We consider the problem of surface segmentation, where the goal is to partition a surface represented by a triangular mesh. The segmentation is based on the similarity of the normal vector field to a given set of label vectors. We propose a variational approach and compare two different regularizers, both based on a total variation measure. The first regularizer penalizes the total variation of the assignment function directly, while the second regularizer penalizes the total variation in the label space. In order to solve the resulting optimization problems, we use variations of the split Bregman (ADMM) iteration adapted to the problem at hand. While computationally more expensive, the second regularizer yields better results in our experiments. In particular it removes noise more reliably in regions of constant curvature. In order to mitigate the computational cost, we present a manifold Newton scheme for the most expensive subproblem, which is related to the Riemannian center of mass on a sphere. This significantly improves the computational cost.

An intriguing aspect of accretionary orogen dynamics is the crustal growth of the West Gondwana margin throughout the Terra Australis Orogeny, particularly regarding the development of the Patagonian crust and whether it involved periods of collisional or non-collisional orogenesis. This study examines the Devonian tectono-thermal evolution of the western North Patagonian Massif (southern South America), through the investigation of high-grade metamorphic rocks associated with the Devonian arc of Central Patagonia. Phase equilibrium modelling and geothermobarometry indicate an initial MP-HT metamorphic event (M1) under contractional conditions at the amphibolite- to granulite-facies transition, with metamorphic conditions of 6.7 f 1 Kbar and 760 degrees C, previously dated at 379 f 5 Ma. Successive crustal thickening and associated anatexis are recorded by metamorphic conditions at 8.9 f 1 Kbar and 750 degrees C. Zircon U-Pb geochronology indicates leucosome crystallization at 360 f 2 Ma, while an associated megacrystic granite records a 368 f 2 Ma crystallization age, suggesting it represents an earlier magmatic pulse within the prolonged anatectic scenario. Decompression and cooling led to zircon crystallization near the solidus, marking an MP-MT (M2) metamorphic event at amphibolite facies conditions ( 6.5 Kbar and 620 degrees C), recorded by zircon ages of 353 f 2 Ma. A final retrograde metamorphic event (M3) is recorded at 660 degrees C and 4.6 Kbar with monazite ages of 323 f 5 Ma. This event is linked to decompression and intrusion of gondwanide magmatism. These metamorphic conditions reveals an overall counterclockwise P-T-t path for the Taquetren range from the Devonian to Carboniferous. Combined with the study of magmatic addition rates in the arc and forearc during the Devonian, this pattern supports an accretionary orogen model characterized by alternating periods of advancing and retreating subduction, potentially driven by trenchward and landward slab folding, which may account for short-cycle variation ( 15 Myr). These dynamic slab movements may have influenced variations in magmatic activity in the forearc and arc, coupled with shifts in metamorphic conditions and tectonic regimes.

Volcanic ash aggregation occurs during transport in the atmosphere when individual ash particles collide and stick together. It significantly impacts ash residence time in the atmosphere, with major consequences for hazard assessment and ash dispersal forecasts. Nonetheless, aggregation processes are still not adequately parametrized, mostly due to the low preservation potential of most aggregate types. We present here the first, detailed structural and morphological characterization of the major aggregate types, combining an innovative field collection strategy, which allows for the original aggregate structure to be preserved at deposition, coupled to X-Ray micro-tomography. Resulting observations together with weather information, allowed for the structure of fragile ash clusters and of the elusive cored Ash Pellets (cAP1s) to be fully resolved and their genesis to be better described. The collected dataset represents a fundamental advancement towards a comprehensive characterization of the principal aggregate categories, which is key to accurately interpreting and modelling the process of volcanic ash aggregation and dispersal.

We present a novel approach to denoising and inpainting problems for surface meshes. The purpose of these problems is to remove noise or fill in missing parts while preserving important features such as sharp edges. A discrete variant of the total variation of the unit normal vector field serves as a regularizing functional to achieve these goals. In order to solve the resulting problem, we use a version of the split Bregman (ADMM) iteration adapted to the problem. A new formulation of the total variation regularizer, as well as the use of an inexact Newton method for the shape optimization step, bring significant speed-up compared to earlier methods. Numerical examples are included, demonstrating the performance of our algorithm with some complex 3D geometries.

Patient specific brain mesh generation from MRI can be a time consuming task and require manual corrections, e.g., for meshing the ventricular system or defining subdomains. To address this issue, we consider an image registration approach. The idea is to use the registration of an input magnetic resonance image (MRI) to a respective target in order to obtain a new mesh from a template mesh. To obtain the transformation, we solve an optimization problem that is constrained by a linear hyperbolic transport equation. We use a higher-order discontinuous Galerkin finite element method for discretization and motivate the numerical upwind scheme and its limitations from the continuous weak space--time formulation of the transport equation. We present a numerical implementation that builds on the finite element packages FEniCS and dolfin-adjoint. To demonstrate the efficacy of the proposed approach, numerical results for the registration of an input to a target MRI of two distinct individuals are presented. Moreover, it is shown that the registration transforms a manually crafted input mesh into a new mesh for the target subject whilst preserving mesh quality. Challenges of the algorithm are discussed.

The measurements and application of triple O-isotope system is a relatively new and powerful tool in tracing water-rock interaction, allowing to distinguish the temperature-dependent fractionation from the water amount that interacted with the rock. While the use of O-18/O-16 fractionation between minerals and fluids is well-established, most natural mineral-water reactions remain uncharacterized in terms of the triple isotope fractionation (O-17/O-16 and O-18/O-16). The triple O-isotope approach is especially promising when it comes to natural samples, where an array of exchanged samples constrains the fluid endmembers. However, multiple exchange mechanisms are likely to occur between the reacting rock and water, which has not been investigated for triple O-isotopes. This study examines the triple O-isotope exchange between fluid and olivine experimentally, as this is a common reaction in nature and mechanisms/rates of reaction are societally important for CO2 sequestration. Water-olivine reaction in batch experiments was investigated at 275 degrees C at the saturated water vapor pressure of 59.5 bar. Reactants were loaded at mass ratios 0.6 to 2 and exchanged for periods of time between 44 and 1048 h. Local meteoric water and mantle olivine were taken as the initial reactants. The mineral products are brucite, serpentine and minor magnetite that occur as coatings on unreacted olivine as well as individual crystals. The progress of this dissolution-precipitation reaction was traced with the delta D-delta ' O-18-Delta ' O-17 values of reacted fluids and mineral products. After 1048 h of reaction, similar to 50 wt% of unreacted olivine remained. In general, experimental data conforms with the triple O-isotope fractionation factors calculated for the co-existing secondary minerals forming in equilibrium with fluid. However, there is scatter and deviations in the reacted fluid compositions likely driven by the difference in relative rates of secondary mineral formation and changing modal and chemical mineral composition. We observe that brucite and magnetite form abundant aggregates early in the progress of the reaction, while chrysotile forms fine-grained coatings that become abundant later. Since individual mineral-water fractionation 10(3)ln(18/16)alpha range over 10 parts per thousand with theta ranging between 0.51 and 0.53, the dynamic behavior of dissolution-precipitation mechanism during alteration of olivine is the main factor to the "wandering" triple O-isotope trajectories in our relatively short experiments.

In geological reservoirs, pore fluid chemistry can affect rock strength by inducing mineral dissolution, precipitation, and alteration, among other processes. Increasing pressure and temperature can shift deformation from localized to ductile, decreasing permeability and affecting reservoir exploitability. The role of fluid chemistry in this transition remains marginally understood. Deformation experiments were performed on a porous silicate sandstone (Adamswiller sandstone) at effective confinement pressures of 0, 20, and 100 MPa, under dry conditions and saturated with deionized water, pH 1 (0.1 M HCl), 6 M NaCl, and pH 13 (0.1 M NaOH) solutions. Spectral electrical conductivity was measured during deformation, and pore fluid chemistry variations were determined with ICP-MS and ICP-OS on pore fluid samples collected before and after the experiments. SEM microstructural analyses and chemical characterization were conducted post-mortem. Water presence and fluid chemistry had a marginal effect on localized deformation, reducing peak strength by 5%-10%. In the ductile regime, deionized water reduced strength by 25%, pH 1 and NaCl solutions by 30%, and pH 13 by 35%. Surface electrical conductivity increased during ductile deformation due to mineral alteration. Greater weakening in ductile samples was hypothesized to be linked to increased silica solubility and dissolution rates in chemically enriched solutions under higher effective pressures.

K2O-poor or trondhjemite leucosome is a common feature of migmatites in the Himalayas and other orogens. The origin of K2O-depleted leucosomes has been attributed to several melting scenarios, such as residuum left after melt extraction and magma accumulation. However, the process leading to the formation of leucosome of trondhjemite composition needs to be better understood. In the kyanite zone of the Higher Himalaya Crystallines (HHC) along the Bhagirathi valley, partial melting of metapelite resulted in the formation of two types of leucosomes: K2O enriched granitic L-1 leucosomes formed stromatic veins of variable thickness and K2O poor trondhjemitic L-2 leucosomes occur as patches and lenses. The L-1 leucosomes are characterized by positive and negative Eu anomaly, variable depleted REE content, and represent in-source leucosomes. The L-2 leucosomes are REE depleted, have small negative Eu anomaly (0.8-0.9), and show a clear trend for anatectic melt-residuum-protolith in major-oxide plots of compatible versus incompatible elements. The overall depletion of REE, Sc, V, Cr, Ni, Co, Ti, Th, Nb, Hf, P2O5, and Zr/Zr*

The concentric oscillatory zoning pattern of igneous zircon is generally interpreted as evidence for core to rim growth during magmatic crystallization. This interpretation anchors a wide variety of qualitative and quantitative studies of zircon age, chemistry, and texture. We show, via detailed trace element mapping, that euhedral magmatic zircon with apparently typical cathodoluminescence oscillatory zoning instead displays evidence of dendritic growth. This observation challenges the unique interpretation of oscillatory zoning in zircon. Dendritic growth occurs under conditions of substantial undercooling, resulting in disequilibrium trace element concentrations in the zircon. Geochronological and geochemical analyses of zircon with this type of growth history require a different interpretative framework, with implications for time scales of magmatic and volcanic systems.

Silicic large igneous provinces (SLIPs) are periods of particularly voluminous felsic volcanism in the geologic record. Previous work has suggested an overall long lifespan for SLIPs of 20 to 40 Myr, commonly punctuated by shorter-lived 'flare-ups' of higher volcanic productivity (1-5 Myr), but detailed studies of individual flare-up events are lacking. The Jurassic Chon Aike SLIP (CASP) is the product of an exceptional geological event wherein voluminous felsic volcanism (ca. 219,000 km(3)) was generated predominately via crustal anatexis over 45 Myr. We focus on the Late Jurassic El Quemado Complex (EQC), which marked the final stages of felsic volcanism for the CASP. In-situ U-Pb ages for the EQC previously suggested a duration of similar to 5 Myr; however, new high-precision CA-ID-TIMS ages indicate the total durations of ignimbrite successions were shorter than 350 kyr. A compilation of zircon U-Pb ages for the eight CASP formations in Patagonia and the Antarctic Peninsula reveals changes in volcanic duration between formations deposited in the intraplate relative to the continental margin, suggesting a spatial control over the magmatic lifespans of geographically restricted systems. We suggest that the rate of magmatism in the CASP was primarily controlled by heterogeneities in the crust, largely between Proterozoic igneous crust and younger, metasedimentary crust that was recently accreted relative to the timing of Jurassic volcanism. The observed duration of volcanism was modulated by these differences in crustal properties from the injection of mafic magmas into the lower crust during extension and mantle upwelling, following rollback of the subducting oceanic slab towards the Paleo-Pacific margin of Gondwana. The short duration in the EQC is the product of unique overlapping conditions that favored crustal melting and resulted in the voluminous ignimbrite flareup (10(4) km(3)) of some of the Earth's highest delta O-18 magmas measured.

Mechanisms relating to growth and/or compositional modification of zircon occur at the atomic scale. For felsic igneous systems, processes responsible for growth patterns in zircon have previously remained elusive as the volume of material needed to analyze these compositional features using traditional in-situ methods is considerably larger than the typical sub-micron scale distribution of trace elements. To illuminate some of these driving forces, we characterize and quantify minor and trace element concentrations in igneous zircon grains by combining methods of cathodoluminescence (CL) imaging, electron microprobe microanalysis (EMPA) elemental maps for Hf, Y, Yb and U or Th, and atom probe tomography (APT). We focus on igneous zircon from the Chon Aike Silicic Large Igneous Province (Patagonia) that provide novel insights into (1) dissolution and re-crystallization during crustal anatexis, (2) crystallization to produce oscillatory zonation patterns that are typical of igneous zircons, and (3) the incorporation of trace element impurities (e.g., P, Be, and Al) at the nanoscale. Significantly, these APT volumes provide nanoscale sampling of boundaries between oscillatory growth zones in an igneous zircon to reveal compositional zoning of Y and, to a lesser extent P, which appear as high-angle, planar features. These concentration boundaries measured on the order of 10 to 12 nm are difficult to reconcile with proposed mechanisms for generating fine-scaled oscillations. Lastly, we fit diffusional profiles to measured Y concentrations to provide an estimate on the maximum timescales of zircon growth prior to eruption, as a function of the temperature at which diffusion occurred. When combined with known pressure-temperature-time paths for the magmatic system considered, these extremely short diffusion profiles that are resolvable by APT provide a powerful method to constrain timescales of crystal growth.

To help understand bioapatite microstructures and related chemical variations, their impact on O‐isotope compositions measured and give insights on sample preparation, this study analysed conodonts and shark teeth prepared in different orientations through microanalytical and bulk sampling techniques: scanning electron microscopy (SEM); electron probe microanalysis (EPMA); continuous‐flow and high‐temperature reduction – isotope ratio mass spectrometry; and secondary ion mass spectrometry (SIMS). The SEM and EPMA measurements in conodonts allowed to distinguish the tissues commonly analysed by SIMS, which included albid and hyaline crowns but given their often small‐scale intergrowth, mixtures of these are difficult to avoid. In situ SIMS O‐isotope analyses provided different δ 18 O values: lower values with higher variance (16 ± 1‰ n = 13, 15.7 ± 1.9‰ n = 11) for mixed albid‐hyaline tissues, and higher, homogeneous values (17.1 ± 0.2‰, n = 13) for mainly hyaline tissues. Recent shark teeth δ 18 O SIMS value for dentine of the same tooth was 10‰ lower than the mean δ 18 O SIMS value for enameloid whereas the δ 18 O PO4 values measured for enameloid and dentine using the HTR method were identical. The variation of δ 18 O seems sensitive to analytical artefacts related to sample textures, caused during the sample preparation over more porous biomineral surfaces.

The forsterite zone of the Ubehebe Peak contact aureole, Death Valley, USA consists of an outer zone of tabular/jack-straw olivine and an inner zone of subequant polyhedral olivine. Subequant polyhedral forsterite crystals close to the intrusion are small and tabular forsterite crystals farther away are larger. To investigate the formation of the two morphologies, forsterite growth experiments were conducted in cold seal pressure vessels in the CaO-MgO-SiO2-CO2-H2O system. Forsterite precipitation follows a disequilibrium reaction pathway made of three reactions: [1] tabular forsterite growth from quartz and dolomite, [2] forsterite growth from tremolite dissolution, and [3] subequant polyhedral forsterite growth from tabular forsterite dissolution. Initially, quartz reacts with dolomite to simultaneously form twinned tabular forsterite and tremolite. As quartz reacts away, forsterite precipitation continues at a slower rate through tremolite dissolution. A second generation of forsterite then precipitates on top of some tabular forsterite but has different habit and tracht. Once all the tremolite reacts away, subequant polyhedral forsterite precipitation continues at an even slower rate through dissolution of tabular forsterite. The tabular morphology of jack-straw olivine is a consequence of twin-mediated unidirectional growth; the abundance of twins being due to rapid nucleation and growth at initially high reaction affinities. Twin junctions are preferential nucleation centers for steps, so faceted growth is enhanced on 100. This phenomenon is the twin plane re-entrant effect. Subequant polyhedral forsterite in the Ubehebe Peak inner contact aureole recrystallized and ripened from tabular forsterite. In the outer contact aureole, conditions were not conducive to recrystallization and ripening so well-developed tabular forsterite persists.

High-relief glacial valleys shape the modern topography of the Southern Patagonian Andes, but their formation remains poorly understood. Two Miocene plutonic complexes in the Andean retroarc, the Fitz Roy (49 degrees S) and Torres del Paine (51 degrees S) massifs, were emplaced between 16.9-16.4 Ma and 12.6-12.4 Ma, respectively. Subduction of oceanic ridge segments initiated ca. 16 Ma at 54 degrees S, leading to northward opening of a slab window with associated mantle upwelling. The onset of major glaciations caused drastic topographic changes since ca. 7 Ma. To constrain the respective contributions of tectonic-mantle dynamics and fluvio-glacial erosion to rock exhumation and landscape evolution, we perform inverse thermal modeling of a new data set of zircon and apatite (U-Th)/He from the two massifs, complemented by apatite 4He/3He data for Torres del Paine. Our results show rapid rock exhumation recorded only in the Fitz Roy massif between 10 and 8 Ma, which we ascribe to local mantle upwelling forcing surface uplift and intensified erosion around 49 degrees S. Both massifs record a pulse of rock exhumation between 7 and 4 Ma, which we interpret as enhanced erosion during the beginning of Patagonian glaciations. After a period of erosional and tectonic quiescence in the Pliocene, increased rock exhumation since 3-2 Ma is interpreted as the result of alpine glacial valley carving promoted by reinforced glacial-interglacial cycles. This study highlights that glacial erosion was the main driver to rock exhumation in the Patagonian retroarc since 7 Ma, but that mantle upwelling might be a driving force to rock exhumation as well. The isotopic system (U-Th)/He in apatite and zircon record the ages in which a rock experiences relatively low temperatures (200-60 degrees C) at shallow crustal depths (6-1 km). We present a new data set of low-temperature thermochronometers for rocks of the Fitz Roy and Torres del Paine mountains in the Southern Patagonian Andes. Fast rock cooling can be forced by intensified surface erosion, and/or tectonic and mantle activity. An episode of fast cooling between 10 and 8 Ma was identified in the Fitz Roy mountains, and mantle upwelling forcing surface uplift, combined with high fluvial erosion may have caused fast rock exhumation. A regional episode of fast rock cooling between 7 and 4 Ma causing 1-3 km of exhumation in the Fitz Roy and Torres del Paine is coincident with the onset of Patagonian glaciations, which would have enhanced erosion and, thus, rock exhumation. An episode of fast rock cooling in the Quaternary is recorded in Torres del Paine rocks, interpreted as enhanced fluvio-glacial erosion during the Plio-Pleistocene climate transition toward faster glacial/interglacial cycles. Therefore, we were able to quantify separately the effects of tectonics and climate changes on rock exhumation, what is usually difficult due to simultaneously occurring processes. Mantle upwelling in Southern Patagonia is the most likely mechanism forcing rock exhumation between 10 and 8 Ma in the Fitz Roy massif Apatite (U-Th)/He data reveal glacial erosion as the main driver to the exhumation of the Fitz Roy and Torres del Paine between 7 and 4 Ma Apatite 4He/3He data reveal intensified fluvio-glacial erosion in Torres del Paine as a result of the Plio-Pleistocene climate transition

Fossilized remains of marine calcifiers constitute the physical basis for reconstructions of both deep ocean and sea-surface temperatures going back millions of years, but paleoclimate records derived from their isotope and trace-element chemistry can be biased by diagenesis. Experiments simulating diagenesis in the presence of an 18O-rich seawater analogue were conducted with modern and 14 Myr old foraminifera (Ammonia sp.) tests to investigate their relative susceptibility to oxygen isotope exchange. The fossilized tests were of exceptional preservation and similar to modern tests in terms of structure and crystalline organization, but had experienced partial loss of embedded organic structures, thus a priori offering fewer preferential pathways for porewaters to penetrate the tests. NanoSIMS imaging revealed that oxygen isotope exchange was pervasive in fossil tests, with isotopic exchange occurring at approximately half the rate of modern tests. The results unequivocally show that fossil biocalcites are metastable and remain more susceptible to isotope exchange than abiotic calcites millions of years after sedimentation and burial.

The oxygen isotopic compositions of fossil foraminifera tests constitute a continuous proxy record of deep-ocean and sea-surface temperatures spanning the last 120 million years. Here, by incubating foraminifera tests in 18 O-enriched artificial seawater analogues, we demonstrate that the oxygen isotopic composition of optically translucent, i.e., glassy, fossil foraminifera calcite tests can be measurably altered at low temperatures through rapid oxygen grain-boundary diffusion without any visible ultrastructural changes. Oxygen grain boundary diffusion occurs sufficiently fast in foraminifera tests that, under normal upper oceanic sediment conditions, their grain boundaries will be in oxygen isotopic equilibrium with the surrounding pore fluids on a time scale of <100 years, resulting in a notable but correctable bias of the paleotemperature record. When applied to paleotemperatures from 38,400 foraminifera tests used in paleoclimate reconstructions, grain boundary diffusion can be shown to bias prior paleotemperature estimates by as much as +0.86 to −0.46 °C. The process is general and grain boundary diffusion corrections can be applied to other polycrystalline biocarbonates composed of small nanocrystallites (<100 nm), such as those produced by corals, brachiopods, belemnites, and molluscs, the fossils of which are all highly susceptible to the effects of grain boundary diffusion.

Abstract Background Left ventricular ejection fraction (LVEF) has prevailed as the gold standard for quantifying LV function in acute heart failure (AHF) for both clinical trials and routine clinical practice. Most landmark studies in AHF stratify patients according to LVEF-based cut-offs. AHF is a clinical syndrome resulting from insufficient cardiac output, defined as LV stroke volume (LVSV) x heart rate. Thus, LVSV and its derived value LVSV index (LVSVI = LVSV/body surface area) may be better suited than LVEF for assessing LV function and heart failure severity, as well as predicting outcome in AHF. Purpose This study compared the predictive power for 1-year all-cause mortality of readily available echocardiographic parameters related to LV function (LVEF, LVSV and LVSVI) in patients with AHF. Methods Automatic data extraction was performed in 966 patients fulfilling criteria for AHF, retrospectively included between 2015-19 in 4 tertiary centres in Switzerland constituting the SwissHeart Failure Network (SHFN). Patients were selected if they had a standardised TTE study performed upon diagnosis of AHF, wherein all necessary values were reported. Cut-off values were chosen in consideration of the cohort’s median values. Patient follow-up was censored at 365d. Values are displayed as medians and interquartile ranges. Hazard ratios (HR) for 1-year all-cause mortality were computed with univariate Cox Proportional Hazards models. Kaplan-Meier curves were derived along with log-rank p-values. Results Median values for the evaluated parameter were as follows: LVEF (%): 38 (28–54); LVSV (mL): 45 (35–58); LVSVI (ml/m2): 24 (19–31). 1-year all-cause mortality was 33.7% (326/966 patients). The highest predictive capacity for 1-year all-cause mortality was observed for LVSVI<25ml/m2 (HR = 1.57 [1.26–1.97], p<0.001), followed by LVSV<45ml (HR = 1.57 [1.26–1.96], p<0.001). The lowest predictive capacity was seen for LVEF<40% (HR = 1.35 [1.08–1.68], p = 0.007, Figure 1). Applying the rounded medians as cut-off values, Kaplan-Meier curves showed greater divergence for higher vs. lower LVSVI (log-rank p<0.001) than for higher vs. lower LVEF (log-rank p = 0.007, Figures 2A and 2B). For patients with higher LVSVI, mortality rates did not change irrespective of higher or lower LVEF (Figure 2C, blue vs. green curves: log-rank p = 0.885). Patients with lower LVEF showed significantly higher mortality when they also had lower LVSVI (green vs. orange curves: log-rank p= 0.001). Conclusions In patients with AHF, LVSV and its derived value LVSVI are superior in predicting 1-year all-cause mortality compared to LVEF. Requiring the same echocardiographic measurements and thus being as readily available as the currently prevailing LVEF, the assessment of LVSV and LVSVI deserves intensified attention, both for future studies and clinical routine.Figure 1:Hazard RatiosFigure 2:Kaplan-Meier Analyses

The volcanic rocks of the Chon Aike Silicic Large Igneous Province (CASP) are recognized as magmas dominantly produced by crustal anatexis. Investigating the zircon of the CASP provides an opportunity to gain further insight into geochemical and isotopic differences of the potential magmatic sources (i.e., crust versus mantle), to identify crustal reservoirs that contributed to the felsic magmas during anatexis, and to quantify the contributions of the respective sources. We present a combined zircon oxygen and hafnium isotope and trace element dataset for 16 volcanic units of the two youngest volcanic phases in Patagonia, dated here with LA-ICP-MS U–Pb geochronology at ca. 148–153 Ma (El Quemado Complex, EQC) and ca. 159 Ma (western Chon Aike Formation, WCA). The EQC zircon have 18 O-enriched values (δ 18 O from 7 to 9.5‰) with correspondingly negative initial εHf values (− 2.0 to − 8.0). The WCA zircon have δ 18 O values between 6 and 7‰ and εHf values ranging between − 4.0 and + 1.5. Binary δ 18 O-εHf mixing models require an average of 70 and 60% melt derived from partial melting of isotopically distinct metasedimentary basements for the EQC and WCA, respectively. Zircon trace element compositions are consistent with anatexis of sedimentary protoliths derived from LIL-depleted upper continental crustal sources. The overlap between a high heat flux environment (i.e., widespread extension and lithospheric thinning) during supercontinental breakup and a fertile metasedimentary crust was key in producing voluminous felsic volcanism via anatexis following the injection and emplacement of basaltic magmas into the lower crust.

The Schistes Lustrés form a large and complex unit at the top of the Penninic nappe stack of the Alpine belt. Calcschists, partly of Late Cretaceous age, constitute the dominant lithology. They are closely associated both with blueschist facies Piemont-Ligurian ophiolites and continent-derived Mesozoic metasediments. The question of whether the Schistes Lustrés originated on continental or oceanic crust has been extensively debated among Alpine geologists and is locally still controversial. We present here new structural and stratigraphic observations, as well as Raman graphite thermometry (RSCM) data, for the Schistes Lustrés complex of the Combin zone in the Hérens, Dix and Bagnes valleys. Our observations indicate that the basal part of this Schistes Lustrés complex (defined as the Série Rousse) is systematically devoid of ophiolitic material, and rests in stratigraphic contact on the underlying Triassic - Lower Cretaceous metasediments and Paleozoic basement of the Mont Fort nappe (Prepiemont paleogeographic domain). The unconformity at the base of the Schistes Lustrés complex is interpreted as resulting from the sedimentation of the Série Rousse on a paleorelief formed by remnants of Jurassic normal fault scarps, and not as an Alpine tectonic contact, as previously proposed. The lithostratigraphic comparison with the Breccia nappe in the Prealps, as well as a foraminifer discovery, allows us to better constrain the age of the Série Rousse. It extends from the middle of the Early Cretaceous (Aptian?) to the Late Cretaceous (Campanian to earliest Maastrichtian?). In contrast, the upper contact of the Série Rousse with the ophiolite-bearing Schistes Lustrés clearly corresponds to an Alpine thrust. The thrust zone is underlined by thin and discontinuous slices of highly strained continental-margin derived Mesozoic metasediments (Frilihorn slices). RSCM data show that the recrystallization of the organic matter progressively increases on both sides towards this contact. This contact, internal to the Schistes Lustrés complex, is reinterpreted as the major tectonic contact separating the Middle Penninic Mont Fort nappe from the Upper Penninic Tsaté nappe (defined here as including only the ophiolite-bearing Schistes Lustrés and associated meta(ultra-)basites). This study clearly documents that the Schistes Lustrés consist of sediments either deposited on oceanic crust, showing locally preserved stratigraphic contacts with ophiolitic or serpentinized sub-continental mantle slivers, or sediments still resting stratigraphically on a former hyper-extended continental margin.