contents and low Th/U ratios (≤0·1). Texturally between these two, there is a range of zircon crystals with complex inclusion populations of Y-HREE-Th phases and fluid inclusions, showing variable progress of replacement- recrystallization. Both end-members yield distinct sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages. The pristine generation has an age of 80·2 ± 1·6 Ma from a metagabbro, and 76·4 ± 2·1 Ma from a meta-plagiogranite dyke. The skeletal, low-Th/U zircon generation yields an age of 52·4 ± 0·8 Ma. The older, Late Cretaceous, zircons are interpreted to date emplacement of the magmatic protoliths in a small segment of oceanic crust. The younger, Eocene, age, however, dates a zircon recrystallization event, which possibly coincides with high solubility and mobility of high field strength elements in a high-pressure aqueous fluid phase. Intergrowth relations between zircon and peak-metamorphic garnet, and excellent agreement of the U-Pb ages with white mica Ar-Ar ages for the same samples support the conclusion that Eocene is the true age of high-pressure metamorphism on Syros

Jörg Jenatsch, a leading freedom fighter during the Thirty Year's War in Graubünden, Switzerland, was assassinated on carnival 1639. Jenatsch's controversial biography and the unclear circumstances of his death inspired the formation of various legends, novels and films. In 1959, a skeleton discovered in the cathedral of Chur with remains of wealthy baroque clothing was tentatively attributed to Jenatsch. Here, we reassess the skeleton based on a new exhumation. Our multidisciplinary analysis and the head injuries are consistent with reports of the eyewitnesses of the crime, demonstrating that Jenatsch was killed from behind with a semi-sharp implement, supposedly an axe, as well as by a blow with a broad-surfaced object. Moreover, our facial reconstruction closely matches an oil portrait of Jenatsch, and the HIrisPlex system applied to DNA-extracts from the femoral bone reveals brown eye and dark brown hair colour, which coincides well with the portrait, too. Finally, isotope analysis of the femoral bone and a molar support Jenatsch's high social status, luxury diet and a high mobility in the last decade of his life. This multidisciplinary approach thus reinforces personal identification and provides additional insight into the life of this important historic person beyond written resources.

Jörg Jenatsch, a leading freedom fighter during the Thirty Year's War in Graubünden, Switzerland, was assassinated on carnival 1639. Jenatsch's controversial biography and the unclear circumstances of his death inspired the formation of various legends, novels and films. In 1959, a skeleton discovered in the cathedral of Chur with remains of wealthy baroque clothing was tentatively attributed to Jenatsch. Here, we reassess the skeleton based on a new exhumation. Our multidisciplinary analysis and the head injuries are consistent with reports of the eyewitnesses of the crime, demonstrating that Jenatsch was killed from behind with a semi-sharp implement, supposedly an axe, as well as by a blow with a broad-surfaced object. Moreover, our facial reconstruction closely matches an oil portrait of Jenatsch, and the HIrisPlex system applied to DNA-extracts from the femoral bone reveals brown eye and dark brown hair colour, which coincides well with the portrait, too. Finally, isotope analysis of the femoral bone and a molar support Jenatsch's high social status, luxury diet and a high mobility in the last decade of his life. This multidisciplinary approach thus reinforces personal identification and provides additional insight into the life of this important historic person beyond written resources.

This study investigates processes of sediment generation in equatorial central Africa. An original, complete and integrated mineralogical-geochemical database on silt-sized sediments derived from different parent rocks (basalt, granite, gneiss, metapsammite, sandstone) along the East African Rift from 5°S in Tanzania to 5°N in Sudan is presented and used to assess the incidence of diverse factors controlling sediment composition (source-rock lithology, geomorphology, hydraulic sorting, grain size, recycling), with particular emphasis on chemical weathering.