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High-pressure and ultra-high-pressure metamorphic terrains display an internal architecture consisting of a pile (or stack) of several coherent tectonic thrust sheets or units. Their identification is fundamental for understanding the scale and mechanisms active during subduction and exhumation of these crustal slices. This study investigates the geometry of the northern Dora-Maira Massif and the kinematics of the major tectonic boundaries, combining field and geochronological data. The tectonic stack of the northern Dora-Maira Massif comprises the following units. The lowermost unit (the Pinerolo Unit) is mainly characterized by Upper Carboniferous fluvio-lacustrine (meta-)sediments. The Pinerolo unit is overthrust by a pre-Carboniferous basement. The latter is subdivided in two tectonic units (the Chasteiran and Muret Units) with different Alpine metamorphism (ultra-high-pressure and high-pressure, respectively). The pre-Carboniferous basement of the Muret Unit is thicker than previously thought for two main reasons. Firstly, some paragneisses, traditionally assumed to be Carboniferous and/or Permian in age, display detrital zircon ages indicating a main source at about 600 Ma. Secondly, three samples of the Granero Orthogneiss, previously assumed to be a Permian intrusive body, have provided zircon U–Pb ages of 447 ± 1 Ma, 456 ± 2 Ma and 440 ± 2 Ma, indicating a late Ordovician or early Silurian age for the protoliths. The uppermost unit (the Serre Unit) comprises porphyritic (meta-) volcanic and volcaniclastic rocks dated to the Permian (271 ± 2 Ma), on top of which remnants of the Mesozoic cover is preserved. Detailed mapping of an area about 140 km2 shows that (i) the ultra-high pressure Chasteiran Unit is localized at the boundary between the Pinerolo and Muret Units, (ii) the Granero Orthogneiss may be considered as the mylonitic sole of the Muret Unit, characterized by a top-to-W sense of shear, and (iii) the contact between the Muret and Serre Units displays ductile-to brittle structures (La Fracho Shear Zone), indicating a top-to-the-NW displacement of the hangingwall with respect to the footwall. A final episode of brittle faulting, cutting across the nappe stack (the Trossieri Fault), indicates an extensional stage in the core of the Alpine belt, as previously documented in more external zones. This work provides a necessary and robust basis before an accurate discussion of processes acting during continental subduction of the Dora-Maira Massif may be understood. [ABSTRACT FROM AUTHOR]

The provenance of Triassic Vieux Emosson Formation, autochthonous sediments of the Aiguilles Rouges massif (External Alps), was determined from U–Pb ages of detrital zircons. In addition, two samples of Late Carboniferous sandstones from the Salvan‐Dorénaz basin were included to extend the database of potential source rocks. Overall, age data from the four samples are largely comparable, each with a wide range of ages, indicating similar source rocks. The compositionally and texturally immature strata of the Vieux Emosson Formation suggest a local sediment source. However, not all detrital zircons can be accounted for by the ages of the local polymetamorphic pre-Mesozoic basement, which consists mainly of paragneiss, Ordovician orthogneiss and Late Carboniferous, Variscan-related, magmatic and sedimentary rocks. Ordovician zircons were common in the samples, but Late Carboniferous zircons were only abundant in one sample. Early Cambrian and older zircons were likely recycled from the paragneiss. Recycled zircons primarily represent Cadomian orogenic events (~ 550–650 Ma); older zircons are from eastern Gondwana and West African craton sources. Abundant late Cambrian (~ 500 Ma) and Silurian (~ 425 Ma) zircons likely represent Cadomian rifting and the magmatic events that produced the Ordovician orthogneiss, respectively. Permian zircons were only found in one Triassic sample, and are possibly related to magmatic activity associated with post-Variscan extension. The age data of the detrital zircons in the Triassic Vieux Emosson Formation and in the sandstones from the Late Carboniferous Salvan-Dorénaz basin indirectly dates the source rocks and for the first time confirms Cadomian basement in the Aiguilles Rouges massif. Source rocks for the Silurian, Permian, and to a lesser degree, late Cambrian zircons are not documented in the local basement, and either have been eroded away or are now located to the southeast beneath Penninic nappes. [ABSTRACT FROM AUTHOR]

Rock surface dating, a relatively new approach within luminescence dating, determines when a rock surface was last exposed to sunlight by measuring the amount of latent OSL signal accumulated after burial. However, the potential and applicability of rock surface dating in glaciofluvial settings of the Alps has seen very limited application so far (Rades et al., 2018). Therefore, different luminescence methods including rock surface dating have been applied in a unique setting at the Hartheim gravel pit in the southern Upper Rhine Graben to establish a chronological frame for distal glaciofluvial deposits. First, a detailed field study was conducted in order to gather a comprehensive understanding of the different sediment types present. Fine grain sand, cobbles, pebbles and matrix sediments embedded within large clasts were collected and analyzed using a combination of OSL and IRSL dating. Conventional OSL dating of fine sand quartz is considered as robust age control compared to the other sediment types. A substantial amount of luminescence measurement has been done on the sand lens and gravel matrix sediment collected from Hartheim. OSL ages range around from ca. 19 ka to 32 ka for the different sediment types. Feldspar IRSL has been measured using a MET-pIRIR protocol to avoid problems with fading. Furthermore, a detailed dosimetry study was conducted to measure the varying levels of radionuclide concentration within materials of different grain size, in order to obtain accurate depositional ages. Overall, the purpose of this research contributes to our existing knowledge in the field of luminescence dating by showing the potential and versatility of different luminescence methods in different sediment types and environments that provide an ideal framework for future studies in similar contexts. [ABSTRACT FROM AUTHOR]

Dating the construction of dry-stone walls is challenging since such structures are typically built without any mortar that can be used for dating. Rock surface luminescence dating is a developing dating method that could advance chronological insights from structures constructed using dry-stone techniques. This study explores rock surface luminescence dating by targeting dry-stone walls from two enclosure complexes and a hut located in the pastoral upland landscape in Val di Sole, Italy. Gneissic rocks were collected from the dry-stone walls, including surfaces that were either exposed or covered (buried) during the time of sampling. Their respective exposure and burial histories were investigated by measuring the luminescence intensity in feldspar minerals from polymineral rock slices. From covered rock surfaces from one enclosure complex, we calculated recent burial ages (∽ 200 a) from one rock, and burial of ∽ 500 a (bottom surface) and 3750 ± 660 a (top surface) from a second rock. The top surfaces of two additional rocks date the construction of an adjacent hut to the Early Middle Ages. The luminescence-depth profile from one such rock has a complex exposure and burial history, including events that predate the hut's construction. Fitted exposure ages from a second enclosure complex suggest with significant errors either a recent age (<10 a) or construction during the 19th century AD. Burial dating using rock surface luminescence dating appears feasible for dry-stone walls provided that the rock surface was sufficiently exposed before being incorporated into the structure; here, the gneissic surfaces were bleached to depths of ∽ 0-2 mm before the last burial. Contrariwise, exposure dating generally underestimates the expected age. The variation in ages observed from our rock surfaces indicates that the degree of preservation of the wall, the position of the rock, erosion, and knowledge regarding the general archaeological setting are essential to interpreting the estimated ages. In this study, rock surface luminescence dating provides new, previously inaccessible chronological data with implications for interpreting human activities in the alpine areas of Val di Sole. [ABSTRACT FROM AUTHOR]

Rock glaciers, usually preserved in periglacial environments of cold-climate high-relief regions, are useful (palaeo)climate indicators. In the European Alps, numerous studies have focused on describing these geomorphological features. However, very few have attempted directly dating them. This lack of measurement is particularly evident in the French Alps. To fill this gap, we performed Cosmic Ray Exposure (CRE) dating through beryllium-10 (10Be) on 10 granitic rock samples collected from two relict rock glaciers, hereafter referred as RG1 and RG2, located at col du Lautaret in the French Alps. This first CRE dating of rock glaciers in the French Alps yielded mean ages of 11.8 ± 0.5 kyrs and 11.6 ± 0.6 kyrs for RG1 and RG2, respectively. While RG2 is clearly a talus-derived rock glacier, the origin of RG1 is less clear. It could potentially be talus-derived, glacier-derived or of mixed origin. The 10Be ages indicate that both rock glaciers became inactive during the transition between the Younger Dryas and the onset of the Holocene, consistently with other studies in the Northern Hemisphere. Considering surface velocity measurements carried out since the 1980s on neighbouring rock glaciers, we hypothesise that the rock glaciers were formed either during the Younger Dryas or slightly earlier, between the Heinrich Stadial 1 and the Younger Dryas. During this period, we estimated temperatures ~3.6 °C lower than the 1980s and precipitation up to 30% lower than at present. • We performed the first direct 10Be dating of two rock glaciers in the French Alps. • Both glaciers were probably formed between Heinrich Stadial 1 and the Younger Dryas. • We suspect they became inactive at about 11 kyrs. • This pattern is consistent with other rare observations from the Alps and Pyrenees. • Rock glacier formation may be associated to temperatures ~3.6 °C lower than in the 1980s. [ABSTRACT FROM AUTHOR]

Abstract: Between the cities of Domodossola and Locarno, the complex “Centovalli Line” tectonic zone of the Central Alps outlines deformation phases over a long period of time (probably starting ~30Ma ago) and under variable P–T conditions. The last deformation phases developed gouge-bearing faults with a general E–W trend that crosscuts the roots of the Alpine Canavese zone and the Finero ultramafic body. Kinematic indicators show that the general motion was mainly dextral associated with back thrusting towards the S. The <2μm clay fractions of fault gouges from Centovalli Line consist mainly of illite, smectite and chlorite with varied illite–smectite, chlorite–smectite and chlorite–serpentine mixed-layers. Constrained with the illite crystallinity index, the thermal conditions induced by the tectonic activity show a gradual trend from anchizonal to diagenetic conditions. The <2 and <0.2μm clay fractions, and hydrothermal K-feldspar separates all provide K–Ar ages between 14.2±2.9Ma and roughly 0Ma, with major episodes at about 12, 8, 6 and close to 0Ma. These ages set the recurrent tectonic activity and the associated fluid circulations between Upper Miocene and Recent. On the basis of the K–Ar ages and with a thermal gradient of 25–30°C/km, the studied fault zones were located at a depth of 4–7km. If they were active until now as observed in field, the exhumation was approximately 2.5–3.0km for the last 12Ma with a mean velocity of 0.4mm/y. Comparison with available models on the recent Alpine evolution shows that the tectonic activity in the area relates to a continuum of the back-thrusting movements of the Canavese Line, and/or to several late-extensional phases of the Rhône–Simplon Line. The Centovalli–Val Vigezzo zone therefore represents a major tectonic zone of the Central–Western Alps resulting from different interacting tectonic events. [Copyright &y& Elsevier]

The Triassic succession of the central Southern Alps (Italy) is stacked into several units bounded by south-verging low-angle thrust faults, which are related to two successive steps of crustal shortening. The thrust surfaces are cut by high-angle extensional and strike-slip faults, which controlled the emplacement of hypabissal magmatic intrusions that post-date thrusts motions. Intrusion ages based on SHRIMP U-Pb zircon dating span between 42 ± 1 and 39 ± 1 Ma, suggesting close time relationships with the earliest Adamello intrusion stages and, more in general, with the widespread calc-alkaline magmatism described in the Southern Alps. Fission-track ages of magmatic apatites are indistinguishable from U-Pb crystallization ages of zircons, suggesting that the intrusion occurred in country rocks already exhumed above the partial annealing zone of apatite (depth < 2-4 km). These data indicate that the central Southern Alps were already structured and largely exhumed in the Middle Eocene. Although we describe minor faults affecting magmatic bodies and local reactivations of older structures, no major internal deformations have occurred in the area after the Bartonian. Neogene deformations were instead concentrated farther south, along the frontal part of the belt. [ABSTRACT FROM AUTHOR]

One of the most significant topics in the history of Alpine geology involves the practice which began in the late eighteenth century of incorporating the sense of geohistory as recorded in the strata within the primarily structural classification of formations and mountains. Historical studies concerning this aspect in the scientific literature and unpublished primary sources related to the Alps and the pre-Alps from this period have shown that rocks and formations were then considered as central elements in a proto-stratigraphy or lithostratigraphy, which as yet was not based on the prominent use of fossils. This article presents an introductory overview of some pivotal eighteenth-century studies to suggest their role in the development of historical geology. [ABSTRACT FROM AUTHOR]

Abstract: Kyanite–staurolite–garnet micaschists from the Plankogel unit, Saualpe–Koralpe region, Eastern European Alps, document a poly-metamorphic evolution. Textures indicate two stages of garnet growth, interpreted as (i) relics of an early, pre-Alpine metamorphic event and (ii) newly-grown garnet of Alpine age. The age of the first crystallisation event during prograde Permian metamorphim is constrained by Sm–Nd dating of the almandine-rich garnet core domains. Mineral–wr ages of nine high-Sm/Nd garnet single crystal core fractions from three distant localities (Laaken, SE Koralpe; Plankogel, NW Saualpe; Friesach, E Gurktal Alps) range between 275.0±2.7 and 264.1±3.6 Ma. The pooled mean regression age of just the garnet fractions is 269.6±6.2 Ma (MSWD=4.3; n =9), with an initial Nd isotope composition of εNd(270)=−8.6. Leaching experiments and whole rock analyses revealed slight Nd isotope disequilibrium between garnet porphyroblasts, REE-rich inclusions, and the matrix of the polyphase mineral assemblage. Kyanite inclusions in the inner and sillimanite in the outer parts of the garnet cores, decreasing grossular and increasing pyrope contents indicate variable pressure/temperature conditions during Permian garnet growth. Modelling of mineral assemblages in pressure–temperature pseudosections suggests that the first-generation, Permian garnet crystallized at about 0.46 GPa and 540 °C, whereas the eo-Alpine garnet documents distinctly higher pressures of 1.0 GPa and 600 °C. The data document regional prograde metamorphism in metapelites, at low or moderate pressure conditions, during the Middle Permian. Crustal-scale extensional processes and heat input from the mantle, induced by ongoing Paleotethys subduction and Neotethys opening in the course of the separation of Europe and Africa-related Adria were responsible for this low-P tectonothermal event. [Copyright &y& Elsevier]

We discuss the important role of tangential stretching in the Central Alps highlighting that the Alps are a truly three-dimensional orogen. A review of pressure-temperature (P-T) conditions allows us to define three major breaks in metamorphic pressure (P-breaks) across the nappe pile. We constrain the kinematics of mylonites associated with these P-breaks and report eight new Rb Sr multi-mineral isochrons that define the age of the mylonites. Kinematic data and Rb Sr geochronology indicate that the timing of top-SE normal shearing in the Avers-Turba mylonite zone (≥45–34 Ma; P-break1) and in a zone of distributed top-E normal shearing (>35–30 Ma) above the (ultra)high-P Adula nappe of the distal, thinned European margin (P-breaks 2 and 3). The ages from both sets of mylonite are grading into each other at about 35–34 Ma. All ages appear to postdate high-P metamorphism in the Pennine nappes but are, in part, coeval with and predate (ultra)high-P metamorphism in the underlying Adula nappe of the distal European (Helvetic) margin. The oldest Rb Sr age of 42.3 ± 2.5 Ma (2σ uncertainties) dates the waning stage of mylonitization and indicates that the Avers-Turba mylonite zone started to operate ≥45 Ma, and predated the exhumation of the Adula nappe by ~10 Ma. We suggest that the motion in the Avers-Turba mylonite zone overlapped with backfolding of the Schams nappe in an extrusion wedge. When this process started, the Adula nappe was still being underthrust/underplated. The ages for distributed top-E normal shearing are contemporaneous with thrusting of the Adula nappe on top of distinctly lower-P Helvetic nappes. When the Adula nappe was being thrust onto non-high-P nappes the necessary reduction of its overburden was largely accomplished by distributed top-E normal faulting above the Adula nappe, and possibly still ongoing top-SE normal shearing. We discuss that major normal shearing occurred during lithospheric shortening. Our data indicate considerable tangential (out-of-plane) movements during overall top-N/NW thrust propagation in the Central Alps and have implications for current tectonic models of the Alps. • Rb Sr isotopic data reveal movement history of shear zones in eastern Central Alps. • Major breaks in P-T conditions across nappe pile shows importance of normal shearing in eastern Central Alps. • Orogen-parallel movements are important in the Central Alps highlighting the three-dimensionality of the Alps. [ABSTRACT FROM AUTHOR]

Metabasic rocks from different parts of the Antrona ophiolites, Western Alps, as well as from the Misox zone, Central Alps, were dated using ion microprobe (SHRIMP) U-Pb analyses of zircon, in association with cathodoluminescence (CL) imaging. HP metamorphism must have affected at least the major part of the Antrona ophiolites, although HP relics are rarely preserved, probably due to the Lepontine metamorphic overprint. HP metamorphism has affected also the area of the Misox zone. The origin of the Antrona ophiolites is arguable. They were interpreted as part of both the Piemont–Ligurian (PL) and the Valais ocean, the two main oceans in the area of the Alps before Alpine convergence. SHRIMP-analyses of co-magmatic zircon domains from the Antrona ophiolites (Guggilihorn, Passo del Mottone and Quarata areas) yielded identical (within uncertainty) weighted mean206 Pb/238U ages of 155.2±1.6 Ma, 158±17 Ma (or 163.1±2.4 Ma: one analysis; 1σ error) and 155.6±2.1 Ma, respectively, interpreted as the time of crystallization of the magmatic protoliths. These Late Jurassic ages fit well to the time span considered for the formation of Piemont–Ligurian oceanic crust. The metagabbro of the Misox zone (Hinterrhein area), for which a Valaisan origin is generally accepted, gave also a Late Jurassic, PL protolith age of 161.0±3.9 Ma. The metamorphic zircon domains from the amphibolitized eclogite of Mottone yielded an age of 38.5±0.7 Ma, interpreted as the time of HP metamorphism. This age is in good agreement with the time of metamorphism reported from previous zircon SHRIMP-data for eclogites and amphibolites of other parts in the Valais domain. In order to bring in line the PL protolith ages with the Valaisan metamorphic ages, we suggest a scenario involving emplacement of part of the PL oceanic crust to the north of the newly formed Briançonnais peninsula, inside the Valais geotectonic domain. This paleotectonic configuration was probably established when younger Valaisan oceanic crust formed by spreading and re-rifting, partly within PL oceanic crust. [ABSTRACT FROM AUTHOR]

Dating results from terrestrial records in the northern foreland of the Alps have been compiled in order to establish an independent chronostratigraphy for the climate history of this region. U/Th dates of peat deposited during the final phase of the Last Interglacial indicate that it lasted until at least c. 115 000 yr ago. The Early Würmian started with a period of severe cold climate causing a substitution of forest by tundra-like vegetation. It is assumed that during this period glaciers advanced to the margin of the foreland of at least the Western Alps. Sediments attributed to this glaciation are dated to about 103 000 yr. Three subsequent interstadials, all characterized by coniferous forest, were interrupted by cold stadials with steppe to tundra-like vegetation. The first interstadial is dated to about 95 000 yr. There is evidence for an interstadial with open coniferous woodland and three phases of steppe vegetation during the Middle Würmian, between c. 50 000 and 30 000 yr ago. The last glaciation of the Alpine Foreland reached its maximum extension between 24 000 and 21 500 yr and glaciers rapidly collapsed before ∼17 500 yr ago. A series of minor re-advances during the Lateglacial is reported from within the Alps, but the glaciers barely reached the main Alpine valleys during this time. The last of these advances formed the Egesen moraine and occurred at about 11 800 yr ago during the Younger Dryas. [ABSTRACT FROM AUTHOR]