Search results for "Zone"
showing 10 items of 2029 documents
Benchmarking numerical models of brittle thrust wedges
2016
International audience; We report quantitative results from three brittle thrust wedge experiments, comparing numerical resultsdirectly with each other and with corresponding analogue results. We first test whether the participatingcodes reproduce predictions from analytical critical taper theory. Eleven codes pass the stable wedgetest, showing negligible internal deformation and maintaining the initial surface slope upon horizontaltranslation over a frictional interface. Eight codes participated in the unstable wedge test that examinesthe evolution of a wedge by thrust formation from a subcritical state to the critical taper geometry. Thecritical taper is recovered, but the models show two…
The ~2730 Ma onset of the Neoarchean Yilgarn Orogeny
2017
The timing of the onset of an orogeny is commonly constrained indirectly, because early orogenic structures are rarely exposed, or are overprinted. Establishing the onset of an Archean orogeny is considerably more challenging, because of the more fragmented geological record and the general lack of consensus about Archean geodynamics. We combine existing tectono-stratigraphic data with new structural and geophysical datasets to establish the onset of the Neoarchean Yilgarn Orogeny (Yilgarn Craton, Western Australia). We show that the surface of the c. 2960–2750 Ma deep-marine Yilgarn greenstone sequence was uplifted, eroded and unconformably overlain by a c. 2730 Ma, syntectonic clastic seq…
Plastic ingestion by pelagic and demersal fish from the North Sea and Baltic Sea
2015
Plastic ingestion by marine biota has been reported for a variety of different taxa. In this study, we investigated 290 gastrointestinal tracts of demersal (cod, dab and flounder) and pelagic fish species (herring and mackerel) from the North and Baltic Sea for the occurrence of plastic ingestion. In 5.5% of all investigated fishes, plastic particles were detected, with 74% of all particles being in the microplastic (<5mm) size range. The polymer types of all found particles were analysed by means of Fourier transform infrared (FT-IR) spectroscopy. Almost 40% of the particles consisted of polyethylene (PE). In 3.4% of the demersal and 10.7% of the pelagic individuals, plastic ingestion was …
Marine climate and hydrography of the Coralline Crag (early Pliocene, UK): isotopic evidence from 16 benthic invertebrate taxa
2019
The taxonomic composition of the biota of the Coralline Crag Formation (early Pliocene, eastern England) provides conflicting evidence of seawater temperature during deposition, some taxa indicating cool temperate conditions by analogy with modern representatives or relatives, others warm temperate to subtropical/tropical conditions. Previous isotopic (δ18O) evidence of seasonal seafloor temperatures from serial ontogenetic sampling of bivalve mollusk shells indicated cool temperate winter (<10 °C) and/or summer (<20 °C) conditions but was limited to nine profiles from two species, one ranging into and one occurring exclusively in cool temperate settings at present. We supplement these resu…
Late Quaternary Variations in the South American Monsoon System as Inferred by Speleothems—New Perspectives using the SISAL Database
2019
Here we present an overview of speleothem δ18O records from South America, most of which are available in the Speleothem Isotopes Synthesis and Analysis (SISAL_v1) database. South American tropical and subtropical speleothem δ18O time series are primarily interpreted to reflect changes in precipitation amount, the amount effect, and consequently history of convection intensity variability of convergence zones such as the Intertropical Convergence Zone (ITCZ) and the South America Monsoon System (SAMS). We investigate past hydroclimate scenarios in South America related to the South American Monsoon System in three different time periods: Late Pleistocene, Holocene, and the last tw…
Cretaceous ultrapotassic magmatism from the Sava-Vardar Zone of the Balkans
2020
Highlights • Geochemically diverse Late Cretaceous small-volume magmatism in the Sava-Vardar Zone. • Late Cretaceous ultrapotassic lava, equivalent of minette and kersantite. • Magma derivation from a LREE and K enriched, garnet-bearing anciently metasomatized mantle source. • Magmatism occurred either in a fore-arc setting or is associated with transtensional tectonics. Abstract Late Cretaceous global plate reorganization associated with the inception of counterclockwise rotation of Africa relative to Europe initiated in the Balkan region small-volume magmatism of diverse geochemical signature along the enigmatic Sava-Vardar Zone. We study a Late Cretaceous lamprophyric sill in Ripanj vill…
2D Hydro-Mechanical-Chemical Modeling of (De)hydration Reactions in Deforming Heterogeneous Rock: The Periclase-Brucite Model Reaction
2020
Deformation at tectonic plate boundaries involves coupling between rock deformation, fluid flow, and metamorphic reactions, but quantifying this coupling is still elusive. We present a new two-dimensional hydro-mechanical-chemical numerical model and investigate the coupling between heterogeneous rock deformation and metamorphic (de)hydration reactions. We consider linear viscous compressible and power-law viscous shear deformation. Fluid flow follows Darcy's law with a Kozeny-Carman type permeability. We consider a closed isothermal system and the reversible (de)hydration reaction: periclase and water yields brucite. Fluid pressure within a circular or elliptical inclusion is initially bel…
Ductile strain rate measurements document long-term strain localization in the continental crust
2013
cited By 24; Quantification of strain localization in the continental lithosphere is hindered by the lack of reliable deformation rate measurements in the deep crust. Quartz-strain-rate-metry (QSR) is a convenient tool for performing such measurements once calibrated. We achieve this calibration by identifying the best piezometer-rheological law pairs that yield a strain rate in agreement with that measured on the same outcrop by a more direct method taken as a reference. When applied to two major continental strike-slip shear zones, the Ailao Shan-Red River (ASRR; southwest China) and the Karakorum (northwest India), the calibrated QSR highlights across-strike strain rate variations, from …
The Impact of a Very Weak and Thin Upper Asthenosphere on Subduction Motions
2019
Recent geophysical observations report the presence of a very weak and thin upper asthenosphere underneath subducting oceanic plates at convergent margins. Along these margins, trench migrations are significantly slower than plate convergence rates. We use numerical models to assess the role of a weak upper asthenospheric layer on plate and trench motions. We show that the presence of this layer alone can enhance an advancing trend for the motion of the plate and hamper trench retreat. This mechanism provides a novel and alternative explanation for the slow rates of trench migration and fast-moving plates observed globally at natural subduction zones.
Intermediate-depth earthquake generation and shear zone formation caused by grain size reduction and shear heating
2015
cited By 23; The underlying physics of intermediate-depth earthquakes have been an enigmatic topic; several studies support either thermal runaway or dehydration reactions as viable mechanisms for their generation. Here we present fully coupled thermomechanical models that investigate the impact of grain size evolution and energy feedbacks on shear zone and pseudotachylite formation. Our results indicate that grain size reduction weakens the rock prior to thermal runaway and significantly decreases the critical stress needed for thermal runaway, making it more likely to result in intermediate-depth earthquakes at shallower depths. Furthermore, grain size is reduced in and around the shear z…