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Sphalerite (ZnS) is a sulfide found in a large variety of ore deposits and is frequently hosted in metamorphic terranes that have undergone deformation and related recrystallization. However, the deformation mechanisms of sphalerite are still poorly understood because recrystallization evidence is barely visible under an optical microscope and may reflect complex and frequently multistage mechanisms. Furthermore, sphalerite may host up to a few thousands of parts per million of critical metals such as gallium (Ga), germanium (Ge), and indium (In). Metamorphic conditions and dynamic recrystallization may have induced local or total redistribution of these elements. Modern techniques such as electron backscattered diffraction analyses (EBSD) and laser-induced breakdown spectroscopy (LIBS) applied on sphalerite allow for the examination of grain boundaries, crystal-plastic deformation, and internal chemical diffusion, which classically reflect active deformation mechanisms. In this study, a microstructural and in situ chemical comparison between four sphalerite types (types 1, 2, 3, and 4) has been made for the first time. The four sphalerite types present different deformation imprints, although they are hosted in a similar geological setting: the Pyrenean Axial Zone and the Montagne Noire Variscan massifs (France). Based on EBSD and LIBS mapping, we describe two regional sphalerite growth stages composed of dark red crystals with polygonal shape (type 1, Bentaillou-Liat deposit) and light- to dark-brown euhedral crystals (type 3, Saint Salvy deposit). New investigation at microscale on sphalerite grains from the Saint-Salvy deposit shows late Cu-Ge-Ga enrichment not only in specific sector zonings but also along grain boundaries, growing crystal edges, and in low-angle misorientations or twin boundaries. Following a deformation event that probably occurred during the Pyrenean-Alpine orogeny, these two sphalerite mineralizations have both endured plastic deformation in a dislocation creep regime and dynamically recovered by subgrain rotation (SGR) mechanism. Two mechanisms of Cu-Ga-Ge spatial redistribution are observed and are key processes for the crystallization of Cu-Ga-Ge-rich minerals in sphalerite veins. The first mechanism involved the in situ redistribution of Cu-Ga-Ge contents from a pre-existing concentration in the sphalerite lattice (type 3, Arre deposit), creating Ge-sulfides (briartite), probably during Pyrenean-Alpine orogeny. Formation of this type of Ge-mineral may be related to solid-state diffusion processes. The second mechanism is associated with the circulation of a Cu-Ga-Ge-rich fluid in surrounding rocks. In the pre-existing polygonal sphalerite from Late-Variscan veins (type 2, Pale Bidau deposit), millimeter-size bands of small (<50 μm), recrystallized sphalerite grains are locally observed. Those domains contain inclusions of Cu (chalcopyrite) and Ga and Ge minerals (brunogeierite, carboirite). Fluid-induced diffusion in the polygonal sphalerite aggregates may occur with superimposed dynamic recrystallization, such as the Late-Variscan veins (type 2, Pale Bidau-type). During post-Variscan time, this fluid enriched in Cu-Ga-Ge largely circulated in the upper-crust of this Variscan terrane. This study highlights the key importance of coupled textural (EBSD) and in situ chemical analyses (LIBS) of diverse sphalerite types at a regional scale to indirectly unravel the origin of vein mineralization, and their related critical metal distribution. [ABSTRACT FROM AUTHOR]

Currently, one of the topical directions in the field of production and application of graphene-like nanostructures is the use of renewable natural raw materials, which have unlimited resources for an economically efficient large-scale yield of a product with environmental safety. In this regard, we present the production of graphene oxide (GO) from a renewable natural raw material of plant biomass, birch activated carbon (BAC), and a comparison of the obtained physicochemical, mechanical, and electrical properties of birch activated carbon–graphene oxide (BAC–GO) and graphite–graphene oxide (G–GO) synthesized from the initial materials, BAC and graphite (G). Results obtained from this study confirm the successful oxidation of BAC, which correlates well with the physical–chemical dates of the G–GO and BAC–GO samples. Change in data after the oxidation of graphite and BAC was facilitated by the structure of the starting materials and, presumably, the location and content of functional oxygen-containing groups in the G–GO and BAC–GO chains. Based on the results, the application of a cost-effective, eco-friendly colloidal solution of nanodispersed BAC–GO from a plant biomass-based high-quality resource for producing large-scale nanostructured graphene is validated which has potential applicability in nanoelectronics, medicine, and other fields. [ABSTRACT FROM AUTHOR]

Rock metamorphism releases substantial CO2 over geologic timescales (>1 My), potentially driving long-term planetary climate trends. The nature of carbonate sediments and crustal thermal regimes exert a strong control on the efficiency of metamorphic CO2 release; thus, it is likely that metamorphic CO2 degassing has not been constant throughout time. The Proterozoic Earth was characterized by a high proportion of dolomite-bearing mixed carbonate-silicate rocks and hotter crustal regimes, both of which would be expected to enhance metamorphic decarbonation. Thermodynamic phase equilibria modeling predicts that the metamorphic carbon flux was likely ~1.7 times greater in the Mesoproterozoic Era compared to the modern Earth. Analytical and numerical approaches (the carbon cycle model PreCOSCIOUS) are used to estimate the impact this would have on Proterozoic carbon cycling and global atmospheric compositions. This enhanced metamorphic CO2 release alone could increase pCO2 by a factor of four or more when compared to modern degassing rates, contributing to a stronger greenhouse effect and warmer global temperatures during the expansion of life on the early Earth. [ABSTRACT FROM AUTHOR]

Part VIII of the evolutionary system of mineralogy focuses on 1220 metamorphic mineral species, which correspond to 755 root mineral kinds associated with varied metamorphic rock types, most of which likely formed prior to the Phanerozoic Eon. A catalog of the mineral modes of 2785 metamorphic rocks from around the world reveals that 94 mineral kinds often occur as major phases. Of these common metamorphic minerals, 66 are silicates, 14 are oxides or hydroxides, 8 are carbonates or phosphates, 4 are sulfides, and 2 are polymorphs of carbon. Collectively, these 94 minerals incorporate 23 different essential chemical elements. Patterns of coexistence among these 94 minerals, as revealed by network analysis and Louvain community detection, point to six major communities of metamorphic phases, three of which correspond to different pressure-temperature (P-T) regimes of metamorphosed siliceous igneous and sedimentary rocks, while three represent thermally altered carbonate and calc-silicate lithologies. Metamorphic rocks display characteristics of an evolving chemical system, with significant increases in mineral diversity and chemical complexity through billions of years of Earth history. Earth's first metamorphic minerals formed in thermally altered xenoliths and contact zones (hornfels and sanidinite facies) associated with early Hadean igneous activity (>4.5 Ga). The appearance of new Hadean lithologies, including clay-rich sediments, arkosic sandstones, and carbonates, provided additional protoliths for thermal metamorphism prior to 4.0 Ga. Orogenesis and erosion exposed extensive regional metamorphic terrains, with lithologies corresponding to the Barrovian sequence of index mineral metamorphic zones appearing by the Mesoarchean Era (>2.8 Ga). More recently, rapid subduction and rebound of crustal wedges, coupled with a shallowing geothermal gradient, has produced distinctive suites of blueschist, eclogite, and ultrahigh-pressure metamorphic suites (<1.0 Ga). The evolution of metamorphic minerals thus exemplifies changes in physical and chemical processes in Earth's crust and upper mantle. [ABSTRACT FROM AUTHOR]

This review paper addresses the recent and past advancements in investigating the anisotropic behavior of foliated metamorphic rock strength subjected to uniaxial or triaxial compression loading, direct or indirect tensile loading, and shear loading. The experimental findings published in the literature show that the strength of foliated rocks is significantly affected by varying the angle β between weak planes and major principal stress. A higher value of strength is reported at β = 0° or 90°; whereas a low strength value is noted at intermediate angles between β = 0° and 90°. The strength anisotropy depends on the degree of schistosity or gneissosity, which is the result of the preferred arrangement of phyllosilicate minerals under differential pressures. The failure of foliated rocks starts at the microscopic scale because of the dislocation slip, plastic kinking, and fracturing in phyllosilicate minerals such as mica. Tensile wing cracks at the tip of the mica propagate parallel to the deviatoric stress. Then, intergranular and intragranular shear-tensile cracks coalesce and lead to rock failure. The weak planes' orientation controls the mode of failure such that tensile splitting, slip failure, and shear failure across foliations are observed at β = 0°–30°, β = 30°–60°, β = 60°–90° respectively. In the past, several attempts have been made to formulate failure criteria to estimate rock strength using different mathematical and empirical approaches. Over the years, the trend has shifted towards discontinuum modeling to simulate rock failure processes and to solve problems from laboratory to upscaled levels. [ABSTRACT FROM AUTHOR]

[Display omitted] • RSTEs of Precambrian rocks are crucial for understanding ocean–atmosphere history. • The Mesoproterozoic period seems dynamic with rapid cycles of seawater level change. • Questions persist about biotic and abiotic processes involved in Fe cycling. • This study demonstrates variability of δ56Fe in rocks subjected to high-temperature. • Metamorphic overprinting complicates direct reconstruction of seawater redox state. The concentration of redox sensitive trace metals (RSTEs) and their isotopic composition preserved in Precambrian marine sediments, are critical for the reconstruction of ocean–atmosphere oxygenation history. Particularly, the concentration of Fe, its redox speciation, and isotopic distribution, have gained widespread use for inferring the biogeochemical processes that controlled Fe cycling in Precambrian oceans linked to the reconstruction of Earth surface redox budget. However, questions remain about the biotic and abiotic processes involved in Fe cycling in these ancient oceans, including the impact of post-depositional alterative processes on the reliability of the Fe redox proxy. Here we present a multi-proxy mineralogical and geochemical study of the ∼1.1 Ga Atar and El Mreiti strata of the Taoudeni Basin in Mauritania, to better constrain pathways involved in Fe cycling, linked to Fe mineralogy, redox speciation, isotopic ratios during this time and metamorphism. We compare unmetamorphosed sedimentary deposits with facies metamorphosed by dolerite sill intrusion. The results reveal the occurrence of diagenetic Fe minerals in the basal unmetamorphosed samples associated with light δ56Fe signatures, reflecting dominant anoxic conditions that promoted microbial dissimilatory Fe reduction. Notably, δ56Fe composition of these rocks reveal several fluctuations in evolving seawater redox state from oxic to anoxic/sulfidic conditions associated with changes in sea level stand and periods of full bottom water oxygenation and redox stratification. Overall, Ce anomalies suggest a general up sequence increase in seawater oxygen content. Metamorphosed rocks display heterogeneous δ56Fe distribution, consisting of light and heavy signatures associated with secondary Fe-bearing minerals produced by metamorphic and metasomatic overprinting of carbonated rocks by hot circulating fluids. The results thus indicate metamorphic overprinting of primary seawater δ56Fe promoted by increased mobility of reactive Fe during post-depositional metamorphic transformation. They show that post-depositional metamorphic/metasomatic overprinting complicates direct reconstruction of seawater biogeochemical Fe cycling and redox state using δ56Fe systematics. [ABSTRACT FROM AUTHOR]

Structural, metamorphic, and geochronological study of the Delhi Supergroup rocks near the western margin of the Aravalli-Delhi Mobile Belt (ADMB) elucidate the Neoproterozoic tectonics of the South Delhi Fold Belt (SDFB) and its implication for the evolution of the Greater Indian Landmass (GIL). In this study, we establish three deformational events in the SDFB. While the D1 event produced isoclinal, reclined F1 folds synchronous with prograde amphibolite facies metamorphism (~5 kbar, 650°C), D2 formed outcrop to map-scale upright F2 folds. D3 comprised ‘partitioned transpression’ along two subvertical shear zones. Oblique dextral-reverse movement (D3a) along one shear zone formed an outcrop-scale positive flower structure, while sinistral-reverse movement along the other rotated and steepened the hinges of the F2 folds (D3b). U-Pb zircon dating of post-tectonic (post-D2, but pre-D3) and syntectonic (syn-D3) granite intrusives suggests >844 Ma age for D2 and ca. 820 Ma for D3. An older magmatic event (ca. 990 Ma) is recorded from sheared pink granites (pre- to syn-D1 intrusion). We suggest that the amalgamation of the ADMB and the Marwar Craton was initiated by the Grenville-age (ca. 1000 Ma) subduction-collision, while the younger events (ca. 844 Ma and 820 Ma) mark the final stitching of the ADMB – Marwar Craton along the Phulad-Ranakpur palaeo-suture zone to form the GIL. The distribution of early (ca. 1000–900 Ma) and late (ca. 800–700 Ma) Tonian magmatic and metamorphic ages in the SDFB suggest that the final growth of the GIL took place through multiple stages of oblique collision in a pulsating orogenesis through the Early Neoproterozoic. [ABSTRACT FROM AUTHOR]

Ultrahigh‐temperature (UHT; >900°C) metamorphism drives crustal differentiation and is widely recognized in the rock record, but its geodynamic causes are debated. Previous work on granulite‐facies metapelite xenoliths from San Luis Potosí, Mexico suggests the lower crust experienced a protracted UHT metamorphic event that coincided with the onset of regional extension. To determine the duration, conditions, and heat sources of UHT metamorphism recorded by these xenoliths, this study characterizes the major‐element, trace‐element, and U‐Pb isotopic systematics of quartz, rutile, feldspar, garnet, and zircon by in situ electron microprobe (EPMA) and laser‐ablation inductively coupled‐plasma mass spectrometry (LA‐ICP‐MS), and augments these data with detailed petrography, thermobarometry, phase equilibria modeling, and diffusion modeling. Thermobarometry and phase equilibria modeling suggest peak metamorphic conditions exceeded 0.7 GPa and 900°C. Zircon petrochronology confirms >15 Myr of UHT conditions since its onset at ∼30 Ma. A small population of zircon record elevated temperatures following transition from backarc compression to extension during the waning stages of orogenesis (60–37 Ma). Garnet preserves trace‐element zoning and mineral inclusions consistent with suprasolidus garnet growth and subsequent compositional modification by intracrystalline rare‐earth element diffusion during protracted heating, with diffusion chronometry timescales in agreement with zircon data, followed by fluid‐driven remobilization of trace elements along now‐healed fractures within ∼1 Myr of eruption. In sum, these data are most compatible with lithospheric mantle attenuation or removal as the dominant heat transport mechanism driving synextensional UHT metamorphism and crustal melting, which has bearing on models for crustal differentiation and formation of modern and ancient granulite terranes globally. Plain Language Summary: The production of melt in the deep crust has important implications for how continents are physically and chemically modified, which in turn controls the distribution of critical mineral resources and the expression of plate tectonics at Earth's surface. One setting where significant partial melting can occur is in a high‐temperature granulite terrane, such as the lower crust beneath the Basin and Range province of southwestern North America. The Basin and Range province is a region where the continent is actively experiencing tectonic extension and, in several places, has been interpreted to have lower crust that was (or is currently) heated to above 900°C. To understand the causality between continental extension in North America and these extreme metamorphic conditions, we study exotic rock fragments of the deep crust beneath San Luis Potosí, Mexico that were brought up by a geologically recent volcanic eruption. These rocks record chemical information that tracks the temperature of the geologically modern lower crust prior to eruption and the duration of extreme temperatures and melting in this crust over the last 60 million years. Using this chemical information, we further our understanding of how tectonic extension is actively driving deep crustal melting beneath southwestern North America. Key Points: Lower crustal metapelite xenoliths from San Luis Potosi, Mexico record ultrahigh (>900°C) temperature (UHT) metamorphismZircon petrochronology suggests protracted (>15 Myr) UHT conditions since the onset of regional extensionGarnet preserves complex trace‐element zoning despite extreme temperatures; garnet diffusion chronometry timescales agree with zircon data [ABSTRACT FROM AUTHOR]

The reconstruction of the Early Paleozoic collision metamorphism of the Khan-Khukhei Block (Northern Mongolia) based on 3D modeling of thermal state of the crust and isotope dating is presented. The age of garnet–biotite schist from a metamorphic complex of the Khan-Khukhei Block of 517.4 ± 7.4 Ma is determined for the first time. 3D modeling was conducted to compare this age of metamorphism with the available age determinations of (post-) collision granite formation in the range of 513‒505 Ma. The model considers radiogenic heating at an elevated heat production of rocks of the thickened crust of the Khan-Khukhei block as the cause of the migmatization and granitoid melts formation. 3D modeling was conducted for the first time for thermal-dome type of metamorphism. The results provide a realistic conception of magma generation in typical collision settings in the absence of mantle magmatic heat sources. The time interval between metamorphism and the stage of anatectic magma formation is 5–12 Ma. [ABSTRACT FROM AUTHOR]

Canada's northern cratons record a complex poly‐metamorphic evolution in response to multiple orogenic events. The Snowbird Tectonic Zone (STZ), the principal suture between the Archean Rae and Hearne cratons, is a highly debated structure; it is argued to have accommodated modern‐style accretion in either the Neoarchean (2.6–2.5 Ga) or Palaeoproterozoic (ca. 1.9 Ga). To resolve this controversy, we use Lu–Hf garnet geochronology to date an eclogite collected from the East Athabasca mylonite triangle of the STZ. Garnet shows prograde trace‐element zoning, and we obtained an age of 1914.5 ± 3.4 Ma. The age is interpreted to date the timing of collision related to deep burial of crust along the STZ. This strongly supports Palaeoproterozoic terminal collision between the Rae and Hearne cratons, and that to constrain high‐pressure metamorphism during supercontinent assembly, dating eclogite itself is key. [ABSTRACT FROM AUTHOR]

The conditions of pyrite (Py) stability inform the extent of S mobility during prograde metamorphism, the formation of orogenic Au deposits, and the S cycle in subduction zones. The variables that affect Py stability and chalcophile element mobility are investigated in the Pacific Rim Terrane of Vancouver Island, Canada, where sulfide-bearing carbonaceous sediments have been metamorphosed from 230 to 600 °C and 4 kbar by mid-ocean ridge subduction in a hot fore arc setting during the Eocene. The petrographic evidence in the rocks shows Py can coexist with pyrrhotite (Po) over a wide temperature window to >550 °C as preserved in porphyroblasts of andalusite, staurolite, and garnet. Conversely, equilibrium phase diagrams constructed for the rock compositions conflict with observations and suggest the breakdown of primary Py occurs over a narrow temperature range below 400 °C. The phase diagrams are consistent with the coexistence of Py and Po up to lower amphibolite facies only if S locally comprises a much greater proportion involved in a reaction than that of the overall bulk-rock composition used in the calculations. While the chemistry of the bulk rocks and Po included in porphyroblasts show mobilization of H2O and S with increasing metamorphic grade of the forearc, this process appears unrelated to the distribution of chalcophile elements or Au deposits found in the Pacific Rim Terrane. [ABSTRACT FROM AUTHOR]

The present paper describes some field characteristics of deformation in a high-strain and high temperature zone in migmatitic rocks, with several kilometers wide occurring in Hamedan and Toyserkan regions, NW of the Sanandaj- Sirjan Zone. A number of workers believe deformation and metamorphism are closely related. We tried to establish relationships between deformation evidence and rheological contrasts in different parts of migmatites during the migmatization process. In recent years, several studies have been carried out regarding the deformation and tectonic events of the various rocks of Hamedan region. However, this work is the first attempt to establish the relationship between deformation structure and partial melting in the migmatitic rocks of the study region. The obtained data can be used to interpret probable relationship between deformation and metamorphism and to determine the role of rheology of the various rocks in the region. Regional Geology The Sanandaj-Sirjan Zone (SSZ) comprises a metamorphic belt of low- to high-grade regional and contact metamorphic rocks intruded by mafic, intermediate and felsic plutonic bodies. Plutonic rocks of the Alvand complex in the Hamedan region, belonging to middle Jurassic (Shahbazi et al., 2010; Mahmoudi et al., 2011; Chiu et al., 2013), consisting of gabbro-diorite-tonalite association, granite-granodiorite porphyroid, and hololeucocratic granitoids (Sepahi et al., 2019). Major metamorphic rocks events in the SSZ occurred 160-170 Ma (e.g., Sepahi et al., 2019). The metamorphic rocks of the area with different composition and metamorphic grade, are mainly pelites with small bodies of psammites, quartzites, meta-basites, calc-pelites and calc-silicates. During partial melting, some minerals such as cordierite, aluminosilicate (andalusite, sillimanite) and garnet porphyroblasts, in spite of floated, partly remained stable and when the partial melt reached its critical moving threshold, they were re-distributed in the viscous mush (Sepahi et al., 2009). Analytical methods Description of rock units, structural analyses, accurate measurements of parameters (i.e. lineation, boudins, folds, veins) were carried out during field observation. 44 thin sections parallel to lineation and perpendicular to foliation were prepared at the section preparation laboratory of Bu-Ali Sina University, and then their petrography and microstructures were examined and analyzed. The samples are taken from metatexite dominated migmatites as well as diatexite. Mineral abbreviations are taken from Whitney and Evans (2010). Petrography Following pelites the most abundant rocks of the area, slate, phyllite, pelitic schist/migmatite and hornfels are common rocks of the region under study. The migmatite rocks evolved from the hornfelses (metatexite) and schists (diatexite) of the region. The mesosome of schistic migmatites with similar mineralogy with that of the schists, crosscut by abundant granitic pegmatites, aplites, as well as quartz veins. This zone is associated with partial melting and development of granitic leucosomes in migmatites. Plagioclase-bearing leucosomes are predominant, but some contain K-feldspar as well. Melanosomes are less developed and resemble the mesosomes in their mineralogy and texture, except for greater amounts of mafic minerals (i.e. biotite), and smaller amounts of felsic minerals. Partial melting fronts were initiated around various porphyroblasts, especially Al2SiO5 minerals and cordierite, and migrated to other parts of the rocks. During diatexis, garnet and aluminosilicate (andalusite, sillimanite) porphyroblasts remained partly stable but floated and were re-distributed in the viscous mush when the partial melt reached its critical moving threshold. Discussion and Conclusion The essential processes of migmatites formation, are partial melting, metamorphic differentiation and injection of granitic magma. Leucosome layers appear following the peak of metamorphism and partial melting process. In the course of anatexis, with increasing melt fraction, migmatite strength progressively decreases. The boudinage of high temperature metamorphic rocks is significantly controlled by the evolving rheological contrasts between the leucosome (melt) and mesosome of migmatites. The deformation observed in migmatites, occurred on a large scale in the form of folded leucosome and Boudinage, and on a microscale in the form of intracrystalline (undulose extinction, deformation twinning) and intercrystalline deformation (grain boundary migration, protrusion...). Therefore, the folded and boudinated leucosome represent the activity of tectonic forces in the conditions of the peak transformation of the region. The simultaneous adaptation of tectonic processes with the peak of metamorphism created synmigmatites and probably occurred in the catazone segment. While the performance of tectonic processes after cooling and creating post-tectonic fabrics, possibly happened in the mesozone to epizone. Syn to post-tectonic structures have recorded the relationship between the different phases of the involved melt and deformation in the solid state in the area. Synmigmatites can be seen in different parts of Hamedan, such as Simin, Toyserkan, Cheshme Ghasaban and Morad-Beik valley. Deformation occurred following the melt crystallization in the investigated migmatites. According to the structures of boudin, folds and veins, which played an important role in development of dynamic state of migmatites, the rheological evolution of Hamedan migmatites (Simin and Toyserkan regions) can be divided into three stages: (1) deformation during melting, (2) solid state deformation immediately after crystallization, and (3) subsequent solid-state deformation.

This article focuses on the issues related to the primary nature and metamorphism of gneisses from the Larba block of the Dzhugdzhur–Stanovoy fold area, which are based on the study of the mineralogical composition of supracrustal rocks. The PT-parameters for the highest temperature and pressure metamorphic transformations of rocks of the Larba block are estimated as P = 6.5–8.5 kbar and T > 800°C. Relatively low-temperature garnet–biotite and garnet–biotite–chlorite mineral parageneses were formed at the regressive stage of metamorphism at ~4–6 kbar and temperatures up to 500–600°C. Wide variations in paragneiss compositions indicate that the studied gneisses were derived from protoliths of different composition. Overall, Larba metasedimentary rocks had weakly and moderately weathered source areas. Most of the compositions of paragneisses are located in the field of chlorite–montmorillonite, montmorillonite–kaolinite–hydromica, and chlorite clays formed from the mafic protolith. The low alkalinity in combination with a high MgO content indicates the presence of rock erosion products with a significant admixture of basic volcanic material in the detrital material. Migmatization of the rocks is the most significant factor that distorts the reconstruction of the original rock composition. [ABSTRACT FROM AUTHOR]

New U–Th–Pb chemical data from both electron probe microanalysis and U–Pb laser ablation-inductively coupled plasma mass spectrometry on monazite inclusions in giant andalusite porphyroblasts indicate that the lowermost subdivision of the Rocky Cape Group in northwest Tasmania underwent metamorphism at ca 1100 Ma. The Proterozoic Rocky Cape Group is a ∼10 km-thick succession of quartz arenite, siltstone and pelite. These sediments were deposited between ca 1450 and ca 1010 Ma. Metamorphism within the Rocky Cape Group ranges from the prehnite–pumpellyite to upper greenschist facies, locally reaching garnet grade. In the lowermost formation of the Rocky Cape Group, andalusite-bearing mineral assemblages in the Pedder River Siltstone formed prior to or synchronously with monazite development. The andalusite-bearing mineral assemblage indicates relatively low-pressure conditions of <200 MPa, consistent with the stratigraphic thickness of the Rocky Cape Group (∼10 km). However, the presence of the intermediate-temperature biotite–andalusite mineral assemblages (500 °C) in the study area suggests the contribution of additional heat sources. Garnet porphyroblasts were observed ∼2 km away. Similar-age medium-grade metamorphism and magmatism at about 1100 Ma have been observed regionally in the South Tasman Rise and East Tasman Plateau, and in areas that are thought to have been contiguous with northwestern Tasmania such as Dronning Maud Land, central Arizona (Yavapai–Mazatzal) and Belt–Purcell Basin in the southwestern and northwestern Laurentian crustal sequences. The pressure and temperature relationships, mineral associations and regional data suggest additional heat flow was present through the lower part of the Rocky Cape Group. The higher geothermal gradient could be attributed to burial during basin development and deposition of the upper Rocky Cape Group or associated magmatism on the margin of Laurentia during assembly of Rodinia. Low-pressure, intermediate-temperature mineral associations occur in the Rocky Cape Group. Heat sources are unrelated to nearby Devonian granite. Robust ages reveal the first discovery of 1100 Ma metamorphism in Tasmania. These provide data for a missing link in Rodinian paleogeographic reconstructions. [ABSTRACT FROM AUTHOR]

The Eastern Taurides, which form the imbrication and nappe zone in the northernmost part of the Arabian platform, are located within the Southeastern Anatolian Orogenic Belt. In the present study, spectral enhancement methods such as band ratioing, minimum noise fraction (MNF), relative band depth (RBD), and supervised classification were applied to ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) images of metamorphic massifs, ophiolites, and sedimentary rocks outcropping in the western part of the Eastern Taurides (Göksun, Afşin, and Ekinözü regions). With these methods, the aim was to distinguish geological units from each other accurately. In the study area, arid climatic conditions with relatively poor vegetation, allowing for precise visual interpretations, play a significant role. Vegetation and water bodies were also masked before these procedures. In the Göksun, Afşin, and Ekinözü regions, metamorphic rocks of phyllite, schist, and gneiss types, which underwent metamorphism during the Upper Cretaceous and Eocene periods, are observed. The geologically dominant minerals in these rocks include silica, mica (muscovite, phengite, biotite), chlorite (clinochlore, chamosite), kaolinite, and carbonates (calcite, dolomite). These rocks are accompanied by ophiolitic, volcanic/volcano-sedimentary, and plutonic igneous rocks. Due to geological events during the closure of the Neotethys Ocean and continental collision in the area, it became evident that the lithological diversity from various rock groups was reflected in the ASTER images, in addition to field observations. Image processing analyses applied to the ASTER sensor images, rich in short-wave infrared (SWIR) and thermal infrared (TIR) bands on the Terra platform, revealed distributions of clay, sulfate, carbonate, iron oxide, and silica minerals. The highest geological differentiation potential was observed through ASTER 643 (RGB) and ASTER 13,12,10 (RGB) false-color composites, as well as ASTER 456 (RGB) minimum noise fraction (MNF) analyses and, especially, relative band depth processes. Relative band depth processes were employed to identify epidote-chlorite-amphibole, calcite-chlorite-amphibole, alunite-kaolinitepyrophyllite, muscovite, and silica minerals. The application of these processes revealed lithologies that strongly feature these minerals. Specifically, the goal was to differentiate rock units containing kaolinite, muscovite, phengite, chlorite, and epidote minerals belonging to AlOH and FeOH groups and elucidate their compositions. Moreover, rocks containing primarily quartz and feldspar were distinguished using ASTER TIR bands. The obtained data revealed that mineralogical and corresponding lithological spatial distributions, as depicted by ASTER images, could play a crucial role in geological mapping, particularly in regions where mapping is challenging due to geographical conditions. [ABSTRACT FROM AUTHOR]

Mineral reactions were studied in metamorphic rocks from the Meyeri tectonic zone, and the P–T path of the development of this structure was calculated. According to the P–T path, the Proterozoic granulite complex of the Svecofennian Belt was thrust onto low-temperature rocks of the Archean Karelian Craton. Relict staurolite and other minerals preserved as inclusions in the garnet porphyroblasts made it possible to identify the pre-peak stage of metamorphism with P–T parameters no higher than the low-temperature amphibolite facies of moderate and low pressure. The peak metamorphic conditions of the tectonic zone are estimated at T > 700°C and P ~ 7 kbar using the composition of relict minerals, while the temperature on the prograde trend of metamorphism was 500–600°C at a pressure of about 5 kbar. The post-peak stage began with a distinct decompressional P–T path at the aforementioned high temperatures, with a change from granulite hypersthene-containing assemblages to lower-temperature hydrous ones. The subsequent metamorphic retrogression was characterized by the development of numerous hydrous minerals as a result of the activation of fluids in the shear zone. The P–T path of the tectonic zone is clockwise and reflects the exhumation of the Svecofennian granulite complex during the orogenic events. [ABSTRACT FROM AUTHOR]

The redox state of chromium ores of the main industrially significant types, developed in ultramafic rocks of the Rai-Iz–Voykar complex of the Polar Urals, was studied. The chromitites occurring in various geological settings—dunite–harzburgite complex and large dunite bodies metamorphosed to different degrees—have been investigated. For the first time, oxygen fugacity and temperature of the formation of chromium ores, based on olivine–spinel equilibrium, were studied in more than representative samples from the Rai-Iz and Voikar–Synya massifs. The Fe/(Fe + Mg) of minerals increases linearly from chromitites to their host ultramafic rocks at each of the studied objects. The temperature of olivine–spinel equilibrium in chromitites varies within 550–800°С. The oxygen fugacity in aluminous chromitites averages FMQ +0.5–1.5 log units; in medium chromium, FMQ +1.5–2.5 log units; in high-chromium ones, more than +2.5 log units relative to the FMQ buffer. The oxygen fugacity in densely disseminated chromitites is 0.5–1 log units higher than in poorly disseminated and rarely disseminated ones. The T–fO2 values correspond to the crustal conditions and are close to those established in the metaultramafic rocks of the studied massifs. The data obtained may indicate that the concentration of the ore component and the formation of chromium ore deposits occur not only in mantle or lower crustal conditions, characterized by fO2 values close to the FMQ buffer, but also as a result of ultramafic crustal metamorphism occurring in an oxidizing environment. [ABSTRACT FROM AUTHOR]

Add Zr to A17SiO. 3Mg alloy containing 0. 3% Er, characterize the microstructure of the sample using Optical Microscopy (OM) and Scanning Electron Microscopy (SEM), analyze the phase composition using high resolution X Ray Diffraction(XRD), and test its mechanical properties. Study the effect of different contents of Zr on the microstructure morphology and mechanical properties of the alloy. The results showed that after adding Zr element, Zr and Er formed second phase particles Alg Er and Ab Zr, which played a dual nucleation and refinement role in the solidification process of aluminum liquid, significantly refining a Al. The branching of Al and eutectic Si improves the mechanical properties of the alloy» But if Zr is added too much, it will form too many intermetallic compounds with Er inside the alloy, weaken the modification effect, and cause a decrease in tensile strength and elongation. The best effect is achieved when the Zr content is 0. 2 %, with a tensile strength of 182 MPa and an elongation of 6. 4%, which is 16. 7 % and 33. 3 % higher than the alloy without the addition of Zr element in terms of tensile strength and elongation, respectively. [ABSTRACT FROM AUTHOR]

Late Cretaceous metamorphic events are known in Crete and the Cyclades from klippen above the External Hellenides. This work extends their occurrence to the North Aegean area within the tectonic units of the Internal Hellenides. New 40Ar/39Ar white mica ages from garnet-bearing micaschists of the Upper Metamorphic Unit of Skyros Island, cropping out in the Skyrian Olympus Mountain, document a Late Cretaceous tectono-metamorphic evolution. Several mica generations have been distinguished using electron probe microanalyses and were dated using the 40Ar/39Ar method: a relict mica older than 96 Ma, followed by a foliation-forming mica of about 88–84 Ma and alteration phases ≤ 68 Ma were recognized. This Cretaceous tectono-metamorphic evolution falls between the closure of the internal Axios/Vardar oceanic basin in the Late Jurassic–Early Cretaceous, and the closure of the external Pindos–Cyclades oceanic basin in the Early Cenozoic. The position of the Upper Metamorphic Unit of Skyros was probably within the evolving Hellenic volcanic/magmatic arc during the continuous subduction of the African plate beneath the European plate. The present tectonic position of the units bearing the Late Cretaceous metamorphic event is the result of the Cenozoic tectonic emplacement onto the more external units across the Hellenides from the Pelagonian to the Pindos–Cyclades domain. [ABSTRACT FROM AUTHOR]

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Evidence is presented that the metaconglomerate-hosted Jacobina gold deposits in Brazil represent paleoplacers that became partly remobilized during later metamorphic overprint analogous to Witwatersrand-type deposits elsewhere, notably in South Africa. This includes strong lithological and sedimentological control on the gold, presence of detrital minerals with gold inclusions, and detrital gold particles. Detrital, synsedimentary, and post-depositional pyrite types can be differentiated. Whereas the first two types can be linked to gold accumulation, the latter was associated with gold dispersion. Synsedimentary pyrite has the highest Au content, from which elevated Au concentrations in Archean rivers can be inferred. The nature and extent of post-depositional alteration, mainly in the course of the Paleoproterozoic Orogeny, distinguishes the Jacobina deposits from other Witwatersrand-type gold deposits. Phase equilibria and Zr-in-rutile thermometry indicate peak metamorphic temperatures of ca. 600 °C. Both Mg-chlorite and Fe-chlorite formed in disequilibrium at approximately 280–340 °C during retrograde metamorphism. An igneous signature in the chemistry of some of the tourmaline and the remobilization of gold associated with Fe-oxides, near intrusive rocks, point at a local magmatic influence on the post-depositional mineralization stage. Whether magmatic hydrothermal fluids added Au to the system at that stage remains to be determined. Remobilization during regional metamorphism was insufficient to form substantial ore bodies but led to purification of the initially detrital gold particles that now contain relatively little Ag and Cu and lack Hg. [ABSTRACT FROM AUTHOR]

Carbonate-silicate rocks of unclear origin have been observed in granulites of the Porya Guba of the Lapland-Kolvitsa Belt within the Fennoscandinavian Shield. The present work aims to reconstruct possible protoliths and conditions of metamorphic transformation of these rocks based on oxygen and carbon isotopic ratios combined with phase equilibria modeling. Isotope analysis and lithochemical reconstructions suggest that carbonate-silicate rocks of the Porya Guba represent metamorphosed sediments (possibly marls) with the isotopic composition corresponding to the Precambrian diagenetically transformed carbonates (δ18O ≈ 17.9 ‰, SMOW and δ13C ≈ –3.4 ‰, PDB). The chemical composition varies depending on the balance among the carbonate, clay, and clastic components. Significant changes of the isotopic composition during metamorphism are caused by decomposition reactions of primary carbonates (dolomite, siderite, and ankerite) producing CO2 followed by degassing. These reactions are accompanied by δ18O and δ13C decrease of calcite in isotopic equilibrium with CO2 down to 15 ‰ (SMOW) and –6 ‰ (PDB), respectively. The isotopic composition is buffered by local reactions within individual rock varieties, thus excluding any pronounced influence of magmatic and/or metasomatic processes.

Currently, one of the topical directions in the field of production and application of graphene-like nanostructures is the use of renewable natural raw materials, which have unlimited resources for an economically efficient large-scale yield of a product with environmental safety. In this regard, we present the production of graphene oxide (GO) from a renewable natural raw material of plant biomass, birch activated carbon (BAC), and a comparison of the obtained physicochemical, mechanical, and electrical properties of birch activated carbon–graphene oxide (BAC–GO) and graphite–graphene oxide (G–GO) synthesized from the initial materials, BAC and graphite (G). Results obtained from this study confirm the successful oxidation of BAC, which correlates well with the physical–chemical dates of the G–GO and BAC–GO samples. Change in data after the oxidation of graphite and BAC was facilitated by the structure of the starting materials and, presumably, the location and content of functional oxygen-containing groups in the G–GO and BAC–GO chains. Based on the results, the application of a cost-effective, eco-friendly colloidal solution of nanodispersed BAC–GO from a plant biomass-based high-quality resource for producing large-scale nanostructured graphene is validated which has potential applicability in nanoelectronics, medicine, and other fields.

This review paper addresses the recent and past advancements in investigating the anisotropic behavior of foliated metamorphic rock strength subjected to uniaxial or triaxial compression loading, direct or indirect tensile loading, and shear loading. The experimental findings published in the literature show that the strength of foliated rocks is significantly affected by varying the angle β between weak planes and major principal stress. A higher value of strength is reported at β = 0° or 90°; whereas a low strength value is noted at intermediate angles between β = 0° and 90°. The strength anisotropy depends on the degree of schistosity or gneissosity, which is the result of the preferred arrangement of phyllosilicate minerals under differential pressures. The failure of foliated rocks starts at the microscopic scale because of the dislocation slip, plastic kinking, and fracturing in phyllosilicate minerals such as mica. Tensile wing cracks at the tip of the mica propagate parallel to the deviatoric stress. Then, intergranular and intragranular shear-tensile cracks coalesce and lead to rock failure. The weak planes’ orientation controls the mode of failure such that tensile splitting, slip failure, and shear failure across foliations are observed at β = 0°–30°, β = 30°–60°, β = 60°–90° respectively. In the past, several attempts have been made to formulate failure criteria to estimate rock strength using different mathematical and empirical approaches. Over the years, the trend has shifted towards discontinuum modeling to simulate rock failure processes and to solve problems from laboratory to upscaled levels.

The Wulashan rock group, a set of Early Precambrian high-grade metamorphic rock series with high metamorphic degree of amphibolite facies-granulite facies, has been determined in the Wulashan-Daqingshan Area of central Inner Mongolia. The metamorphic plutons of quartz diorite gneiss and perilla granitic gneiss, intruded into the biotite garnet plagioclase gneiss of the Wulashan rock group, were studied by chronology to divide the protolith formation age and metamorphic age of aluminum-rich gneiss in the Wulashan- Daqingshan Area. The results show as follows. The weighted average ages of perilla granitic gneiss ( TW7 ) and granodiorite gneiss (D1227) are (2 462 ± 13) Ma and and (2 512 ± 24) Ma, respectively. It could be inferred that, the formation age of the protolith of the aluminum-rich gneiss in Wulashan is earlier than 2. 5 Ga, because of the transformation of rock by later tectonic events. Two metamorphic ages of 2. 2 Ga and 1. 9 Ga, respectively, could be confirmed from the quartz diorite gneiss ( TWB6), indicating that the Wulashan- Daqingshan Area has undergone the superposition of early and late Paleoproterozoic tectonic thermal events. Overall it can be concluded that the latest formation age of aluminum-rich gneiss in the Wulashan-Daqingshan area is limited to 2. 5 Ga. [ABSTRACT FROM AUTHOR]

Orthoamphibole, clinoamphibole and magnetite are common minerals in altered rocks associated spatially with Palaeoproterozoic volcanogenic massive sulfide (VMS) deposits in Colorado, USA and metamorphosed to the amphibolite facies. These altered rocks are dominated by the assemblage orthoamphibole (anthophyllite/gedrite)–cordierite–magnetite±gahnite±sulfides. Magnetite also occurs in granitoids, banded iron formations, quartz garnetite, and in metallic mineralisation consisting of semi-massive pyrite, pyrrhotite, chalcopyrite, and sphalerite with subordinate galena, gahnite and magnetite; amphibole also occurs in amphibolite. The precursor to the anthophyllite/gedrite–cordierite assemblages was probably the assemblage quartz–chlorite formed from hydrothermal ore-bearing fluids (~250° to 400°C) associated with the formation of metallic minerals in the massive sulfide deposits. Element–element variation diagrams for amphibole, magnetite and ilmenite based on LA-ICP-MS data and Principal Component Analysis (PCA) for orthoamphiboles and magnetite show a broad range of compositions which are primarily dependent upon the nature of the host rock associated spatially with the deposits. Although discrimination plots of Al/(Zn+Ca) vs Cu/(Si+Ca) and Sn/Ga vs Al/Co for magnetite do not indicate a VMS origin, the concentration of Al+Mn together with Ti+V and Sn vs Ti support a hydrothermal rather than a magmatic origin for magnetite. Principal Component Analyses also show that magnetite and orthoamphibole in metamorphosed altered rocks and sulfide zones have distinctive eigenvalues that allow them to be used as prospective pathfinders for VMS deposits in Colorado. This, in conjunction with the contents of Zn and Al in magnetite, Zn and Pb in amphibole, ilmenite and magnetite, the Cu content of orthoamphibole and ilmenite, and possibly the Ga and Sn concentrations of magnetite constitute effective exploration vectors. [ABSTRACT FROM AUTHOR]

Remarkably well-preserved crustal sections from the Eastern Hellenides offer the chance to evaluate the regional geodynamic evolution of continental crust. Here, we identify and geodynamically interpret eclogite facies metamorphism in the Triassic–Jurassic volcano-sedimentary series of the West Circum Rhodope zone in the eastern Hellenides. Equilibrium phase diagrams and measured mineral compositions were used to inform reconstructions of geodynamic evolution during the early Alpine period. We newly define the existence of the Eohellenic HP belt, consisting of pre-Alpine basement, continental volcano-sedimentary formations, and a Jurassic magmatic arc. We suggest that the Eohellenic HP-Belt was subducted in the late Jurassic to early Cretaceous beneath the European plate margin. Detailed geodynamic reconstructions such as ours provide a robust anchor for future computational models of long-term crustal evolution in the Eastern Hellenides. [ABSTRACT FROM AUTHOR]

The role of S during high-grade metamorphism is a topic that has not garnered much interest in the literature until recently. In this review, the role of S as an active component in high grade hypersaline fluids is reviewed per a series of regional studies involving orthopyroxene-bearing granulite-facies granitoids. These include the Shevaroy Block and Nilgiri Block, southern India; the Bamble Sector, southwest Norway; the Val Strona traverse of the Ivrea-Verbano Zone, northern Italy; and the Lewisian Complex, northwest Scotland. In each these terranes, S-bearing, high-grade, low H2O activity fluids are conjectured to have been present during granulite-facies metamorphism and to have contributed to the dehydration of the rock, the oxidation state of the rock, and trace element mobility, leaving behind pyrite and/or pyrrhotite as traces of its presence. The various mineral equilibria reactions between the various oxidation states of S in these fluids and the oxide and silicate minerals encountered by the fluid are explored and a coherent framework of interdependent chemical reactions are developed, which describe both oxidation of the rock and the formation of pyrite and pyrrhotite during both peak- and post-peak metamorphism. [ABSTRACT FROM AUTHOR]

Measurements of surface heat flux from boreholes of the NIED Hi‐net network of seismometers are used to determine temperature and shear stress on the plate interface beneath northern Honshu. At the maximum depth of thrust‐faulting earthquakes, about 60 km, the temperature is 660 ± 240°C and the average shear stress during slip on the interface is 100 ± 45 MPa. The equivalent quantities from the oceanic setting of the Kermadec trench are 630 ± 140°C and 115 ± 25 MPa. The shear stresses are substantially higher than commonly assumed in models of convergent plate interfaces, but are consistent with measurements made above other convergent plate interfaces where heat flux data are more sparse. They are also consistent with the level of shear stress required to explain measurements of pressure and temperature from high‐pressure‐low‐temperature terrains that experienced metamorphism on subduction interfaces, in particular those from the Cretaceous Sanbagawa belt of SW Japan. Plain Language Summary: The temperatures and stresses under which most of the world's great earthquakes nucleate are poorly known because they take place at depths of tens of kilometers, where conditions cannot be directly observed. Measurements of surface heat flux above plate interfaces provide the strongest indirect constraints, but those measurements are sparse. We use a dense set of heat flux measurements to determine shear stress and temperature on the plate interface of northern Honshu, on which the 2011 Tōhoku earthquake occurred. The shear stress, 100 ± 45 MPa, and temperature, 660 ± 240°C, are significantly higher than previous estimates, but are supported by analysis of heat flux above the Kermadec plate interface—the only location where a comparable density of heat flux measurements has been used to estimate shear stress. Shear stresses of ∼100 MPa can also account for the conditions of temperature and pressure recorded in rocks of the Sanbagawa belt of SW Japan, which are the exhumed remnants of an approximately 90‐million‐year‐old plate interface. This concordance supports arguments that the Sanbagawa, and similar terrains around the world, record physical and chemical conditions relevant to the generation of earthquakes on present‐day plate interfaces. Key Points: Surface heat flux measurements constrain temperature (660 ± 240°C) and shear stress (100 ± 45 MPa) at ∼60 km on the plate interface in N HonshuThese values are supported by estimates from dense heat flux measurements at the Kermadec plate boundary (630 ± 140°C) and (115 ± 25 MPa)Metamorphic temperatures in an exhumed plate interface, the Sanbagawa belt of SW Japan, are also explained by this level of shear stress [ABSTRACT FROM AUTHOR]

In order to decipher the prevalent processes active at depth in orogenic systems, their time sequence and their rates have to be assessed. This is essentially done via absolute dating of accessory and rock-forming metamorphic minerals. The interpretation of dates, now produced in high quantities and low uncertainties, with geochemical and textural information thanks to in situ dating techniques, into ages with a geological meaning, is based on sophisticated multi-disciplinary approaches. The wealth of data produced during the last decades in internal zones of mountain chains today questions some of the seminal concepts in geodynamics as well as in petrochronology. The concept of closure temperature Jäger [1967] but also the notions of metamorphic unit or metamorphic event are now to be considered in the light of campaign-style dating projects, that enable a comprehensive and statistical interpretation of age patterns from the mineral scale to the geodynamic process scale. [ABSTRACT FROM AUTHOR]

This contribution presents a review exploring some aspects and issues surrounding the links between metamorphism and deformation at different scales. I first discuss the quantification methods of thermodynamics and the parameters able to overcome the kinetic barriers for metamorphic reactions. On the basis of some world's type iconic examples I discuss how metamorphism is likely to portray the thermo-mechanical evolution of lithosphere active zones, thus large-scale tectonic processes. Finally, I present the multiple interactions between metamorphism and deformation at rock and outcrop scales. [ABSTRACT FROM AUTHOR]

To study the snow microstructure at various metamorphism times and extract the snow neck area, a constant density (200 kg/m3) snow metamorphism experiment was conducted. The findings show that the neck region is mostly influenced by temperature, sun radiation, snow density and specific humidity, with wind speed having little effect. Additionally, we developed a multiple linear regression equation for the neck area under atmospheric forcing: "S = 288T + 2E + 189ρ + 12,194V − 20,443RH − 42,729". This equation accounts for solar radiation (E), temperature (T), snow density (ρ), specific humidity (RH) and wind speed (V). Notably, the above five factors can account for 84% of the factors affecting the neck area, making it a crucial factor. The relationship between snow hardness and neck area is correlated at 71%, and in later stages of metamorphism, the correlation may increase to 91%. Based on the neck area, the following hardness value prediction is made: "H = 0.002764S + 67.922837". This study documents the growth variations in the neck region of the metamorphic snow cover and elucidates the process by which outside factors impact the microstructure and macroscopic physical characteristics of the snow cover. [ABSTRACT FROM AUTHOR]

Reaction rims contain a wealth of information that can be used to decipher the P-T-t-X history of metamorphic and metasomatic rocks. One of the most important parameters that controls reaction rim growth is the presence of volatiles, which can affect rim thicknesses, phase stabilities and the development of rim microstructures. In this study, reaction rim growth experiments were performed between periclase and quartz at anhydrous to water-saturated conditions at 3–4 kbar and 1100–1300 °C. Controlled minute amounts of water were added through OH-doped periclase, which enabled us to perform experiments at controlled water-undersaturated conditions. At anhydrous conditions, no reaction rim formed at all implying that water acts as a catalyst, and a minimum fluid threshold is needed to initiate metamorphic reactions. At water-undersaturated conditions extremely small variations in water content are sufficient to change reaction rim growth rates by multiple orders of magnitude. This implies that reaction rims have the potential to monitor variations in the amount of water at those grain boundaries that serve as fast pathways for component transport at water-undersaturated conditions during metamorphic and metasomatic reactions in natural systems, allowing them to be used as sensitive "geohygrometers". Additionally, the effect of water on relative layer thicknesses may provide an application for reaction rim microstructures to be used as new physico-chemical gauges that will allow us to discriminate between water-undersaturated and water-saturated conditions during metamorphic events. [ABSTRACT FROM AUTHOR]

Multiple interpretations exist regarding the tectonic evolution model of the Neoarchean North China Craton, requiring a more in-depth study of metamorphic processes. Systematic petrographic observations, mineral chemical analysis, phase equilibrium modeling, and zircon dating were conducted on the basic granulites from Qingyuan in northern Liaoning to elucidate their metamorphic evolution processes and geological significance. The selected samples of mafic granulites were divided into the garnet-bearing domain (19DJ07-GD) and garnet-free domain (19DJ07-NGD), with the garnet-bearing region displaying a banded and inhomogeneous distribution. Both domains exhibit two generations of granulite facies assemblages. In the garnet-bearing domain, the first-generation metamorphic mineral assemblage includes garnet + clinopyroxene + orthopyroxene + hornblende + biotite + plagioclase + quartz. Notably, the first-generation plagioclase (Pl1) exhibits a complex compositional zoning, with anorthite content (xAn) increasing from the core to the mantle and then decreasing towards the rim. Similarly, the titanium component zoning in the first-generation amphibole (Amp1) follows a pattern of increasing from the core to the mantle and then decreasing towards the rim. Based on mineral assemblages and corresponding component zoning, it is inferred that the first-generation granulite facies metamorphic process followed a counterclockwise P-Tpath, involving a pre-peak P-T rise stage and a post-peak P-T drop stage. Phase equilibrium modeling constrains the peak conditions at 0.8~0.9 GPa/900~950 ℃, indicative of high-ultrahigh-temperature (HT-UHT) metamorphism conditions. Zircon dating results yielded a post-peak cooling age of 2498±6.9 Ma (MSWD=0.39). Considering the regional "dome-and-keel" tectonics, the counterclockwise P-T path, and the metamorphic timing of supracrustal rock nearly synchronous with late-stage TTG magmatic pulses, the UHT metamorphism of the supracrustal rocks is believed to be controlled by the unique Archean vertical tectonics/sagduction system. The second-generation metamorphic assemblage is characterized by locally formed coronas or symplectites of garnet + quartz ± clinopyroxene, representing high-pressure (HP) granulite facies metamorphism associated with a Paleoproterozoic orogenic event.

Abstract Measurements of surface heat flux from boreholes of the NIED Hi‐net network of seismometers are used to determine temperature and shear stress on the plate interface beneath northern Honshu. At the maximum depth of thrust‐faulting earthquakes, about 60 km, the temperature is 660 ± 240°C and the average shear stress during slip on the interface is 100 ± 45 MPa. The equivalent quantities from the oceanic setting of the Kermadec trench are 630 ± 140°C and 115 ± 25 MPa. The shear stresses are substantially higher than commonly assumed in models of convergent plate interfaces, but are consistent with measurements made above other convergent plate interfaces where heat flux data are more sparse. They are also consistent with the level of shear stress required to explain measurements of pressure and temperature from high‐pressure‐low‐temperature terrains that experienced metamorphism on subduction interfaces, in particular those from the Cretaceous Sanbagawa belt of SW Japan.

The reasons for the formation of rare minerals and mineral assemblages during metamorphism and metasomatosis are found to be the atypical composition of the protolith, the structural–textural heterogeneity, restricted mass transfer, and high temperatures. This is often observed under shallow conditions (pressure up to 3 kbar) during additional heating of rocks by igneous intrusions. In this paper, these questions are discussed with a series of domestic examples, the processes of mineral formation in which are studied in detail. [ABSTRACT FROM AUTHOR]

Geological, mineralogical, and petrological observations are reported for hornfels-like fine-grained granular mafic rocks in the Early Paleozoic Olkhon collisional orogen (West Baikal area, Russia). The rocks are composed of orthopyroxene, clinopyroxene, amphibole, plagioclase, and ilmenite; some samples also contain olivine, phlogopite, spinel, and titanomagnetite (Opx+Cpx+Amp+Pl+Ilm±Ol±Bt±Spl±Ti-Mag). There are three occurrences of these rocks in the area: a 500 m × 1000 m field in the Shirokaya Valley, another occurrence within the Tazheran Massif (a complex of igneous and metamorphic rocks), and dismembered dikes on the southern margin of the Birkhin gabbro intrusion. The Shirokaya field is located between two 500 Ma intrusions of the Birkhin gabbro; the Tazheran occurrence coexists with syenite, including nepheline syenite, subalkaline gabbro, and marble protrusions; and the dismembered dikes coexist with carbonates and display progressive alteration of dolerite through typical granular varieties. The dikes associated with granite and marble veins mark a part of a large arc-shaped shear zone that traverses the whole intrusive body produced by rotation of a rigid gabbro block during the peak of tectonic deformation at 470–460 Ma. All three occurrences of the hornfels-like rocks lack any evident source of heat that would be responsible for the thermal alteration of the igneous protolith. We hypothesize that the precursor, subvolcanic dolerite, may have undergone autometamorphism maintained by self-generated heat. Mafic magma intruded during high-rate strike–slip faulting, which caused rapid recrystallization of magmatic minerals and produced the observed metamorphic structures. Proceeding from the controversy in the formation mechanisms, with a heat source required for hornfels but lacking from the sampled occurrences of hornfels-like rocks, we suggest identifying the latter as beerbachite, though the term has mostly fallen into disuse. The reason is that the Olkhon rocks we study have a mineralogy, structure, and texture that are perfectly identical to those of beerbachites described in publications from the first half of the 20th century. [ABSTRACT FROM AUTHOR]

Contact metamorphism of carbonate rocks is a complex process, often characterized by chemical and isotopic disequilibrium and dominated by open-system fluid flow. As such, a handful of recent studies have applied the relatively new tool of carbonate clumped isotope thermometry across km-scale contact aureoles to track conditions from low to high grade. Results have been particularly intriguing among low grade carbonates at the extreme outer edge of the metamorphic aureole. We therefore present results of carbonate clumped isotope analysis combined with detailed petrography and sample characterization to explore the onset of metamorphism in the Alta stock contact aureole, Utah. In addition to focusing on a few densely sampled field profiles near the lowest-grade talc isograd, we perform mm-scale microsampling to assess the relationship between heterogeneous reaction features and carbonate clumped isotopes. We find that elevated metamorphic temperatures (~ 275–300 °C) are recorded by matrix dolomite only in samples which underwent corresponding recrystallization and grain size reduction, and that the boundary between recrystallized and un-recrystallized samples is consistently expressed in the field across a ~ 33 m wide zone. At the microscale, clumped isotopes reveal very local equilibration and recrystallization, recording differing prograde and retrograde reaction temperatures within a few millimeters. Carbonate clumped isotope thermometry and traditional stable isotopes are further used to explore heterogeneous fluid compositions and channelized flow in the outer aureole. [ABSTRACT FROM AUTHOR]

Understanding the interplay between bulk composition and metamorphic grade underpins our interpretations of metamorphism in orogenic belts. The focus of this study is the regional garnet–staurolite–kyanite–sillimanite metamorphic sequence of the Whetstone Lake area, southeastern Ontario. In the kyanite and lower sillimanite zones of this area, there is exceptional diversity in metapelitic mineral assemblages that cannot be accounted for by differences in metamorphic grade. We present a data set of petrographic observations, phase proportions, whole-rock geochemical compositions, and mineral compositions, from thirty-two samples that encapsulate the range of assemblages found in these zones. Differences in bulk composition are the primary control on mineral assemblage development. Whole-rock XMg = molar MgO/(MgO + FeO) and |${\textrm{X}}_{\textrm{Fe}^{3+}}=\kern0.5em \textrm{molar}\ 2\times{\textrm{Fe}}_2{\textrm{O}}_3/\left(2\times{\textrm{Fe}}_2{\textrm{O}}_3+\textrm{FeO}\right)$| exert the greatest control on the observed mineral assemblages, whilst variation in MnO, K2O, and Al2O3 have a secondary influence. We use a set of quality factors (Duesterhoeft & Lanari, 2020) to test the ability of thermodynamic models to reproduce the observed mineral assemblages, modal abundances, and mineral compositions in the diverse bulk compositions at Whetstone Lake. Eight samples were selected for phase equilibrium modelling, for which two bulk compositions were calculated for each sample: (1) a whole-rock bulk composition based on an X-ray fluorescence analysis and (2) a carefully considered local bulk composition based on combining mineral proportions with representative mineral compositions, as obtained from a single thin section. Our modelling uses thermodynamic data set 6.2 (Holland & Powell, 2011) and the solution models of White et al. (2014a , 2014b) that incorporate several Fe3+ end members needed to model the natural data. Modelling in both types of bulk composition broadly predicted mineral assemblages that match those observed. In addition, predicted mineral assemblage fields overlap within uncertainty between 620°C and 675°C and between 6.5 and 7.5 kbar, consistent with the limited range of grade represented by the natural rocks. Predicted modal abundances better match those observed when phase diagrams are constructed using local bulk compositions compared to whole-rock bulk compositions. Despite the acceptable agreement between predicted and observed mineral assemblages, consistent discrepancies are found between predicted and observed mineral compositions. These include overestimation of |${\textrm{X}}_{\textrm{Mg}}^{\ast }$| in garnet, staurolite, and cordierite, overestimation of Ti in staurolite and biotite, underestimation of Si in biotite, and overestimation of Al and underestimation of Fe3+, Fe2+, and Mg in muscovite. The Whetstone Lake suite of this study will be useful to test the predictive capability of future thermodynamic models. [ABSTRACT FROM AUTHOR]

Copper–gold porphyry deposits are the world's main source of copper and a significant source of gold. They consist of vein networks and their surrounding alteration zones. Commonly the deposits are centred on narrow intrusions (stocks), but calling these deposits 'porphyries' is unjustified because the name carries little descriptive or genetic value. Extensional veins were formed by hydraulic fracturing of the stocks, at depths where open spaces could not be maintained and where fluid pressure approaches lithostatic pressure. The post-crystallisation timing of the veins is important because it indicates that the host stocks could not have been the direct sources of either metals or ore-forming fluids. In the traditional magmatic model, precursor batholiths, lying at depth, are inferred to be the sources of the Cu and Au in the overlying host stocks. In this model, the batholiths are assumed to have crystallised and produced the mineralising aqueous fluids, Cu and Au. However, in many porphyry deposits, the concept of metal and fluid supply from deeper batholiths is problematic. Neither Cu nor Au is strongly enriched during the crystallisation of silicate magmas, and although hypersaline fluids are a characteristic of Cu–Au porphyry deposits globally, the source of the Cl remains unconstrained. There is little evidence that silicate magmas can release such Cl-rich fluids, and it remains unexplained how elevated levels of Cl may be achieved in a silicate magma. Therefore, the starting assumption that these deposits formed predominantly from magmatic sources and processes is questioned. This study has selectively focused on the roles of rheology, rock mechanics, vein control, metal-enrichment processes and the sources of Cl. Non-magmatic processes may be enough to facilitate strong partitioning of Cu and Au into high-temperature, oxidising, high-salinity, hydrothermal fluids to form Cu–Au porphyry deposits. Mineralised quartz veins were introduced in fluids during hydraulic fracturing of their host intrusions when these stocks were brittle and had cooled significantly below their solidus temperatures. The porphyry intrusions hosting Cu–Au (copper–gold) mineralisation were not the direct sources of either the fluids or the metals. The sources of Cu and Au included large volumes of surrounding and underlying rocks up to kilometres from the sites of deposition. Cu and Au do not become strongly concentrated during crystal fractionation in evolving silicate magmas. Unaltered igneous rocks have relatively low Cl contents, and experiments suggest low Cl solubilities in granitic to granodioritic magmas. It is highly unlikely that all the Cl required for metal complexing and transport was available from within silicate magmas. [ABSTRACT FROM AUTHOR]

The paper presents a reconstruction of metamorphic stages in the Moren and Erzin metamorphic complexes in the Khan-Khuhay block of northern Mongolia. This reconstruction is used as a basis for discussing the general geodynamic history of the Sangilen terrain of the Tuva–Mongolia Massif. The calculated clockwise P–T path shows two stages of metamorphism: (1) collisional metamorphism at 9 kbar, 740°C; and (2) metamorphism related to a regional magmatic episode, at 6–7 kbar, 860–880°C. Geochemical and petrological features of rocks in the Khan-Khuhay block demonstrate that these rocks are similar to those of the metamorphic block of Western Sangilen in southeastern Tuva. Quartz monzodiorite intrusive bodies first found in the Khan-Khuhay block show geochemical features similar to those of Ordovician gabbro–monzodiorite intrusions in the western Sangilen. The Khan-Khuhay quartz monzodiorite intrusions may be small apophyses of an intermediate deep crustal magma chamber and could be a probable thermal source of metamorphic stage M2 in the Khan-Khuhay block. The numerical thermo-mechanical model of metamorphism in the Khan-Khuhay block explains the heating in the thickened crust during collision by a higher (relative to the average crustal) radiogenic heat production of 1.52 μW/m3. Computer modeling indicates that the P–T parameters of the second metamorphic stage could be reached only with the involvement of magmatic heat from the monzodiorite intrusion. The P–T metamorphic parameters calculated using mineral thermobarometry, similarity of geochemical characteristics, and results of the thermomechanical modeling allow us to conclude that the Erzin and Moren complexes have undergone a joint tectono-metamorphic evolution. [ABSTRACT FROM AUTHOR]

We report on new trace element analyses of enstatite chondrites (ECs) to clarify their behavior during the metamorphism. During the transition from a type 3 to a type 5 or higher, silicates lose a large portion of their trace elements to sulfides. Our procedure allows us to obtain trace element abundances of the silicate fraction of an EC quite easily. The element patterns of these fractions (especially REE patterns) are quite different for EH and EL chondrites, and are furthermore dependent on the metamorphic grade. This procedure can be usefull to classify meteorites, in particular when the sulfides are altered. Applied to anomalous ECs, it allows direct recognition of the EH affinity of QUE 94204, and suggests that Zakłodzie, NWA 4301, and NWA 4799 derive from the same EH-like body of previously unsampled composition. We have used the concentrations obtained on the silicate fractions of the most metamorphosed chondrites to discuss the chemical characteristics of the primitive mantles of reduced bodies of EH or EL affinity (i.e., after core segregation). Our data indicate that these mantles are very depleted in refractory lithophile elements (RLEs), particularly in rare earth elements (REEs), and notably show significant positive anomalies in Sr, Zr, Hf, and Ti. These estimates imply that the cores contain most of the REEs, U and Th of these bodies. Interestingly, the inferred primitive mantles of these reduced bodies contrast with that of the Earth. If the Earth accreted essentially from ECs, one would expect similar signatures to be preserved, which is not the case. This mismatch can be explained either by a later homogenization of the bulk silicate Earth, or alternatively, that the materials that were accreted were isotopically similar to ECs, but mineralogically different (i.e., oldhamite-free). [ABSTRACT FROM AUTHOR]

[Display omitted] • Laser ablation Lu-Hf effectively reveals polymetamorphic histories. • Spatial resolution of the laser method allows to deconstruct core-rim relationships. • Obtained results agree with published conventional garnet dates for NW Scotland. Recent advances in laser ablation reaction-cell mass spectrometry have opened the possibility for rapid and efficient Lu-Hf age dating of a variety of minerals. Of particular interest is the important metamorphic mineral, garnet, which is traditionally dated using solution-based Lu-Hf or Sm-Nd methods that are time consuming and often lack micron scale spatial resolution. In this study, we analyse garnets from samples from the 'Moine Supergroup' Scotland with the novel laser ablation inductively coupled quadrupole tandem mass spectrometry (LA-ICP-Q-MS/MS) Lu-Hf dating method, aiming to reveal terrane scale geochronological information in polymetamorphic rocks. We demonstrate that laser ablation Lu-Hf dating of garnet can accurately reveal the timing of different metamorphic events within single multi-growth garnets with precision typically as low as ∼1.5% (2σ, including systematic uncertainties). Garnets analysed from our samples produced dates including 957 ± 33 Ma, corresponding to the Renlandian Orogeny, 808 ± 14 Ma, corresponding to the Knoydartian Orogeny, and 471 ± 8 Ma, corresponding to the Caledonian Orogeny; all events which have previously been recorded from this rock suite. Furthermore, laser ablation Lu-Hf dating of garnet can provide insight into micron-scale processes such as Lu diffusion and garnet recrystallization. We recommend a series of sequential protocols, from sample selection through to laser ablation analysis, which should be used to maximize the likelihood of producing well constrained garnet Lu-Hf dates. [ABSTRACT FROM AUTHOR]

Dating specific pressure–temperature–time–deformation–fluid (P–T–t–d–f) events is a major petrological issue, particularly for polymetamorphic assemblages. In order to better assess such events using mica populations, this study uses a combined in situ Rb–Sr and Ar–Ar dating approach coupled with chemical mapping, with application to an exhumed subduction complex (Schistes Lustrés, Western Alps). Geochronological investigation of the most Si-rich (Tschermak substitution) mica population allows us to investigate the (near-)peak burial ages of the various tectonometamorphic units of this high-pressure/low-temperature subduction complex. In the blueschist-facies units, a wide range of ages between ∼36 (younger than previously obtained peak ages) and ~ 52 Ma suggests a diachronous slicing of units with different initial paleogeography and/or a long residence time at near-peak conditions. The combined use of Ar–Ar and Rb–Sr isochron ages reveals the existence of some excess argon in the studied metamorphic rocks, interpreted as the result of (i) heterogeneous contamination from an argon-rich fluid in the higher grade eclogite-facies units and (ii) partial removal, during pseudomorphic recrystallization, of argon inherited from earlier stages of metamorphism in the lower grade blueschist-facies units. [ABSTRACT FROM AUTHOR]