Showing papers in "Solid Earth in 2022"
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TL;DR: In this article , a tectonic rules-based optimisation approach is presented to construct a plate motion model in a mantle reference frame covering the last billion years and use it as a surface boundary condition for mantle flow models.
Abstract: Abstract. Understanding the long-term evolution of Earth's plate-mantle system is reliant on absolute plate motion models in a mantle reference frame, but such models are both difficult to construct and controversial. We present a tectonic rules-based optimisation approach to construct a plate motion model in a mantle reference frame covering the last billion years and use it as a surface boundary condition for mantle flow models. Our plate motion model results in lithospheric net rotation consistently below 0.25°/Myr, in agreement with mantle flow models, while trench motions are confined to a relatively narrow range of −2/+2 cm/yr since 320 Ma, during Pangea stability and dispersal. In contrast, the period from 600 Ma to 320 Ma, nicknamed here the "zippy tricentenary", displays twice the trench motion scatter compared to more recent times, reflecting a predominance of short and highly mobile subduction zones. Our model supports an orthoversion evolution from Rodinia to Pangea with Pangea offset approximately 90° eastwards relative to Rodinia—this is the opposite sense of motion compared to a previous orthoversion hypothesis based on paleomagnetic data. In our coupled plate-mantle model a broad network of basal mantle ridges forms between 1000 and 600 Ma, reflecting widely distributed subduction zones. Between 600 and 500 Ma a short-lived degree-2 basal mantle structure forms in response to a band of subduction zones confined to low-latitudes, generating extensive antipodal lower mantle upwellings centred at the poles. Subsequently the northern basal structure migrates southward and morphs into a Pacific-centred upwelling while the southern structure is dissected by subducting slabs and disintegrates into a network of ridges between 500 and 400 Ma. From 400 to 200 Ma, a stable Pacific-centred degree-1 convective planform emerges, lacking an antipodal counterpart due to the closure of the Iapetus and Rheic oceans between Laurussia and Gondwana as well as coeval subduction between Baltica and Laurentia and around Siberia, populating the mantle with slabs until 320 Ma when Pangea is assembled. A basal degree-2 structure forms subsequent to Pangea breakup, after the influence of previously subducted slabs in the African hemisphere on the lowermost mantle has faded away. This succession of mantle states is distinct from previously proposed mantle convection models. This Solid Earth Evolution Model for the last 1000 million years (SEEM1000) forms the foundation for a multitude of spatio-temporal data analysis approaches.
17 citations
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TL;DR: An up-to-date summary of the state of the art in the field of basin inversion can be found in this article , where the authors provide a systematic overview of the current state-of-the-art.
Abstract: Abstract. Basin inversion involves the reversal of subsidence in a basin due to compressional tectonic forces, leading to uplift of the basin’s sedimentary infill. A thorough understanding of basin inversion is of great importance for scientific, societal and economic reasons. Analogue tectonic modelling forms a key part our efforts to improve our understanding of basin inversion processes, and researchers have conducted numerous studies on this topic. In this review paper we recap the advances in knowledge of basin inversion tectonics acquired through analogue modelling studies, providing an up-to-date summary of the state of analogue modelling of basin inversion. We describe the different definitions of basin inversion that are being applied by researchers, why basin inversion has been historically an important research topic, and what the general mechanics involved in basin inversion are. We subsequently treat the wide range of different experimental approaches used for basin inversion modelling, with attention to the various materials, set-ups and techniques used for monitoring and analysing the model results. Our new systematic overviews of generalized results reveal the diversity of model results, depending greatly on the chosen set-up, model layering and (oblique) kinematics of inversion, as well as 3D along-strike structural and kinematic variations in the system. We show how analogue modelling results are in good agreement with numerical models, and how these results help to better understand natural examples of basin inversion. In addition to reviewing the past efforts in the field of analogue modelling, we also shed light on future modelling challenges and identify a number of opportunities for follow-up research. These include the testing of force-boundary conditions, adding geological processes such as sedimentation, transport and erosion, applying state-of-the-art modelling and quantification techniques, and establishing best modelling practices. We also suggest expanding the scope of basin inversion modelling beyond the traditional upper crustal "North Sea style" of inversion, which may contribute to the on-going search for clean energy resources. It follows that basin inversion modelling can bring valuable new insights, providing a great incentive to continue our efforts in this field. We therefore hope that this review paper will form an inspiration for future analogue modelling studies of basin inversion.
17 citations
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TL;DR: In this article , a 3D model of the structures causative of the 2010-2014 Pollino seismic activity was reconstructed by integrating structural and high-resolution seismological data, and the model was constrained at the surface with fault-slip data and at depth by using the distributions of selected high-quality relocated hypocenters.
Abstract: Abstract. We reconstruct the 3D fault model of the structures causative of
the 2010–2014 Pollino seismic activity by integrating structural–geological
and high-resolution seismological data. We constrained the model at the
surface with fault-slip data, and at depth, by using the distributions of
selected high-quality relocated hypocenters. Relocations were performed
through the non-linear Bayloc algorithm, followed by the double-difference
relative location method HypoDD applied to a 3D P-wave velocity model.
Geological and seismological data highlight an asymmetric active extensional
fault system characterized by an E- to NNE-dipping low-angle detachment, with
high-angle synthetic splays, and SW- to WSW-dipping, high-angle antithetic
faults. Hypocenter clustering and the time–space evolution of the seismicity suggest
that two sub-parallel WSW-dipping seismogenic sources, the
Rotonda–Campotenese and Morano–Piano di Ruggio faults, are responsible for
the 2010–2014 seismicity. The area of the seismogenic patches obtained
projecting the hypocenters of the early aftershocks on the 3D fault planes,
are consistent with the observed magnitude of the strongest events
(Mw=5.2, and Mw=4.3). Since earthquake-scaling relationships
provide maximum expected magnitudes of Mw=6.4 for the
Rotonda–Campotenese and Mw=6.2 for the Morano–Piano di Ruggio faults,
we may suppose that, during the sequence, the two structures did not entirely release
their seismic potential. The reconstructed 3D fault model also points out the relationships between
the activated fault system and the western segment of the Pollino Fault.
The latter was not involved in the recent seismic activity but could have
acted as a barrier to the southern propagation of the seismogenic faults,
limiting their dimensions and the magnitude of the generated earthquakes.
12 citations
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TL;DR: The Solid Earth Evolution Model for the last 1000 million years (SEEM1000) as discussed by the authors is a tectonic-rules-based optimization approach to construct a plate motion model in a mantle reference frame covering the last billion years.
Abstract: Abstract. Understanding the long-term evolution of Earth's plate–mantle system is reliant on absolute plate motion models in a mantle reference frame, but such models are both difficult to construct and controversial. We present a tectonic-rules-based optimization approach to construct a plate motion model in a mantle reference frame covering the last billion years and use it as a constraint for mantle flow models. Our plate motion model results in net lithospheric rotation consistently below 0.25∘ Myr−1, in agreement with mantle flow models, while trench motions are confined to a relatively narrow range of −2 to +2 cm yr−1 since 320 Ma, during Pangea stability and dispersal. In contrast, the period from 600 to 320 Ma, nicknamed the “zippy tricentenary” here, displays twice the trench motion scatter compared to more recent times, reflecting a predominance of short and highly mobile subduction zones. Our model supports an orthoversion evolution from Rodinia to Pangea with Pangea offset approximately 90∘ eastwards relative to Rodinia – this is the opposite sense of motion compared to a previous orthoversion hypothesis based on paleomagnetic data. In our coupled plate–mantle model a broad network of basal mantle ridges forms between 1000 and 600 Ma, reflecting widely distributed subduction zones. Between 600 and 500 Ma a short-lived degree-2 basal mantle structure forms in response to a band of subduction zones confined to low latitudes, generating extensive antipodal lower mantle upwellings centred at the poles. Subsequently, the northern basal structure migrates southward and evolves into a Pacific-centred upwelling, while the southern structure is dissected by subducting slabs, disintegrating into a network of ridges between 500 and 400 Ma. From 400 to 200 Ma, a stable Pacific-centred degree-1 convective planform emerges. It lacks an antipodal counterpart due to the closure of the Iapetus and Rheic oceans between Laurussia and Gondwana as well as due to coeval subduction between Baltica and Laurentia and around Siberia, populating the mantle with slabs until 320 Ma when Pangea is assembled. A basal degree-2 structure forms subsequent to Pangea breakup, after the influence of previously subducted slabs in the African hemisphere on the lowermost mantle structure has faded away. This succession of mantle states is distinct from previously proposed mantle convection models. We show that the history of plume-related volcanism is consistent with deep plumes associated with evolving basal mantle structures. This Solid Earth Evolution Model for the last 1000 million years (SEEM1000) forms the foundation for a multitude of spatio-temporal data analysis approaches.
10 citations
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TL;DR: The Bedretto Underground Laboratory for Geosciences and Geothermal Systems (BedrettoLab) as discussed by the authors was established in 2018 in the existing Bedretti Tunnel (Ticino, Switzerland), with an average overburden of 1000m.
Abstract: Abstract. The increased interest in subsurface development (e.g., unconventional
hydrocarbon, engineered geothermal systems (EGSs), waste disposal) and the
associated (triggered or induced) seismicity calls for a better
understanding of the hydro-seismo-mechanical coupling in fractured rock
masses. Being able to bridge the knowledge gap between laboratory and
reservoir scales, controllable meso-scale in situ experiments are deemed
indispensable. In an effort to access and instrument rock masses of
hectometer size, the Bedretto Underground Laboratory for Geosciences and
Geoenergies (“BedrettoLab”) was established in 2018 in the existing
Bedretto Tunnel (Ticino, Switzerland), with an average overburden of 1000 m.
In this paper, we introduce the BedrettoLab, its general setting and
current status. Combined geological, geomechanical and geophysical methods
were employed in a hectometer-scale rock mass explored by several boreholes
to characterize the in situ conditions and internal structures of the rock
volume. The rock volume features three distinct units, with the middle fault
zone sandwiched by two relatively intact units. The middle fault zone unit
appears to be a representative feature of the site, as similar structures
repeat every several hundreds of meters along the tunnel. The lithological
variations across the characterization boreholes manifest the complexity and
heterogeneity of the rock volume and are accompanied by compartmentalized
hydrostructures and significant stress rotations. With this complexity, the
characterized rock volume is considered characteristic of the heterogeneity
that is typically encountered in subsurface exploration and development. The
BedrettoLab can adequately serve as a test-bed that allows for in-depth
study of the hydro-seismo-mechanical response of fractured crystalline rock
masses.
9 citations
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TL;DR: A comprehensive overview of the geodynamic modeling process applied to the solid Earth from the choice of governing equations to numerical methods, model setup, model interpretation, and the eventual communication of the model results can be found in this paper .
Abstract: Abstract. Geodynamic modelling provides a powerful tool to investigate processes in the Earth's crust, mantle, and core that are not directly observable. However, numerical models are inherently subject to the assumptions and simplifications on which they are based. In order to use and review numerical modelling studies appropriately, one needs to be aware of the limitations of geodynamic modelling as well as its advantages. Here, we present a comprehensive yet concise overview of the geodynamic modelling process applied to the solid Earth from the choice of governing equations to numerical methods, model setup, model interpretation, and the eventual communication of the model results. We highlight best practices and discuss their implementations including code verification, model validation, internal consistency checks, and software and data management. Thus, with this perspective, we encourage high-quality modelling studies, fair external interpretation, and sensible use of published work. We provide ample examples, from lithosphere and mantle dynamics specifically, and point out synergies with related fields such as seismology, tectonophysics, geology, mineral physics, planetary science, and geodesy. We clarify and consolidate terminology across geodynamics and numerical modelling to set a standard for clear communication of modelling studies. All in all, this paper presents the basics of geodynamic modelling for first-time and experienced modellers, collaborators, and reviewers from diverse backgrounds to (re)gain a solid understanding of geodynamic modelling as a whole.
9 citations
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TL;DR: In this article , a multiscale analysis of lineament patterns helps define the geometric scaling laws and the relationships between outcrop-and regional-scale structures in a fracture network.
Abstract: Abstract. The multiscale analysis of lineament patterns helps
define the geometric scaling laws and the relationships between outcrop-
and regional-scale structures in a fracture network. Here, we present a
novel analytical and statistical workflow to analyze the geometrical and
spatial organization properties of the Rolvsnes granodiorite lineament
(fracture) network in the crystalline basement of southwestern Norway
(Bømlo Island). The network shows a scale-invariant spatial distribution
described by a fractal dimension D≈1.51, with lineament lengths
distributed following a general scaling power law (exponent α=1.88). However, orientation-dependent analyses show that the identified sets
vary their relative abundance and spatial organization and occupancy with scale,
defining a hierarchical network. Lineament length, density, and intensity
distributions of each set follow power-law scaling laws characterized by
their own exponents. Thus, our multiscale, orientation-dependent statistical
approach can aid in the identification of the hierarchical structure of the
fracture network, quantifying the spatial heterogeneity of lineament sets
and their related regional- vs. local-scale relevance. These results,
integrated with field petrophysical analyses of fracture lineaments, can
effectively improve the detail and accuracy of permeability prediction of
heterogeneously fractured media. Our results also show how the geological
and geometrical properties of the fracture network and analytical biases
affect the results of multiscale analyses and how they must be critically
assessed before extrapolating the conclusions to any other similar case
study of fractured crystalline basement blocks.
8 citations
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TL;DR: In this paper , the authors integrate existing DEKORP 2D seismic reflection, well, and surface geological data with the newly acquired FRANKEN 2d seismic survey to investigate the possible westward continuation of Variscan tectonostratigraphic units and structures and their influence on latest to post-Variscan basin development.
Abstract: Abstract. The Bohemian Massif exposes structures and metamorphic rocks remnant from
the Variscan orogeny in central Europe and is bordered by the Franconian
Fault System (FFS) to the west. Across the FFS, Variscan units and
structures are buried by Permo-Mesozoic sedimentary rocks. We integrate
existing DEKORP 2D seismic reflection, well, and surface geological data with
the newly acquired FRANKEN 2D seismic survey to investigate the possible
westward continuation of Variscan tectonostratigraphic units and structures
and their influence on latest to post-Variscan basin development. Subsurface
Permo-Mesozoic stratigraphy is obtained from available wells and tied to
seismic reflection profiles using a synthetic seismogram calculated from
density and velocity logs. Below the sedimentary cover, three main basement
units are identified using seismic facies descriptions that are compared
with seismic reflection characteristics of exposed Variscan units east of
the FFS. Our results show upper Paleozoic low-grade metasedimentary
rocks and possible Variscan nappes bounded and transported by Variscan shear
zones ca. 65 km west of the FFS. Basement seismic facies in the footwall of
the Variscan shear zones are interpreted as Cadomian basement and overlaying
Paleozoic sequences. We show that the location of normal fault-bounded
latest to post-Variscan late Carboniferous–Permian basins are controlled by
the geometry of underlying Variscan shear zones. Some of these late
Carboniferous–Permian normal faults reactivated as steep reverse faults
during the regional Upper Cretaceous inversion. Our results also highlight
that reverse reactivation of normal faults gradually decreases west of the
FFS.
7 citations
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TL;DR: In this paper , an outcrop analogue study was conducted with interdisciplinary geoscientific methods in the Tromm Granite, located in the southern Odenwald at the northeastern margin of the Upper Rhine Graben (URG).
Abstract: Abstract. The crystalline basement is considered a ubiquitous and almost inexhaustible source of geothermal energy in the Upper Rhine Graben (URG) and other regions worldwide. The hydraulic properties of the basement, which are one of the key factors in the productivity of geothermal power plants, are primarily controlled by hydraulically active faults and fractures. While the most accurate in situ information about the general fracture network is obtained from image logs of deep boreholes, such data are generally sparse and costly and thus often not openly accessible. To circumvent this problem, an outcrop analogue study was conducted with interdisciplinary geoscientific methods in the Tromm Granite, located in the southern Odenwald at the northeastern margin of the URG. Using light detection and ranging (lidar) scanning, the key characteristics of the fracture network were extracted in a total of five outcrops; these were additionally complemented by lineament analysis of two different digital elevation models (DEMs). Based on this, discrete fracture network (DFN) models were developed to calculate equivalent permeability tensors under assumed reservoir conditions. The influences of different parameters, such as fracture orientation, density, aperture and mineralization, were investigated. In addition, extensive gravity and radon measurements were carried out in the study area, allowing fault zones with naturally increased porosity and permeability to be mapped. Gravity anomalies served as input data for a stochastic density inversion, through which areas of potentially increased open porosity were identified. A laterally heterogeneous fracture network characterizes the Tromm Granite, with the highest natural permeabilities expected at the pluton margin, due to the influence of large shear and fault zones.
7 citations
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TL;DR: In this article , the structural anisotropy and heterogeneity of the reservoir rocks at the STIMTEC site and the induced highfrequency (>1 kHz) acoustic emission (AE) activity, associated with brittle deformation at the centimetre-to-decimetre scale, were investigated.
Abstract: Abstract. In 2018 and 2019, we performed STIMulation tests with characterising periodic pumping tests and high-resolution seismic monitoring for improving prognosis models and real-time monitoring TEChnologies for the creation of hydraulic conduits in crystalline rocks (STIMTEC). The STIMTEC underground research laboratory is located at 130 m depth in the Reiche Zeche mine in Freiberg, Germany. The experiment was designed to investigate the rock damage resulting from hydraulic stimulation and to link seismic activity and enhancement of hydraulic properties in strongly foliated metamorphic gneiss. We present results from active and passive seismic monitoring prior to and during hydraulic stimulations. We characterise the structural anisotropy and heterogeneity of the reservoir rocks at the STIMTEC site and the induced high-frequency (>1 kHz) acoustic emission (AE) activity, associated with brittle deformation at the centimetre-to-decimetre scale. We derived the best velocity model per recording station from over 300 active ultrasonic transmission measurements for high-accuracy AE event location. The average P-wave anisotropy is 12 %, in agreement with values derived from laboratory tests on core material. We use a 16-station seismic monitoring network comprising AE sensors, accelerometers, one broadband sensor and one AE hydrophone. All instrumentation was removable, providing us with the flexibility to use existing boreholes for multiple purposes. This approach also allowed for optimising the (near)-real-time passive monitoring system during the experiment. To locate AE events, we tested the effect of different velocity models and inferred their location accuracy. Based on the known active ultrasonic transmission measurement points, we obtained an average relocation error of 0.26±0.06 m where the AE events occurred using a transverse isotropic velocity model per station. The uncertainty resulting from using a simplified velocity model increased to 0.5–2.6 m, depending on whether anisotropy was considered or not. Structural heterogeneity overprints anisotropy of the host rock and has a significant influence on velocity and attenuation, with up to 4 % and up to 50 % decrease on velocity and wave amplitude, respectively. Significant variations in seismic responses to stimulation were observed ranging from abundant AE events (several thousand per stimulated interval) to no activity with breakdown pressure values ranging between 6.4 and 15.6 MPa. Low-frequency seismic signals with varying amplitudes were observed for all stimulated intervals that are more correlated with the injection flow rate rather than the pressure curve. We discuss the observations from STIMTEC in context of similar experiments performed in underground research facilities to highlight the effect of small-scale rock, stress and structural heterogeneity and/or anisotropy observed at the decametre scale. The reservoir complexity at this scale supports our conclusion that field-scale experiments benefit from high-sensitivity, wide-bandwidth instrumentation and flexible monitoring approaches to adapt to unexpected challenges during all stages of the experiment.
6 citations
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TL;DR: In this paper , an updated kinematic model of an asymmetric orogenic wedge, with imposed erosion rates on the Ligurian side that are a factor of 2 slower relative to the Adriatic side, is presented.
Abstract: Abstract. Analysis of new detrital apatite fission-track (AFT) ages from modern river sands, published bedrock and detrital AFT ages, and bedrock apatite (U-Th)/He (AHe) ages from the Northern Apennines provides new insights into the spatial and temporal patterns of erosion rates through time across the orogen. The pattern of time-averaged erosion rates derived from AHe ages from the Ligurian side of the orogen illustrates slower erosion rates relative to AFT rates from the Ligurian side and relative to AHe rates from the Adriatic side. These results are corroborated by an analysis of paired AFT and AHe thermochronometer samples, which illustrate that erosion rates have generally increased through time on the Adriatic side but have decreased through time on the Ligurian side. Using an updated kinematic model of an asymmetric orogenic wedge, with imposed erosion rates on the Ligurian side that are a factor of 2 slower relative to the Adriatic side, we demonstrate that cooling ages and maximum burial depths are able to replicate the pattern of measured cooling ages across the orogen and estimates of burial depth from vitrinite reflectance data. These results suggest that horizontal motion is an important component of the overall rock motion in the wedge, and that the asymmetry of the orogen has existed for at least several million years.
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TL;DR: In this article , the authors provide a systematic comparison of all of these elements for the first time and conclude that the stable Taylor-Hood element is the most robust and reliable choice for geodynamical simulations, despite the greater complexity in their implementation and substantially higher computational cost when solving linear systems.
Abstract: Abstract. Geodynamical simulations over the past decades have widely been built on quadrilateral and hexahedral finite elements. For the discretization of the key Stokes equation describing slow, viscous flow, most codes use either the unstable Q1×P0 element, a stabilized version of the equal-order Q1×Q1 element, or more recently the stable Taylor–Hood element with continuous (Q2×Q1) or discontinuous (Q2×P-1) pressure. However, it is not clear which of these choices is actually the best at accurately simulating “typical” geodynamic situations. Herein, we provide a systematic comparison of all of these elements for the first time. We use a series of benchmarks that illuminate different aspects of the features we consider typical of mantle convection and geodynamical simulations. We will show in particular that the stabilized Q1×Q1 element has great difficulty producing accurate solutions for buoyancy-driven flows – the dominant forcing for mantle convection flow – and that the Q1×P0 element is too unstable and inaccurate in practice. As a consequence, we believe that the Q2×Q1 and Q2×P-1 elements provide the most robust and reliable choice for geodynamical simulations, despite the greater complexity in their implementation and the substantially higher computational cost when solving linear systems.
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TL;DR: In this paper , the authors performed an ambient seismic experiment to ascertain the relationship between the shallow shear wave velocity and mineralized zones in the Erzgebirge in Germany, one of the most important metal provinces in Europe.
Abstract: Abstract. Ambient seismic noise tomography is a novel, low-impact method for investigating the earth's structure. Although most passive seismic studies focus on structures on crustal scales, there are only a few examples of this technique being applied in a mineral exploration context. In this study, we performed an ambient seismic experiment to ascertain the relationship between the shallow shear wave velocity and mineralized zones in the Erzgebirge in Germany, one of the most important metal provinces in Europe. Late Variscan mineralized greisen and veins occurring in the Geyer-Ehrenfriedersdorf mining district of the Central Erzgebirge were mined from medieval times until the end of the 19th century. These occurrences represent a significant resource for commodities of high economic importance, such as tin, tungsten, zinc, indium, bismuth and lithium. Based on ambient noise data from a dense “LARGE-N” network comprising 400 low-power, short-period seismic stations, we applied an innovative tomographic inversion technique based on Bayesian statistics (transdimensional, hierarchical Monte Carlo search with Markov Chains using a Metropolis/Hastings sampler) to derive a three-dimensional shear wave velocity model. An auxiliary 3D airborne time-domain electromagnetic dataset is used to provide additional insight into the subsurface architecture of the area. The velocity model shows distinct anomalies down to approximately 500 m depth that correspond to known geological features of the study area, such as (a) gneiss intercalations in the mica schist-dominated host rock, imaged by a SW–NE striking low-velocity zone with a moderately steep northerly dip, and (b) a NW-trending strike-slip fault, imaged as a subvertical linear zone cross-cutting and offsetting this low-velocity domain. Similar to the velocity data, the electromagnetic data exhibit north-dipping (high-conductivity) structures in the mica schists, corresponding to the strike and dip of the predominant metamorphic fabric. An unsupervised classification performed on the bivariate 3D dataset yielded nine spatially coherent classes, one of which shows a high correspondence with drilled greisen occurrences in the roof zone of a granite pluton. The relatively high mean shear velocity and resistivity values of this class could be explained by changes in density and composition during greisen formation, as observed in other areas of the Erzgebirge. Our study demonstrates the great potential of the cost-efficient and low-impact ambient noise technology for mineral exploration, especially when combined with other independent geophysical datasets.
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TL;DR: In this article , a two-stage fuzzy inference system is applied to prospectivity modelling and exploration-target delineation for rare earth element (REE) deposits associated with carbonatite-alkaline complexes in the western part of the state of Rajasthan in India.
Abstract: Abstract. A two-stage fuzzy inference system (FIS) is applied to prospectivity modelling and exploration-target delineation for rare earth element (REE) deposits associated with
carbonatite–alkaline complexes in the western part of the state of Rajasthan in India. The design of the FIS and selection of the input predictor
map are guided by a generalised conceptual model of carbonatite–alkaline-complex-related REE mineral systems. In the first stage, three FISs are
constructed to map the fertility and favourable geodynamic settings, favourable lithospheric architecture for fluid transportation and favourable
shallow crustal (near-surface) emplacement architecture, respectively, for REE deposits in the study area. In the second stage, the outputs of the
above FISs are integrated to map the prospectivity of REE deposits in the study area. Stochastic and systemic uncertainties in the output
prospectivity maps are estimated to facilitate decision-making regarding the selection of exploration targets. The study led to the identification
of prospective targets in the Kamthai–Sarnu-Dandeli and Mundwara regions, where detailed project-scale ground exploration is
recommended. Low-confidence targets were identified in the Siwana ring complex region, north and northeast of Sarnu-Dandeli, south of Barmer, and
south of Mundwara. Detailed geological mapping and geochemical sampling together with high-resolution magnetic and radiometric surveys are
recommended in these areas to increase the level of confidence in the prospectivity of these targets before undertaking project-scale ground
exploration. The prospectivity-analysis workflow presented in this paper can be applied to the delineation of exploration targets in geodynamically
similar regions globally, such as Afar province (East Africa), Paraná–Etendeka (South America and Africa), Siberia (Russia), East European
Craton–Kola (eastern Europe), Central Iapetus (North America, Greenland and the Baltic region) and the pan-superior province (North America).
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TL;DR: The field-mapping course for second-year Geology BSc students from Cardiff University was replaced with a virtual mapping course set in the same area as previous years, the Esla Nappe (Cantabrian Zone, NW Spain) as discussed by the authors .
Abstract: Abstract. The restrictions implemented to contain the spread of the
COVID-19 pandemic during 2020 and 2021 have forced university-level
educators from around the world to seek alternatives to the residential physical
field trips that constitute a fundamental pillar of Geoscience programmes.
The field-mapping course for second-year Geology BSc students from
Cardiff University was replaced with a virtual mapping course set in the
same area as previous years, the Esla Nappe (Cantabrian Zone, NW Spain). The
course was designed with the aim of providing the students with the same
methodology employed in physical mapping, including such skills as gathering discrete data at stops
located along five daily itineraries. Data included bedding attitude,
outcrop descriptions with a certain degree of ambiguity, photographs and/or
sketches, panoramic photos, and fossil images. Data were provided to the
students through georeferenced KMZ files in Google Earth. Students were
asked to keep a field notebook, define lithological units of mappable scale,
identify large structures such as thrust faults and folds with the aid of
age estimations from fossils, construct a geological map on a hard-copy
topographic map, draw a stratigraphic column and cross sections, and plot
the data in a stereonet to perform structural analysis. The exercise allowed
for successful training of diverse geological field skills. In light of
the assessment of reports and student surveys, a series of improvements for
the future is considered. Though incapable of replacing a physical field
course, the virtual exercise could be used in preparation for the
residential field trip.
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TL;DR: In this article , the authors applied time-domain 3D acoustic full-waveform inversion (FWI) to build a high-resolution P-wave velocity model, which was subsequently used for pre-stack depth imaging with reverse time migration (RTM) to produce the complementary reflectivity section.
Abstract: Abstract. A sparse 3D seismic survey was acquired over the Blötberget iron oxide deposits of the Ludvika Mines in south-central Sweden. The main aim of the survey was to delineate the deeper extension of the mineralisation and to better understand its 3D nature and associated fault systems for mine planning purposes. To obtain a high-quality seismic image in depth, we applied time-domain 3D acoustic full-waveform inversion (FWI) to build a high-resolution P-wave velocity model. This model was subsequently used for pre-stack depth imaging with reverse time migration (RTM) to produce the complementary reflectivity section. We developed a data preprocessing workflow and inversion strategy for the successful implementation of FWI in the hardrock environment. We obtained a high-fidelity velocity model using FWI and assessed its robustness. We extensively tested and optimised the parameters associated with the RTM method for subsequent depth imaging using different velocity models: a constant velocity model, a model built using first-arrival travel-time tomography and a velocity model derived by FWI. We compare our RTM results with a priori data available in the area. We conclude that, from all tested velocity models, the FWI velocity model in combination with the subsequent RTM step provided the most focussed image of the mineralisation and we successfully mapped its 3D geometrical nature. In particular, a major reflector interpreted as a cross-cutting fault, which is restricting the deeper extension of the mineralisation with depth, and several other fault structures which were earlier not imaged were also delineated. We believe that a thorough analysis of the depth images derived with the combined FWI–RTM approach that we present here can provide more details which will help with better estimation of areas with high mineralisation, better mine planning and safety measures.
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TL;DR: In this paper , the vectoring capacities of trace element and sulfur isotope characteristics of pyrite, combined with quantitative statistical methods of whole-rock geochemical datasets, are tested for the Rajapalot gold-cobalt project in northern Finland.
Abstract: Abstract. Discovering ore deposits is becoming increasingly difficult, and this is particularly true in areas of glaciated terrains. As a potential exploration tool for such terrains, we test the vectoring capacities of trace element and sulfur isotope characteristics of pyrite, combined with quantitative statistical methods of whole-rock geochemical datasets. Our target is the Rajapalot gold–cobalt project in northern Finland, where metamorphosed Paleoproterozoic volcanic and sedimentary rocks of the Peräpohja belt host recently discovered gold prospects, which also have significant cobalt enrichment. The focus is particularly put on a single gold–cobalt prospect, known as Raja, an excellent example of this unusual cobalt-enriched gold deposit, common in the metamorphosed terranes of northern Finland. The major lithologies at Rajapalot comprise amphibolite facies metamorphosed and polydeformed calcsilicate rocks that alternate with albitic units, mafic volcanic rocks, mica schist and quartzite. Mineralization at Rajapalot prospects is characterized by an older Co-mineralizing event and a younger high-grade Au mineralization with re-mobilization and re-deposition of Co. Detailed in situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a powerful technique that produces robust trace element and sulfur isotope databases from paragenetically and texturally well-characterized pyrite from the Raja prospect. The results are treated with appropriate log-ratio transformations and used for multivariate statistical data analysis, such as the computation of principal components. Application of these methods revealed that elements such as Co, Ni, Cu, Au, As, Ag, Mo, Bi, Te, Se, Sn, U, Tl and W have high vectoring capacities to discriminate between Co-only and Au–Co zones, as well as between mineralization stages. The systematic pyrite study suggests that homogenous sulfur isotopic characteristics (+1.3 ‰ to +5.9 ‰) and positive loadings of Co, Se, As, Te, Bi and Au onto PC1 are reflective of an early stage of Co mineralization, while the opposing negative loadings of Mo, Ni, W, Tl, Cu and Ag along PC1 are associated with pyrites from the Au-mineralizing event. The sulfur isotopic signature of the latter pyrite type is between −1.2 ‰ and +7.4 ‰. Subtle patterns recognized from the whole-rock geochemistry favor an As–Au–Se–Te–W–U signature along the positive axis of PC1 for the localization of high-grade Au–Co zones, whereas the element group Ni, Cu, Co, Te, Se and As, which has negative loadings onto PC2, will predict Co-only zones. This study shows the efficiency of trace element geochemistry in mineral exploration targeting, which has the capacity to define future targets by characterizing the metallogenic potential of a host rock, as well as distinguishing various stages of mineralization.
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TL;DR: In this article , the authors used time-resolved (4-D) microtomographic data to capture the dynamic evolution of the porosity in layered NaCl-NaCl/biotite samples over 1619 and 32h of compaction.
Abstract: Abstract. Phyllosilicates are generally regarded to have a reinforcing effect on chemical compaction by dissolution–precipitation creep (DPC) and thereby
influence the evolution of hydraulic rock properties relevant to groundwater resources and geological repositories as well as fossil fuel
reservoirs. We conducted oedometric compaction experiments on layered NaCl–biotite samples to test this assumption. In particular, we aim to analyse
slow chemical compaction processes in the presence of biotite on the grain scale and determine the effects of chemical and mechanical feedbacks. We
used time-resolved (4-D) microtomographic data to capture the dynamic evolution of the porosity in layered NaCl–NaCl/biotite samples over 1619 and
1932 h of compaction. Percolation analysis in combination with advanced digital volume correlation techniques showed that biotite grains influence
the dynamic evolution of porosity in the sample by promoting a reduction of porosity in their vicinity. However, the lack of preferential strain
localisation around phyllosilicates and a homogeneous distribution of axial shortening across the sample suggests that the porosity reduction is not
achieved by pore collapse but by the precipitation of NaCl sourced from outside the NaCl–biotite layer. Our observations invite a renewed discussion
of the effect of phyllosilicates on DPC, with a particular emphasis on the length scales of the processes involved. We propose that, in our
experiments, the diffusive transport processes invoked in classical theoretical models of DPC are complemented by chemo-mechanical feedbacks that
arise on longer length scales. These feedbacks drive NaCl diffusion from the marginal pure NaCl layers into the central NaCl–biotite mixture over
distances of several hundred micrometres and several grain diameters. Such a mechanism was first postulated by Merino et al. (1983).
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TL;DR: In this article , the authors used legacy 2-D seismic data together with newly acquired 3-dimensional seismic data for the first time, precisely imaged sub-Zechstein (i.e., sub-evaporitic) upper Palaeozoic successions in NW Poland in order to develop a quantitative, balanced 2D model of the late Palaeo-recent evolution of this area, characterised by a complex pattern of repeated extension and inversion.
Abstract: Abstract. In Europe, formation of the Palaeozoic Variscan orogenic
belt, and the Mesozoic–Cenozoic Alpine–Carpathian orogenic belt led to a
widespread inversion events within forelands of both orogenic domains. We
used legacy 2-D seismic data together with the newly acquired 3-D seismic data
that, for the first time, precisely imaged sub-Zechstein (i.e.
sub-evaporitic) upper Palaeozoic successions in NW Poland in order to
develop a quantitative, balanced 2-D model of the late Palaeozoic–recent
evolution of this area, characterised by a complex pattern of repeated
extension and inversion. Four main tectonic phases have been determined: (1) Late Devonian–early Carboniferous extension and subsidence possibly
related to extensional reactivation of Caledonian thrusts, (2) late
Carboniferous inversion caused by the Variscan orogeny, (3) Permo-Mesozoic
subsidence related to the development of the Polish Basin and (4) its Late
Cretaceous–Paleogene inversion. Variscan and Alpine structures form a
superimposed multilayer inversion system, mechanically decoupled by the
Zechstein evaporites.
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TL;DR: In this article , a semi-automatic workflow for the extraction of the path-average dispersion curves (DCs) from ambient seismic noise data is proposed, including identification of time windows with strong coherent SW signal, azimuth analysis and two-station method for DC picking.
Abstract: Abstract. Surface wave (SW) methods offer promising options for an effective and sustainable development of seismic exploration, but they still remain under-exploited in hard rock sites. We present a successful application of active and passive surface wave tomography for the characterization of the southern continuation of the Siilinjärvi phosphate deposit (Finland). A semi-automatic workflow for the extraction of the path-average dispersion curves (DCs) from ambient seismic noise data is proposed, including identification of time windows with strong coherent SW signal, azimuth analysis and two-station method for DC picking. DCs retrieved from passive data are compared with active SW tomography results recently obtained at the site. Passive data are found to carry information at longer wavelengths, thus extending the investigation depth. Active and passive DCs are consequently inverted together to retrieve a deep pseudo-3D shear-wave velocity model for the site, with improved resolution. The southern continuation of the mineralization, its contacts with the host rocks and different sets of cross-cutting diabase dikes are well imaged in the final velocity model. The seismic results are compared with the latest available geological models to both validate the proposed workflow and improve the interpretation of the geometry and extent of the mineralization. Important large-scale geological boundaries and structural discontinuities are recognized from the results, demonstrating the effectiveness and advantages of the methods for mineral exploration perspectives.
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TL;DR: In this article , a Bayesian approach was proposed to evaluate how well a seismic network, used to monitor natural and/or induced micro-seismicity, estimates focal mechanisms as a function of magnitude, location, and kinematics of the seismic source and consequently their reliability in defining seismotectonic models.
Abstract: Abstract. Improving the knowledge of seismogenic faults requires the integration of
geological, seismological, and geophysical information. Among several
analyses, the definition of earthquake focal mechanisms plays an essential
role in providing information about the geometry of individual faults and
the stress regime acting in a region. Fault plane solutions can be retrieved
by several techniques operating in specific magnitude ranges, both in the
time and frequency domain and using different data. For earthquakes of low magnitude, the limited number of available data and
their uncertainties can compromise the stability of fault plane solutions.
In this work, we propose a useful methodology to evaluate how well a seismic
network, used to monitor natural and/or induced micro-seismicity, estimates
focal mechanisms as a function of magnitude, location, and kinematics of
seismic source and consequently their reliability in defining seismotectonic
models. To study the consistency of focal mechanism solutions, we use a
Bayesian approach that jointly inverts the P/S long-period spectral-level
ratios and the P polarities to infer the fault plane solutions. We applied
this methodology, by computing synthetic data, to the local seismic network
operating in the Campania–Lucania Apennines (southern Italy) aimed to
monitor the complex normal fault system activated during the Ms 6.9, 1980
earthquake. We demonstrate that the method we propose is effective and can
be adapted for other case studies with a double purpose. It can be a valid
tool to design or to test the performance of local seismic networks, and more
generally it can be used to assign an absolute uncertainty to focal
mechanism solutions fundamental for seismotectonic studies.
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TL;DR: In this paper , the Szozdy delta has been shown to have developed in the axial part of the mid-Polish Trough during the Late Cretaceous, and three facies associations have been distinguished: (1) dark grey sedimentary mudstones, (2) a yellow calcareous sandstone, and (3)calcareous calcicaize lithofacies.
Abstract: Abstract. The Polish Basin is a part of a trans-European sedimentary basin comprising
the Central European Basin System and stretching from Denmark through
Germany to southeastern Poland, and even further to the south into Ukraine.
It experienced uplift during the Late Cretaceous, which consequently
resulted in the inversion of its axial part (i.e., the Mid-Polish Trough) and
development into the Mid-Polish Anticlinorium. In many existing
paleotectonic interpretations, southeast Poland – i.e., the subsurface San
Anticlinorium and the present-day Roztocze Hills – was included in the
Mid-Polish Trough during the Late Cretaceous, representing its axial, most
subsiding part. This paleotectonic model was the basis for facies and
bathymetric interpretations that assumed Upper Cretaceous sediments,
deposited close to the axial part of the Mid-Polish Trough (e.g., in the
Roztocze Hills), constituted the deepest facies. In recent years, several
studies have contradicted this notion. A growing body of data suggests that
this area (southeast Poland) was already a landmass by the Coniacian and
Santonian – and certainly in the Campanian and Maastrichtian – rather than
forming the deepest part of the Polish Basin. The shallow marginal marine, cyclic middle Campanian, marly to sandy
deposits, recently discovered in the Roztocze Hills, were interpreted to be
of deltaic origin. This has led to the adoption of new facies and
bathymetric models, which – notably – are in stark opposition to most
previous interpretations. Notably, the new interpretation implies the
presence of a landmass in the place where, in prior frameworks, the deepest
and most subsiding part of the Polish Basin (i.e., Mid-Polish Trough) was
located during the Cretaceous. Here, we document this Late Cretaceous depositional system – the Szozdy
delta developed in the axial part of the Mid-Polish Trough. These middle
Campanian deposits crop out extensively in the Roztocze Hills region, close
to the village of Szozdy, and exhibit coarsening-upward tripartite
cyclothems. Three facies associations have been distinguished: (1) dark grey
calcareous mudstones, (2) a yellow calcareous sandstone, and (3) calcareous
gaize lithofacies. The sequence, as a whole, was accumulated via the
repeated progradation and abandonment of deltaic complexes on the delta
front platform setting, with the primary transport direction originating
from the axis of the inverting Mid-Polish Trough (thus from the subsurface
San Anticlinorium) toward the northeast. This interpretation is supported by
a suite of sedimentological, palynofacies, and heavy mineral data. The development of the Szozdy delta system is framed in the context of the
dynamic tectonic processes operating contemporaneously in southeast Poland:
that is, tectonic inversion (uplift) on one hand, and the generation of new
accommodation space via enhanced subsidence on the other. This discovery
sheds new light on our understanding of Late Cretaceous facies distribution,
bathymetry, and paleogeography and might potentially suggest a different burial
history than assumed so far.
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TL;DR: In this article , a comprehensive analysis integrating diagenesis with structure pattern, fracture and in situ stress is performed following a structural diagenetic approach, and the results show that the pore spaces include residual intergranular pores, inter-granular and intragranular dissolution pores, and micro-fractures.
Abstract: Abstract. The Lower Cretaceous Bashijiqike Formation of the Kuqa Depression is made up of ultra-deeply buried sandstones in fold-and-thrust belts. Few researches have linked diagenetic processes with structure. To fill this gap, a comprehensive analysis integrating diagenesis with structure pattern, fracture and in situ stress is performed following a structural diagenetic approach. The results show that the pore spaces include residual intergranular pores, intergranular and intragranular dissolution pores, and micro-fractures. The sandstones experienced a high degree of mechanical compaction, but compaction is limited in well-sorted rocks or abundant in rigid quartz grains. The most volumetrically important diagenetic minerals are calcites. The framework grains experienced a varied degree of dissolution, and intergranular and intragranular dissolution pores are formed. Special attention is paid on the dissolution associated with the fracture planes. Large numbers of natural fractures are cemented by carbonate cements, which limit fluid flow. In addition, the presence of fracture enhances dissolution and the fracture planes are enlarged by dissolution. Cementation and dissolution can occur simultaneously in fracture surfaces, and the enlarged fracture surfaces can be cemented by late-stage cements. The in situ stress magnitudes are calculated using well logs. The horizontal stress difference (Δσ) determines the degree of mechanical compaction, and rocks associated with low Δσ experienced a low degree of compaction, and these contain preserved intergranular pores. Natural fractures are mainly related to the low Δσ layers. The presence of intergranular and intragranular dissolution pores is mainly associated with the fractured zones. The high-quality reservoirs with intergranular pores or fractures are related to low Δσ layers. The structural diagenesis researches above help the prediction of reservoir quality in ultra-deep sandstones and reduce the uncertainty in deep natural gas exploration in the Kuqa Depression.
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TL;DR: In this paper , a case study of 3D reflection-seismic exploration at the Blötberget iron oxide mining site belonging to the Bergslagen mineral district in central Sweden is presented, where a tailored pre-processing workflow and two different seismic imaging approaches, Kirchhoff pre-stack depth migration (KPSDM) and Fresnel volume migration (FVM), are applied.
Abstract: Abstract. We present pre-stack depth-imaging results for a case study of 3D reflection
seismic exploration at the Blötberget iron oxide mining site belonging
to the Bergslagen mineral district in central Sweden. The goal of the study
is to directly image the ore-bearing horizons and to delineate their
possible depth extension below depths known from existing boreholes. For
this purpose, we applied a tailored pre-processing workflow and two
different seismic imaging approaches, Kirchhoff pre-stack depth migration
(KPSDM) and Fresnel volume migration (FVM). Both imaging techniques deliver
a well-resolved 3D image of the deposit and its host rock, where the FVM
image yields a significantly better image quality compared to the KPSDM
image. We were able to unravel distinct horizons, which are linked to known
mineralization and provide insights on their possible lateral and depth
extent. Comparison of the known mineralization with the final FVM reflection
volume suggests a good agreement of the position and the shape of the imaged
reflectors caused by the mineralization. Furthermore, the images show
additional reflectors below the mineralization and reflectors with opposite
dips. One of these reflectors is interpreted to be a fault intersecting the
mineralization, which can be traced to the surface and linked to a fault
trace in the geological map. The depth-imaging results can serve as the
basis for further investigations, drilling, and follow-up mine planning at
the Blötberget mining site..
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TL;DR: In this paper , the authors studied the Zuccale Fault (ZF) on Elba, part of the Northern Apennines, to unravel the complex deformation history that is responsible for the remarkable architectural complexity of the fault.
Abstract: Abstract. We studied the Zuccale Fault (ZF) on Elba,
part of the Northern Apennines, to unravel the complex deformation history that is
responsible for the remarkable architectural complexity of the fault. The ZF
is characterized by a patchwork of at least six distinct, now tightly
juxtaposed brittle structural facies (BSF), i.e. volumes of deformed
rock characterized by a given fault rock type, texture, colour, composition,
and age of formation. ZF fault rocks vary from massive cataclasite to
foliated ultracataclasite, from clay-rich gouge to highly sheared talc
phyllonite. Understanding the current spatial juxtaposition of these BSFs
requires tight constraints on their age of formation during the ZF lifespan
to integrate current fault geometries and characteristics over the time
dimension of faulting. We present new K–Ar gouge dates obtained from three
samples from two different BSFs. Two top-to-the-east foliated gouge and talc
phyllonite samples document faulting in the Aquitanian (ca. 22 Ma),
constraining east-vergent shearing along the ZF already in the earliest
Miocene. A third sample constrains later faulting along the exclusively
brittle, flat-lying principal slip surface to < ca. 5 Ma. The new
structural and geochronological results reveal an unexpectedly long faulting
history spanning a ca. 20 Myr time interval in the framework of the
evolution of the Northern Apennines. The current fault architecture is
highly heterogeneous as it formed at very different times under different
conditions during this prolonged history. We propose that the ZF started as
an Aquitanian thrust that then became selectively reactivated by early
Pliocene out-of-sequence thrusting during the progressive structuring of the
Northern Apennine wedge. These results require the critical analysis of
existing geodynamic models and call for alternative scenarios of continuous
convergence between the late Oligocene and the early Pliocene with a major
intervening phase of extension in the middle Miocene allowing for the
isostatic re-equilibration of the Northern Apennine wedge. Extension
started again in the Pliocene and is still active in the innermost portion
of the Northern Apennines. In general terms, long-lived, mature faults can
be very architecturally complex. Their unravelling, including understanding
the dynamic evolution of their mechanical properties, requires a
multidisciplinary approach combining detailed structural analyses with
dating the deformation events recorded by the complex internal architecture,
which is a phenomenal archive of faulting and faulting conditions through
time and space.
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TL;DR: In this paper , the authors conducted load-stepping creep experiments on basalts from the CarbFix site (Iceland) under several pore fluid conditions (dry, H2O saturated and CO2 saturated) at temperature,
Abstract: Abstract. Geological carbon sequestration provides permanent
CO2 storage to mitigate the current high concentration of CO2 in
the atmosphere. CO2 mineralization in basalts has been proven to be one
of the most secure storage options. For successful implementation and future
improvements of this technology, the time-dependent deformation behavior of
reservoir rocks in the presence of reactive fluids needs to be studied in
detail. We conducted load-stepping creep experiments on basalts from the
CarbFix site (Iceland) under several pore fluid conditions (dry,
H2O saturated and H2O + CO2 saturated) at temperature,
T≈80 ∘C and effective pressure, Peff=50 MPa,
during which we collected mechanical, acoustic and pore fluid chemistry
data. We observed transient creep at stresses as low as 11 % of the
failure strength. Acoustic emissions (AEs) correlated strongly with strain
accumulation, indicating that the creep deformation was a brittle process in
agreement with microstructural observations. The rate and magnitude of AEs
were higher in fluid-saturated experiments than in dry conditions. We infer
that the predominant mechanism governing creep deformation is time- and
stress-dependent subcritical dilatant cracking. Our results suggest that
the presence of aqueous fluids exerts first-order control on creep
deformation of basaltic rocks, while the composition of the fluids plays
only a secondary role under the studied conditions.
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TL;DR: In this article , the authors investigate the effect of basal heat flow, shear heating, thermal blanketing by sediments, and the thickness of incoming sediments on the local topography of the accretionary prism and its topography.
Abstract: Abstract. The local topographic slope of the accretionary prism is often used together with the critical taper theory to determine the effective friction on subduction megathrust. In this context, extremely small topographic slopes associated with extremely low effective basal friction (μ≤0.05) can be interpreted either as seismically locked portions of megathrust, which deforms episodically at dynamic slip rates or as a viscously creeping décollement. Existing mechanical models of the long-term evolution of accretionary prism, sandbox models, and numerical simulations alike, generally do not account for heat conservation nor for temperature-dependent rheological transitions. Here, we solve for advection–diffusion of heat with imposed constant heat flow at the base of the model domain. This allows the temperature to increase with burial and therefore to capture how the brittle–ductile transition and dehydration reactions within the décollement affect the dynamic of the accretionary prism and its topography. We investigate the effect of basal heat flow, shear heating, thermal blanketing by sediments, and the thickness of the incoming sediments. We find that while reduction of the friction during dewatering reactions results as expected in a flat segment often in the forearc, the brittle–ductile transition results unexpectedly in a local increase of topographic slope by decreasing internal friction. We show that this counterintuitive backproduct of the numerical simulation can be explained by the onset of internal ductile deformation in between the active thrusts. Our models, therefore, imply significant viscous deformation of sediments above a brittle décollement, at geological rates, and we discuss its consequences in terms of interpretation of coupling ratios at subduction megathrust. We also find that, with increasing burial and ductile deformation, the internal brittle deformation tends to be accommodated by backthrusts until the basal temperature becomes sufficient to form a viscous channel, parallel to the décollement, which serves as the root to a major splay fault and its backthrust and delimits a region with a small topographic slope. Morphologic resemblances of the brittle–ductile and ductile segments with forearc high and forearc basins of accretionary active margins, respectively, allow us to propose an alternative metamorphic origin of the forearc crust in this context.
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TL;DR: An up-to-date review of basin inversion can be found in this article , where a wide range of different experimental approaches are reviewed, with attention to the various materials, set-ups, and techniques used for model monitoring and analysing the model results.
Abstract: Abstract. Basin inversion involves the reversal of subsidence in a basin due to compressional tectonic forces, leading to uplift of the basin's sedimentary infill. Detailed knowledge of basin inversion is of great importance for scientific, societal, and economic reasons, spurring continued research efforts to better understand the processes involved. Analogue tectonic modelling forms a key part of these efforts, and analogue modellers have conducted numerous studies of basin inversion. In this review paper we recap the advances in our knowledge of basin inversion processes acquired through analogue modelling studies, providing an up-to-date summary of the state of analogue modelling of basin inversion. We describe the different definitions of basin inversion that are being applied by researchers, why basin inversion has been historically an important research topic and what the general mechanics involved in basin inversion are. We subsequently treat the wide range of different experimental approaches used for basin inversion modelling, with attention to the various materials, set-ups, and techniques used for model monitoring and analysing the model results. Our new systematic overviews of generalized model results reveal the diversity of these results, which depend greatly on the chosen set-up, model layering and (oblique) kinematics of inversion, and 3D along-strike structural and kinematic variations in the system. We show how analogue modelling results are in good agreement with numerical models, and how these results help researchers to better understand natural examples of basin inversion. In addition to reviewing the past efforts in the field of analogue modelling, we also shed light on future modelling challenges and identify a number of opportunities for follow-up research. These include the testing of force boundary conditions, adding geological processes such as sedimentation, transport, and erosion; applying state-of-the-art modelling and quantification techniques; and establishing best modelling practices. We also suggest expanding the scope of basin inversion modelling beyond the traditional upper crustal “North Sea style” of inversion, which may contribute to the ongoing search for clean energy resources. It follows that basin inversion modelling can bring valuable new insights, providing a great incentive to continue our efforts in this field. We therefore hope that this review paper will form an inspiration for future analogue modelling studies of basin inversion.
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TL;DR: The Luangwa Rift Active Fault Database (LRAFD) as discussed by the authors is an open-source geospatial database containing active fault traces and their attributes and is freely available at https://doi.org/10.5281/zenodo.6513691.
Abstract: Abstract. Seismic hazard assessment in slow straining regions is challenging because earthquake catalogues only record events from approximately the last 100 years, whereas earthquake recurrence times on individual faults can exceed 1000 years. Systematic mapping of active faults allows fault sources to be used within probabilistic seismic hazard assessment, which overcomes the problems of short-term earthquake records. We use Shuttle Radar Topography Mission (SRTM) data to analyse surface deformation in the Luangwa Rift in Zambia and develop the Luangwa Rift Active Fault Database (LRAFD). The LRAFD is an open-source geospatial database containing active fault traces and their attributes and is freely available at https://doi.org/10.5281/zenodo.6513691. We identified 18 faults that display evidence for Quaternary activity, and empirical relationships suggest that these faults could cause earthquakes up to Mw 8.1, which would exceed the magnitude of historically recorded events in southern Africa. On the four most prominent faults, the median height of Quaternary fault scarps varies between 12.9 ± 0.4 and 19.2 ± 0.9 m, which suggests they were formed by multiple earthquakes. Deformation is focused on the edges of the Luangwa Rift: the most prominent Quaternary fault scarps occur along the 207 km long Chipola and 142 km long Molaza faults, which are the rift border faults and the longest faults in the region. We associate the scarp on the Molaza Fault with possible surface ruptures from two 20th century earthquakes. Thus, the LRAFD reveals new insights into active faulting in southern Africa and presents a framework for evaluating future seismic hazard.
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TL;DR: In this paper , the authors investigate if and how the strongly and weakly coupled patches revealed by these models relate to the distribution of deformation along the plate interface, i.e., basal erosion and/or underplating.
Abstract: Abstract. What controls the location and segmentation of mega-earthquakes in subduction zones is a long-standing problem in Earth sciences. Prediction of earthquake rupture extent
mostly relies on interplate coupling models based on Global Navigation Satellite Systems providing patterns of slip deficit between tectonic plates. We here investigate if and how the strongly and weakly coupled patches revealed by these models relate to the distribution of deformation along the plate interface, i.e., basal erosion
and/or underplating.
From a mechanical analysis of the topography applied along the Chilean subduction zone, we show that extensive plate interface deformation takes place along most of the margin.
We show that basal erosion occurs preferentially at 15 km depth while underplating does at 35 ± 10 and 60 ± 5 km depth, in agreement with P-T conditions of recovered underplated material, expected pore pressures and the spatial distribution of marine terraces and uplift rates.
South of the Juan Fernández Ridge, large sediment input favors shallow accretion and underplating of subducted sediments, while along northern Chile, extensive basal erosion provides material for the underplating.
We then show that, along the accretionary margin, the two last major earthquakes were limited along their down-dip end by underplating while, along the erosive margin, they were surrounded by both basal erosion and underplating.
Segments with heterogeneously distributed deformation largely coincide with lateral earthquake terminations. We therefore propose that long-lived plate interface deformation promotes stress build-up and leads to earthquake nucleation. Earthquakes then propagate along fault planes shielded from this long-lived permanent deformation, and are finally stopped by segments of heterogeneously distributed deformation.
Slip deficit patterns and earthquake segmentation therefore reflect the along-dip and along-strike distribution of the plate interface deformation. Topography acts as a mirror of distributed plate interface deformation and should be more systematically studied to improve the prediction of earthquake ruptures.