Miocene siliciclastic deposits of Naxos Island: Geodynamic and environmental implications for the evolution of the southern Aegean Sea (Greece)

An interdisciplinary study has been carried out on Naxos Island, located in the southern Aegean Sea (Greece), which shows Miocene geodynamic and environmental changes in a classic example of a collapsing orogen. Early to Mid-Miocene siliciclastic deposits on Naxos have been shed from an uplifting mountainous realm in the south, which included a patchwork of at least four source terrains of different thermal histories.Petrography of pebbles suggests that the source units formed part of a passivecontinental margin succession (external Pelagonian unit), and an ophiolite succession mainly of deep-water cherts and limestones deposited on basalt substratum (Pindos unit). The continental margin source contributed rounded zircon crystals of Late Jurassic to Early Cretaceous age and broadly scattering Paleozoic zircon fission-track cooling ages. A distal pebble assemblage of Paleogene shallow-water carbonates passing into flysch-like, mixed calcarenitic and siliciclastic components with volcanic arc components is subordinately present. High-grade metamorphic components from the nearby metamorphic core complex are not present. The depositional evolution reflects increasing relief and, in some parts, a fluvial succession with rhythmic channel deposition, possibly due to runoff variability forced by orbital cyclicity. Upsection, the depositional trend indicates increasing seasonality and decreasing humidity in the source region. The Miocene sedimentary succession has been deposited on an ophiolite nappe. Juxtaposition of this ophiolite nappe occurred as an extensional allochthon during large-scale extension in the Aegean region at the margins of an exhuming metamorphic core complex

Phases of Enhanced Exhumation During the Cretaceous and Cenozoic Orogenies in the Eastern European Alps: New Insights From Thermochronological Data and Thermokinematic Modeling

Austroalpine nappes in the Eastern European Alps have preserved the record of orogenies in the Cretaceous and Cenozoic but their cooling and exhumation history remains poorly constrained. Here we use low-temperature thermochronology and thermokinematic modeling to unravel the exhumation history of the Austroalpine nappes in the Gurktal Alps. Our data reveal marked differences between the exhumation of units located at different positions within the nappe stack and relative to the Adriatic indenter. Units located at a high structural level and farther away from the indenter cooled through the zircon fission track closure temperature in the Late Cretaceous and have resided at depths of ≤5–6 km since the Oligocene, as indicated by apatite fission track ages of 35–30 Ma. Thermokinematic modeling constrained that these units experienced enhanced exhumation (∼0.60 km/Ma) between ∼99 and ∼83 Ma due to syn- to late-orogenic Late Cretaceous extension. After a phase of slow exhumation (∼0.02 km/Ma), the exhumation rate increased to ∼0.16 km/Ma at ∼34 Ma due to the onset of the Europe-Adria collision. In contrast, zircon fission track ages from units at a lower structural level and near the indenter indicate cooling during the Eocene; apatite fission track ages cluster at ∼15 Ma. These units were rapidly exhumed (∼0.76 km/Ma) from ∼44 to ∼39 Ma during an Eocene phase of shortening prior to the Europe-Adria collision. After slow exhumation (∼0.13 km/Ma) between ∼39 and ∼18 Ma, the exhumation rate increased to ∼0.27 km/Ma in the wake of Miocene escape tectonics in the Eastern Alps

The evolution of a thrust belt within a continental indenter: Investigating the internal deformation of the Dolomites Indenter (Southern European Alps) using low-temperature thermochronology

The Dolomites Indenter represents the front of the Neogene to ongoing N(W)-directed continental indentation of the Adriatic microplate into Europe. Concomitant shortening within the indenter is accommodated within a dominantly WSW – ENE striking and S-vergent thrust belt. In this contribution, we present a new low-temperature thermochronological dataset (apatite U-Th/He (AHe) and apatite fission track (AFT)) over the Dolomites Indenter, with a north to south extent from the Periadriatic fault system (Pustertal-Gailtal fault) to the footwall of the Bassano thrust. In west-east direction, the AFT data cover the area from Lake Garda to San Martino di Castrozza. The AHe dataset, on the other hand, extents further east to Bled in Slovenia. The extensive dataset covers several major fault systems (from north to south): west of Lozzo di Cadore the Villnöß-, Truden-, Valsugana-, Belluno-, and Bassano-Valdobbiadene faults; east of Lozzo di Cadore the Fella-Sava-, Sauris-, Ampezzo-Tolmezzo-, Dof-Auda-, Pinedo-Uccea- and Barcis-Staro Selo faults. It includes several elevation profiles and aims to capture the cooling and exhumation history of the Dolomites Indenter. The AFT data obtained range from Jurassic to Miocene age. The vast majority of modelled cooling paths show a plateau and a long residence time of the samples within the Apatite partial annealing zone (APAZ), often from the beginning of the Jurassic to the Miocene. The location of the plateau within the APAZ during the long residence time can be responsible for whether a sample gives a Mesozoic or Cenozoic AFT age without major faults being involved. The basement and Permian intrusive rocks in the northern part of the Dolomites Indenter show cooling below ZFT between ~140 and 110 Ma and Eocene AFT data (~50-40 Ma). The modelled cooling paths based on apatite confined length distributions indicate a flat plateau in the upper APAZ delimited by two phases of accelerated cooling, one predating the AFT data and one in the middle Miocene. The latter is present in nearly all modelled cooling paths of our dataset besides the southernmost samples located in the footwall of the Bassano fault. The bend point varies between 20 and 12 Ma, tending to be earlier in the north and later in the south. We assign this middle Miocene change in cooling rate to the Valsugana deformation phase. For the older accelerated cooling phase, a tectonic interpretation is still in elaboration. Within the AHe dataset the most striking pattern is a significant trend towards younger ages in the direction east (lower Miocene in the west to upper Miocene to Pliocene in the east)