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The core samples of B member of upper sand reservoir rocks of the lower Goru Formation from three wells of the Badin block were studied using thin section, XRD, and SEM techniques to investigate the diagenetic trends andtheir effect on reservoir quality. Microscopic study indicates that the B sand unit is mature with quartz as the predominant mineral constituent with variable amount of feldspar and lithic minerals. The QFL plot indicates that most of the samples are plotted in the field of quartz arenite, sub-litharenite and sub-arkose respectively. A few samples belong to the category of litharenite and feldspathic litharenite. The feldspars were partially to completely altered to kaolinite and other clay minerals. Coarse-crystalline or micro-crystalline calcite is the predominant cementing material. Bulk rock XRD analysis also confirms that the main mineral constituents of theresamples are quartz and calcite in variable proportions. The undulose extinction and fracturing of quartz grains indicatethat thearea remained under stress. Moreover, such fracturing is post-depositional and therefore is the product of late diagenesis. Scanning Electron Microscopic (SEM) images at 50 micrometer (μm)size show irregular type of fracturing within the quartz grains. This late stage fracturing of quartz has also generated various types of channels which may serve as secondary porosity. The quartz overgrowth was observed in some samples due to late stage diagenesis. The micro-crystalline cement in the form of calcite is mostly present within the pores in fractured quartz. The results indicate that the diagenesis played a significant role in improving the reservoir characteristics of B sand by increasing the porosity due to quartz fracturing, feldspar dissolution, alteration and quartz corrosion. Hence, better understanding of reservoir heterogeneities in porosity through diagenetic studies can be helpful in evaluating potential reservoir horizons for hydrocarbon accumulation on spatial and temporal scales

Intracrystalline distortions (like undulose extinction, dislocations, and subgrain boundaries) in olivine from naturally-deformed peridotites are generally taken as signs of dislocation creep. However, similar features in olivine phenocrysts that have been found in basaltic magmas are still not well understood. In particular, whether subgrain boundaries in olivine phenocrysts arise from plastic deformation or grain growth is still debated (in the latter case, they are essentially grain boundaries but not subgrain boundaries. Therefore, we used hereinafter subgrain-boundary-like structures instead of subgrain boundaries to name this kind of intracrystalline distortion). Here we carried out a detailed study on dislocations and subgrain-boundary-like (SG-like) structures in olivine phenocrysts from two Hawaiian basaltic lavas by means of petrographic microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). Abundant and complex dislocation substructures (free dislocations, dislocation walls, and dislocation tangles) were observed in the decorated olivine grains, similar to those in olivine from peridotite xenoliths entrained by the Hawaiian basalts. The measured average dislocation density is (2.9±1.3)×1011 m−2, and is three to five orders of magnitude higher than that in laboratory-synthesized, undeformed olivine. TEM observations on samples cut across the SG-like structures by FIB (focused ion beam) demonstrated that this kind of structures is made of an array of dislocations. These observations clearly indicate that these structures are real subgrain boundaries rather than grain boundaries. These facts suggest that the observed high dislocation densities and subgrain boundaries cannot result from crystal crystallization/growth, but can be formed by plastic deformation. These deformation features do not prove that the olivine phenocrysts (and implicitly mantle xenoliths) were deformed after their capture by the basaltic magmas, but can be ascribed to a former deformation event in a dunitic cumulate, which was formed by magmatic fractionation, then plastically deformed, and finally disaggregated and captured by the basaltic magma that brought them to the surface.

To explore the role of the olivine grain size and crystal preferred orientation (CPO) on the evolution of the microstructure and the mechanical behaviour of upper mantle rocks up to large strains, we performed axial extension experiments at 1200C, 300MPa confining pressure, and constant displacement rate on three natural peridotites: a fine-grained mylonitic harzburgite with a weak CPO and two coarse-grained well-equilibrated dunites with CPO of variable intensity. Initial flow stresses show a limited range of variation (115-165MPa), with the fine-grained sample showing the highest initial strength. However, the evolution of both mechanical behavior and microstructure differs between fine and coarse-grained peridotites. In the fine-grained harzburgite, necking resulted in decrease in the apparent differential stress. Focusing of strain and stress produced increase of the olivine recrystallized fraction and decrease of the recrystallized grain size in the neck. Analysis of the final stress and strain in the neck indicates softening due to evolution of the microstructure and CPO. In contrast, necking of the coarse-grained samples produced weak or no decrease in the apparent differential stress. This implies hardening, consistently with the increase in bulk intragranular misorientation and final stresses in the neck similar or higher than initial ones. Coarse-grained dunites deformed heterogeneously. Crystals well oriented to deform by dislocation glide became elongated, whereas those in hard orientations remained almost undeformed. In the neck, stress and strain concentration resulted in formation of kinks in hard crystals and dynamic recrystallization in soft crystals. We interpret the more effective strain-induced softening of the fine-grained peridotite as due to easier dynamic recrystallization, probably due to the higher proportion of grain boundaries acting as nucleation sites., Comment: Revised version of the article submitted to Tectonophysics in June 2021. Supported by the European Research Council under the European Union Horizon 2020 research and innovation programme grant agreement No 882450 ERC RhEoVOLUTION and by a postdoctoral fellowship co-funded by the European Union and the Government of the Principality of Asturias,Spain COFUND Action grant ACA17-32 to MALS

Given the increased availability of EBSD and fabric analyzer facilities, quartz microstructural and CPO analysis have become ‘tools of-the-trade’ for studies investigating crustal tectonics. Therefore, improved understanding of the complexities of quartz deformation is needed to ensure that such analyses distinguish primarily between tectonic outcomes and artefacts of the quartz deformation behaviours in different deformed rock volumes. We contribute to this understanding by comparing quartz deformation between monomineralic rocks, which have simple compositions; and polymineralic rocks, which are more complex and representative of the crust. Mylonite quartzites and gneisses of the Main Central Thrust (NW Himalaya) are used for comparison. Under similar deformation conditions, quartz inside monomineralic rocks forms well-developed CPOs and dynamically recrystallized microstructures, typical of grain size insensitive (GSI) creep mechanisms. Quartz inside polymineralic rocks, by contrast, exhibits weak CPOs and fine-grained microstructures commonly interpreted as grain size sensitive creep; but also exhibits lattice distortions (e.g. undulose extinction, sub-grain boundaries), associated with GSI creep. We postulate that intrinsic factors, such as interphase boundaries, cause these ambiguous results. The lack of clear evidence for deformation mechanisms in polymineralic rocks casts doubt on the reliability of quartz microstructures and CPOs for rapid diagnoses of their rheology and broader tectonic significance.

In an extensional shear zone in the Talea Ori, Crete, quartz veins occur in high-pressure low-temperature metamorphic sediments at sites of dilation along shear band boundaries, kink band boundaries and boudin necks. Bent elongate grains grown epitactically from the host rock with abundant fluid inclusion trails parallel to the vein wall indicate vein formation by crack-seal increments during dissolution-precipitation creep of the host rock. The presence of sutured high-angle grain boundaries and subgrains shows that temperatures were sufficiently high for recovery and strain-induced grain boundary migration, i.e. higher than 300–350 °C, close to peak metamorphic conditions. The generally low amount of strain accumulated by dislocation creep in quartz of the host rock and most veins indicates low bulk stress conditions of a few tens of MPa on a long term. The time scale of stress-loading to cause cyclic cracking and sealing is assumed to be lower than the Maxwell relaxation time of the metasediments undergoing dissolution-precipitation creep at high strain rates (10−10 s−1 to 10−9 s−1), which is on the order of hundred years. In contrast, some veins discordant or concordant to the foliation show heterogeneous quartz microstructures with micro-shear zones, sub-basal deformation lamellae, short-wavelength undulatory extinction and recrystallized grains restricted to high strain zones. These microstructures indicate dislocation glide-controlled crystal-plastic deformation (low-temperature plasticity) at transient high stresses of a few hundred MPa with subsequent recovery and strain-induced grain boundary migration at relaxing stresses and temperatures of at least 300–350 °C. High differential stresses in rocks at greenschist-facies conditions that relieve stress by creep on the long term, requires fast stress-loading rates, presumably by seismic activity in the overlying upper crust. The time scale for stress loading is controlled by the duration of the slip event along a fault, i.e. a few seconds to minutes. This study demonstrates that microstructures can distinguish between deformation at internal low stress-loading rates (to tens of MPa on a time scale of hundred years) and high (coseismic) stress-loading rates to a few hundred MPa on a time scale of minutes. Keywords: High-stress crystal plasticity, Crack-seal, Seismic cycle, Stress-loading rates, Talea Ori, Crete

Deformation microstructures of albitic plagioclase and K-feldspar were investigated in mylonitic pegmatites from the Austroalpine basement south of the western Tauern Window by polarized light microscopy, electron microscopy and electron backscatter diffraction to evaluate feldspar deformation mechanisms at greenschist facies conditions. The main mylonitic characteristics are alternating almost monophase quartz and albite layers, surrounding porphyroclasts of deformed feldspar and tourmaline. The dominant deformation microstructures of K-feldspar porphyroclasts are intragranular fractures at a high angle to the stretching lineation. The fractures are healed or sealed by polyphase aggregates of albite, K-feldspar, quartz and mica, which also occur along intragranular fractures of tourmaline and strain shadows around other porphyroclasts. These polyphase aggregates indicate dissolution–precipitation creep. K-feldspar porphyroclasts are partly replaced by albite characterized by a cuspate interface. This replacement is interpreted to take place by interface-coupled dissolution–precipitation driven by a solubility difference between K-feldspar and albite. Albite porphyroclasts are replaced at boundaries parallel to the foliation by fine-grained monophase albite aggregates of small strain-free new grains mixed with deformed fragments. Dislocation glide is indicated by bent and twinned albite porphyroclasts with internal misorientation. An indication of effective dislocation climb with dynamic recovery, for example, by the presence of subgrains, is systematically missing. We interpret the grain size reduction of albite to be the result of coupled dislocation glide and fracturing (low-temperature plasticity). Subsequent growth is by a combination of strain-induced grain boundary migration and formation of growth rims, resulting in an aspect ratio of albite with the long axis within the foliation. This strain-induced replacement by nucleation (associated dislocation glide and microfracturing) and subsequent growth is suggested to result in the observed monophase albite layers, probably together with granular flow. The associated quartz layers show characteristics of dislocation creep by the presence of subgrains, undulatory extinction and sutured grain boundaries. We identified two endmember matrix microstructures: (i) alternating layers of a few hundred micrometres' width, with isometric, fine-grained feldspar (on average 15 µm in diameter) and coarse-grained quartz (a few hundred micrometres in diameter), representing lower strain compared to (ii) alternating thin layers of some tens of micrometres' width composed of fine-grained quartz (<20 µm in diameter) and coarse elongated albite grains (long axis of a few tens of micrometres) defining the foliation, respectively. Our observations indicate that grain size reduction by strain-induced replacement of albite (associated dislocation glide and microfracturing) followed by growth and granular flow simultaneous with dislocation creep of quartz are playing the dominating role in formation of the mylonitic microstructure.

The central Bundelkhand domains consisting of deformed gneisses and granitoids are delineated by E-W subvertical Neoarchean Babina–Prithvipur shear zone (~500 m wide). The tonalite-trondjhemite-granodiorite (TTG) gneisses (3.5–3.2 Ga), streaky to mafic gneisses, belonging to an oldest complex unit, and metabasic, banded iron formation (BIF), felsic volcanics, with metasedimentaries constituting greenstone complex were subjected to three sets of folding in D1 and D2 compressive phases. The S1 foliation trending ESE-WNW to E-W directions were developed in tight to isoclinals F1 folds during D1 phase. The F2 and F3 open folds generated in the D2 phase are characterized by S2 and S3 foliations. The NNE-SSW and NNW-SSE trends were observed in S2 and S3 foliations. The K-rich Neoarchean granitoids (2.6–2.49 Ga) intruded as large granitic complex were transected by E-W strike-slip Babina–Prithvipur shear zone (syn-to post-tectonic D3 phase). These sheared rocks are characterized by the E-W to ESE-WNW trending mylonitic foliation and stretching lineation. The mylonitic foliation, asymmetrical rotated porhyroclasts (σa and σb mantled clasts), asymmetrical pressure shadows and deformation lamellae were identified as macroscopic and microscopic shear indicators in protomylonite and mylonites. The minor folds and crinkles developed due to back rotation of axial plane and reorientation of fold axis during progressive shearing were found important features. The scattered few porphyroclasts of quartz and feldspar were examined in a recrystallized quartz matrix of ultramylonite. The sinistral top–to–SW sense of shear movement was exhibited by most of the asymmetrical porphyroclasts. The presence of undulose extinction deformation lamellae in asymmetrical fabrics reveals that the crystal plastic process was dominant during the evolution of mylonite under low to medium temperature conditions.

The anisotropy of magnetic susceptibility (AMS) in sedimentary rocks results from depositional, diagenetic, syn- and post-sedimentary processes that affect magnetic grains. Some studies have also shown the potential role played by post-depositional fluid flow in detrital and carbonate formations. Here we present a new case study of Middle-Upper Jurassic sandstones where secondary iron oxides, precipitated from fluids that migrated through pores, give rise to the AMS. These sandstones are well exposed in the Uncompahgre Uplift region of the Central Colorado Trough, Colorado. The magnetic foliation of these undeformed, subhorizontal strata consistently strike NE-SW over a large distance with an average 45° dip to the SE. This steep AMS fabric is oblique with respect to the regional subhorizontal bedding and therefore does not reflect the primary sedimentary fabric. Also, outcrop-scale and microscopic observations show a lack of post-depositional plastic (undulose extinction) or pressure-solution (stylolites) deformation microstructures in these sandstones, hence precluding a tectonic origin. The combination of magnetic hysteresis, isothermal remanent magnetization, and thermal demagnetization of the natural remanent magnetization indicate that these rocks carry a chemical remanent magnetization born primarily by hematite and goethite. High-field magnetic hysteresis and electron microscopy indicate that detrital magnetite and authigenic hematite are the main contributors to the AMS. These results show that post-depositional iron remobilization through these porous sandstones took place due to the action of percolating fluids which may have started as early as Late Cretaceous along with the Uncompahgre Uplift. The AMS fabric of porous sandstones does not systematically represent depositional or deformation processes, and caution is urged in the interpretation of magnetic fabrics in these types of reservoir rock. Conversely, understanding these fabrics may advance our knowledge of fluid flow in porous sandstones and may have applications in hydrocarbon exploration.

Feldspar is the most abundant mineral in the Earth&rsquo, s crust and is widely distributed in rocks. It is also one of the most common minerals in meteorites. Shock-metamorphic features in feldspar are widely used to calibrate the temperature and pressure of shock events and can also provide clues for searching for impact craters on Earth. In this study, shocked alkali feldspars in the lithic breccia and suevite from Xiuyan Impact Crater were investigated using polarizing optical microscopes, Raman spectroscopy and electron microprobes to better constrain the shock history of this crater. For this study, feldspar grains occurring in gneiss clasts in the impact breccia and four shock stages were identified, e.g., weakly shocked feldspar, moderately shocked feldspar, strongly shocked feldspar, and whole rock melting. According to the shock classification system for alkali feldspar and felsic rocks, we estimated the shock pressure (SP) and post-shock temperature (PST) histories of these gneiss clasts. Weakly shocked feldspars display irregular fractures and undulatory extinction, and their shock stage is F-S2, which indicates that SP and PST are from ~5 to ~14 GPa and ~100 &deg, C, respectively. Moderately shocked feldspars show planar deformation features and are partially transformed into diaplectic glass, which indicates that the F-S5 shock stage of SP and PST is from ~32 to ~45 GPa and 300&ndash, 900 &deg, C. Strongly shocked feldspars that occur as vesicular glass indicate a shock stage of F-S6, and the SP and PST are 45&ndash, 60 GPa and 900&ndash, 1500 &deg, C, respectively. The whole felsic rock melting occurs as mixed melt glass clast and belongs to the F-S7 stage, and SP and PST are &gt, 60 GPa and &gt, C, respectively.

This paper highlights published and new field and petrographic observations for late-stage (crustal level) deformation associated with the emplacement of kimberlites and other mantle-derived magmas. Thus, radial and tangential joint sets in the competent 183 Ma Karoo basalt wall rocks to the 5 ha. Lemphane kimberlite blow in northern Lesotho have been ascribed to stresses linked to eruption of the kimberlite magma. Further examples of emplacement-related stresses in kimberlites are brittle fractures and close-spaced parallel shears which disrupt olivine macrocrysts. In each of these examples, there is no evidence of post-kimberlite regional tectonism which might explain these features, indicating that they reflect auto-deformation in the kimberlite during or immediately post-emplacement. On a microscopic scale, these inferred late-stage stresses are reflected by fractures and domains of undulose extinction which traverse core and margins of some euhedral and anhedral olivines in kimberlites and olivine melilitites. Undulose extinction and kink bands have also been documented in olivines in cumulates from layered igneous intrusions. Our observations thus indicate that these deformation features can form at shallow levels (crustal pressures), which is supported by experimental evidence. Undulose extinction and kink bands have previously been presented as conclusive evidence for a mantle provenance of the olivines—i.e. that they are xenocrysts. The observation that these deformation textures can form in both mantle and crustal environments implies that they do not provide reliable constraints on the provenance of the olivines. An understanding of the processes responsible for crustal deformation of kimberlites could potentially refine our understanding of kimberlite emplacement processes.

The morphotectonic elements of the Baijnath Klippe (BK) have been examined to understand the kinematics of the Inner Kumaun Lesser Himalaya from Tertiary to Late Quaternary. The BK is bounded by two thrusts: the Askot Thrust (AT), to the north and the Baijnath Thrust (BjT), to the south. The older (20 Ma) hanging wall rocks (mylonites and phyllites) are underlain and surrounded by quartzites (equivalent to Nagthat Formation of Outer Lesser Himalaya). The kinematics study and strain analysis along Dewal–Narayanbagarh transect provides the varied intensity of deformation (D1, D2, and D3) within the zone of BK. The D1 event is characterized by isoclinal tight folds in phyllite and mylonite; the D2 phase is characterized by open folding in mylonite. However, the youngest event D3 phase is observed as a regional synclinal folding of BK and associated rocks. The presence of 1–3-km-thick mylonite zone parallel to the thrust planes is related to the compressional event of Miocene age. The geomorphic pattern and chronologically constraints (OSL ages) with spatial variability in the incision/uplift rate suggests that the terrain is undergoing differential crustal deformation during Late Quaternary. Kinematic indicators such as streaky foliations, S–C foliation, mantled porphyroclasts, micro-shears with bookshelf gliding, and mica fish found in mylonites (macroscopic as well as microscopic) indicate ductile deformation in the area. We used Flinn plot (Rf/ϕ) and Fry (Tectonophysics 60:89–105, 1979) analysis to delineate the finite strain pattern in 21 oriented samples collected across the BK bound thrusts (BjT and AT). The strain analysis revealed an increasing trend of strained quartz grains, which presents triaxialoblate strain geometry (flattening i.e., 0

The role of deformation on the equilibration of Ti concentrations in quartz was investigated by running experiments on out-of-equilibrium quartz crystals embedded as porphyroclasts within quartz aggregates. Quartz crystals were first grown from a hydrostatic fluid to set the initial Ti content; crystals grown at temperatures above (925 °C) and below (875 °C) the deformation temperature (900 °C) contain Ti contents ∼60 ppm higher or lower than the equilibrium solubility. These out-of-equilibrium quartz crystals were then deformed as porphyroclasts by embedding them in a matrix composed of either dry or wet quartz to induce two end-member deformation regimes, high-stress or low-stress, respectively. In high-stress experiments, quartz porphyroclasts contain deformation bands and undulose extinction, with some grains showing evidence for grain boundary bulging (BLG) recrystallization. In low-stress experiments, some grains deformed to high strains with minimal evidence for dynamic recrystallization, resulting in ribbon grains, whereas others recrystallized by dislocation creep processes, showing microstructural evidence for subgrain rotation (SGR) and grain boundary migration (GBM) recrystallization. By comparing quartz microstructures with patterns of Ti re-distribution in variably deformed and recrystallized porphyroclasts, we find that grains deformed to high strain with minimal recrystallization show little to no evidence for re-equilibration, whereas grains that recrystallized via grain boundary processes have equilibrated Ti contents that reflect the pressure-temperature conditions of deformation.

In the present study we investigate the microstructural development in mullite, quartz and garnet in an anatectic migmatite hosted within a Grenvillian-age shear zone in the Aravalli–Delhi Fold Belt. The migmatite exhibits three main deformation structures and fabrics (S1, S2, S3). Elongated garnet porphyroblasts are aligned parallel to the metatexite S2 layers and contain crenulation hinges defined by biotite–sillimanite–mullite–quartz (with S1 axial planar foliation). Microstructural evidence and phase equilibrium relations establish the garnet as a peritectic phase of incongruent melting by breakdown of biotite, sillimanite ± mullite and quartz at peak P–T of ~ 8 kbar, 730 °C along a tight-loop, clockwise P–T path. Monazite dating establishes that the partial melting occurred between ~ 1000 and 870 Ma. The absence of subgrains and systematic crystal lattice distortions in these garnets despite their elongation suggests growth pseudomorphing pre-existing 3-D networks of S1 biotite aggregates rather than high-temperature crystal plastic deformation which is noted in the S1 quartz grains that exhibit strong crystallographic preferred orientation (CPO), undulatory extinction and subgrains. Mode-I fractures in these garnet porphyroblasts induced by high melt pressure during late stage of partial melt crystallization are filled by retrograde biotite–sillimanite. Weak CPO and non-systematic crystal lattice distortions in the coarse quartz grains within the S2 leucosome domains indicate these crystallized during melt solidification without later crystal plastic deformation overprint. In the later stages of deformation (D3), strain was mostly accommodated in the mullite–biotite–sillimanite-rich restite domains forming S3 which warps around garnet and leucosome domains; consequently, fine-grained S3 quartz does not exhibit strong CPOs.

Centimetre-sized grains of Al-rich clinopyroxene within the granulitic anorthosites of the Bergen Arcs, W-Norway undergo deformation by faults and micro-shear zones (kinks) along which fluid has been introduced. The clinopyroxene (11 wt% Al2O3) reacts to the deformation and hydration in two different ways: reaction to garnet (Alm41Prp32Grs21) plus a less aluminous pyroxene (3 wt% Al2O3) along kinks and the replacement of the Al-rich clinopyroxene by chlorite along cleavage planes. These reactions only take place in the hydrated part of a hand specimen that is separated from dry, unreacted granulite by a sharp interface that defines the limit of hydration. We use electron probe microanalysis (EPMA) and X-Ray mapping together with electron backscatter diffraction (EBSD) mapping to investigate the spatial and possible temporal relationships between these two parageneses. Gresens' analysis (Gresens, 1967) has been used to determine the mass balance and the local volume changes associated with the two reactions. The reaction to garnet + low-Al clinopyroxene induces a loss in volume of the solid phases whereas the chlorite formation gains volume. Strain variations result in local variation in undulose extinction in the parent clinopyroxene. EBSD results suggest that the density-increasing reaction to garnet + low-Al clinopyroxene takes place where the strain is highest whereas the density-decreasing reaction to chlorite forms away from shear zones where EBSD shows no significant strain. Modelling of phase equilibria suggest that the thermodynamic pressure of the assemblage within the shear zones is > 6 kbar higher than the pressure conditions for the whole rock for the same range of temperature (~ 650 °C). This result suggests that the stress redistribution within a rock may play a role in determining the reactions that take place during retrograde metamorphism.

Precambrian rocks exposed around Pur are a part of Pur-Banera belt that is stratigraphically placed within Aravalli Quartzite, Calc Silicate Gneiss, Quartzite and Garnetiferous Mica Supergroup. The different lithological units exposed in the area are Banded Magnetite Schist. These rocks have been subjected to multi-deformational episodes. In accordance with the modern system of multi-level deformation analysis proposed by Fedor Yakovlev in 2012, the results of the The work belongs to the scientific direction of tectonophysics, which was called “strain analysis of linear folding structures”. The present study involves analysis of strain in the rocks around Pur, Bhilwara District, Rajasthan (India). The deformation analysis at the level of folds (level three of seven) are presented in this work. The outcrop pattern is an isoclinal fold of D2 generation, whose axis plunges steeply NE’ly with an axial plane trending NNE-SSW. The quartzite band in this Pur Synform was sampled for the purpose of strain analysis. This section parallel to the YZ plane of finite strain ellipsoid was prepared (perpendicular to both Schistosity and the lineation). The accepted methods used to estimate strain are a) Fry method and b) “Isogon Rosette” method. The axial ratio of the strain ellipse and the orientation of the long axis of the strain ellipse were computed for every location. It was seen that the strain ratio is nearly uniform in magnitude. The orientation of the long axis of the strain ellipse (Y direction of the finite strain ellipsoid) is also constant in space and parallel to the axial trace of D2 Synform. From the analysis it was suggested a strong flattening following the buckling. The amount of this flattening strain was computed using the”Isogon rosette” method. We calculated reflects the flattening strain recorded in the rock with the very high constancy of the strain ratio and the orientation of the long axis of the strain ellipse irrespective of the methodology adopted. The results of performed researches bring tectonophysics database up-to-date providing an excellent opportunity for provenance analysis of the Pur-basin using the different types of undulose extinction of the quartzite for development of prospective mining projects around the area including iron deposits.

Pseudotachylyte-bearing, amphibole-rich gneisses with quartz-rich layers concordant to the foliation from the base of the Silvretta nappe were analyzed by polarized light microscopy and scanning electron microscopy to constrain the deformation history. Amphibole shows microfractures, kink bands and mechanical twins associated with pseudotachylytes. (−101,101] twins document high differential stresses of ≥400 MPa and coeval pseudotachylyte formation. Quartz grains in contact with twinned amphibole in gneisses show subbasal deformation lamellae, short-wavelength undulatory extinction and new grains along cracks with diameters of Quartz-rich layers concordant to the gneiss' foliation commonly show evidence of dislocation creep by homogenous recrystallized grain aggregates with CPO indicating dislocation glide. Systematic differences in distribution of the recrystallized grains and grain sizes, indicate deformation at differential stresses from a few tens to hundred MPa. Yet, no evidence of increasing strain towards the contact to amphibole-rich gneisses is observed. In contrast, a decreasing number of recrystallized grains towards the contact occurs locally. In relation to pseudotachylytes, the recrystallized quartz is affected by shear fractures offsetting the recrystallized microstructure. This, and the missing or decreasing strain gradient of dislocation creep towards the contact to amphibole-rich gneisses, indicate that 1) dislocation creep in quartz-rich layers is preceding and 2) not directly related to the high-stress and high strain-rate deformation, ruling out a major influence of thermal runaway for the formation of the pseudotachylytes. The differences in the deformation behavior is interpreted to be controlled by the distance to the propagating fault tip. This study demonstrates the potential of microstructures to constrain the deformation history controlling seismic faulting and creep at hypocentral depth not directly accessible for in-situ stress measurements.

This paper presents a detailed case study of decorated dislocations of olivine with C-type fabric in the Luliangshan garnet peridotite from the North Qaidam ultrahigh-pressure (UHP) metamorphic belt in NW China. Electron backscatter diffraction (EBSD) measurements reveal a weak C-type fabric in olivine, i.e., the crystallographic [100] axes form a weak point maximum subnormal to the foliation while the [001] axes form a girdle in the foliation plane with a weak point maximum subparallel to the lineation. Oriented hydrous mineral of sodic amphibole and pyroxene were found in porphyroclastic garnet indicating considerable water content in the parental majoritic garnet at high pressure conditions. However, the water content of olivine and garnet is below the detection limit (less than a few ppm wt. H2O) of the instrument (a Nicolet 6700 FTIR with Continuum FTIR Microscope). Two distinctive deformation features of decorated olivine grains were recognized: (1) linear morphologies of many dislocations with long straight segments parallel to the [001] orientation, which are likely screw dislocations with b = [001]; (2) olivine grains with planar dislocation, subgrain boundaries or undulose extinction are scarce in thin sections under optical microscopy. The dislocation structures and densities in olivine are heterogeneous at multi-scales. The mean 3D dislocation density and the estimated differential stress based on the dislocation density piezometer are 0.4–0.8 × 10−12 m−2 and 65–108 MPa, respectively. Decorated dislocations and EBSD analyses suggest the most likely dominant activation slip systems with b = [001]. Considering that most C-type fabric of olivine are reported from UHP garnet peridotites, we emphasize the important effects of high pressure and relatively low temperature on the formation of the C-type fabric in olivine.

The Parauapebas meteorite, an ordinary chondrite, was investigated through a systematic classification method, applying non-destructive analytical techniques: Electron Microprobe Micro-Analyzer (EPMA), X-Ray Fluorescence (XRF), Proton-Induced X-Ray Emission (PIXE), Cathodoluminescence (CL), and Optical Microscopy (OM). The goal was to achieve a complete and detailed chemical and petrological description of the official Parauapebas meteorite (MB 107). Additionally an inter-technique comparison was included for the bulk chemical composition obtained by means of the X-ray fluorescence PIXE and XRF techniques. The measured elemental compositions were compared to XRF and INAA average values reported in previous works on chondrites. The physical properties, such as density and magnetic susceptibility, of Parauapebas meteorite were also included as a tool for the chemical group classification. The meteorite is rich in iron metal, except into the silicates, thus Parauapebas is an H chemical group chondrite. Nevertheless some elemental compositions were found within the range of L chemical group chondrites. It presents two different lithologies with homogeneous chemistry observed in the analyzed thin sections, which point the meteorite as a genomict breccia (indicated by shock melt veins) formed by petrologic type 4 and 5. A shock stage S3/S4 is indicated by the olivine crystals with undulatory extinction, irregular and some planar fractures and a weak mosaicism, Neumann lines in iron-nickel, in addition to the presence of shock melt veins and pockets. The weathering degree is the lowest (W0), since the fragment was recovered soon after the fall.

The Goulamina LCT spodumene pegmatite field, located south of Bamako in Mali, is one of the largest hard-rock lithium deposits in the world, with a resource of 103 Mt at 1.32% Li2O for 1.4 Mt of contained Li2O. Outcrops of spodumene pegmatite at Goulamina were recognised at least as early as the nineteen sixties, but the first recorded exploration activity was in 2007. This paper presents the first substantial description of the deposit and its mineralogy and geochemical composition. The deposit consists of a series of five sub-parallel spodumene pegmatite dykes (Main, West, West I, Sangar I & II) and an anastomosing dyke swarm (Danaya) all of which intrude the peraluminous Goulamina Granite. The dykes are dominated by spodumene pegmatite but contain lesser volumes of spodumene-bearing aplite and hydrothermal albitite but do not show systematic compositional zoning either at regional or local scale. Deformation, presumably during peak Eburnean compression at ca. 2.1 Ga, is evident in undulose extinction of constituent quartz and feldspar. The pegmatites were partially albitised after peak deformation. An unusual feature is the presence of primary magmatic loellingite, suggesting a possible genetic link with nearby hybrid gold deposits such as Morila.

In the Herbeira massif, Cabo Ortegal Complex, Spain, a well exposed assemblage of deformed dunites and pyroxenites offers a unique opportunity to investigate key upper mantle tectonic processes. Four types of pyroxenites are recognized: clinopyroxenites with enclosed dunitic lenses (type-1), massive websterites (type-2), foliated and commonly highly amphibolitized clinopyroxenites (type-3) and orthopyroxenites (type-4). Field and petrological observations together with EBSD analysis provide new insights on the physical behavior of the pyroxenes and their conditions of deformation and reveal the unexpected journey of the Cabo Ortegal pyroxenites. We show that, during deformation, type-1 pyroxenites, due to their enclosed dunitic lenses, are more likely to localize the deformation than types-2 and -4 pyroxenites and may latter act as preferred pathway for fluid/melt percolation, eventually resulting in type-3 pyroxenites. All pyroxenite types display a similar response to deformation. Orthopyroxene deformed mostly by dislocation creep; it shows kink bands and undulose extinction and its fabric is dominated by [001](100). Clinopyroxene displays subgrain rotation, dynamic recrystallization and fabric with [010] axes clustering next to the foliation pole and [001] axes clustering next to the lineation suggesting activation of [001]{110} and [001](100) in some samples. These observations are in good agreement with deformation at temperatures greater than 1000 °C. Olivine in type-1 and type-4 pyroxenites shows [100](010) or [001](010) fabrics that are consistent with deformation at temperatures >1000 °C and may indicate deformation in a hydrous environment. The amphibole [001](100) fabric gives insights on a lower-temperature deformation episode (∼800 to 500 °C). Our results, interpreted in the light of published experimental data, together with the regional geological and geochemical studies are consistent with the following tectonic evolution of the Cabo Ortegal pyroxenites: (1) delamination from an arc root in a mantle-wedge setting at temperatures above 1000 °C and (2) introduction into a relatively softer subduction channel where deformation was accommodated by localized shear zones, thus preserving the high-temperature fabrics of pyroxenites. The Cabo Ortegal pyroxenites may therefore be seen as a rare exposure of deformed mantle-wedge material.

The ubiquitous presence of undulose extinction and subgrain boundaries in olivine crystals is commonly perceived as originating in the mantle, however these plastic deformation features are also well developed in the Poyi ultramafic intrusion, NW China. In this case, olivine was deformed through kinetic processes in a crustal magma chamber, rather than by deformation processes in the upper mantle. Moreover, accumulation and textural coarsening were critical to the characteristics of crystal size distributions (CSDs) of olivines in the Poyi intrusion. The axial deformational compaction of crystal mush was revealed by virtue of other quantitative textural analyses (e.g., spatial distribution patter, alignment factor and aspect ratio). Additionally, based on the contrast of density between crystal matrix and interstitial melt, adequate stress was generated by the km-scale crystal framework in Poyi body (~ 2–11 MPa) which triggered the distortion of grain-lattice in olivine. The deformation mechanisms of olivine primarily are dislocation creep and dislocation-accommodated grain boundary sliding (DisGBS), while diffusion creep is subsidiary. This study has revealed various kinetic processes in a magmatic system by first demonstrating the genetic relationship between mineral deformation and axial compaction of crystal mush while highlighting the uncertainty of employing the deformation features of olivine in peridotite xenoliths as an indicator for a mantle origin. In contrast to the olivine populations of xenocrysts that underwent fragmentation during ascent, the deformed primitive olivines in compaction exhibit a distinct shortage of small grains, which is conducive to delimiting these two types of deformed grains.

Elongated NE-SW trending bodies of iron-rich rock are exposed adjacent to pyroxenite dyke within Sukinda ultramafic complex, Odisha. Field study followed by optical and electron microscopy, XRD and EPMA investigation reveal the rocks to be fine grained, weathered, limonitised; containing quartz, magnetite, hematite/ martite and goethite. The rock has suffered from deformation during intrusion of chromiferous magma. It rarely shows banding/ lamination, but largely exhibits mylonitic fabric, resulting from magmatic intrusion. The stronger deformation is evident from subgrain formation, deformed mineral grains; often with orientation, stretching (boudinage) and shortening (folding); presence of porphyroclasts, pull-apart structure, undulose extinction, dynamic recrystallisation etc. From the microstructure and mineral abundance, the rock is designated as "Mylonitic Magentite Quartzite" (MMQ). Enrichment of some elements like Ni, Mg, Cr in the magnetite phase of MMQ is attributed to solid state diffusion of these elements from chromiferous mafic magma during thermal metamorphism. This is determined from electron probe microanalysis of ironrich phase in MMQ, which is found to contain 88-90 wt% of FeO(t) with ~1%, NiO, ~1%, MgO and 0.1% Cr 2 O 3 having around 3 mole% of trevorite; 4-6% of magnesioferrite; 0.15-0.3% of chromite; 86-87% of magnetite and 3-4% of wustite. Considering presence of wustite as temperature indicator, the temperature of magma envisaged to be around 950-1100°C. In a later period, the MMQ has undergone oxidation and lateritisation owing to its prolonged exposure. During this process, new minerals like hematite and goethite substituted magnetite, resulting leaching of iron (FeO: 62-68%) and magnesium (MgO: 0.1-0.35) and enrichment of chromium (Cr 2 O 3 :4-7%) and nickel (NiO: 1.6-2.3%). The silica (SiO 2 : 4-5%), alumina (Al 2 O 3 :~1%) are contributed by kaolinite, formed during lateritisation. The field and laboratory studies confirm these iron-rich exposures to be enclaves of BIFs, banded magnetite quartzite (BMQ) in particular, within the Sukinda chromiferous ultramafic complex. Micro-structural features and microchemical composition of iron minerals in these exposures are interpreted as the influence of forceful ultramafic intrusion into the existing BMQ and effect of thermal metamorphism followed by oxidation, weathering/lateritisation.

The deformation features (e.g., undulose extinction and subgrain boundaries) and low Ca content (

The processes occurring in the basal region of concentrated pyroclastic density currents (PDCs) influence the mobility, runout distance, and damage potential of a current, but directly observing these processes is extremely difficult. Instead, we must investigate the deposits to glean information regarding the conditions of sediment transport and deposition. The PDC deposits of the May 18, 1980 eruption of Mount St. Helens (WA, USA) contain sedimentary structures consisting of bed material reworked into undulose structures and recumbent flame structures. The structures vary over two orders of magnitude in size with lengths ranging from 8 cm to 18 m and heights ranging from 4 cm to 1.8 m. Despite the large range in sizes, the structures remain self-similar in form, suggesting a common mechanism for formation. The structures are interpreted as the record of granular shear instabilities, similar to Kelvin-Helmholtz instabilities, formed at the interface between a shearing, high-concentration flow and the substrate in the moments just prior to deposition. The morphology of the structures suggests that the basal region of PDCs must be both highly concentrated and also highly mobile in the moments before final deposition, likely a result of elevated pore fluid pressures. We use a modified instability growth criterion to estimate PDC flow velocities at the time of formation; for the Mount St. Helens PDCs, the velocity estimates range from 0.2 to 7.5 m s−1 with larger structures requiring higher flow velocities. Combining the velocity estimates with the dimensions of the structures suggests deposition rates of 4 to 32 cm s−1. Such high deposition rates indicate that the deposits likely accumulated in a stepwise manner, rather than either progressively or en masse. The structures suggest that sections of the deposit accumulated during punctuated periods of high deposition lasting at most a few seconds followed by periods of bypassing (i.e., non-deposition) or erosion lasting minutes to tens of minutes. Our findings motivate continued experimental and numerical work to understand how the formation of recumbent flame (and similar) structures affects subsequent flow behavior in terms of runout distance and hazard potential.

The Etam shear zone is the NNE-SSE to NE-SW trending fault zone with coexistence of a sinistral shearing mylonitic corridor and a brecciated quartz vein. The mylonitic zone is evidence of progressive deformation. Primary minerals include Qtz1 + Kfs1 + Pl1 + Bt1. These minerals increasingly and gradually reduce from the wall rock towards the shear zone center. Quartz recrystallization also gradually increases in the same direction. Microstructures observed include: recrystallization, sub-grain boundary, myrmekites and undulose extinction. Mica-chlorite-epidote assemblages define the greenschist assemblage, but the observation of amphibole in the mylonite and the presence of flame perthite in feldspar suggest a transitional greenschist-amphibolite metamorphic condition in the Etam Shear Zone. The brecciated quartz vein has dimensions of about 2.5 × 0.5 km and shows several quartzitic blocks, mainly composed of milky to transparent quartz clasts and a siliceous matrix. Quartz clasts are pure and the observation of thin sections of these quartz under polarized microscope shows grains free of microstructures or displays small micro quartz veins and rare feldspar inclusions. These are some criteria, which can lead to a preliminary assessment of the purity of quartz in Etam area.

Geological mapping and petrological studies were carried out within the placer gold (Au) mineralized zones in the Wonaka Schist Belt in order to establish detailed petrographic and structural features. Thin sections were produced for petrographic and microstructural studies and lineament analysis was coupled with field structural observations for interpretation. The study area comprises of quartz-mica-schist, phyllite, metasandstone, medium to coarse grained porphyritic granite, granitic gneiss, and diorite as the five major rock types with aplite, quartz and quartzo-feldspathic veins representing minor rock occurrences. The structural pattern is dominated by regional scale, NE striking foliation, and N striking brittle lineament. However, the dominant tectonic fabric within the metasediments and the granite gneiss are the steeply dipping, N, NW and NE-trending phyllitic cleavage, schistose foliations (S1) and gneissocity respectively, formed from first phase of deformation (D1). The emplacement of brittle tectonic features, undulose extinction observed in the quartz crystals, inter- and intra-granular microfractures are evidences of the late stage deformation that occur toward the end of the Pan African. Similarities with other mineralized belts in term of structures provide weight to the possibility of the NW-SE, N-S and NE-SW trending lineaments and specifically the NW-SE quartz and quartz ± feldspar ± hematite ± mica ± sulphide veins to host Au within the study area.

We examined the shock effects on 12 basaltic and 4 cumulate eucrites, using the petrographic and X-ray diffraction (XRD) methods. Petrographic and XRD measurements were conducted on the same polished sections of the eucrites. On the basis the ranges of undulatory extinction angles and occurrence of maskelynite, we defined five shock degrees: A (unshocked to very weakly shocked), B (weakly shocked), C (moderately shocked), D (moderately to highly shocked), and E (highly shocked). We performed macroscopic XRD analyses of the polished sections of the eucrites using the in-plane rotation method. The results of XRD analysis are correlated with the shock degrees obtained through the petrographic observations. The averaged full width at half maximum (FWHM) values of diffraction peaks are increase from shock degree A to E. As the FWHM value reflects the lattice spacing, the observed increase in the averaged FWHM values indicates the reduction in their crystallinities because of shock metamorphism. Therefore, the petrographic and XRD methods are both useful indicators in the evaluation of the shock degrees of eucrites.

Late Jurassic to Early Cretaceous extensional structures are widespread in Northeast China and the eastern part of the Asian continent. The Yiwulushan ductile detachment shear zone, the master ductile detachment zone of the Yiwulushan metamorphic core complex (MCC), occurs in the northern North China Craton. This shear zone dips to the northwest on the western flank and to the southeast on the eastern flank of the MCC and consists of brittle faults, breccia, chloritized microbreccia, and ductile (mylonite) zones. The well-developed mylonitic foliation and stretching lineation are characterized by oriented minerals (quartz and feldspar) that exhibit ductile deformation, including undulose extinction, deformation bands, subgrain formations, and recrystallized grains. The shear indicators, such as asymmetric porphyroclasts, S-C fabrics, and shear bands, suggest consistent top-to-the-NW shear on both the western and eastern flanks of the MCC. Strain measurements using feldspar porphyroclasts show that...

The Jiufeng Sn deposit is located in the outer contact zone southwest of the Neoproterozoic Motianling granitic pluton, in northern Guangxi, South China. The deposit is characterized by a NNE-striking, 30–200-m-wide ductile shear zone, named the Jiufeng ductile shear zone. Majority of the Sn orebodies, including four large ones, are hosted by the shear zone. Field and microstructural observations, electron backscatter diffraction measurements, and magnetic fabric analyses show that the shear zone is characterized by sinistral thrust shearing. The shear zone has also slightly modified the Sn orebodies. Quartz in the shear zone exhibits core-mantle structure and undulose extinction. Quartz has experienced significant sub-grain rotation and grain-boundary migration recrystallization. Lattice preferred orientation analysis reveals primarily basal , rhomb , and prism slips. Cassiterite grains in the shear zone, however, demonstrate brittle deformation. Therefore, the deformation temperature during the ductile shearing is estimated lower than 650 °C and below U-Pb closure temperature of cassiterite. As such, the U-Pb isotopic composition of the cassiterite was not disturbed by the shearing and the U-Pb age of the cassiterite could be used for the age of the Sn mineralization. LA-ICP-MS U-Pb dating of cassiterite grains selected from a cassiterite-bearing tourmalinite sample performed in this study yielded a Tera–Wasserburg U-Pb lower intercept age of 832.3 ± 5.3 Ma. This age is consistent within error with that of the neighboring Neoproterozoic Motianling granitic pluton, which suggests a close genetic relationship between the Sn mineralization and the granitic magmatism. Studies show that the Jiufeng ductile shear zone was produced by a widespread Caledonian (or Kwangsian) tectonic event in South China, indicating that the shearing was much later than the Sn mineralization and has no generic relationship to the Sn deposit.

The formation of strain shadows and strain fringes is described from diamictite and siltstone of the Grand Conglomerat unit (Nguba Group) at the Kamoa copper deposit located within the DRC at the western end of the Central African Copperbelt (CACB). Fringes reveal a straight orientation of fibres during a coaxial deformation; this supports the interpretation of a single phase of deformation during fringe growth within the deposit area. The non-deformed distal part of fringes and the straight orientation of fibres demonstrate the simple geometry of strain fringes. Quartz grains within strain fringes and strain shadows have generally straight or smoothly curved boundaries and lack undulose extinction. In strain fringes, muscovite and chlorite are generally observed on quartz grains where they define a foliation. These characteristics suggest a static recrystallisation that developed under relatively high temperature and wet conditions. A NW crustal shortening during the Kolwezian deformation event of the Lufilian orogeny is believed to be responsible for the coeval development of foliation, strain shadows and strain fringes. A syn-orogenic origin of the copper sulphides during the Lufilian orogeny is proposed.

The study addressed the geology, petrography and associated microstructures of the study area. The geological mapping indicated three to four (3-4) including various migmatite morphological units, granitoid and leucosome bands occurring in and around Lallangi in the Northern Nigerian Basement complex of Nigeria. Petrographic studies showed the presence of the various metamorphic and rock forming minerals which include - orthopyroxene, biotite, plagioclase, quartz, microcline, and graphite as observed within the field of view under plane and crossed polarized light Field. Field geology and petrographic analyses of structures carried out from outcrop to microscopic scale in the area reveal that the rocks were affected by multiple phases of deformations; the syn-tectonic deformation that includes regional metamorphism and post-tectonic typified by prograde metamorphism and shearing. The grade of metamorphism varies from low grade in the metatexites to medium grade that increases progressively from the mesocratic diatexites through to the granulitic granitoids manifested by foliation in biotites of the metatexites, coarsening of quartz grains and development of porphyroblastic microcline in the diatexite migmatite. The microstructures in the form of interlobing/ grain boundary migration of quartz, undulose extinction and interstitial filling of micro fractures, reveal that the rocks of the area are generally deformed.

Defects in the crystalline structure of quartz facilitate the connection with the alkali hydroxides, since under a high alkalinity condition (e.g., in concrete), the Si-O bonds of quartz are easily broken. This study set out to investigate the influence of the deformation structures of quartz on its susceptibility to the alkali–silica reaction. A granite, a protomylonite, and a mylonite were selected for this study. Using optical microscopy, the quartz grains contained in these rocks were quantified and their texture characterized. The quartz samples extracted from the rocks were analyzed by magnetic nuclear resonance, to evaluate their potential for dissolving silica as well as changes in their atomic scale before and after the reaction with alkali hydroxides. These analyses were compared with the results of the accelerated mortar bar test. The study showed that the quartz with intense undulatory extinction and deformation bands denotes the most favorable condition to the development of the alkali–silica reaction. However, on an atomic scale, the slightly deformed grains were highly prone to react. Thus, in a high alkalinity condition, over a long period of time, any quartz tends to develop the alkali–silica reaction, regardless of the deformation degree of the grain.

Coral patch reefs from Middle Triassic (upper Pelsonian–lower Illyrian) strata in the Upper Silesia region of southern Poland (Germanic domain of the Peri-Tethys) are rare examples of the first scleractinian buildups. The shallowing-upward succession in the Tarnow Opolski quarry records a transition from sponge to coral patch reefs interbedded with bioclastic limestones. Coral pillarstones built by thin, branching Volzeia szulci are succeeded by platy Pamiroseris silesiaca constructing two platestone layers, each up to 50 cm thick. Serial sections through platestones revealed flat to undulose growth form of P. silesiaca. The maximum observable dimension of the coral plates is 24 cm wide (typically up to 12 cm), while thickness of most plates is 1–1.5 cm. Coral plates are interlayered with crinoidal wacke- to packstone and microbialites, which are locally important component of the platestone. Platy corals grew in a shallow, turbid-water environment with changing, but dominantly moderate hydrodynamics. Net sedimentation was low, as indicated by the epibionts encrusted to the undersides of the coral plates, and locally common microbial fabrics. Growth-interruptions of P. silesiaca record events of storm-induced sediment input and resuspension of carbonate mud. Based on the euphotic floor model, the flattened morphology of P. silesiaca is interpreted as an optimal growth form in a turbid, low-light environment. Platy scleractinian assemblages from Silesia are the oldest occurrences of this ecological coral group (mostly representing deeper, mesophotic habitats) and support the hypothesis that some of the earliest scleractinians had photosymbionts like modern zooxanthellae.

The alkali silica reaction (ASR), which originates in highly alkaline conditions in concrete where reactive forms of silica are available, causes serious damage to concrete structures. The ASR potential of various quartz-rich aggregates (pegmatite quartz, quartzite, quartz meta-greywacke, and chert) was quantified using accelerated mortar bar test (AMBT), chemical test (CT), and scanning electron microscopy combined with petrographic image analysis (SEM-PIA). Only two samples (quartz meta-greywacke, and pegmatite quartz) were judged as deleterious according to the CT; the other aggregates were classified as innocuous. AMBT gave different results. Quartz meta-greywacke, chert, and quartzite exceeded the 0.100 % expansion limit after 14 days of testing. Pegmatite quartz indicated a lower value. The results of SEM-PIA confirmed the results of AMBT, indicating the most extensive ASR in those AMBs containing chert and quartz meta-greywacke. Parts of aggregates were leached out and massive deposits of alkali–silica gels were found filling air voids, microcracks, and the aggregate/cement paste interface. The medium or low degree of ASR was confirmed in AMBs containing quartzite or pegmatite quartz, respectively. ASR accentuated pre-existing microcracks and formed new dissolution gaps. In contrast, no correlation was found with the results of CT, which under-evaluated the ASR potential of chert and quartzite and over evaluated the ASR potential of pegmatite quartz. The variable ASR potential of the investigated aggregates was explained by the significant content of poorly crystalline matrix (in chert and quartz meta-greywacke), and by the presence of strained quartz typical with undulose extinction and the origin of quartz subgrains (in quartzite and pegmatite quartz).

Quartz is among the most common minerals in the Earth’s crust and is stable within a wide range of temperature and pressure conditions. As its microstructure is sensitive to different deformation mechanisms, quartz may present information about the structural evolution of many different rock types. The Szentlőrinc-1 well with its drill cuttings brought to the surface from approximately 2 km depth provides an exclusive chance to investigate the shear zone beneath. The drill cutting collection includes only a few small rock grains, and more than 80 % of the material consists of tiny (

This work investigates the mineralogical properties and the morphology of aeolian quartz sand in the Toshka dune area, southeastern Western Desert of Egypt. The dunes are composed mostly of subangular to subrounded fine to medium quartz sands together with minor proportions of feldspars and lithic fragments. Significant roundness variations are observed both between different dune types and within the dune sites. Barchan sands are the most rounded, whilst sand shadows are angular and fine. Barchans are also relatively enriched in polycrystalline quartz, where most of these grains are more rounded and more durable than monocrystalline quartz. Roundness characteristics of the Toshka sands are considerably managed by their grain size as medium quartz grains are more rounded than the finer ones. Angularity is a characteristic property of most monocrystalline quartz grains that exhibit undulose extinction. This maintenance of undulose extinction in quartz perhaps as a result of less stability and minimal transport from the source in the vicinity of the dune fields, as shown by the increase of angularity of quartz and short-distance transfer of these grains. These Toshka sand grains also show signs of a fluvial transportation signature. The analysis of grain surface features by scanning electron microscope (SEM) performed on dune sand grains from the Toshka area showed that quartz grains demonstrate a variety of surface textures indicating mechanical and chemical processes developed during transportation of these grains in subaqueous and aeolian environments, respectively, reflecting the mixed mode of formation of these dunes.

Several aubrites (e.g., LAP 03719, Bishopville, Khor Temiki, ALH 83015) contain orthopyroxene grains that exhibit more-pronounced shock effects than associated olivine grains. The orthopyroxene grains in these samples have clinoenstatite lamellae on (100) and exhibit weak mosaic extinction, characteristic of shock stage S4; the olivine grains exhibit either sharp optical extinction, characteristic of shock stage S1 (as in LAP 03719), or undulose extinction (shock stage S2), as in Bishopville and ALH 83015. The Khor Temiki regolith breccia contains S1 and S2 olivine grains. Because literature data show that diffusion is much slower in orthopyroxene than in olivine, it seems likely that aubrites experienced postshock, impact-induced annealing. After differentiation, the aubrite parent asteroid suffered major collisions that caused extensive brecciation of near-surface materials and damaged orthopyroxene and olivine crystal lattices. As a result of these impact events, some aubrites were shocked and buried within warm ejecta blankets or beneath fallback debris under the crater floor. Entombed olivine crystal lattices healed (and became unstrained, reaching shock stage S1), but orthopyroxene lattices retained their S4-level shock-damaged features. Aubrites with S4 orthopyroxene and S2 olivine were probably very weakly shocked again after olivine was annealed to S1.