Dry Quartz Research Articles

Evolution in H2O contents during deformation of polycrystalline quartz: An experimental study

Shear experiments were performed in a Griggs-type apparatus at 800 °C and 1.5 GPa, at a strain rate of 2.1 × 10−5s−1 using different starting materials: (i) Powder (grain size 6–10 μm) of dry Brazil quartz with 0.15 wt% added H2O, (ii) “dry” Brazil quartz porphyroclasts (grain size ∼100–200 μm), devoid of fluid inclusions embedded in the same fine grained powder, and (iii) “wet” porphyroclasts (grain size ∼100–200 μm), containing initially a high density of μm-scale fluid inclusions embedded in the same powder. After hot pressing, samples were deformed to large shear strains (γ∼3 to 4.5), in order for the microstructures and H2O distribution to approach some state of “equilibrium”. The H2O content and speciation in quartz were analyzed by Fourier Transform Infra-Red (FTIR) spectroscopy before and after the experiments. Mechanical peak strength is generally lower in experiments with 100% hydrated matrix, intermediate in experiments incorporating wet porphyroclasts (with a proportion of 30 or 70%) and highest in those with dry porphyroclasts. All experiments with porphyroclasts show pronounced strain weakening, and the strengths of most samples converge to similar values at large strain. Wet porphyroclasts are pervasively recrystallized during deformation, while dry porphyroclasts recrystallize only at their rims and remain weakly deformed. Recrystallization of the initially fluid-inclusion-rich porphyroclasts results in a decrease in inclusion abundance and total H2O content, while H2O content of initially dry clasts increases during deformation. H2O contents of all high strain samples converge to similar values for matrix and recrystallized grains. In samples with wet porphyroclasts, shear bands with high porosity and fluid contents develop and they host the precipitation of euhedral quartz crystals surrounded by a free-fluid phase. These high porosity sites are sinks for collecting H2O in excess of the storage capacity of the grain boundary network of the recrystallized aggregate. The H2O storage capacity of the grain boundary network is determined as a H2O-boundary-film of ∼0.7 nm thickness.

Umbrisols at Lower Altitudes, Case Study from Borská lowland (Slovakia)

AbstractUmbrisols generally develop in a cool and humid climate. Therefore, occurrence of these soils in the Borská lowland of southwestern Slovakia is very uncommon, and this inspired the aim of this paper: Analysis of the natural conditions suitable for Umbrisol development. Umbrisols in the Borská lowland developed from aeolian quartz sands accumulated on Neogenne marine clay sediments. Their occurrence is connected with the groundwater table relatively close to the ground surface and this particularly determines Umbrisol genesis in this area. Sufficient input via organic matter is an important factor for formation of the umbric horizon, and only the rich herbaceous undergrowth of the prevailing planted pine and mixed pine-oak forests is capable of providing it. A growth of diep-rooted grass is closely connected with higher soil moisture content, and quite moist areas occur in the deeper inter-dunes depressions. Constant soil moisture in these sites is facilitated by water capillary elevation. While Umbrisols are transformed to Arenosols at increased altitude, they can be transformed to Gleysols in deep depressions. Herein, induced polarization provided suitable geophysical method for detection of arenic Umbrisol inclusions. Sharp transformation of the humus layer to dry non-polarized aeolian quartz sands enabled the surface horizon to be distinguished by induced polarization

The Effect of Lineation on Anisotropy in Dry and Saturated Himalayan Schistose Rock Under Brazilian Test Conditions

The paper presents experimental observations of the anisotropic effect of dry and saturated lineated schistose rock on deformational behaviour and fracture patterns under indirect tensile loading conditions. Dry mylonitic quartz–mica schist (M-QMS) shows strength minima in between lineation orientation of 20°–30° with loading direction, whereas dry crenulated quartz–mica schist (C-QMS) shows strength minima in between 45° and 60°. Water saturation significantly reduces the failure strength and shifts the strength minima towards a higher angle. In addition, the water saturation effect induces plasticity along the lineation direction. P-wave velocity is found to be maximum along lineation direction, which continuously decreases to a minimum value across the lineation. Three types of fracture patterns, namely layer activation, central and non-central, are observed for both the rock types. For both the rock types, tensional fractures occur when the lineation is inclined at 0° and 90° to the loading direction, whereas shear and mixed-mode fractures occur at all other orientations. Fracture through the layer activation is prominent in saturated specimens compared to the dry specimens for β angle range of 15°–60° and 15°–45° in the case of M-QMS and C-QMS, respectively.

Capillary effects on phase behavior of liquid and gaseous propane and dynamics of hydrate formation and dissociation in porous media

Using a precision adiabatic calorimetry method the phase behavior of liquid and gaseous propane with water in bulk as well as in dry and water saturated porous media have been studied in the temperature range from 240 to 350 K and the pressure range from 0.1 to 12 MPa. Quartz powder with a grain size from 25 to 38 mk as a porous medium was used. Water saturation of the porous medium was about 0.247 ± 0.001 of porous volume. From thermodynamic point of view such water saturation of the porous volume is sufficient to consider the pore water phase practically as a bulk phase. A composite porous medium is formed from the quartz powder grains covered by a water film. In fact, the water film is a mechanical continuation of the quartz powder grains. The water film forms a configuration (a curvature) of the porous space as well predetermines a surface wettability of the composite porous medium. We study capillary effect in composite porous media due to capillary condensation and capillary evaporation of propane, both on a lyophilic surface and on a lyophobic surface of water film. Based on the experimental data of specific heat and temperature derivative of pressure at constant volume, the phase diagrams of propane in bulk and in water saturated and dry quartz powder have been constructed (including the gas hydrate field of phase diagram).

Water redistribution in experimentally deformed natural milky quartz single crystals—Implications for H2O‐weakening processes

AbstractNatural quartz single crystals were experimentally deformed in two orientations: (1) ⊥ to one prism plane and (2) in O+ orientation at 900 and 1000°C, 1.0 and 1.5 GPa, and strain rates of ~1 × 10−6 s−1. In addition, hydrostatic and annealing experiments were performed. The starting material was milky quartz, which consisted of dry quartz with a large number of fluid inclusions of variable size up to several 100 µm. During pressurization fluid inclusions decrepitated producing much smaller fluid inclusions. Deformation on the sample scale is anisotropic due to dislocation glide on selected slip systems and inhomogeneous due to an inhomogeneous distribution of fluid inclusions. Dislocation glide is accompanied by minor dynamic recovery. Strongly deformed regions show a pointed broad absorption band in the ~3400 cm−1 region consisting of a superposition of bands of molecular H2O and three discrete absorption bands (at 3367, 3400, and 3434 cm−1). In addition, there is a discrete absorption band at 3585 cm−1, which only occurs in deformed regions and reduces or disappears after annealing, so that this band appears to be associated with dislocations. H2O weakening in inclusion‐bearing natural quartz crystals is assigned to the H2O‐assisted dislocation generation and multiplication. Processes in these crystals represent recycling of H2O between fluid inclusions, cracking and crack healing, incorporation of structurally bound H in dislocations, release of H2O from dislocations during recovery, and dislocation generation at very small fluid inclusions. The H2O weakening by this process is of disequilibrium nature because it depends on the amount of H2O available.

Design of a split Hopkinson pressure bar with partial lateral confinement

This paper presents the design of a modified split Hopkinson pressure bar (SHPB) where partial lateral confinement of the specimen is provided by the inertia of a fluid annulus contained in a long steel reservoir. In contrast to unconfined testing, or a constant cell pressure applied before axial loading, lateral restraint is permitted to develop throughout the axial loading: this enables the high-strain-rate shear behaviour of soils to be characterised under conditions which are more representative of buried explosive events. A pressure transducer located in the wall of the reservoir allows lateral stresses to be quantified, and a dispersion-correction technique is used to provide accurate measurements of axial stress and strain. Preliminary numerical modelling is utilised to inform the experimental design, and the capability of the apparatus is demonstrated with specimen results for a dry quartz sand.

A refined circumscription of Notobubon striatum and the resurrection of Dregea collina Ecklon & Zeyher (Apiaceae, Apioideae)

Extensive field surveys of the Critically Endangered Central and Eastern Rûens Shale Renosterveld have uncovered that Notobubon striatum, as currently circumscribed, comprises two distinct species. Upon careful examination of the type material it has become clear that names exist for both species. The type specimen of N. striatum clearly matches the lesser known species, a large shrub, ca. 1 m. tall, with a powerful anise-scent and which is restricted to the banks of seasonal rivers and watercourses in the Central and Eastern Rûens Shale Renosterveld. The second and better known entity, with a wider distribution, corresponds to the type material of Dregea collina Ecklon & Zeyher. As such, a new combination, Notobubon collinum (Ecklon & Zeyher) Magee, is here made to accommodate this taxon, restricted to dry quartz and silcrete patches or outcrops in Eastern Rûens Shale Renosterveld. In their revised circumscriptions N. striatum and N. collinum are readily distinguished by habit, scent, leaf size and division, as well as leaf lobe shape and sepal size. Comprehensive descriptions of both species are provided, together with notes on their ecology and conservation status, and the existing key to the species of Notobubon updated. This brings the number of recognised species in the genus to thirteen.

Dislocation creep of dry quartz

AbstractSmall‐scale shear zones within the Permian Truzzo meta‐granite developed during the Alpine orogeny at amphibolite facies conditions. In these shear zones magmatic quartz deformed by dislocation creep and recrystallized dynamically by grain boundary migration with minor subgrain rotation recrystallization to a grain size of around 250–750 µm, consistent with flow at low differential stresses. Fourier transform infrared (FTIR) spectroscopy reveals very low water contents in the interior of recrystallized grains (in the form of discrete OH peaks, ~20 H/106Si and very little broad band absorption, <100 H/106Si). The spectral characteristics are comparable to those of dry Brazil quartz. In FTIR spectra, magmatic quartz grains show a broad absorption band related with high water concentrations only in those areas where fluid inclusions are present while other areas are dry. Drainage of fluid inclusions and synkinematic growth of hydrous minerals indicates that a hydrous fluid has been available during deformation. Loss of intragranular water during grain boundary migration recrystallization did not result in a microstructure indicative of hardening. These FTIR measurements provide the first evidence that quartz with extremely low intragranular water contents can deform in nature by dislocation creep at low differential stresses. Low intragranular water contents in naturally deformed quartz may not be necessarily indicative of a high strength, and the results are contrary to implications taken from deformation experiments where very high water contents are required to allow dislocation creep in quartz. It is suggested that dislocation creep of quartz in the Truzzo meta‐granite is possible to occur at low differential stresses because sufficient amounts of intergranular water ensure a high recovery rate by grain boundary migration while the absence of significant amounts of intragranular water is not crucial at natural conditions.

Initiation of a thrust fault revealed by analog experiments

To reveal in detail the process of initiation of a thrust fault, we conducted analog experiments with dry quartz sand using a high-resolution digital image correlation technique to identify minor shear-strain patterns for every 27μm of shortening (with an absolute displacement accuracy of 0.5μm). The experimental results identified a number of “weak shear bands” and minor uplift prior to the initiation of a thrust in cross-section view. The observations suggest that the process is closely linked to the activity of an adjacent existing thrust, and can be divided into three stages. Stage 1 is characterized by a series of abrupt and short-lived weak shear bands at the location where the thrust will subsequently be generated. The area that will eventually be the hanging wall starts to uplift before the fault forms. The shear strain along the existing thrust decreases linearly during this stage. Stage 2 is defined by the generation of the new thrust and active displacements along it, identified by the shear strain along the thrust. The location of the new thrust may be constrained by its back-thrust, generally produced at the foot of the surface slope. The activity of the existing thrust falls to zero once the new thrust is generated, although these two events are not synchronous. Stage 3 of the thrust is characterized by a constant displacement that corresponds to the shortening applied to the model. Similar minor shear bands have been reported in the toe area of the Nankai accretionary prism, SW Japan. By comparing several transects across this subduction margin, we can classify the lateral variations in the structural geometry into the same stages of deformation identified in our experiments. Our findings may also be applied to the evaluation of fracture distributions in thrust belts during unconventional hydrocarbon exploration and production.

Equipment for the studies of the acoustic properties of hydrate-containing samples in laboratory conditions

Equipment for simulation in laboratory conditions of hydrate-containing artificial samples and measuring their acoustic properties (wave velocities, absorption and attenuation) at different temperature and pressures is designed and constructed. The plant consists of a high-pressure chamber (up to 45 MPa), a measuring system intended for the excitation and reception of acoustic waves, systems for temperature and pressure control (axial and lateral) and for gas/liquid delivery into the sample. The measurements are performed on cylindrical samples with a 30-mm diameter and height of 10–50 mm. A set of successful test experiments was performed, including measurements of acoustic velocities of consolidated (plexiglas, sandstone, and frozen sand) and unconsolidated (dry and wet quartz sand) samples and formation of methane-hydrate bearing samples.

Characterizing the sediment bed in terms of resistance to motion: Toward an improved model of saltation thresholds for aeolian transport

Abstract Models of aeolian transport thresholds generate a wide range of predictions, and error in threshold modeling leads to uncertainty in predicting aeolian events. This paper proposes a new characterization of the representative grain size for use in prediction of transport thresholds. This characterization is based on the distribution of resistance to motion in the sediment bed. The traditional grain size distribution uses a mean diameter to represent the sediment bed. However, the distribution of inertial forces resisting motion is not linearly proportional to the distribution of grain diameters, so that an arithmetic mean does not adequately represent the distribution of the resisting forces. A simple relation of shear stress to weight force is used to represent the threshold condition. Based on comparison with threshold observations drawn from the literature, the model provides reliable predictions of threshold stress and shear velocity for dry quartz grains over a wide range of grain sizes. Given that the dataset was drawn from studies employing a variety of experimental conditions and techniques, and that these studies spanned a range of nearly eight decades, the model is considered to provide a robust approximation of threshold conditions.

The influence of viscosity of thin fluid films on the frictional interaction mechanism of rock blocks

In the past few years, as a result of accomplishment of a number of international drilling projects in frac� ture zones, new important results have been published about the structure of fractures of megaearthquakes and the properties of the geomaterials that make them up (1). Especially interesting data were obtained as a result of sampling in the Nankai Trough (2, 3) and the Japan Trench including sampling in the fracture of the Tohuku megaearthquake fracture of March 11, 2011, with moment amplitude М w = 9.0 (4, 5). We focus attention on the fact that the frictional properties of the materials taken from various fractures are signifi� cantly different (2-4). This leads to the formation of different deformation regimes under the conditions of a close stressed state: slow earthquakes (2, 3), tsunami� genic earthquakes of the Tohuku type (4), and "typi� cal" events (2). Some of the authors think that the dif� ferent frictional behaviors may be related to the differ� ent composition of clayey materials, which compose from 37 to 85% of the ground material sampled from the central parts of the fracture zones (2, 4). Such a high concentration of clay is characteristic of the upper part of the fracture located within the accretion prism and near it. As the depth increases, the concen� tration of clay decreases and the content of quartz increases, which leads to the possibility of instability (3). Nevertheless, the material at sufficiently shallow depths in the main part of the fracture invariably con� tains minerals such as smectite, kaolinite, and others. Colloidal films formed by the clayey minerals have clearly manifested viscous properties and even being present in small quantities can have a strong influence on the frictional characteristics of the fracture. In this paper we present the results of laboratory experiments in which we found a new effect of the rad� ical variation in the shear deformation of a crack after passing a specific viscosity limit of the thin fluid films that wet the particle surfaces of the filling material. In our experiments a granite block with a size of 8 × 8 × 3 cm was located on an immovable granite basement. The contact between the rough surfaces was filled with a layer of quartz sand 2.5 mm thick with a mean size of the grains d = 0.2-0.3 mm. The mean depth of the inhomogeneities of the rough surface was notably greater than the grain size; it was equal to 0.5- 0.8 mm. A normally directed load was applied to a mobile block using a special device that excluded the appearance of shear stresses at its upper surface. The applied stress σn ranged between 50 and 150 kPa. The shear load was applied to the block using a spring ele� ment with rigidness K = 10-40 N/mm. The rate of the spring deformation was constant and equal to us = 20 µm/s. The shear stress applied to the upper block was measured with a force sensor SMS/5kN with an accuracy to 1 N, while the relative displacement of the blocks was recorded using laser sensors ILD2220-10 (G) in the frequency band 0-5 kHz with an accuracy to 0.1 µm. In the series of experiments described here, the sand was moistened with a small amount of fluid (ψ ≈ 0.5% of mass) whose viscosity varied from one experiment to another in the range from 0.3 mPa s to 20 Pa s. The contact filled with dry quartz sand in the entire range of the applied normal loads does not manifest velocity weakening demonstrating stable sliding after the tangential stresses reach the Coulomb strength limit (Fig. 1).

Three-dimensional geometry of thrust surfaces and the origin of sinuous thrust traces in orogenic belts: Insights from scaled sandbox experiments

Sinuous traces of emerging thrust tips, comprising multiple salients and recesses, are commonly observed in orogenic belts (e.g. Lesser Himalayas of India, Nepal and Bhutan) and in accretionary prisms (e.g. Nankai Trough off the coast of Japan). Lateral (along the strike of the deformation zone) variation in the depths of foreland basins (i.e. variable sediment thickness) or in the strength of the basal detachment, or presence of a curved indenter has been traditionally cited to explain the formation of salients in fold-and-thrust belts, although they are not applicable in all cases. In the present work, we have carried out four series of scaled analog model experiments using dry quartz sand, changing the dip of the basal decollément (β = 0° or 5°) and the basal friction (μb = 0.5 or 0.3) to investigate the 3D shape of thrust surfaces under varying overall boundary conditions, but without any lateral variation of these parameters, within the models. The experimental results show that under all boundary conditions, thrust surfaces are curved both in their dip and strike directions (i.e. spoon-shaped in 3D). Multiple concave-upward and convex-upward segments constitute a thrust surface, which produces a sinuous trace when the tip line intersects the Earth's surface. It is also shown that thrust surface curvatures occur at different scales, and the overall thrust surface roughness (corrugations) has a self-affine fractal geometry.

Determining the geotechnical properties of planetary regolith using Low Velocity Penetrometers

Measurements of mechanical and thermophysical properties of planetary surface allow determining many important parameters useful for planetologists. For example, effective heat conductivity or thermal inertia of the regolith can help to better understand the processes occurring in the bodies interior. Chemical and mineralogical composition gives us a chance to determine the origin and evolution of moons and satellites. Mechanical properties of the surface are one of the key factors needed by civil engineers for developing future bases on space bodies.Space missions to planetary bodies highly restrict the payload concerning its mass and power consumption. Therefore, it is quite impossible to use a standard terrestrial technique like the Load Plate Test or Direct Shear Tests to determine the geotechnical parameters of the planetary regolith. Even the Dynamic Cone Penetration (DCP) method, which is frequently used for field testing, does not fit well with the constraints imposed by a space mission. Nevertheless, its operation principle is very similar to that of at the Low Velocity Penetrators (LVP), several of them being currently on their way to planetary bodies (e.g. the MUPUS instrument) or which were developed in the last couple of years (e.g. the CHOMIK instrument or the KRET device).In this paper we present a comparison between DCP method and LVP operation which was observed during several tests campaigns during mole KRET and CHOMIK instrument development. The tests were performed in different planetary analogues: JSC-1A, Chenobi and AGK-2010, Phobos analogue, cometary analogues F1, F2 and F3 (SRC) and dry quartz sand. In the last part of the paper the concept of results׳ interpretation is presented.

Effect of fluid H2O on compressional wave velocities in quartz aggregate up to 500°C at 0.5 GPa

Compressional wave velocities (V p) in quartz aggregate were measured to quantify the effect of pore fluid (H2O) on V p at high pressure-temperature (P-T). Ultrasonic measurements were conducted on dry and wet quartz aggregate from room temperature to 500°C at 0.5 GPa using a piston cylinder apparatus. The experiment showed a 4% decrease in measured V p in quartz aggregate with increasing H2O content to 1 wt.%, whereas the temperature derivative of V p (∂V p/∂T = -2.8 to -4.9 × 10-4 km s-1°C-1) in wet quartz aggregate remained almost the same as for the dry quartz aggregate (∂V p/∂T = -5.2 × 10-4 km s-1°C-1). Our high-pressure, high-temperature experiments show that a small amount of pore fluid (0.4 to 1.0 wt.% H2O) can significantly reduce V p under the P-T conditions of the middle crust.

Wettability Alteration of the Quartz Surface in the Presence of Metal Cations

Experimental research was conducted to clarify the wettability alteration mechanism in the presence of metal cations. Wettability was studied by measuring the contact angle on a quartz–crude oil–water system. The quartz surface is aged in an asphaltene/toluene solution to study the effect of aging time, asphaltene concentration, water film on the quartz surface, and metal cations in the water film on wettability alteration of the quartz surface. The quartz surface property is characterized with ζ-potential measurements and infrared (IR) spectroscopy to clarify the wettability alteration mechanism. Results show that quartz surface becomes more oil-wet with the increase of the asphaltene concentration. The quartz with a pure water film shows less oil-wetting after soaking compared to the dry quartz surface, while the presence of metal cations in the water film can improve oil wettability of the surface. ζ-Potential measurements show that Ca2+ and Mg2+ compress a diffused double layer of quartz powder more effectively than Na+, which makes asphaltene adsorption easier because of the reduced electrostatic repulsion. IR spectra analysis indicates that asphaltene molecules can interact with hydroxyls on the quartz surface by polar interactions and asphaltene can be absorbed on the quartz surface with ion binding of hydrated divalent metal cations.

Influence of particle breakage on the dynamic compression responses of brittle granular materials

The dynamic compression responses of dry quartz sand are tested with a modified spilt Hopkinson pressure bar (MSHPB), and the quasi-static compression responses are tested for comparison with a material testing system. In the experiments, the axial stress–strain responses and the confining pressure of the jacket are both measured. Comparison of the dynamic and the quasi-static axial stress–strain curves indicate that dry quartz sand exhibits obvious strain-rate effects. The grain size distributions of the samples after dynamic and quasi-static loading are obtained with the laser diffractometry technique to interpret the rate effects. Quantitative analyses of the grain size distributions show that at the same stress level, the particle breakage extent under quasi-static loading is larger than that under dynamic loading. Moreover, the experimental and the theoretical relationships of the particle breakage extent versus the plastic work show that the energy efficiency in particle breakage is higher under quasi-static loading, which is the intrinsic cause of the strain-rate effects of brittle granular materials. Using the discrete element method (DEM), the energy distributions in the brittle granular material under confined compression are discussed. It is observed that the input work is mainly transformed into the frictional dissipation, and the frictional dissipation under dynamic loading is higher than that under quasi-static loading corresponding to the same breakage extent. The reason is that more fragmentation debris is produced during dynamic breakage of single grains, which promotes particle rearrangement and the corresponding frictional dissipation significantly.

Effects of grinding on the preg-robbing potential of quartz in an acidic chloride medium

The effect of high-energy milling on the surface properties of quartz is examined with regard to its preg-robbing behavior towards gold. A standard ring mill is used to process dry quartz samples, and the changes in the morphology of the particles, structural deformations and surface chemistry are investigated to explain the increased preg-robbing ability of quartz in acidic chloride solutions. The transition from fine grinding to mechanochemical activation of quartz can be observed from changes in the morphology of the particles, as well as the types of structural deformations. The transition occurs between 1 and 5min of grinding in the mill used, corresponding to particle sizes around 0.55μm. Structural studies differentiate two stages of fine grinding: particle breakage with limited structural disruption, and structural disturbance by mechanochemical alteration, which occurs after particles reach their grinding limits. Quartz keeps its structural order to some degree even after 30min of aggressive grinding. The surface chemistry of ground quartz demonstrates generation of point defects including low valence silicon and non-bridging oxygen centers. These defect sites play an important role in the surface reactivity of the quartz, and influence the extent of gold loss during preg-robbing.

A further study on seismic response of a set of parallel rock fractures filled with viscoelastic materials

Abstract The purpose of this study is to further investigate the seismic response of a set of parallel rock fractures filled with viscoelastic materials, following the work by Zhu et al. Dry quartz sands are used to represent the viscoelastic materials. The split Hopkinson rock bar (SHRB) technique is modified to simulate 1-D P-wave propagation across the sand-filled parallel fractures. At first, the displacement and stress discontinuity model (DSDM) describes the seismic response of a sand-filled single fracture. The modified recursive method (MRM) then predicts the seismic response of the sand-filled parallel fractures. The SHRB tests verify the theoretical predictions by DSDM for the sand-filled single fracture and by MRM for the sand-filled parallel fractures. The filling sands cause stress discontinuity across the fractures and promote displacement discontinuity. The wave transmission coefficient for the sand-filled parallel fractures depends on wave superposition between the fractures, which is similar to the effect of fracture spacing on the wave transmission coefficient for the non-filled parallel fractures.

Analogue Modelling of Inverted Oblique Rift Systems

The geometric evolution of brittle fault systems in inverted oblique and offset rift systems has been simulated using scaled sandbox analogue models. Dry fine-grained quartz sand was used to represent the brittle upper crust. Extensional faults geometries in the models were governed by the geometry and orientation of a stretching zone at the base of the models. Oblique rift models were characterized by segmented en-echelon border fault systems trending parallel to the rift axis and the underlying zone of basement stretching. Offset rift models promoted highly-segmented border faults as well as offset sub-basins within the rift. In both types of models, intra-rift fault arrays were oriented sub-perpendicular to the extension direction. Inversion of the oblique and offset extensional models was achieved by horizontal shortening. This resulted in partial inversion of the border and intra-rift faults as well as the formation of new reverse faults. The geometries, distribution, orientations and number of these new reverse faults were strongly controlled by the earlier-formed fault extensional architectures. At the margins of the rift zone, shortening was mainly accommodated by partial inversion of the border faults together with the formation of hanging-wall bypass faults and footwall shortcut thrusts. Inversion of the offset rift models produced reactivation of the extensional accommodation zones as soft-linked transfer zones between new thrust faults. The analogue model results have been compared with natural inversion structures in the Atlas Mountains of Morocco and the Ukrainian Donbas fold belt. The analogue modelling results suggest that the High Atlas formed as the result of oblique inversion of an oblique rift system, and the contractional structures in the Ukranian Donbas belt were generated by partial inversion of the earlier-formed Donbas extensional graben via two major newly developed short-cuts that uplifted and exhumed the basin.