Search Results (5)

We present a data set of calcite twinning strain results (n = 209 samples; 9919 measured calcite twins) from the internal Alpine nappes northwestward across the Alps and Alpine foreland to the older extensional margin along the Atlantic coast in Ireland. Along the coast of Northern Ireland, Cretaceous chalks and Tertiary basalts are cross-cut by calcite veins and offset by calcite-filled normal and strike-slip faults. Both Irish sample suites (n = 16 with four U-Pb vein calcite ages between 70–42 Ma) record a sub-horizontal SW-NE shortening strain with vertical extension and no strain overprint. This sub-horizontal shortening is parallel to the margin of the opening of the Atlantic Ocean (~58 Ma), and this penetrative fabric is only observed ~100 km inboard of the margin to the southeast. The younger, collisional Alpine orogen (~40 Ma) imparted a stress–strain regime dominated by SE-NW sub-horizontal shortening ~1200 km northwest from the Alps preserved in Mesozoic limestones and calcite veins (n = 32) in France, Germany and Britain. This layer-parallel shortening strain (−3.4%, 5% negative expected values) is preserved across the foreland in the plane of Alpine thrust shortening (SE-NW) along with numerous outcrop-scale contractional structures (i.e., folds, thrust faults). Calcite veins were observed in the Alpine foreland in numerous orientations and include both a SE-NW layer-parallel shortening fabric (n = 11) and a sub-vertical NE-SW vein-parallel shortening fabric (n = 4). Alpine foreland strains are compared with twinning strains from the frontal Jura Mountains (n = 9; layer-parallel shortening), the Molasse basin (n = 26; layer-parallel and layer-normal shortening), Pre-Alp nappes (n = 39; layer-parallel and layer-normal shortening), Helvetic and Penninic nappes (Penninic klippe; n = 46; layer-parallel and layer-normal shortening plus four striated U-Pb calcite vein ages ~24 Ma) and calcsilicates from the internal Tauern window (n = 4; layer-normal shortening). We provide a chronology of the stress–strain history of the European plate from 58 Ma through the Alpine orogen. Full article

The composite Albian–Eocene orogenic wedge of the northern part of the Inner Western Carpathians (IWC) comprises the European Variscan basement with the Upper Carboniferous–Triassic cover and the Jurassic to Upper Cretaceous sedimentary successions of a large oceanic–continental Atlantic (Alpine) Tethys basin system. This paper presents an updated evolutionary model for principal structural units of the orogenic wedge (i.e., Fatricum, Tatricum and Infratatricum) based on new and published white mica ⁴⁰Ar/³⁹Ar geochronology and P–T estimates by Perple_X modeling and geothermobarometry. The north-directed Cretaceous collision led to closure of the Jurassic–Early Cretaceous basins, and incorporation of their sedimentary infill and a thinned basement into the Albian–Cenomanian/Turonian accretionary wedge. During this compressional D1 stage, the subautochthonous Fatric structural units, including the present-day higher Infratatric nappes, achieved the metamorphic conditions of ca. 250–400 °C and 400–700 MPa. The collapse of the Albian–Cenomanian/Turonian wedge and contemporary southward Penninic oceanic subduction enhanced the extensional exhumation of the low-grade metamorphosed structural complexes (D2 stage) and the opening of a fore-arc basin. This basin hemipelagic Coniacian–Campanian Couches-Rouges type marls (C.R.) spread from the northern Tatric edge, throughout the Infratatric Belice Basin, up to the peri-Pieniny Klippen Belt Kysuca Basin, thus tracing the south-Penninic subduction. The ceasing subduction switched to the compressional regime recorded in the trench-like Belice “flysch” trough formation and the lower anchi-metamorphism of the C.R. at ca. 75–65 Ma (D3 stage). The Belice trough closure was followed by the thrusting of the exhumed low-grade metamorphosed higher Infratatric complexes and the anchi-metamorphosed C.R. over the frontal unmetamorphosed to lowest anchi-metamorphosed Upper Campanian–Maastrichtian “flysch” sediments at ca. 65–50 Ma (D4 stage). Phengite from the Infratatric marble sample SRB-1 and meta-marl sample HC-12 produced apparent ⁴⁰Ar/³⁹Ar step ages clustered around 90 Ma. A mixture interpretation of this age is consistent with the presence of an older metamorphic Ph1 related to the burial (D1) within the Albian–Cenomanian/Turonian accretionary wedge. On the contrary, a younger Ph2 is closely related to the late- to post-Campanian (D3) thrust fault formation over the C.R. Celadonite-enriched muscovite from the subautochthonous Fatric Zobor Nappe meta-quartzite sample ZI-3 yielded a mini-plateau age of 62.21 ± 0.31 Ma which coincides with the closing of the Infratatric foreland Belice “flysch” trough, the accretion of the Infratatricum to the Tatricum, and the formation of the rear subautochthonous Fatricum bivergent structure in the Eocene orogenic wedge. Full article

This work quantifies the amount of erosion associated with the Cretaceous and Miocene erosional unconformities recognised in the distal part of the Northern Alpine Foreland Basin (NAFB), north-eastern Switzerland. To achieve this goal, the basin thermal modelling approach is applied, calibrated by two different sets of data collected in previous studies: vitrinite reflectance (%R_o) and the temperature estimated from apatite fission tracks (AFT) data modelling. The novelty of this approach is the possibility to constrain the timing and magnitude of multiple erosion events by integrating thermal modelling with thermochronologic data. Combining these two methods allows the erosional events to be separated which would not be possible using only irreversible paleothermometers, such as vitrinite reflectance data. Two scenarios were tested, based on the data of two published thermochronology studies. For the Cretaceous unconformity, similar results are obtained for the two scenarios, both indicating that the deposition and the subsequent complete erosion of Lower Cretaceous deposits, in the order of 500–1300 m, depending on the area, are necessary, in order to attain the temperatures estimated by the thermal history modelling of AFT data. Thus, a depositional hiatus for this period is not likely. For the Miocene-Quaternary unconformity, the magnitude of erosion calculated for the two scenarios differs by 300–1400 m, depending on the AFT data considered. The two scenarios lead to a different evaluation of the subsidence and uplift rate of the study area, thus to a different interpretation of the tectono-stratigraphic evolution of this distal sector of the NAFB. Full article

This work critically reviews the Eocene–Oligocene source-to-sink systems accumulating volcanogenic sequences in the basins around the Alps. Through the years, these volcanogenic sequences have been correlated to the plutonic bodies along the Periadriatic Fault System, the main tectonic lineament running from West to East within the axis of the belt. Starting from the large amounts of data present in literature, for the first time we present an integrated 4D model on the evolution of the sediment pathways that once connected the magmatic sources to the basins. The magmatic systems started to develop during the Eocene in the Alps, supplying detritus to the Adriatic Foredeep. The progradation of volcanogenic sequences in the Northern Alpine Foreland Basin is subsequent and probably was favoured by the migration of the magmatic systems to the North and to the West. At around 30 Ma, the Northern Apennine Foredeep also was fed by large volcanogenic inputs, but the palinspastic reconstruction of the Adriatic Foredeep, together with stratigraphic and petrographic data, allows us to safely exclude the Alps as volcanogenic sources. Beyond the regional case, this review underlines the importance of a solid stratigraphic approach in the reconstruction of the source-to-sink system evolution of any basin. Full article

This work presents new apatite fission track LA–ICP–MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry) data from Mid–Late Paleozoic rocks, which form the substratum of the Swiss Jura mountains (the Tabular Jura and the Jura fold-and-thrust belt) and the northern margin of the Swiss Molasse Basin. Samples were collected from cores of deep boreholes drilled in North Switzerland in the 1980s, which reached the crystalline basement. Our thermochronological data show that the region experienced a multi-cycle history of heating and cooling that we ascribe to burial and exhumation, respectively. Sedimentation in the Swiss Jura Mountains occurred continuously from Early Triassic to Early Cretaceous, leading to the deposition of maximum 2 km of sediments. Subsequently, less than 1 km of Lower Cretaceous and Upper Jurassic sediments were slowly eroded during the Late Cretaceous, plausibly as a consequence of the northward migration of the forebulge of the neo-forming North Alpine Foreland Basin. Following this event, the whole region remained relatively stable throughout the Paleogene. Our data show that the Tabular Jura region resumed exhumation at low rates in early–middle Miocene times (≈20–15 Ma), whereas exhumation in the Jura fold-and-thrust belt probably re-started later, in the late Miocene (≈10–5 Ma). Erosional exhumation likely continues to the present day. Despite sampling limitations, our thermochronological data record discrete periods of slow cooling (rates of about 1°C/My), which might preclude models of elevated cooling (due to intense erosion) in the Jura Mountains during the Miocene. The denudation (≈1 km) of the Tabular Jura region and the Jura fold-and-thrust belt (≈500 m) has provided sediments to the Swiss Molasse Basin since at least 20 Ma. The southward migration of deformation in the Jura mountains suggests that the molasse basin started to uplift and exhume only after 5 Ma, as suggested also by previous authors. The data presented here show that the deformation of the whole region is occurring in an out-of-sequence trend, which is more likely associated with the reactivation of thrust faults beneath the foreland basin. This deformation trend suggests that tectonics is the most determinant factor controlling denudation and exhumation of the region, whereas the recently proposed “climate-induced exhumation” mechanism might play a secondary role. Full article