Polyphase Deformation of the High-Grade Metamorphic Rocks along the Neusspruit Shear Zone in the Kakamas Domain: Insights into the Processes during the Namaquan Orogeny at the Eastern Margin of the Namaqua Metamorphic Province, South Africa

The central part of the Namaqua Metamorphic Province was subjected to intense deformation under high-grade metamorphic conditions up to granulite facies, but also shows greenschist facies overprints denoting the metamorphic nature during the 1.2–1.0 Ga Namaquan Orogeny. This study examines the structural development of the central Kakamas Domain of the eastern Namaqua Metamorphic Province, which has not been extensively studied previously. The compressional orogenic phase is associated with D1 and D2 deformation events during which northeast–southwest-directed shortening resulted in southwest-directed thrusting illustrated by an intra-domain thrust and southwest-verging isoclinal folds. The post-tectonic Friersdale Charnockite of the Keimoes Suite is emplaced during the D3 deformation event. Late reactivation of the intra-domain thrust in the Kakamas Domain to form the Neusspruit Shear Zone during the D4 event is of a monoclinic nature and is described as a deeply rooted structure with shear direction towards the east. This structure, together with the more local Neusberg Thrust Fault, forms part of an intensely flattened narrow basin in the eastern Namaqua Metamorphic Province. Strain and vorticity indices suggest a transpressional shearing across the Neusspruit Shear Zone and adjacent regions probably initiated during the reactivation of the intra-domain thrust. The ~1.2 to 1.8 km-wide, northwest–southeast striking dextral-dominated Neusspruit Shear Zone constitutes a western regional boundary for the supracrustal Korannaland Group and is composed of steep, narrow zones of relatively high strain, characterised by ductile deformation and penetrative strain.

Adsorption of SF6 Decomposed Products on ZnO-Modified C3N: A Theoretical Study

SF6, as an outstanding insulation medium, is widely used in the high-voltage insulation devices, guaranteeing the safe operation of the power system. Nevertheless, the inevitable partial discharge in a long-running device causes the decomposition of SF6 and deteriorates its insulation performance. In this work, DFT calculations were performed to study the adsorbing and sensing properties of ZnO-modified C3N (ZnO-C3N) nanosheet towards SF6 decomposed products, in order to propose a novel nano-candidate for evaluating the operation status of SF6 insulation devises. We first investigated the structure of ZnO-C3N monolayer and then simulated its adsorption behaviour upon four typical SF6 decomposed species, namely H2S, SO2, SOF2, and SO2F2. It is found that the ZnO-C3N monolayer can exhibit desirable reactivity and sensitivity on SO2, SOF2, and SO2F2, leading to the intense deformation of gas molecules and large adsorption energies. These consequences allow the potential application of gas adsorbent based on ZnO-C3N monolayer for removing impurity gases from SF6 insulation equipment. According to the analysis, it is supposed that ZnO-C3N monolayer is qualified to be used in maintaining insulation strength and ensuring the safe operation of power system.

Structural evolution of continental and marine Permian rock salt of the North German Basin: constraints from microfabrics, geochemistry and U–Pb ages

Analyzing the dynamics of microstructural response on natural deformation in rock salt, we present microfabric, EBSD, geochemical and U–Pb data, obtained from Permian salt formations of the Kiel-Honigsee salt wall in Northern Germany. The samples were recovered from deep drillings, which penetrated through an overturned rock salt sequence of both Rotliegend and Zechstein deposits. The bromide concentration in halite indicates a continental and marine origin for the Rotliegend and Zechstein deposits, respectively. Despite intense deformation, relics of early diagenetic fabrics are still preserved. Deformation of the impure Rotliegend rock salt was accommodated by pressure solution and hydrofracturing as is indicated by the microfabrics and bromide concentration in halite. Fractures in siliciclastic domains were filled with fibrous halite and deformed by subgrain rotation recrystallization (SGR). Fluid-rich Zechstein rock salt, on the other hand, was deformed by formation of subgrains and grain boundary migration (GBM). The distribution of mineral phases and fluids had a significant impact on the fabric evolution and on strain localization. U–Pb dating of carbonate phases of the Rotliegend sequence yielded Permian depositional ages and Jurassic to Cretaceous deformation ages, the latter related to diapiric ascent. The combination of results traces a dynamic evolution of the rock fabric inside the diapir structure driven by locally active deformation processes that can be correlated with early stages of halite deposition and diagenesis and syntectonic fabric reorganization related to diapirism in an extensional setting.

The structural evolution of the Straumsnutane and western Sverdrupfjella areas, western Dronning Maud Land, Antarctica: implications for the amalgamation of Gondwana

The study area is located across the Kalahari Craton – Maud Belt boundary in Dronning Maud Land (DML), Antarctica. The ∼1100 Ma Maud Belt in the east is situated where the ∼900–600 Ma East African and ∼530–500 Ma Kuunga orogenies overlap. The Kalahari Craton cover in the west of the study area comprises ∼1100 Ma Straumsnutane Formation lavas in Straumsnutane. In Straumsnutane, early ∼1100 Ma low-grade structures suggest top-to-the-NW deformation. Younger ∼525 Ma structures suggest conjugate top-to-ESE and -WNW transport under low-grade conditions. Western Straumsnutane and Ahlmannryggen do not show the same complex deformation, the intense deformation being restricted to NE Straumsnutane along the eastern margin of the Kalahari Craton. In Sverdrupfjella, in the east, the Maud Belt is underlain by medium-grade, deformed ∼1140 Ma supracrustal gneisses and younger intrusions. Four deformation phases in the gneisses comprise D1 + D2 with top-to-the-N and -NW folds, D3 top-to-the-S and -SE folding and D4 brittle faulting. Syn-D3 emplacement of granitoid veins is inferred at ∼490 Ma. Comparison of the deformation vergence of NE Straumsnutane with western Sverdrupfjella suggests D1 in Straumsnutane is correlatable with D1 + D2 Mesoproterozoic structures in western Sverdrupfjella. D2 deformation in Straumsnutane can be correlated with D3 structures and Cambrian-age granites in Sverdrupfjella. D2 deformation in eastern Straumsnutane and D3 in western Sverdrupfjella are inferred to have occurred in a mega-nappe footwall, implying the Ritscherflya Supergroup cratonic cover in eastern Straumsnutane was partially submerged in the footwall, the mega-nappe formed during Gondwana amalgamation, involving collision between N and S Gondwana in the Kuunga Orogeny, ∼530–500 Ma ago.

Ballooning emplacement and alteration of the Chah-Musa subvolcanic intrusion (NE Iran) inferred from magnetic susceptibility and fabric

The porphyritic diorite Chah-Musa subvolcanic intrusion is located in the Toroud-Chah Shirin magmatic arc in the northern Central Iranian structural zone. The elliptical Chah-Musa body hosts a copper deposit and intrudes an Eocene sequence of volcanic breccia, agglomerate and red tuffaceous sediment. High magnetic susceptibility values are attributed to the presence of magnetite as a magnetic carrier. Changes in bulk magnetic susceptibility correlate with zonation of alteration in the intrusion. Although the degree of anisotropy of magnetic susceptibility decreases due to hydrothermal alteration, the field observations confirm that this parameter can be used as a strain marker. Strongly oblate magnetic ellipsoids are found in the eastern half of the intrusion where isolated outcrops of flat-lying tuffaceous host cover dioritic rocks (roof zone). Stations with prolate ellipsoids mostly belong to the centre of the intrusion where the magnetic lineations plunge steeply. They are interpreted as indicating the main feeder zone. The concentric fabric pattern at the periphery of intrusion, the oblate magnetic ellipsoids at the roof, the highest anisotropy degree along the small diameter of the intrusion, and an intense deformation of the host rocks, especially at the western margin, all are evidence that the intrusion was ballooning during the late stages of its emplacement. Ascent and emplacement of the Chah-Musa body is ascribed to the tensional space provided by a dextral shear zone created by the regional left-lateral movement on the bounding Anjilow and Toroud strike-slip faults.

Fault Core Thickness: Insights from Siliciclastic and Carbonate Rocks

Fault core accommodates intense deformation in the form of slip surfaces and fault rocks such as fault gouge, cataclasite, breccia, lenses, shale smear, and diagenetic features. The complexity and variation in fault core geometry and thickness affect fluid flow both along and across the fault. In this study, we have investigated a total of 99 faults in siliciclastic and carbonate rocks. This has resulted in two large datasets that include 871 fault core thickness measurements T in siliciclastic rocks and 693 measurements in carbonates, conducted at regular intervals along fault elevations (fault height) on the outcrop or photos of the outcrop. Many of these measurements have been analyzed with respect to fault displacement measurements D in order to study the relationship between displacement and fault core thickness and to further uncover the fault growth process. We found that the fault type and geometry, displacement, type of fault rocks, lithology, and competency contrasts between faulted layers lead to significant variations in the fault core internal structure and thickness. Analysis of average values of fault core thickness-displacement data of this study and of previously published studies shows that the core thickness-displacement relationship follows an overall power law, in which its exponent and intercept change depending on the lithology of the faulted rocks. In general, small faults in carbonate and siliciclastic rocks (D≤5 m) show comparable T/D ratios, with a slightly higher ratio in carbonate rocks. The outcomes of this study contribute to the understanding of the fault core internal structure and variation in fault core thickness as a result of the interplay between fault displacement and host rock in different lithologies. These outcomes have significant implication for characterizing the sealing and conductivity potential of faulted rocks, which is relevant to different applications such as petroleum exploration and development of existing fields, hydrogeology, geothermal energy storage and extraction, and CO2 sequestration.

Combined process “helical rolling-pressing” and its effect on the microstructure of ferrous and non-ferrous materials

Ultrafine-grained materials are one of the most promising structural and functional materials. However, the known methods of obtaining them are not enough powerful and technologically advanced for profitable industrial applications. Development of the combined process “helical rolling-pressing” is an attempt to bring technology to produce ultrafine-grained materials to the industry. The combination of intense processing of the surface by helical rolling and the entire cross section of workpiece in equal channel angular matrix, with intense deformation by torsion between rolls and matrix will increase the degree of deformation per pass and allows to mutually compensate disadvantages of these methods in the case of their separate use. This paper describes the development of a laboratory stand and study of influence of combined process “helical rolling-pressing”on the microstructure of tool steel, technical copper and high alloy stainless high-temperature steel.

Deformation-driven catalysis of nanocrystallization in amorphous Al alloys

Nanocrystals develop in amorphous alloys usually during annealing treatments with growth- or nucleation-controlled mechanisms. An alternative processing route is intense deformation and nanocrystals have been shown to develop in shear bands during the deformation process. Some controversy surrounded the idea of adiabatic heating in shear bands during their genesis, but specific experiments have revealed that the formation of nanocrystals in shear bands has to be related to localized deformation rather than thermal effects. A much less debated issue has been the spatial distribution of deformation in the amorphous alloys during intense deformation. The current work examines the hypothesis that intense deformation affects the regions outside shear bands and even promotes nanocrystal formation in those regions upon annealing. Melt-spun amorphous Al88Y7Fe5 alloy was intensely cold rolled. Microcalorimeter measurements at 60 °C indicated a slight but observable growth of nanocrystals in shear bands over the annealing time of 10 days. When the cold-rolled samples were annealed at 210 °C for one hour, transmission electron images did not show any nanocrystals for as-spun ribbons, but nanocrystals developed outside shear bands for the cold rolled samples. X-ray analysis indicated an increase in intensity of the Al peaks following the 210 °C annealing while the as-spun sample remained “X-ray amorphous”. These experimental observations strongly suggest that cold rolling affects regions (i.e., spatial heterogeneities) outside shear bands and stimulates the formation of nanocrystals during annealing treatments at temperatures well below the crystallization temperature of undeformed ribbons.

The Ankara Mélange: an indicator of Tethyan evolution of Anatolia

The Ankara Mélange is a complex formed by imbricated slices of limestone block mélanges (Karakaya and Hisarlıkaya Formations), Neotethyan ophiolites (Eldivan, Ahlat and Edige ophiolites), post-ophiolitic cover units (Mart and Kavak formations) and Tectonic Mélange Unit (Hisarköy Formation or Dereköy Mélange). The Karakaya and Hisarlıkaya formations are roughly similar and consist mainly of limestone block mélange. Nevertheless, they represent some important geological differences indicating different geological evolution. Consequently, the Karakaya and Hisarlıkaya formations are interpreted as Eurasian and Gondwanian marginal units formed by fragmentation of the Gondwanian carbonate platform during the continental rifting of the Neotethys in the Middle Triassic time. During the latest Triassic, Neotethyan lithosphere began to subduct beneath the Eurasian continent and caused intense deformation of the marginal units. The Eldivan, Ahlat and Edige ophiolites represent different fragments of the Neotethyan oceanic lithosphere emplaced onto the Gondwanian margin during the Albian–Aptian, middle Turonian and middle Campanian, respectively. The Eldivan Ophiolite is a NE–SW trending and a nearly complete assemblage composed, from bottom to top, of a volcanic-sedimentary unit, a metamorphic unit, peridotite tectonites, cumulates and sheeted dykes. The Eldivan Ophiolite is unconformably covered by Cenomanian–Lower Turonian sedimentary unit. The Eldivan Ophiolite is overthrust by the Ahlat Ophiolite in the north and Edige Ophiolite in the west. The Ahlat ophiolite is an east–west oriented assemblage comprised of volcanic-sedimentary unit, metamorphic unit, peridotite tectonites and cumulates. The Edige Ophiolite consists of a volcanic-sedimentary unit, peridotite tectonites, dunite, wherlite, pyroxenite and gabbro cumulates. The Tectonic Mélange Unit is a chaotic formation of various blocks derived from ophiolites, from the Karakaya and Hisarlıkaya formations and from post-ophiolitic sedimentary units. It was formed during the collision between Anatolian Promontory and Eurasian Continent in the middle Campanian time.