Extensive micro-porosity can be found in numerous examples of quartz-rich mylonites deformed in crustal shear zones, but whether or not deformation is involved in the production of such pores remains a matter of active debate. The occurrence of syn-kinematic micro-scale porosity could result in overall changes in rock strength, as well as potentially generating a deep permeability. This would have major implications for fluid-rock interactions, earthquake nucleation and ore deposits. In this study, we focus on micro-pores occurring in quartz-rich shear bands from mylonitic granitoids which outcrop in Ikaria (Cyclades, Greece). Related to the back-arc geodynamics of the Aegean domain during the Miocene, this granitic body intruded the Cycladic basement during active detachment faulting, which has led to heterogeneous deformation of the pluton. While the granite exhibits large-scale levels of strain, increasing with proximity to the detachment fault, quartz-rich shear bands develop as a result of viscous strain localisation, giving rise to S-C structures. Micro- (to nano-) pores occur in pure quartz aggregates of these shear bands, where micro-structural features indicate dominant crystal plasticity, mostly recovering by subgrain rotation.

Based on five samples collected at different distances from the detachment fault, we performed microprobe-based hyperspectral cathodoluminescence and electron backscatter diffraction (EBSD) to characterise the micro-pores in pure quartz aggregates. In cathodoluminescence maps, parent and recrystallized quartz grains produce blue (420 nm wavelength) and yellow (650 nm wavelength) signals respectively. Furthermore, both parent and recrystallised grains exhibit a distinct increase in luminescence at 650 nm, which appear visually as very bright yellow rims/halos at their grain boundaries and, to a minor extent, at their subgrain boundaries. Using high-resolution and standard EBSD, we highlight high (to very high) geometrically necessary dislocation densities that partly coincide with such rims/halos, particularly where micro-pores are described. Most of the dislocations that may contribute to these high densities are related to the main dislocation slip system of quartz (prism <a>), as deduced from from lattice preferred orientation and subgrain analyses. Our findings, therefore, suggest that highly luminescent "yellow" boundaries of quartz grains result from dislocation accumulation, and hence, from crystal plasticity, which can be linked to the production of micro-porosity in these rocks. 

How to cite: McGill, G., Précigout, J., Prigent, C., Arbaret, L., Airaghi, L., and Wallis, D.: Micro-porosity found in quartz shear bands from Ikaria, Greece: insights from Hyperspectral Cathodoluminescence and High-Resolution Electron Backscatter Diffraction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9750, https://doi.org/10.5194/egusphere-egu24-9750, 2024.

Micropores are commonly observed in quartz-rich rocks that deformed at depths of the viscous, metamorphic continental crust. Although the presence of such porosity – often occurring with angular, pyramidal shapes – has major implications for fluid circulations and rock strength, whether or not they are produced by deformation remains unclear. Here we provide detailed documentations of pure quartz aggregates decorated by micropores in granitic shear bands from Naxos (Greece). Through estimations of geometrically necessary dislocation densities, we first document very high values (>> 10¹⁵ m^-2) along intragranular boundaries, several of them containing micropores. We then performed focused ion beam (FIB) cross-sectioning and transmission electron microscopy to image pore shapes along all types of quartz boundaries. Pores do not necessarily arise with angular shapes, but they are systematically embedded within amorphous SiO₂, i.e., silica glass, along both grain and intragranular boundaries. FIB volume reconstruction also revealed pyramid-like pits occurring with round-shape faceted pores, the shape of which challenges long-lasting hypotheses for pores to originate. Together with recent studies^[1,2], our findings support deformation to produce porosity through (1) mechanical amorphization where dislocations accumulate and (2) fluid exsolution from the resulting glass because of a pressure/stress drop, here attributed to grain boundary sliding.

[1] Idrissi, H., Carrez, P. & Cordier, P. On amorphization as a deformation mechanism under high stresses. Current Opinion in Solid State and Materials Science 26: 100976 (2022)

[2]Li, B. Y., Li, A. C., Zhao, S. & Meyers, M. A. Amorphization by mechanical deformation. Materials Science & Engineering R 149: 100673 (2022)

How to cite: Précigout, J., Prigent, C., McGill, G., Arbaret, L., Airaghi, L., and Wallis, D.: Quartz amorphization to produce porosity in crustal shear zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9882, https://doi.org/10.5194/egusphere-egu24-9882, 2024.

Recognition of seismically induced microstructures is important to unravel the different deformation processes during seismic cycles, especially at the base of the upper crust where many earthquakes nucleate. Deformed quartz veins related to a strike-slip shear zone within the Schobergruppe (Austroalpine Crystalline Complex, Eastern Alps) contain intense kinking in elongated quartz grains. The kink band boundaries are inclined into the general dextral sense of shear. Cathodoluminescence (CL) images reveal that the entire thin section contains a very high density of intragranular, sub-planar microstructures developed as thin dark CL lamellae accompanied with nanometre-scale fluid inclusions. Based on the oscillating orientation variation across low angle boundaries (misorientation angle 1-9°) these lamellar microstructures are referred as short-wavelength undulatory extinction microstructures - SWUE (Trepmann & Stöckhert, 2013). Only grains with SWUE, orientated parallel to the foliation, are kinked. In general, kinked microstructures mainly develop in strongly anisotropic material or minerals with a strong cleavage, e.g. micas. Deformation at high differential stresses e.g. during coseismic loading can produce a strong anisotropic microstructure in quartz by the development of deformation lamellae. Trepmann & Stöckhert (2013) showed in deformation experiments of quartz that SWUE preserve evidence of an earlier coseismic stress peak, even when overprinted during subsequent crystal plastic creep deformation at lower stress. The SWUE in the deformed Schober quartz veins are interpreted in a similar way. These microstructures were primary deformation lamellae developed during coseismic loading. TEM images reveal a high degree of recovery (low dislocation density) across the SWUE. Subsequent overprint by ongoing creep at lower stresses is recorded by vein quartz samples with mylonitic microstructures. The densely spaced sub-planar microstructures cause a high anisotropy of the quartz grains, which finally were kinked. Electron backscatter diffraction data give evidence of different slip systems that were active during the development of the deformation lamellae followed by recovery (SWUE), and during the subsequent kink band formation. The opposite direction of the Burges vectors (based on Weighted Burges Vector analysis, Wheeler et al., 2009) at the corresponding kink band boundaries is geometrical consistent with sinistral shearing within the kink domain along the anisotropic deformation lamellae/SWUE related to the dextral sheared kink band. Intensively kinked micas (muscovite and biotite) in the mica-rich host rock (in direct contact to the kinked quartz vein sample) point to seismic induced kinking, which is supported by the vicinity (1-1.5m) of a fault zone with pseudotachylytes.

How to cite: Bestmann, M., Grasemann, B., Pennacchioni, G., Kilian, R., Wheeler, J., Morales, L. F. G., and Bezold, A.: Seismic induced anisotropy and kinking in quartz, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2884, https://doi.org/10.5194/egusphere-egu24-2884, 2024.

In the realm of modern solid Earth research, a profound understanding of rocks' intricate microstructures is essential for unraveling geological history and addressing critical challenges in the energy transition. These microstructures—grain boundaries, preferred orientation, twinning, and porosity—play a pivotal role, influencing the physical strength, chemical reactivity, and fluid flow properties of rocks. Their direct impact on subsurface reservoirs used in geothermal energy, nuclear waste disposal, and hydrogen/carbon dioxide storage underscores the importance of comprehending their distribution for the stability and efficacy of subsurface activities.

However, addressing the need for statistical representativeness requires imaging numerous samples at high magnification. In response, our research introduces an innovative image enhancement process for scanning electron microscopy datasets, showcasing a substantial potential for resolution improvement through Deep-Learning-Enhanced Electron Microscopy (DLE-EM).

Our proposed workflow involves capturing one or more high-resolution (HR) regions within a low-resolution (LR) area. Precise image registration is achieved in two steps: first, determining the HR region's location within the LR region using a Fast Fourier Transform algorithm (Lewis, 2005), and second, refining image registration through iterative calculation of a deformation matrix. This matrix, utilizing Newton's optimization method, aims to minimize differences between both images (Tudisco et al., 2017). Subsequently, paired HR and LR images undergo processing in a Generative Adversarial Network (GAN), comprising a generator and a discriminator. This GAN learns to generate HR images from LR counterparts through joint training in an adversarial process.

We benchmark our workflow using four distinct rock types and demonstrate that this approach accelerates imaging processes up to a factor of 16 with minimal impact on quality, offering possibilities for real-time super-resolution imaging of unknown microstructures. Additionally, we show that a model trained on a specific geological material is able to generalize its learned features to new domains, reducing the need for extensive training data.

[1] Lewis, J. P. "Fast normalized cross-correlation, Industrial Light and Magic." unpublished (2005).

[2] Tudisco, Erika, et al. "An extension of digital volume correlation for multimodality image registration." Measurement Science and Technology 28.9 (2017): 095401

How to cite: van Melick, H. and Plümper, O.: Breaking Boundaries: Deep-Learning-Enhanced Electron Microscopy for Accelerated Super-Resolution Imaging in Solid Earth Research, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8470, https://doi.org/10.5194/egusphere-egu24-8470, 2024.

The earth's internal dynamic processes are closely related to the rheological behavior of its internal constituent minerals under high temperature and high pressure conditions. Feldspar and pyroxene are the main constituent minerals in granulite in the continental lower crust. High-temperature experimental research on them is one of the main ways to understand the rheology of the continental lower crust. This experiment uses the Paterson high temperature and high pressure rheology device, at a temperature of 1273K-1423K and a strain rate of 6×10-6 s ^-2×10-5s^-1, to test the hot-pressed feldspar and pyroxene aggregates with and without water respectively. Creep experiments were carried out under added water conditions to determine the rheological parameters of the two-phase aggregate under different water conditions. By collecting infrared spectra and microscopic pictures of the two-phase aggregate of hot-pressed feldspar and pyroxene, the water content in the samples before and after deformation was calculated and its microstructural characteristics were analyzed. The Q value of the sample without adding water is 797.87±184.7 KJ/mol, and the n value is about 3. The Q value of the water-added sample is 472.57±96.29KJ/mol. From 1273K to 1373K, the n value is about 2. At 1373K, the n value is about 4. This shows that water has a significant weakening effect on rocks.

How to cite: zhang, Q. and Zhou, Y.: Experimental study on high-temperature rheology of hot-pressed mafic granulite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8853, https://doi.org/10.5194/egusphere-egu24-8853, 2024.

The Kapıdağ Shear Zone (KSZ) is located in the Kapıdağ Peninsula (NW Anatolia) and syn-kinematically intruded by Northern Kapıdağ Pluton (NKP) along the northern coastline of the peninsula. The NKP displays a granodioritic composition with a discernible progressive deformation from south to north. The southern part is characterized by an isotropic granodiorite with no trace of deformation. Towards the north, it gradually passes into a deformed granodiorite in which the development of ductile and brittle structures is widely observed. To comprehend the nature and origin of deformation within the KSZ, a thorough analysis of micro- and mesostructural features was undertaken, accompanied by a three-dimensional kinematic analysis of the NKP. The NKP exhibits a well-defined mylonitic foliation and stretching lineation, characterized by the shape-preferred alignment of feldspar, quartz, and biotite crystals. Various shear sense indicators, including S-C fabrics and "σ"-type rotated porphyroclasts, are extensively distributed throughout the NKP, pointing to a dextral sense of shear. Microstructures such as chessboard extinction and Grain-Boundary Migrations (GBM) in quartz, myrmekitic textures, and flame pertites in feldspar, as well as sub-grain rotations and bulging recrystallization of quartz, along with the presence of micro-faults and cracks collectively suggest continuous deformation of the NKP from temperatures starting at 600°C to those below 250°C.

Three-dimensional strain analysis was conducted on the Northern Kapıdağ Pluton (NKP) using quartz crystals as shear sense indicators, and various parameters including kinematic vorticity (Wk) numbers, Flinn k values, Lode’s ratio, and octahedral shear strains were computed. The outcomes reveal a range of Flinn k values from 1.1 to 5.32. On Flinn’s diagram, the majority of samples plot above the k=1 line, indicative of a transtensional regime. Lode’s ratios exhibit a variation from -0.64 to +0.13, with the Hsu diagram showing that the majority of samples fall within the general constrictional field. To discern the strain component of the NKP, kinematic vorticity numbers (Wk) were determined, ranging from 0.73 to 0.99. This suggests a dominance of simple shear in the deformation rather than pure shear components. The U-Pb zircon and ⁴⁰Ar/³⁹Ar biotite dating results show that this deformation has developed between 48-36 Ma. 

In summary, both micro/mesostructural data and three-dimensional strain analyses of the NKP collectively suggest that the Kapıdağ Shear Zone (KSZ) is characterized by a dextral transtensional shear zone dominated by simple shear. We hypothesize that the KSZ was likely formed during the Eocene period as a consequence of strain localization along the break-off of the Tethyan oceanic slab.

How to cite: Arık, T., Ünal, A., and Altunkaynak, Ş.: Three-dimensional kinematic analysis of Northern Kapıdağ Pluton: Implications for a transtensional deformation in NW Anatolia , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9288, https://doi.org/10.5194/egusphere-egu24-9288, 2024.

Mantle heterogeneity is closely related to the distribution and circulation of volatile components in the Earth’s interior, and the behavior of volatiles in the mantle strongly influences the rheological properties of silicate rocks. In mantle xenoliths, these physicochemical properties of the upper mantle can be recorded in the form of microstructures and fluid inclusions. In this paper, I summarized and reviewed the results of previous studies related to the characteristics of microstructures and fluid inclusions from peridotite xenoliths beneath the Rio Grande Rift (RGR) in order to understand the evolution and heterogeneity of upper mantle. In the RGR, the mantle peridotites are mainly reported in the rift axis (EB: Elephant Butte, KB: Kilbourne Hole) and rift flank (AD: Adam’s Diggings) regions. In the case of the former (EB and KB peridotites), the type-A lattice preferred orientation (LPO), formed under low-stress and low-water content, was reported. In the case of the latter (AD peridotites), the type-C LPO, formed under low-stress and high-water content, was reported. In particular, in the case of AD peridotites, at least two fluid infiltration events, such as early (type-1: CO₂-N₂) and late (type-2: CO₂-H₂O), have been recorded in orthopyroxene. The upper mantle heterogeneity recorded by these microstructures and fluid inclusions is considered to be due to the interaction between the North American plate and the Farallon plate.

How to cite: Park, M.: Upper Mantle Heterogeneity Recorded by Microstructures and Fluid Inclusions from Peridotite Xenoliths Beneath the Rio Grande Rift, USA, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5017, https://doi.org/10.5194/egusphere-egu24-5017, 2024.

Semi-brittle deformation, which is characterized by the simultaneous occurrence of fracturing and crystal plasticity, plays a critical role in determining the mechanical properties of the middle crust. Laboratory experiments have identified semi-brittle deformation as ductile flow involving distributed microfracturing, an absence of localized macroscopic failure, and widespread plasticity. However, a constitutive law of semi-brittle deformation remains elusive, and a lack of quantitative microstructural analyses has hindered the development of micromechanical models for semi-brittle deformation.

This study aims to address these limitations by providing quantitative characterization of twins, lattice distortion, and intragranular fractures in Carrara marble that has undergone semi-brittle deformation. Three sets of samples were uniaxially shortened to varying strains up to 8% under a confining pressure of 400 MPa and different temperatures at 20, 200, and 350ºC. The tested samples were examined by forescattered electron imaging and electron backscattered diffraction mapping. The results reveal that, in the early stages of deformation (strain < 2%), deformation is primarily accommodated by twins. Lattice distortion, linked to geometrically necessary dislocations, becomes prominent in the later stages (strain > 4%). Intragranular fracture intensity shows a linear correlation with strain. Despite some nuanced variations, the qualitative development of each microstructure type remains similar at different temperatures. At the onset of semi-brittle deformation, microstructural evidence has shown that the nucleation of microfractures or lattice distortion is induced by strain incompatibility at granular scale. The local stress concentrations associated with such strain incompatibility are enhanced by irregularities of grain boundaries. These observations provide a foundational microstructural understanding, facilitating the development of a robust microphysical model for semi-brittle deformation in the lithosphere.

How to cite: Qu, T., Brantut, N., Wallis, D., and Harbord, C.: On the microstructural evolution of Carrara marble during semi-brittle deformation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13583, https://doi.org/10.5194/egusphere-egu24-13583, 2024.

Orhaneli ophiolite is an Upper Cretaceous ophiolitic suite obducted over the Late Cretaceous high-pressure rocks. It covers approximately 43 km in length and 14 km in width. It is part of the Neotethyan ophiolite belt along the southern side of the Izmir-Ankara-Erzincan Suture. The lithological and structural mapping of the Orhaneli ophiolite revealed that the mantle rocks, the Moho Transition Zone (MTZ), and the ophiolitic lower crust are exposed along the region but the subvolcanic and volcanic sequences are missing. The study of the deformation mechanisms of available three units is our research.

The mantle rocks in the Orhaneli ophiolite comprise harzburgite (~50%), dunite (~40%), websterite, and clinopyroxenite (~10%). Harzburgite and dunite are coarse-grained and show well-developed L-S tectonic fabric. Websterite and clinopyroxenite are coarse/very coarse-grained with granular texture. The mantle tectonites (harzburgite and dunite) in the region are characterized by widespread high-temperature (1200-1250 °C) deformation partially overprinted by low-temperature (800-1000 °C) deformation. The grain boundary migration (GBM) and subgrain rotation (SGR) recrystallizations are the dominant mechanisms of the high-temperature deformation in this unit. The subsequent low-temperature deformation predominantly proceeded through subgrain rotation (SGR), and bulging (BLG) recrystallizations accompanied by kinking and twinning. Contrarily to the mantle tectonites, the pyroxenite (websterite and clinopyroxenite) predominantly shows low-temperature deformation structures. They are mainly deformed through the kinking of the pyroxene grains, however, high-temperature deformation structures also exist. A possible explanation is that the pyroxenite predominantly deformed through viscous flow under spreading center conditions.

The MTZ in the Orhaneli ophiolite is a ~1 km thick, strongly sheared zone between the mantle and lower crustal rocks. It mainly consists of serpentinite, layered gabbro, and mylonitic peridotite. The serpentinite, the most prevalent lithology in this zone, commonly shows anastomosing foliation. The layered gabbro mainly consists of orthopyroxene and plagioclase. It is characterized by thin and continuous layers of plagioclase and orthopyroxene. In some cases, these layers are transposed into isoclinal folds with detached limbs by continuous, layer-parallel, simple shearing. The stretching lineation is well-developed and defined by plagioclase and orthopyroxene. The mylonitic peridotite mainly consists of olivine and orthopyroxene. It is characterized by ribbons of orthopyroxene and elongated aggregates of olivine within a fine-grained olivine and pyroxene-rich matrix. The orthopyroxene ribbons indicate high-strain conditions within the MTZ. The aggregates of olivine suggest that the SGR recrystallization is an important mechanism of deformation within this zone.

The lower crust in the Orhaneli ophiolite comprises cumulates of gabbro, peridotite, pyroxenite, and anorthosite, in order of prevalence. Peridotite is more abundant in the stratigraphically lower sections of the crust and it diminishes stratigraphically upward. The serpentinization of peridotite is commonly over 90%. In general, the crustal section does not show evident plastic deformation. The gabbroic rocks commonly show magmatic foliation defined by the preferred orientation of undeformed plagioclase and pyroxene grains. This suggests that the crustal section is mainly deformed through viscous flow in the magmatic state.

How to cite: Paksoy, Y. C., Paksoy, N., and Natal'in, B. A.: The deformation mechanisms of Upper Cretaceous Neotethyan Orhaneli ophiolite, NW Turkey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12851, https://doi.org/10.5194/egusphere-egu24-12851, 2024.

This study presents the conditions of pressure, temperature, and breccia mechanisms that allow the migration of emerald-bearing hydrothermal fluids within the emerald belts of Colombia. Based on detailed petrographic analysis, three different hydrothermal events were determined, establishing a chronological framework that enhances our understanding of geological processes in these emerald belts. The first event is characterized by the high presence of albite, due to an albitization event that altered the rock. The other events are marked by an early stage of carbonatization (second) and a late carbonatization stage (third). After understanding the hydrothermal events, Fermi diad bands were obtained by Raman spectroscopy in fluid inclusions. This approach permits the calculation of the rock pressure using the vibrational modes of the CO2 and their relationship with its density. These analysis was performed in minerals associated with each hydrothermal event. The data obtained from these analyses provides the evolution of the pressure in the whole hydrothermal history. 

Finally, a fractal analysis applied to breccias from both (western and eastern) emerald belts was performed. This analytical approach aimed to understand the breccia mechanisms throughout the entire hydrothermal history, providing a view of the geological evolution of these emerald belts. Even though both belts present similar events, the western emerald belt reveals higher mechanical energy in comparison with the eastern emerald belt, in which the pressure is generally lower and breccia mechanisms show a higher-intensity corrosive event, the presence of fluidization breccias manifests that the migration of the fragments may be fluid assisted against Halokinesis

How to cite: Betancur Acevedo, C. A., Kammer, A., and Garcia Toloza, J.: Breccia Mechanisms and Hydrothermal Evolution from Both Colombian Emerald Belts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15060, https://doi.org/10.5194/egusphere-egu24-15060, 2024.

The Strandja Massif, exposed along northwestern Turkey is an NW striking polymetamorphic belt. The massif is mainly composed of a Neoproterozoic-Paleozoic metamorphic sedimentary complex intruded by plutons of various ages, all of which are covered by Mesozoic metasedimentary units. In previous studies Natal’in and co-authors have shown crosscutting relations between bedding or intrusive contacts were well documented all above-mentioned rocks reveal uniform penetrative foliation, which is observed in stratigraphic units of various ages. Isotopic dating shows that the massif has undergone at least two metamorphic events during the Mesozoic and Paleozoic. Greenschist to lower amphibolite facies metamorphism and intense deformation occurred in the Middle Jurassic to Early Cretaceous times as is evident from Ar-Ar and Rb-Sr studies. However, the formation of migmatites in some rocks assigned to the Paleozoic and the heterogeneous distribution of metamorphic rock types contrary to the more or less regular behavior of fabric require additional attention to the reconstruction of P-T conditions of deformations and their variations in time. The goal of this research is to improve our understanding of the P-T conditions during Paleozoic metamorphism and deformation. For this purpose, we studied the northwest part of the Strandja Massif which mainly consists of migmatitic biotite gneiss, metagranite, migmatitic biotite garnet gneiss, amphibolite, and quartzo-feldspathic schist.

The metamorphic conditions of the Paleozoic metamorphism are restricted by the following criteria: (1) The units that have undergone the Paleozoic metamorphism show evidence of migmatization. The temperature should exceed ~650 °C for the beginning of partial melting. (2) The occurrence of amphibolite indicates that the Paleozoic metamorphism was within the amphibolite facies conditions. (3) The founding of partially preserved kyanite restricts the pressure conditions of the Paleozoic metamorphism. By these criteria, the peak metamorphic conditions of the Paleozoic metamorphism are restricted to 650-720 °C and 6-12 kbar.

The Paleozoic metamorphism is accompanied by highly ductile deformation compatible with the metamorphic conditions. The Paleozoic deformation is characterized by mesoscale intrafolial folds, macroscale sheath folds, and migmatitic foliation. The intrafolial folds have foliation parallel axial planes and can only be recognized through their hinges since their limps are commonly detached. The presence of melt, due to migmatization, possibly has a crucial role on the rheological properties during this deformation.

The microstructural imprints of the Paleozoic metamorphism are investigated within the framework of this study. The chessboard subgrain pattern of quartz within the leucosomes of the migmatitic gneiss provides evidence that peak metamorphism occurred during one of the episodes of a prolog structural history of the Strandja Massif. The absence of this subgrain pattern out of leucosomes supports that the Paleozoic metamorphism did not advance into the granulite facies. The grain boundary migration (GBM) and subgrain rotation (SGR) recrystallizations and the growth of deformation myrmekites along the high-stress sites of feldspar also require higher temperature conditions than the compared with those that are seen in rocks that are assigned to the Mesozoic. These structures could be formed or represent relicts of Paleozoic metamorphism.

How to cite: Paksoy, N., Paksoy, Y. C., and Natal'in, B. A.: Relicts of high-temperature fabric in the Strandja Massif, NW Turkey, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16284, https://doi.org/10.5194/egusphere-egu24-16284, 2024.

Deformation of polymineralic rocks at elevated temperatures usually results in grain size refinement but also in a grain scale mixture of mineral phases. Phase mixtures may either be homogeneous or exhibit a compositional and microstructural layering. Depending on the host rock stability, mixtures may consist of combinations of redistributed or newly, synkinematically formed phases. In general either neighbour-switching or heterogeneous nucleation are envisaged as processes responsible for mixing during diffusion creep s.l. including grain boundary sliding and grain-scale transport processes. In order to quantify phase mixtures, neighbourhood relations can be analysed to differentiate random, clustered or anti-clustered distributions. Heterogeneous nucleation is usually considered to allow for anti-clustered distributions, while neighbour switching during grain boundary sliding potentially produces random distributions.

Here, phase mixing is explored based on contact densities as well as on centre-to-centre distances. In particular, the effect of directionality that is neighbour relations as a function of the relative position in a 2D section is considered. The direction of neighbours is considered by the normal of the boundary trace as well as alternatively, by the direction of the centre-to-centre join.

Given sufficiently large datasets and non-extreme mixtures (e.g. with 0.2 < phase proportion < 0.8) a confidence interval of the results can be defined. Large datasets of ultramylonites of different metamorphic grade, phase proportions, compositions (ultramafic, mafic, quartzo-feldspatic) and microstructures (layered, isotropic) are tested.

It is found that phase anti-clustering is generally more pronounced in a direction close to the stretching direction in either layered or homogeneous ultramylonites. In layered mylonites, layer-normal relations are frequently found to be random while intralayer relations are often anti-clustered.

In the different rock types, specific anti-clustered phases can be discriminated, e.g., orthopyroxene with respect to olivine, k-feldspar with respect to plagioclase and quartz, and hornblende with respect to plagioclase. Other phase assemblages e.g. quartz-plagioclase are frequently found to be distributed randomly, hinting at mineral specific roles during diffusion creep s.l. and generally at element mobilities in deforming metamorphic rocks.

How to cite: Kilian, R.: Phase mixtures in shear zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17253, https://doi.org/10.5194/egusphere-egu24-17253, 2024.

Texture formation in rocks is modeled using a quantitative phase-field model of eutectic growth with three thermodynamic phases (e.g. Diopside - Anorthite - Melt) in a quasi-binary magmatic system with unlimited quantity of crystals of different orientation and anisotropy. In nature, specific layering microstructures have been observed for which many possible explanations have been provided. Moreover, textural irregularities initially induced during nucleation, by fluctuation in crystal size or by other mechanisms continue to develop and sharpen over time. By phase-field modeling, we verify two models of igneous layering. The first mechanism is that, due to the formation of a layer with crystals of larger size, these crystals will grow faster at the expense of smaller crystals. The second mechanism is that a layer with an increasing fraction of the second phase is formed on top of the initial layer of the first phase to have crystallized. We have found that, in this case, without anisotropy of surface energies, no layering is produced. The boundary conditions and parameters of the models necessary for the formation of layers will be discussed.

How to cite: Kundin, J. and Chakraborty, S.: Phase-field modeling of texture evolution in magmatic rocks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8497, https://doi.org/10.5194/egusphere-egu24-8497, 2024.