1,721,042 research outputs found
Intraplate brittle deformation and states of paleostress constrained by fault kinematics in the central German platform
No full textThe structural evolution of Central Europe reflects contrasting tectonic regimes after the Variscan orogeny during Mesozoic – Cenozoic time. The brittle deformation related to each tectonic regime is localized mainly along major fault zones, creating complex fracture patterns and kinematics through time with diverging interpretations on the number and succession of the causing events. By contrast, fracture patterns in less deformed domains often provide a pristine structural inventory. We investigate the brittle deformation of a relatively stable, wide area of the central German platform using fault-slip data to identify the regional stress fields required to satisfy the data. In a non-classical approach, and in order to avoid local stress variations and misinterpretations, the fault-slip data are scaled up throughout the study area into subsets of consistent kinematics and chronology for sedimentary cover and crystalline basement rocks. Direct stress tensor inversion was performed through an iterative refining process, and the computed stress tensors were verified using field-based observations. Criteria on relative tilt geometry and indicators of kinematic change suggest a succession of events, which begins with a post-Triassic normal faulting regime with ?3 axis trending NE-SW. The deformation then follows by strike-slip and thrust faulting regimes with a change of ?1 axis from N-S to NE-SW, supposedly in the Late Cretaceous. Two younger events are characterized by Cenozoic normal and oblique thrust faulting regimes with NW-SE-trending ?3 and ?1 axes, respectively. The fracture patterns of both the cover and basement rocks appear to record the same states of stress
Post-20 Ma Motion of the Adriatic Plate: New Constraints From Surrounding Orogens and Implications for Crust-Mantle Decoupling
Get PDFA new kinematic reconstruction that incorporates estimates of post-20 Ma shortening and extension in the Apennines, Alps, Dinarides, and Sicily Channel Rift Zone (SCRZ) reveals that the Adriatic microplate (Adria) rotated counterclockwise as it subducted beneath the European Plate to the west and to the east, while indenting the Alps to the north. Minimum and maximum amounts of rotation are derived by using, respectively, estimates of crustal extension along the SCRZ (minimum of 30 km) combined with crustal shortening in the Eastern Alps (minimum of 115 km) and a maximum amount (140 km) of convergence between Adria and Moesia across the southern Dinarides and Carpatho-Balkan orogens. When combined with Neogene convergence in the Western Alps, the best fit of available structural data constrains Adria to have moved 113 km to the NW (azimuth 325°) while rotating 5 ± 3° counterclockwise relative to Europe since 20 Ma. Amounts of plate convergence predicted by our new model exceed Neogene shortening estimates of several tens of kilometers in both the Apennines and Dinarides. We attribute this difference to crust-mantle decoupling (delamination) during rollback in the Apennines and to distributed deformation related to the northward motion of the Dacia Unit between the southern Dinarides and Europe (Moesia). Neogene motion of Adria resulted from a combination of Africa pushing from the south, the Adriatic-Hellenides slab pulling to the northeast, and crustal wedging in the Western Alps, which acted as a pivot and stopped farther northwestward motion of Adria relative to Europe
Kinematics and Age of the Orogen-Perpendicular Shkoder-Peja Normal Fault in North Albania Constrained by Fault-Slip Data, Raman Spectroscopy and K-Ar Fault-Gouge Dating
Get PDFAbstract The Shkoder‐Peja Normal Fault (SPNF) is the largest orogen‐perpendicular fault on the Balkan Peninsula, separating the Dinarides fold‐and‐thrust belt in the north from the Hellenides in the south. It has accommodated orogen‐parallel extension during clockwise oroclinal bending of the Hellenic segment and juxtaposes Adriatic shelf successions in its footwall against obducted ophiolites in its hanging wall. Despite its length of at least 100 km, it is still an improperly understood fault. In this study, we combine results of geological mapping of a c. 13 km swath along the fault segment in Northern Albania with fault‐slip data, Raman spectroscopy of carbonaceous matter (RSCM) and K‐Ar dating of fault gouges to better constrain its kinematics and age. Our results provide evidence of top‐to‐the SSE extension across the SPNF, post‐dating Eocene nappe stacking and truncating nappe‐internal folds within the footwall. Illite crystallinity and RSCM data suggest that epizonal versus anchizonal conditions were reached in the footwall and hanging wall units, respectively. K‐Ar dates of various grain size fractions (2–6, <2 and <0.2 μm) from fault gouges yielded ages between 47 and 106 Ma. Since these ages overlap with the minimum depositional ages of the stratigraphically youngest unit in the footwall, they are interpreted as mixed detrital and authigenic illite ages. Modeled ages for a pure authigenic illite fraction range between c. 34.4 and 6.2 Ma. As minimum temperatures of c. 100°C are required for the formation of authigenic illite, younger or even still ongoing fault activity at lower temperatures is likely.Plain Language Summary The Shkoder‐Peja Fault in northern Albania separates two mountain ranges: the Dinarides in the north and the Hellenides in the south. This study examines relative movements along this fault to better understand its history and significance for recent tectonic plate movements in the region by mapping and dating structures in the fault zone. By estimating the impact of heating of carbonaceous matter in sediments beneath the fault, we were able to determine that several km of rocks have been removed along the fault. Folds in the underlying rock formations were cut off during faulting and new clay minerals were formed along the interface, where the two rock formations slipped past each other. This clay mineral (illite) contains tiny amounts of a radioactive isotope ( 40 K) that was used for radiometric dating. Since the formation of this mineral requires temperatures above 100°C, the results indicate that the last movements along this section of the fault above this temperature occurred until some 6 Ma ago. Even younger deformation that occurred below this temperature (e.g., with less overburden) is to be expected; in fact, the fault could still be active today.Key Points Post‐Eocene brittle top‐to‐the SSE normal faulting along the Shkoder‐Peja Normal Fault (SPNF) confirmed by detailed mapping and kinematic indicators Illite age analyses of fault gouges yielded Early Oligocene and Late Miocene ages for authigenic illite Post‐Eocene SPNF activity is either continuous since early Oligocene or episodic with renewed (likely ongoing) extension since MioceneAbstract The Shkoder‐Peja Normal Fault (SPNF) is the largest orogen‐perpendicular fault on the Balkan Peninsula, separating the Dinarides fold‐and‐thrust belt in the north from the Hellenides in the south. It has accommodated orogen‐parallel extension during clockwise oroclinal bending of the Hellenic segment and juxtaposes Adriatic shelf successions in its footwall against obducted ophiolites in its hanging wall. Despite its length of at least 100 km, it is still an improperly understood fault. In this study, we combine results of geological mapping of a c. 13 km swath along the fault segment in Northern Albania with fault‐slip data, Raman spectroscopy of carbonaceous matter (RSCM) and K‐Ar dating of fault gouges to better constrain its kinematics and age. Our results provide evidence of top‐to‐the SSE extension across the SPNF, post‐dating Eocene nappe stacking and truncating nappe‐internal folds within the footwall. Illite crystallinity and RSCM data suggest that epizonal versus anchizonal conditions were reached in the footwall and hanging wall units, respectively. K‐Ar dates of various grain size fractions (2–6, <2 and <0.2 μm) from fault gouges yielded ages between 47 and 106 Ma. Since these ages overlap with the minimum depositional ages of the stratigraphically youngest unit in the footwall, they are interpreted as mixed detrital and authigenic illite ages. Modeled ages for a pure authigenic illite fraction range between c. 34.4 and 6.2 Ma. As minimum temperatures of c. 100°C are required for the formation of authigenic illite, younger or even still ongoing fault activity at lower temperatures is likely.Plain Language Summary The Shkoder‐Peja Fault in northern Albania separates two mountain ranges: the Dinarides in the north and the Hellenides in the south. This study examines relative movements along this fault to better understand its history and significance for recent tectonic plate movements in the region by mapping and dating structures in the fault zone. By estimating the impact of heating of carbonaceous matter in sediments beneath the fault, we were able to determine that several km of rocks have been removed along the fault. Folds in the underlying rock formations were cut off during faulting and new clay minerals were formed along the interface, where the two rock formations slipped past each other. This clay mineral (illite) contains tiny amounts of a radioactive isotope ( 40 K) that was used for radiometric dating. Since the formation of this mineral requires temperatures above 100°C, the results indicate that the last movements along this section of the fault above this temperature occurred until some 6 Ma ago. Even younger deformation that occurred below this temperature (e.g., with less overburden) is to be expected; in fact, the fault could still be active today.Key Points Post‐Eocene brittle top‐to‐the SSE normal faulting along the Shkoder‐Peja Normal Fault (SPNF) confirmed by detailed mapping and kinematic indicators Illite age analyses of fault gouges yielded Early Oligocene and Late Miocene ages for authigenic illite Post‐Eocene SPNF activity is either continuous since early Oligocene or episodic with renewed (likely ongoing) extension since MioceneAbstract The Shkoder‐Peja Normal Fault (SPNF) is the largest orogen‐perpendicular fault on the Balkan Peninsula, separating the Dinarides fold‐and‐thrust belt in the north from the Hellenides in the south. It has accommodated orogen‐parallel extension during clockwise oroclinal bending of the Hellenic segment and juxtaposes Adriatic shelf successions in its footwall against obducted ophiolites in its hanging wall. Despite its length of at least 100 km, it is still an improperly understood fault. In this study, we combine results of geological mapping of a c. 13 km swath along the fault segment in Northern Albania with fault‐slip data, Raman spectroscopy of carbonaceous matter (RSCM) and K‐Ar dating of fault gouges to better constrain its kinematics and age. Our results provide evidence of top‐to‐the SSE extension across the SPNF, post‐dating Eocene nappe stacking and truncating nappe‐internal folds within the footwall. Illite crystallinity and RSCM data suggest that epizonal versus anchizonal conditions were reached in the footwall and hanging wall units, respectively. K‐Ar dates of various grain size fractions (2–6, <2 and <0.2 μm) from fault gouges yielded ages between 47 and 106 Ma. Since these ages overlap with the minimum depositional ages of the stratigraphically youngest unit in the footwall, they are interpreted as mixed detrital and authigenic illite ages. Modeled ages for a pure authigenic illite fraction range between c. 34.4 and 6.2 Ma. As minimum temperatures of c. 100°C are required for the formation of authigenic illite, younger or even still ongoing fault activity at lower temperatures is likely.Plain Language Summary The Shkoder‐Peja Fault in northern Albania separates two mountain ranges: the Dinarides in the north and the Hellenides in the south. This study examines relative movements along this fault to better understand its history and significance for recent tectonic plate movements in the region by mapping and dating structures in the fault zone. By estimating the impact of heating of carbonaceous matter in sediments beneath the fault, we were able to determine that several km of rocks have been removed along the fault. Folds in the underlying rock formations were cut off during faulting and new clay minerals were formed along the interface, where the two rock formations slipped past each other. This clay mineral (illite) contains tiny amounts of a radioactive isotope ( 40 K) that was used for radiometric dating. Since the formation of this mineral requires temperatures above 100°C, the results indicate that the last movements along this section of the fault above this temperature occurred until some 6 Ma ago. Even younger deformation that occurred below this temperature (e.g., with less overburden) is to be expected; in fact, the fault could still be active today.Key Points Post‐Eocene brittle top‐to‐the SSE normal faulting along the Shkoder‐Peja Normal Fault (SPNF) confirmed by detailed mapping and kinematic indicators Illite age analyses of fault gouges yielded Early Oligocene and Late Miocene ages for authigenic illite Post‐Eocene SPNF activity is either continuous since early Oligocene or episodic with renewed (likely ongoing) extension since MioceneDeutsche Forschungsgemeinschaft https://doi.org/10.13039/50110000165
Active tectonics and tectonic geomorphology in the region of the Fella-Sava Fault
Get PDFThe Southern Alps are known to be a seismically active region. Despite this, the sources for most of the few, but strong historic earthquakes especially behind the Alpine front are still debated or completely unknown. In this study, we conducted a paleoseismological investigation around the FellaSava Fault in the border area between Austria, Italy, and Slovenia. We first carried out literature research and remote sensing to choose targets for field work. We tried to find primary evidence for the activity of the Fella-Sava Fault, believed to be the source of the 1348 earthquake with MW 6.6-7.0. Beside primary evidence for fault activity (like surface ruptures, fault scarps or offset geomorphic markers), we put a special emphasis on sackungen, features created by gravitational collapse of mountains known to occur coseismically (although they can be (re-)activated by other processes as well). During field work, we could field-prove every feature believed to be a sackung but were not able to identify evidence for surface ruptures along the Fella-Sava Fault. We sampled sediments accumulated inside a sackung that were dated to an age of 100-300 years. After field work, a systematic remote sensing mapping of sackungen in an area 15 km north and south of a segment of the Fella-Sava Fault believed to be epicentral area of the 1348 earthquake was carried out using the available high-resolution (1 m) digital elevation models. An analysis of the distribution of the sackungen showed that they cluster within 5 km of north and south of the Fella-Sava Fault. A directional analysis shows that the preferred trend of the sackungen is parallel to the Fella-Sava Fault. Those observations indicate postglacial activity of the Fella-Sava Fault, which very likely was the source of the 1348 earthquake.Die Südalpen sind bekannt als seismisch aktive Region, und es wurden zahlreiche Studien durchgeführt, um seismisch aktive Störungen zu identifizieren. Trotzdem sind die Quellen für die meisten der wenigen, aber starken historischen Erdbeben insbesondere hinter der Alpenfront noch immer umstritten oder völlig unbekannt. In dieser Studie wurde eine paläoseismologische Untersuchung im Bereich der Fella-Sava-Störung im Grenzgebiet zwischen Österreich, Italien und Slowenien absolviert. Zunächst führten wir Literaturrecherchen und Fernerkundung durch, um Ziele für die Geländearbeit auszuwählen. Wir versuchten, primäre Beweise für die Aktivität der Fella-Sava-Störung zu finden, von der angenommen wird, dass sie die Quelle des Erdbebens von 1348 mit MW 6,6-7,0 war. Neben primären Beweisen für die Aktivität der Verwerfung (wie Oberflächenrupturen, Bruchstufen oder versetzten geomorphologischen Markern) legten wir einen besonderen Schwerpunkt auf Sackungen, d.h. Strukturen, die durch das gravitative >Zerfließen< von Bergen entstehen und von denen bekannt ist, dass sie koseismisch auftreten können (sie können aber auch durch andere Prozesse (re)aktiviert werden). Die Feldarbeiten wurden im September 2022 durchgeführt. Während der Feldarbeiten konnten wir jede Struktur, die wir für eine Sackung hielten, im Gelände als solche nachweisen, waren aber nicht in der Lage, Oberflächenrupturen entlang der Fella-Sava-Störung zu finden. Wir nahmen Proben von Sedimenten aus dem Inneren einer Sackung, die auf ein Alter von 100-300 Jahren datiert wurden. Die beprobte Sackung hatte eine steile interne Hangneigung und war offensichtlich durch Entwässerung verändert worden, so dass unsere Datierung bestätigte, dass selbst Sackungen, die dynamischen Erosionsprozessen unterliegen (wie sie in Gebirgsregionen wie unserem Untersuchungsgebiet häufig anzutreffen sind), in der Lage sind, ein bis mehrere Jahrhunderte lang Sedimente anzusammeln und somit die (De-)Formationsgeschichte der einzelnen Sackungen aufzuzeichnen. Nach der Feldarbeit wurde eine systematische Fernerkundungskartierung der Sackungen in einem Gebiet 15 km nördlich und südlich eines Segments der Fella-Sava-Störung, Epizentralgebiet des Erdbebens von 1348 vermutet wird, unter Verwendung der verfügbaren hochauflösenden (1 m) digitalen Geländemodellen durchgeführt. Eine Analyse der Verteilung der Sackungen ergab, dass sie innerhalb von 5 km nördlich und südlich der Fella-Sava-Verwerfung gehäuft auftreten. Eine Richtungsanalyse zeigt, dass der bevorzugte Trend der Sackungen parallel zur Fella-Sava-Verwerfung verläuft. Eine klare Korrelation zwischen Richtung und Auftreten der Sackungen mit dem Auftreten bestimmter Lithologien, der Taltiefen und der bevorzugten Richtung der Höhenlinie konnte hingegen nicht beobachtet werden. Diese Beobachtungen weisen auf postglaziale Aktivität der Fella-Sava-Störung hin, die sehr wahrscheinlich die Quelle des Erdbebens von 1348 war
A geomorphological perspective of active tectonics and Quaternary landscape development at the Dinarides-Hellenides transition (Northern Albania and Southern Montenegro) - APPENDIX
No full textThe coastal Albania-Montenegro border region between Bar (Montenegro), Shkodra Lake and Lezha (Albania) is a domain of enhanced seismic activity, as proven by major earthquakes (e.g., Montenegro 1979, Mw = 7.1). The area hosts the southwestern termination of the Shkodra-Peja Fault Zone, marking the transition between the Dinarides and Hellenides fold-and-thrust belts. Seismicity is largely governed by thrust faulting connected to NE-ward continental subduction of the Adriatic microplate below Eurasia. Far-field effects of oceanic subduction along the Aegean arc (mostly expressed in extensional tectonics) affect the area, while representing the dominant force in close-by surrounding regions. These influences endow the target area with one of the most complex geological settings on the entire Balkan peninsula. Few reliable studies exist, but still deliver mostly inconsistent statements on the overall tectonic regime as well as local uplift and subsidence. To overcome this shortcoming, this PhD thesis aims at identifying seismically-induced young patterns of ground movements and landscape development to relate them with responsible large-scale active tectonic processes. The tectonically active area hosts numerous textbook geomorphological features of different scale and age that our paleoseismologic studies are based on. Windgaps show that fault-bound coast-parallel anticlines are actively uplifting with respect to interjacent synclinal valleys to form a horst-graben-like pattern. Different windgap elevations on single anticlines indicate tendentially greater differential offsets toward the hinterland (NE) and toward the NW. We interpret the young and recent uplift of anticlines as non-folding related but driven by the activity and geometry of underlying thrust faults. In a similar sense, we interpret three major normal fault scarp segments on the Rumija mountain chain as secondary structures associated with the dominant thrust-faulting earthquakes. The properties of 6-9-m-high free faces in bedrock limestone evidence repeated Mw≈5-7 seismic events and movement rates of ca. 0.3 - 0.5 mm/yr since the LGM. In the alluvial plains between Shkodra and the coast, 17 shallow sediment vibracores reconstruct aspects of regional landscape development during the middle to late Holocene. Around 6 - 7 kyr ago, during the Holocene transgressional maximum, the Adriatic coastline was situated ca. 11 km further inland. A combination of climatic, tectonic and anthropogenic triggers induced repeated vast hydrological changes with pulses of delta-progradation at different locations. Detailed studies at Šasko Lake reveal that climatic effects induced very rapid siltation as such, while tectonics crucially co-determined the locations of deposition. Šasko Lake itself evolved from a marine bay over a brackish residual lake to its current state. With our overall study, we contribute to a significantly improved resolution in terms of known differential tectonic movement modes and rates in an area that we corroborate as a complex mosaic of different-scale zones of relative uplift and subsidence. We identify the well-acquainted local thrust faulting tectonics and associated earthquakes as decisive drivers responsibe for the characteristics of (partly secondary) structures and processes
Interplay between tectonics and magmatism in the internal Dinarides
Get PDFThe Sava suture zone that runs across the Balkan peninsula contains Maastrichtian trench-fill sediments, termed Sava flysch, that record the closure of the northern branch of the Neotethys. Subsequent collision between Adria-derived thrust sheets and blocks of European affinity in Latest Cretaceous to Paleogene times culminated in the formation of the Dinarides fold-andthrust-belt. The suture zone hosts numerous plutons of I-type granitic composition of Oligocene age. Many of these intrusions are located in the center of metamorphic core complexes (MCCs) that were exhumed in early Miocene times. This phase of post-collisional extension was concomitant with the opening of the northerly adjacent Pannonian Basin and associated with granitic S-type magmatism. The processes responsible for extensional deformation and magmatic activity in the internal Dinarides are still a matter of debate. The data of the present study shows an asynchronous extensional reactivation of formerly contractional structures that gave rise to these core complexes as low-angle detachments in the early Miocene. This is indicated by a variation in deformation ages of 3 Ma, obtained by Ar-Ar in-situ dating of white mica from deformed rocks of the respective shear zones. While Motajica MCC was exhumed from within the Sava zone during E-W extension at approximately 20 Ma, Cer MCC was exhumed as part of the underlying Adriatic basement during N-S extension between 17-16 Ma. For the Cer MCC, a concordia age of 17.6±0.1 Ma (2σ) obtained by U-Pb LA-ICP-MS on zircons from a structurally and petrographically well constrained and undeformed S-type granite in combination with an Ar-Ar inverse isochron age of 16.6±0.2 Ma (2σ) obtained on white mica from the same sample, indicate a cooling rate of approximately 400°C/Ma. The results of this study contribute to the idea of rapid exhumation of mid-crustal material in the form of MCCs in response to the opening of the Pannonian Basin
A parametric study of thermomechanical 3D nite element simulations of subduction zones and its application to the Central Andes using realistic geometries
Get PDFThe western margin of central South America is one of the best studied regions of subduction zones. The oceanic Nazca plate descends beneath the continental South American plate at an oceanward concave trench. This form of the trench is unique on Earth and lead to the formation of the Andes. Here, I focus on a three-dimensional thermomechanical finite element model along the north Chilean margin. At first a reference model with simplified geometry reaching down to 400 km depth is created that makes use of an elasto-viscoplastic rheology including shear heating along the plate interface. The subduction process is simulated for geologically short timescales to reflect the recent state of subduction and the model results are in first-order agreement with observations. The model is analyzed within the framework of a parametric study revealing the most important parameters to be convergence and slab pull velocity, type and number of elements of the finite element mesh, type of rheology, cohesion, friction coefficient and angle of internal friction. Because of its lower thickness the oceanic crust is generally more affected by changes in these parameters than the continental crust. The final model includes a realistic geometry and density distribution that is based on a well constrained density model, not considering topography and bathymetry. It simulates 100,000 years of subduction and accounts for elastic deformations. The geometry has a major impact on the model results causing significant differences between the northern and southern parts of the model. This, as well as the final distributions of shear stress, strain rate and heat flux is in good agreement with observations from global models except for the magmatic arc because inelastic deformations are neglected. The usage of a realistic geometry and density distribution for finite element simulations of subduction zones can thus help to significantly improve future geodynamic models
Tectonometamorphic and hydraulic processes along a fossil subduction plate interface in the northern Mirdita Ophiolites (Bajram Curri, Albania)
Get PDFThe Western Vardar ophiolite crops out along the entire Balkan Peninsula. In northeast Albania near Bajram Curri, the Jurassic plate interface reveals a metamorphic sole below peridotites of the Mirdita Ophiolite. There, I mapped an area of around 35 km2 along the southeast-dipping fossil plate interface and performed various micro-scale analyses such as polarisation microscopy, Raman-spectrometry, Raster-electron microscopy and Micro-x-ray fluorescence on metamorphic sole as well as mantle lithologies. Three major units are distinguishable. The mantle harzburgites overthrust a tectonic mélange which itself can be separated into a non-metamorphic broken formation and a metamorphic sole. The metamorphic sole itself was accreted at a lower structural level than the broken formation and later emplaced on top of it. The tectonic mélange is tightly folded with fold axes plunging gently towards NNW or NNE. The metamorphic sole shows an inverse metamorphic field gradient up to greenschist-facies conditions near Bajram Curri and granulite-facies conditions near Shkelzen. Granulite-facies conditions are preserved as relictic blasts with albite, margarite & muscovite as pseudomorphs after feldspar; as well as garnet and monazite. S-c’-fabrics in calcschists show top to the west shear sense direction, suggesting westward emplacement of the overlying ophiolites. All lithologies in the metamorphic sole are characterised by a later lower-greenschist-facies overprint, evolving from dynamic to static recrystallisation. Stilpnomelane, quartz and white mica form a typical mineral assemblage giving temperatures between 280°-450°C and pressures between 4.3-5.5 kbar. Right above the southeast-dipping plate interface, foliated upper plate harzburgites with southeast dips crop out. Mylonitic layers preserve a mineral assemblage with major olivine and minor orthopyroxene, clinopyroxene, as well as chromium-rich spinel (Cr# 72). Clinopyroxene lamellae in Aluminium- depleted (Al2O3 0.85 wt%) orthopyroxene clasts give lower temperature limits for recrystallisation of 1042°-1063°C under low-pressure conditions. The mantle source was either already depleted or the primary harzburgite was melted in a second stage. In the later evolving ultramylonitic layers, the mineral phases exhibit average grain sizes of 5 µm. There, phases of two clinopyroxene with low-calcium and high-calcium content respectively occur. Serpentinisation decreases upsection and developed in three texturally distinct types that bear different serpentine minerals and opaque phases
Geophysical survey (GPR, ERT, magnetic) on active faults in Slovenia and Italy
No full textThe transition zone between the Southern Eastern Alps and the Dinarides is situated in western Slovenia and northeastern Italy. Here, a system of mainly NW-SE trending, right-lateral strike-slip faults accommodates the shortening between the Adriatic Plate and Eurasia. Due to the low deformation rates, geodetic techniques and seismology provide only limited insights into the activity of those faults. Geomorphological studies are confronted with problems arising from the low fault slip rates, distributed deformation, and unfavourable conditions due to the karst environment. One way to overcome these problems is the use of paleoseismology, i.e. the excavation of active faults to study their earthquake history and slip behaviour. A prerequisite for paleoseismological trenching is knowledge on the precise location of the fault trace and the availability of a suitable sediment record. We performed geophysical surveys across the potentially active faults in Slovenia and Italy to select sites for paleoseismic trenching. We used a ground-penetrating radar (GPR) system from Geophysical Survey Systems Inc (GSSI) with monostatic 100 MHz, 270 MHz, and 400 MHz antennas and a Pulse EKKO Pro Sensors & Software system equipped with bistatic 250 MHz antennas. All data were processed with the ReflexW software (Sandmeier Geophysical Research). Processing included frequency bandpass filtering, background removal, gain adjustments, and topographic corrections. The topographic data were extracted from the 1 m DEM. Electric resistivity tomography (ERT) was performed with a 4-point-light system (Lippmann Geophysikalische Messgeräte). We used up to 80 electrodes with varying electrode spacing for Wenner, Schlumberger, and Dipole-Dipole arrays, depending on target resolution and depth. Data inversion was done with Res2DInv (Geotomo Software) and included manual de-spiking and topographic corrections. Along several profiles we measured the vertical gradient of the geomagnetic field and the total magnetic field strength with a proton magnetometer GSM - 19T (GEM Systems). The system consists of a rover and a base station, which allows correcting the data for diurnal variation. Depending on the equipment used and the survey parameters, these methods allow insights into the first few metres of the subsurface with a resolution of few centimetres (georadar) to a few metres (ERT). We focussed on sites that host Quaternary sediments. Most of the data in this dataset are 2D profiles perpendicular to the mapped traces of active faults. Several promising sites were investigated in 2.5D, i.e. the profile line spacing was dense enough to compute a pseudo-3D dataset. We collected the data in May and June, 2018. This dataset contains ~2.5 km of magnetic data, ~20 km of GPR data, and ~1.7 km of ERT data. This work was undertaken for the DFG project "Earth surface response to Quaternary faulting and shallow crustal structure in the eastern Adria-Alpine collision zone and the Friulian plain" within the DFG-funded priority programme SPP2017 - Mountain building processes in 4D
Horizontal vs. vertical tectonics: analysis of large-scale structures related to the deformation history of the Archean Barberton Greenstone Belt
Get PDFOne of the major unresolved questions in Precambrian geology is the nature of tectonic processes during Earth’s early history and the timing of the transition to modern-style plate tectonics. The Barberton Greenstone Belt (BGB) of South Africa and Eswatini features prominently in this discussion because it represents, along with the Pilbara region of Australia, the prime geological archive of the late Paleoarchean (ca. 3.5-3.2 Ga). This time period may mark the transition from a pre-plate tectonic setting to Phanerozoic-style plate tectonics. The cuspate-lobate geometry of the BGB, together with its general structural make-up (defined by folding style, stratigraphic fill and strain distribution) appears to represent a non-actualistic Archean tectonic style characterized by vertical rather than horizontal displacements, as known from modern plate tectonics. A compilation of geological data from the entire greenstone belt demonstrates its heterogeneity and complex deformation history is compared with own investigations in this work. A critical comparison of suggested tectonic settings to recent observations shows that no pure plate-tectonic scenarios are applicable. The temporal and spatial heterogeneity of deformation, the relative greenstone-down sense of shear along many of its contacts to the adjacent plutons, and the overall synclinal structure of the BGB emphasize a non-plate-tectonic setting dominated by vertical movements. Local subsidence due to folding, tilting and sagging of thick, dense greenstone regions into an incompetent granitoid middle crust during partial convective overturn plausibly explains the rotation of the enormous Onverwacht Anticline, the characteristic folding pattern and the temporally and spatially heterogeneous deformation history of the BGB
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