The deglaciation history of the Simplon region (southern Swiss Alps) constrained by 10Be exposure dating of ice-molded bedrock surfaces

The deglaciation history of the Swiss Alps after the Last Glacial Maximum involved the decay of several ice domes and the subsequent disintegration of valley glaciers at high altitude. Here we use bedrock exposure dating to reconstruct the temporal and spatial pattern of ice retreat at the Simplon Pass (altitude: ∼2000 m) located 40 km southwest of the ‘Rhône ice dome’. Eleven 10Be exposure ages from glacially polished quartz veins and ice-molded bedrock surfaces cluster tightly between 13.5 ± 0.6 ka and 15.4 ± 0.6 ka (internal errors) indicating that the Simplon Pass depression became ice-free at 14.1 ± 0.4 ka (external error of mean age). This age constraint is interpreted to record the melting of the high valley glaciers in the Simplon Pass region during the warm Bølling–Allerød interstadial shortly after the Oldest Dryas stadial. Two bedrock samples collected a few hundred meters above the pass depression yield older 10Be ages of 17.8 ± 0.6 ka and 18.0 ± 0.6 ka. These ages likely reflect the initial downwasting of the Rhône ice dome and the termination of the ice transfluence from the ice dome across the Simplon Pass toward the southern foreland. There, the retreat of the piedmont glacier in Val d’Ossola was roughly synchronous with the decay of the Rhône ice dome in the interior of the mountain belt, as shown by 10Be ages of 17.7 ± 0.9 ka and 16.1 ± 0.6 ka for a whaleback at ∼500 m elevation near Montecrestese in northern Italy. In combination with well-dated paleoclimate records derived from lake sediments, our new age data suggest that during the deglaciation of the European Alps the decay of ice domes was approximately synchronous with the retreat of piedmont glaciers in the foreland and was followed by the melting of high-altitude valley glaciers after the transition from the Oldest Dryas to the Bølling–Allerød, when mean annual temperatures rose rapidly by ∼3 °C.

Visual dating of rockfall scars in Larix decidua trees

Dating past mass wasting with growth disturbances in trees is widely used in geochronology as the approach may yield dates of past process activity with up to subannual precision. Past work commonly focused on the extraction of increment cores, wedges, or stem cross sections. However, sampling has been shown to be constrained by sampling permissions, and the analysis of tree-ring samples requires considerable temporal efforts. To compensate for these shortcomings, we explore the potential of visual inspection of wound appearance for dating purposes. Based on a data set of 217 wood-penetrating wounds of known age inflicted to European larch (Larix decidua Mill.) by rockfall activity, we develop guidelines for the visual, noninvasive dating of wounds including (i) the counting of bark rings, (ii) a visual assessment of exposed wood and wound bark characteristics (such as the color and weathering status of wounds), and (iii) the relationship between wound age and tree diameter. A characterization of wounds based on photographs, randomly selected from the data set, reveals that young wounds typically can be dated with high precision, whereas dating errors gradually increase with increasing wound age. While visual dating does not reach the precision of dendrochronological dating, we clearly demonstrate that spatial patterns of and differences in rockfall activity can be reconstructed with both approaches. The introduction of visual dating approaches will facilitate fieldwork, especially in applied research, assist the conventional interpretation of tree-ring signals, and allow the reconstruction of geomorphic processes with considerably fewer temporal and financial efforts.

Multiple metamorphic stages within an eclogite-facies terrane (Sesia Zone, Western Alps) revealed by Th-U-Pb petrochronology

Convergent plate margins typically experience a transition from subduction to collision dynamics as massive continental blocks enter the subduction channel. Studies of high-pressure rocks indicate that tectonic fragments are rapidly exhumed from eclogite facies to midcrustal levels, but the details of such dynamics are controversial.To understand the dynamics of a subduction channel we report the results of a petrochronological study from the central Sesia Zone, a key element of the internalWestern Alps.This comprises two polymetamorphic basement complexes (Eclogitic Micaschist Complex and Gneiss Minuti Complex) and a thin, dismembered cover sequence (Scalaro Unit) associated with pre-Alpine metagabbros and metasediments (Bonze Unit). Structurally controlled samples from three of these units (Eclogitic Micaschist Complex and Scalaro-Bonze Units) yield unequivocal petrological and geochronological evidence of two distinct high-pressure stages. Ages (U-Th-Pb) of growth zones in accessory allanite and zircon, combined with inclusion and textural relationships, can be tied to the multi-stage evolution of single samples.Two independent tectono-metamorphic ‘slices’ showing a coherent metamorphic evolution during a given time interval have been recognized: the Fondo slice (which includes Scalaro and Bonze rocks) and the Druer slice (belonging to the Eclogitic Micaschist Complex).The new data indicate separate stages of deformation at eclogite-facies conditions for each recognized independent kilometer-sized tectono-metamorphic slice, between ~85 and 60 Ma, with evidence of intermittent decompression (∆P~0.5 GPa) within only the Fondo slice. The evolution path of the Druer slice indicates a different P-T-time evolution with prolonged eclogite-facies metamorphism between ~85 and 75Ma. Our approach, combining structural, petrological and geochronological techniques, yields field-based constraints on the duration and rates of dynamics within a subduction channel.

Quaternary uplift rates of the Central Anatolian Plateau, Turkey: insights from cosmogenic isochron-burial nuclide dating of the Kızılırmak River terraces

The Central Anatolian Plateau (CAP) in Turkey is a relatively small plateau (300 × 400 km) with moderate average elevations of ∼1 km situated between the Pontide and Tauride orogenic mountain belts. Kızılırmak, which is the longest river (1355 km) within the borders of Turkey, flows within the CAP and slowly incises into lacustrine and volcaniclastic units before finally reaching the Black Sea. We dated the Cappadocia section of the Kızılırmak terraces in the CAP by using cosmogenic burial and isochron-burial dating methods with 10Be and 26Al as their absolute dating can provide insight into long-term incision rates, uplift and climatic changes. Terraces at 13, 20, 75 and 100 m above the current river indicate an average incision rate of 0.051 ± 0.01 mm/yr (51 ± 1 m/Ma) since ∼1.9 Ma. Using the base of a basalt fill above the modern course of the Kızılırmak, we also calculated 0.05–0.06 mm/yr mean incision and hence rock uplift rate for the last 2 Ma. Although this rate might be underestimated due to normal faulting along the valley sides, it perfectly matches our results obtained from the Kızılırmak terraces. Although up to 5–10 times slower, the Quaternary uplift of the CAP is closely related to the uplift of the northern and southern plateau margins respectively.

Gender Differences in Online Dating: What Do We Know So Far? A Systematic Literature Review

With millions of users worldwide, online dating platforms strive to assert themselves as powerful tools to find dates and form romantic relationships. However, significant differences exist in male and female use of this mate-matching technology with respect to motivation, preferences, self-presentation, interaction and outcomes. While existing research has routinely reported on gender differences in online dating, these insights remain scattered across multiple studies. To gain a systematic insight into existing findings, in this study we conduct a meta-review of existing research. We find that evolutionary theory generally holds true in online dating: Users still follow natural stereotypes when it comes to choosing a mate online. Physical attractiveness is the key criteria for men; while women, being much more demanding, prioritize socio-economic attributes when choosing a male partner. Together, our structured findings offer a deeper insight into the underlying dynamics of gender differences in online dating.

Effects of sample mass and macrofossil type on radiocarbon dating of arctic and boreal lake sediments

Dating lake sediments by accelerator mass spectrometry (AMS) 14C analysis of terrestrial plant macrofossils overcomes one of the main problems associated with dating bulk sediment samples, i.e., the presence of old organic matter. Even so, many AMS dates from arctic and boreal sites appear to misrepresent the age of the sediment. To understand the nature of these apparent dating anomalies better, we conducted a series of 14C dating experiments using samples from Alaskan and Siberian lake-sediment cores. First, to test whether our analytical procedures introduced a sample-mass bias, we obtained 14C dates for different-sized pieces of single woody macrofossils. In these sample-mass experiments, statistically equivalent ages were found for samples as small as 0.05 mg C. Secondly, to assess whether macrofossil type influenced dating results, we conducted sample-type experiments in which 14C dates were obtained for different macrofossil types sieved from the same depth in the sediment. We dated materials from multiple levels in sediment cores from Upper Capsule Lake (North Slope, northern Alaska) and Grizzly Lake (Copper River Basin, southern Alaska) and from single depths in other records from northern Alaska. In several of the experiments there were significant discrepancies between dates for different plant tissues, and in most cases wood and charcoal were older than other macrofossil types, usually by several hundred years. This pattern suggests that 14C dates for woody macrofossils may misrepresent the age of the sediment by centuries, perhaps because of their longer terrestrial residence time and the potential in-built age of longlived plants. This study identifies why some 14C dates appear to be inconsistent with the overall age-depth trend of a lake-sediment record, and it may guide the selection of 14C samples in future studies.

Oxygen isotope record of oceanic and high-pressure metasomatism: a P-T-time-fluid path for the Monviso eclogites (Italy)

Fluids are considered a fundamental agent for chemical exchanges between different rock types in the subduction system. Constraints on the sources and pathways of subduction fluids thus provide crucial information to reconstruct subduction processes. The Monviso ophiolitic sequence is composed of mafic, ultramafic and minor sediments that have been subducted to ~80 km depth. In this sequence, both localized fluid flow and channelized fluids along major shear zones have been documented. We investigate the timing and source of the fluids that affected the dominant mafic rocks using microscale U-Pb dating of zircon and oxygen isotope analysis of mineral zones (garnet, zircon and antigorite) in high pressure rocks with variable degree of metasomatic modification. In mafic eclogites, Jurassic zircon cores are the only mineralogical relicts of the protolith gabbros and retain δ18O values of 4.5–6 ‰, typical of mantle melts. Garnet and metamorphic zircon that grew during prograde to peak metamorphism display low δ18O values between 0.2 and 3.8 ‰, which are likely inherited from high-temperature alteration of the protolith on the sea floor. This is corroborated by δ18O values of 3.0 and 3.6 ‰ in antigorite from surrounding serpentinites. In metasomatised eclogites within the Lower Shear Zone, garnet rim formed at the metamorphic peak shows a shift to higher δ18O up to 6‰. The age of zircons in high-pressure veins and metasomatised eclogites constrains the timing of fluid flow at high pressure at around 45–46 Ma. Although the oxygen data do not contradict previous reports of interaction with serpentinite-derived fluids, the shift to isotopically heavier oxygen compositions requires contribution from sediment-derived fluids. The scarcity of metasediments in the Monviso sequence suggests that such fluids were concentrated and fluxed along the Lower Shear Zone in a sufficient amount to modify the oxygen composition of the eclogitic minerals.

Radiocarbon dating of modern peat profiles: Pre- and post-bomb C-14 variations in the construction of age-depth models

We present studies of 9 modern (up to 400-yr-old) peat sections from Slovenia, Switzerland, Austria, Italy, and Finland. Precise radiocarbon dating of modern samples is possible due to the large bomb peak of atmospheric 14C concentration in 1963 and the following rapid decline in the 14C level. All the analyzed 14C profiles appeared concordant with the shape of the bomb peak of atmospheric 14C concentration, integrated over some time interval with a length specific to the peat section. In the peat layers covered by the bomb peak, calendar ages of individual peat samples could be determined almost immediately, with an accuracy of 23 yr. In the pre-bomb sections, the calendar ages of individual dated samples are determined in the form of multi-modal probability distributions of about 300 yr wide (about AD 16501950). However, simultaneous use of the post-bomb and pre-bomb 14C dates, and lithological information, enabled the rejection of most modes of probability distributions in the pre-bomb section. In effect, precise age-depth models of the post-bomb sections have been extended back in time, into the wiggly part of the 14C calibration curve.

Radiometric 81Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica

We present successful 81 Kr-Kr radiometric dating of ancient polarice. Krypton was extracted from the air bubbles in four∼350-kg polar ice samples from Taylor Glacier in the McMurdo Dry Valleys, Antarctica, and dated using Atom Trap Trace Analysis (ATTA). The 81 Kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean abso-lute age offset of 6±2.5 ka. Our experimental methods and sampling strategy are validated by (i) 85 Kr and 39 Ar analyses that show the samples to be free of modern air contamination and (ii)air content measurements that show the ice did not experience gas loss. We estimate the error in the 81 Kr ages due to past geomagnetic variability to be below 3 ka. We show that ice from the previous interglacial period (Marine Isotope Stage 5e, 130–115 ka before present) can be found in abundance near the surface of Taylor Glacier. Our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old ice and meteorites. At present, ATTA 81Kr analysis requires a 40–80-kg ice sample; as sample requirements continue to decrease, 81 Kr dating of ice cores is a future possibility.

Dating prograde fluid pulses during subduction by in situ U–Pb and oxygen isotope analysis

Keywords High-pressure fluids · Whiteschists · U–Pb dating · Oxygen isotopes · Ion microprobe · Metasomatism Introduction The subduction of crustal material to mantle depths and its chemical modification during burial and exhumation contribute to element recycling in the mantle and the formation of new crust through arc magmatism. Crustal rocks that Abstract The Dora-Maira whiteschists derive from metasomatically altered granites that experienced ultrahighpressure metamorphism at ~750 °C and 40 kbar during the Alpine orogeny. In order to investigate the P–T–time– fluid evolution of the whiteschists, we obtained U–Pb ages from zircon and monazite and combined those with trace element composition and oxygen isotopes of the accessory minerals and coexisting garnet. Zircon cores are the only remnants of the granitic protolith and still preserve a Permian age, magmatic trace element compositions and δ18O of ~10 ‰. Thermodynamic modelling of Si-rich and Si-poor whiteschist compositions shows that there are two main fluid pulses during prograde subduction between 20 and 40 kbar. In Si-poor samples, the breakdown of chlorite to garnet + fluid occurs at ~22 kbar. A first zircon rim directly overgrowing the cores has inclusions of prograde phlogopite and HREE-enriched patterns indicating zircon growth at the onset of garnet formation. A second main fluid pulse is documented close to peak metamorphic conditions in both Si-rich and Si-poor whiteschist when talc + kyanite react to garnet + coesite + fluid. A second metamorphic overgrowth on zircon with HREE depletion was observed in the Si-poor whiteschists, whereas a single metamorphic overgrowth capturing phengite and talc inclusions was observed in the Si-rich whiteschists. Garnet rims, zircon rims and monazite are in chemical and isotopic equilibrium for oxygen, demonstrating that they all formed at peak metamorphism at 35 Ma as constrained by the age of monazite (34.7 ± 0.4 Ma) and zircon rims (35.1 ± 0.8 Ma). The prograde zircon rim in Si-poor whiteschists has an age that is within error indistinguishable from the age of peak metamorphic conditions, consistent with a minimum rate of subduction of 2 cm/year for the Dora-Maira unit. Oxygen isotope values for zircon rims, monazite and garnet are equal within error at 6.4 ± 0.4 ‰, which is in line with closed-system equilibrium fractionation during prograde to peak temperatures. The resulting equilibrium Δ18Ozircon-monazite at 700 ± 20 °C is 0.1 ± 0.7 ‰. The in situ oxygen isotope data argue against an externally derived input of fluids into the whiteschists. Instead, fluidassisted zircon and monazite recrystallisation can be linked to internal dehydration reactions during prograde subduction. We propose that the major metasomatic event affecting the granite protolith was related to hydrothermal seafloor alteration post-dating Jurassic rifting, well before the onset of Alpine subduction.