Metamorphic Stages Research Articles

Cравнительный анализ структуры углей различных стадий метаморфизма по данным ЯМР 13С

In this paper, the method of cross-polarization with magic angle rotation and decoupling from protons (CPMAS) 13C NMR spectroscopy obtained quantitative data on the distribution of carbon over structural fragments and calculated the degree of aromaticity (fa) of some coal samples from various Siberian deposits of a wide range of metamorphism. All the coals used in the work were characterized by standard methods (proxymate and ultimate analysis). The optimal parameters of the pulse program for recording the spectra of coals have been determined. To obtain quantitative data, the spectra were simulated. The spectrum model included from 9 to 13 components, depending on the stage of coal metamorphism. The dependences of the degree of aromaticity and the sum of oxygen-containing functional groups on the stage of coal metamorphism were constructed. The results obtained show that the structure of coals regularly changes depending on the stage of their metamorphism. The revealed relationships of the structure and properties of coals, together with the parameters of their reactivity, can ensure the safe behavior of coals in the processes of mining and processing, as well as in determining possible ways of using the studied coal samples as a valuable chemical raw material.

Appendage regeneration in anamniotes utilizes genes active during larval-metamorphic stages that have been lost or altered in amniotes: The case for studying lizard tail regeneration.

This review elaborates the idea that organ regeneration derives from specific evolutionary histories of vertebrates. Regenerative ability depends on genomic regulation of genes specific to the life-cycles that have differentially evolved in anamniotes and amniotes. In aquatic environments, where fish and amphibians live, one or multiple metamorphic transitions occur before the adult stage is reached. Each transition involves the destruction and remodeling of larval organs that are replaced with adult organs. After organ injury or loss in adult anamniotes, regeneration uses similar genes and developmental process than those operating during larval growth and metamorphosis. Therefore, the broad presence of regenerative capability across anamniotes is possible because generating new organs is included in their life history at metamorphic stages. Soft hyaluronate-rich regenerative blastemas grow in submersed or in hydrated environments, that is, essential conditions for regeneration, like during development. In adult anamniotes, the ability to regenerate different organs decreases in comparison to larval stages and becomes limited during aging. Comparisons of genes activated during metamorphosis and regeneration in anamniotes identify key genes unique to these processes, and include thyroid, wnt and non-coding RNAs developmental pathways. In the terrestrial environment, some genes or developmental pathways for metamorphic transitions were lost during amniote evolution, determining loss of regeneration. Among amniotes, the formation of soft and hydrated blastemas only occurs in lizards, a morphogenetic process that evolved favoring their survival through tail autotomy, leading to a massive although imperfect regeneration of the tail. Deciphering genes activity during lizard tail regeneration would address future attempts to recreate in other amniotes regenerative blastemas that grow into variably completed organs.

Field trials of chemical suppression of embryonic cane toads (Rhinella marina) by older conspecifics.

Laboratory experiments have shown that the viability of embryos of the invasive cane toad (Rhinella marina) can be reduced by exposure to chemical cues from older conspecific larvae. These effects (very strong in laboratory trials) may offer an exciting new approach to controlling this problematic invasive species in Australia. However, the degree to which the method works in natural environments has yet to be assessed.Our experiments in the laboratory and in seminatural outdoor waterbodies show that chemical cues from tadpoles do indeed suppress the growth, development, and survival of conspecific larvae that are exposed as embryos and do so in a dose‐dependent manner; higher tadpole densities cause greater suppression of embryos.In seminatural outdoor waterbodies, suppressor‐exposed tadpoles were less than half as likely to survive to metamorphosis as were controls, and were much smaller when they did so and hence, less likely to survive the metamorph stage. Additionally, female cane toads were less likely to oviposit in a waterbody containing free‐ranging (but not cage‐enclosed) tadpoles, suggesting that the presence of tadpoles (rather than the chemical cues they produce) may discourage oviposition.Broadly, our results suggest that the suppression effect documented in laboratory studies does indeed occur in the field also, and hence that we may be able to translate that approach to develop new and more effective ways to reduce rates of recruitment of peri‐urban populations of cane toads in their invasive range.

Indentation of bituminous coals: Fracture, crushing and dust formation

Bituminous coals are still the main source of energy in the world. However, these brittle porous materials are prone to crushing under action of industrial tools. Our early depth-sensing nanoindentation tests of bituminous coals showed that even if the depth of indentation is within the nanoscale, these brittle coals are no longer continuous elastic media within the indentation zone but rather fine powders of crushed particles irrespectively to the coal maceral. Dust formation of the materials is a problem of great practical importance for the mining industry. Indeed, the powders of coal particles formed during crushing may cause not only explosions in mines but they also contaminate the environment around the roads of the coal transportation. In this study, the crushing of coals due to action of rigid conical indenters and formation of small coal particles is investigated. The studies are based on development of the Galanov-Grigoriev (GG) model of crushing of brittle porous materials and the model adjustment to specific features of coal fracture. Using the indentation tests, we estimate the size distribution of the dust particles formed within the region of fully crushed material. Results are presented for coals of three different stages of metamorphism.

Deep subduction of felsic rocks hosting UHP lenses in the central Saxonian Erzgebirge: Implications for UHP terrane exhumation

Contrasting metamorphic conditions determined by chemical geothermobarometric investigations of ultrahigh-pressure (UHP) lenses surrounded by high-pressure (HP) and medium-pressure (MP) felsic country rocks are an enigmatic feature of UHP terranes. One of the major questions arising is whether the UHP lenses and the country rocks are a product of different peak metamorphic conditions corresponding to different maximum depth or whether country rocks also experienced UHP conditions but equilibrated and/or re-equilibrated at a different metamorphic stage. Here we address this question to the central Saxonian Erzgebirge in the northwestern Bohemian Massif, Germany. In order to screen the variety of garnet from lithologies occurring in the study area, we analyzed the detrital garnet record from seven modern stream sands. In addition to 700 inclusion-bearing garnet grains previously studied from the 125–250 μm grain-size fraction, we analyzed the 63–125 and 250–500 μm fractions and extended the dataset to overall 2100 inclusion-bearing grains. The new findings of coesite and diamond inclusions in several garnet grains, which are in compositional contrast to garnet of the known UHP lenses but match with those of the felsic country rocks, show that considerable parts of the country rocks underwent UHP metamorphism. Melt inclusions containing cristobalite, kokchetavite, and kumdykolite in garnet derived from the country rocks point to partial melting and re-equilibration during exhumation at HP/HT conditions. Although an amalgamation of rocks which reached different maximum depth may be responsible for some of the contrasting peak metamorphic conditions, the mineralogical evidence for UHP conditions in the felsic country rocks surrounding the UHP lenses proves a largely coherent slab subducted to UHP conditions. Furthermore, the presence of coesite in the subducting voluminous felsic crust and its transformation to quartz during exhumation have great implications for buoyancy development during the metamorphic cycle, which may explain the high exhumation rates of UHP terranes.

Early Carboniferous HP metamorphism in the Hida Gaien Belt, Japan: Implications for the Palaeozoic tectonic history of proto‐Japan

AbstractWe report two new eclogite localities (at Kanayamadani and Shinadani) in the high‐P(HP) metamorphic rocks of the Omi area in the western most region of Niigata Prefecture, Japan, which form part of the Hida Gaien Belt, and determine metamorphic conditions and pressure–temperature (P–T) paths. The metamorphic evolution of the eclogites is characterized by a tight hairpin‐shapedP–Tpath from prograde epidote–blueschist facies to peak eclogite facies and then retrograde blueschist facies. The prograde metamorphic stage is characterized by various amphibole (winchite, barroisite, glaucophane) inclusions in garnet, whereas the peak eclogite facies assemblage is characterized by omphacite, garnet, phengite and rutile. PeakP–Tconditions of the eclogites were estimated to be ~600°C and up to 2.0 GPa by conventional cation‐exchange thermobarometry, Ti‐in‐zircon thermometry and quartz inclusion Raman barometry respectively. However, the Raman spectra of carbonaceous material thermometry of metapelites associated with the eclogites gave lower peak temperatures, possibly due to metamorphism at different conditions before being brought together during exhumation. The blueschist facies overprint following the peak of metamorphism is recognized by the abundance of glaucophane in the matrix. Zircon grains in blueschist facies metasedimentary samples from two localities adjacent to the eclogites have distinct oscillatory‐zoned cores and overgrowth rims. Laser ablation inductively coupled plasma mass spectrometry U–Pb ages of the detrital cores yield a wide range between 3,200 and 400 Ma, with a peak at 600–400 Ma. In the early Palaeozoic, proto‐Japan was located along the continental margin of the South China craton, providing the source of the older population of detrital zircon grains (3,200–600 Ma) deposited in the trench‐fill sediments. In addition, subduction‐related magmatismc. 500–400 Ma is recorded in the crust below proto‐Japan, which might have been the source for the younger detrital zircon grains. The peak metamorphic age was constrained by SHRIMP dating of the overgrowth rims, yielding Tournaisian ages of 347 ± 4 Ma, suggesting subduction in the early Carboniferous. Our results provide clear constraints on the initiation of subduction, accretion and the development of an arc‐trench system along the active continental margin of the South China craton and help to unravel the Palaeozoic tectonic history of proto‐Japan.

Petrology, geochemistry and Sm-Nd systematics of the Paleoproterozoic Itaguara retroeclogite from São Francisco/Congo Craton: One of the oldest records of the modern-style plate tectonics

Paleoproterozoic retrogressed eclogite (retroeclogite) occurs in the Itaguara Sequence included in the suture zone formed by collision between the Archean Divinópolis and Campo Belo/Bonfim Complexes in the southern São Francisco Craton, which represents the South American counterpart of the African Congo Craton. The Itaguara retroeclogite contains scarce omphacite and phengite but abundant garnet porphyroblasts embedded in a fine-grained, amphibole, biotite and quartz-bearing matrix. The 2.20 ± 0.05 Ga eclogitization event (garnet and whole rock Sm-Nd isochronic age) of the E-MORB protolith (TDM ~ 2.47 Ga) is recorded by omphacite formation during high-pressure prograde stage in amphibole eclogite facies due to ~70 km depth subduction process. Amphibole eclogite facies metamorphic peak stage of 17–20 kbar and 600–700 °C occurred during ~2.1 Ga continental collision. Tectonic exhumation-related decompression during collision probably triggered partial melting of the eclogitic rock. Finally, decompression late stage estimated between 5 and 8 kbar and 550–650 °C under amphibolite facies overprint during orogenic collapse was responsible for appearance of kelyphitic reaction rims (symplectite) around garnet crystals. As its Paleoproterozoic contemporary analogues from Congo Craton, the Itaguara retroeclogite is one of the oldest records of the modern-style plate tectonics.

Исследование структурных характеристик витринитов некоторых углей Кузнецкого бассейна

The article is devoted to research of the main structural parameters of vitrinites of bituminous coals of various metamorphism degrees carried out by methods of X-ray phase and X-ray structural analysis. Vitrinite concentrates were obtained from coal of the Kuznetsk Basin. The main X-ray structural parameters were estimated: the number of carbon atoms in the lamellae (natC), the longitudinal size of the lamellae, and the height of their stacking (La and Lc), the number of polyaromatic layers in the package (N), and the packing density of the lamellae (ρ). It is shown in the work that in vitrinite concentrates, an increase in all analyzed structural parameters (Lc, La, natC, N, ρ) is observed with an increase in the degree of metamorphism, at the same time, a decrease in the value of the interplanar distance (d002) is observed. The XRD analysis showed that for the average number of layers in a package and carbon atoms per monolayer, in the samples of vitrinite concentrates of bituminous coals of high stages of metamorphism (Ro, r = 1.41%) varies from 7 to 8 and 14-15, respectively. It was found a correlation between the linear nature of the number of polyarene-layers and the height of their stacking. The results obtained were in good agreement with the literature data given for coals of various deposits.

From subduction initiation to arc–polarity reversal: Life cycle of an Archean subduction zone from the Zunhua ophiolitic mélange, North China Craton

Subduction initiation and arc–polarity reversal have rarely been recognized in the Archean rock record. We document Neoarchean subduction initiation, fore-arc magmatism, and an arc–polarity reversal event from the Zunhua ophiolitic mélange along the eastern margin of the Central Orogenic Belt (COB) of the North China Craton (NCC). The Zunhua ophiolitic mélange is a mappable unit characterized by blocks of metamorphosed harzburgite/lherzolite, podiform chromite–bearing dunite, pyroxenite, amphibolite, metabasites (basalt and diabase) with rare intermediate volcanics, chert, and tectonic lenses of banded iron formation in a strongly sheared metapelitic matrix. New geochronological and geochemical analyses of magmatic blocks within the ophiolitic mélange show that the crustal magmatic rocks were produced in a fore-arc region at 2.55–2.52 Ga from depleted harzburgitic–lherzolitic mantle tectonites. Chemical, petrological, and temporal links between the depleted mantle blocks, and the suite of magmatic blocks derived from partial melting and metasomatism of these depleted mantle blocks, unequivocally shows that they represent part of the same original Neoarchean fore-arc ophiolite suite. After formation and accretion in the oceanic realm, the mélange was emplaced on the continental margin of the Eastern Block between 2.52 and 2.50 Ga, and underwent two stages of metamorphism at ca. 2.48–2.46 Ga and 1.81 Ga. Metamorphosed intermediate–mafic volcanic blocks exhibit systematic successive geochemical variations, from MORB-like to volcanic arc-like, and the N-MORB-like meta-basalts show remarkable similarity with the subduction initiation-related Izu–Bonin–Mariana (IBM) fore-arc basalts. We suggest that the Zunhua fore-arc complex records continuous geodynamic processes from subduction initiation to arc magmatism. The Zunhua ophiolitic mélange is part of a ca. 2.5 Ga suture between an oceanic arc of the COB and Eastern Block of the NCC. After the arc–continent collision, an arc–polarity reversal event initiated a new eastward–dipping subduction zone on the western side of the COB. This arc–polarity reversal is traced for more than 1600 km along the length of the orogen, similar in scale, geometry, and duration between collision and polarity flip to the present-day arc–polarity reversal of the Sunda–Banda arc during its ongoing collision with the Australia continent. This indicates that a life cycle of an Archean subduction zone, including birth (subduction initiation), maturity (arc magmatism), death (arc-continent collision) and re-birth (arc–polarity reversal), is recorded in the Zunhua ophiolitic mélange, and the geodynamics of plate tectonics at the end of the Archean was similar to those of today.

The distinct metamorphic stages and structural styles of the 1.94–1.86 Ga Snowbird Orogen, Northwest Territories, Canada

Abstract Palaeoproterozoic orogenesis within the Archean southeastern Rae craton is related to the initial amalgamation of Laurentia. Characterizing the accompanying tectonic processes during this time has been complicated due to polymetamorphism, which results in the obscuring of the age record of the terranes involved. To improve the knowledge of the tectonic evolution of the South Rae Craton, petrologic and structural analyses are applied in conjunction with in situ trace element chemistry, inclusion barometry, U–Pb monazite and titanite, and Lu–Hf garnet chronology. The data robustly constrain Palaeoproterozoic pressure–temperature–time paths of major deformational events along the southeastern Rae craton margin. D1 occurred between 1.94 and 1.93 Ga in the Dodge‐Snowbird domain, which included prograde burial of metasedimentary rocks, deposited at 2.2–2.0 Ga, and the development of migmatitic layering and east‐southeast trending folds (S1, F1). Peak metamorphism is recorded in metasedimentary units at c. 1.93 Ga when rocks reached conditions of 9.0–10.5 kbar and 810–830°C. Within the Dodge‐Snowbird domain, D2 imparted north‐northeast trending open folds and associated axial planar cleavage (S2, F2) between 1.93 and 1.90 Ga during east‐west compression that appears to have been synchronous with cooling and exhumation. Later D2 deformation, localized within the Wholdaia Lake shear zone (WLsz; ST1), developed in the footwall of this thrust‐sense structure at 1,873 ± 5 Ma at conditions of 9.5–11.0 kbar and 820–850°C. The hangingwall Dodge‐Snowbird domain had already cooled to below 300°C by then, indicating a significant structural and metamorphic break across the domain's western boundary. A new phase of unroofing (D3) involved pervasive amphibolite‐ to greenschist facies extensional shearing (ST2) within the WLsz, which overprinted ST1 foliations between 1.87 and 1.86 Ga. Continued greenschist facies shearing younger than 1.86 Ga likely ended by c. 1.83 Ga when lamprophyre dykes cut the structure, which was followed by cooling until c. 1.80 Ga. This work highlights the utility and application of multiple chronometers (zircon, monazite, titanite, garnet) along with structural and petrologic analysis that together can resolve precise orogenic cycles in polymetamorphic terranes that may otherwise be undetected. The time‐resolved P–T–D histories derived here enable more robust interpretations regarding the nature and evolution of 1.9 Ga tectonism along the southeast Rae craton margin, which may be used to refine models for Laurentian terrane amalgamation.

Spectral manifestations of coal metamorphism: Insights from coal microstructural framework

The present study investigates the microstructural framework of coals from the Raniganj and the Jharia Basins as well as from the Himalayan fold-thrust belts of Sikkim, India, by vitrinite reflectance, Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The mean random vitrinite reflectance data may imply that the coal samples from the Raniganj and the Jharia Basins range from the bituminous D to B, and would have experienced the burial heating corresponding to ~92 °C to 143 °C unlike the anthracite A samples that might have undergone the hydrothermal metamorphism at ~333 °C to 367 °C. The Raman spectra exhibit preferential removal of sp3 hybridized moieties from the anthracite samples at anchizonal metamorphic stage due to thermo-stress degradation effect induced by the Himalayan orogeny. Further, this study records the reduction of net dipole moment change due to the expulsion of functional groups from the aromatic rings making them infrared inactive. Additionally, the C1s spectra reveal the thinning of CC peaks and the lowering of the CO peak intensity with an increase in coal rank. This study, hence, documents the microstructural transformations in coal that can be used for structural maneuvering to control the liquefaction, gasification, pyrolysis, combustion as well as synthetic graphitization behavior.

The Main Central Thrust zone along the Alaknanda and Dhauli Ganga valleys (Garhwal Himalaya, NW India): Insights into an inverted metamorphic sequence

New tectono-metamorphic data along the Alaknanda-Dhauli Ganga valleys in the Garhwal Himalaya (NW India) are presented focusing on sheared rocks of the Main Central Thrust zone (MCTz), one of the first order regional structures in the Himalaya. In regard of large hot orogens (LHOs), the MCTz corresponds to the base of the low-viscosity infrastructure. Our new findings support that the MCTz is a c. 4 km thick mylonitic zone, affecting different lithologies and encompassing a possible (previously defined) protolith boundary. Four selected mylonitic samples, at different structural position along the MCTz, were studied with a multi-disciplinary approach in detail, supporting that an inverted metamorphic field gradient, with temperature (T) and pressure (P) ranging from c. 500 up to c. 700 °C and c. 0.50–0.60 GPa up to >1.0 GPa, was present. This inverted P-T array is also discernable by the distribution of Al-rich minerals (e.g. chloritoid, staurolite, kyanite) in the intercalation of sheared quartzite. In situ U-(Th)-Pb monazite geochronology indicates that the high-T shearing in the upper part of the MCTz mylonites developed from c. 20 Ma on after a stage of prograde metamorphism that lasted until c. 23 Ma.The integration of our data with available structural, metamorphic and geochronological information along the MCTz profile, in the study area, sheds light on the development of the associated inverted metamorphic sequence (IMS). These data carry also empirical finite patterns to be tested against theoretical models investigating the possible roles of viscous heating and “tectonic overpressure” in the development of the IMS in the Himalaya, and possibly in LHOs in general. Both phenomena, if have been active at all, are not obvious in regard of the current state of geothermobarometric methods. On the contrary, a model for the tectonic assembly of the IMS is favored. The anomalous apparent P and T inverted field gradients are interpreted to be the result of the differential and diachronous transport along a shear zone experiencing heterogeneous vertical thinning linked to the non-coaxial flow.

Major lithologies of the high-grade Zhoutan terrane within the Cathaysia Block and their tectonic implications for the Neoproterozoic - Paleozoic South China

Pre-Devonian crystalline basement of the Cathaysia Block was united through the Wuyi-Yunkai orogeny. The uplifted orogenic core is dominantly composed of Paleozoic high-grade terranes occurring in a northeast-southwest trending belt. The Zhoutan terrane in the middle part of this belt is one of the key terranes to reveal the tectonic architecture of the South China Block. However, how to correlate it with other high-grade terranes, what kind of rock records are preserved in this terrane and their tectonic implications for the Wuyi-Yunkai orogen are still unresolved. This paper carries out an integrated study on the petrology, zircon U--Pb geochronology, geochemistry and zircon Lu--Hf isotopic compositions of the main rock types in the Zhoutan terrane, with a purpose of better understanding the Wuyi-Yunkai orogeny. Mafic granulite (noritic) of high-T and low-P conditions occurs as lenses within the Zhoutan Formation. The zircon U--Pb geochronological data give magmatic and metamorphic ages of 460–450 Ma and ~ 430 Ma, respectively. Neoproterozoic and Paleoproterozoic (1.89 Ga) xenocrysts also occur. Meta-pelites of the Zhoutan Formation experienced high T/P amphibolite facies metamorphism, and ages of their detrital zircons are dominantly Neoproterozoic (810–820 Ma) with some subordinate Paleo- to Mesoproterozoic and Archean signatures. Amphibole gneiss layers of this formation give a Paleozoic metamorphic age of ~450 Ma, consistent with the high-P amphibolite facies metamorphism of the neighboring Longyou terrane. Fine-grained garnet mica-schist of the Wanyuan Formation consists of greenschist to amphibolite facies mineral assemblage and detrital zircons of these meta-sediments display both Neoproterozoic and early Precambrian ages at ~770 Ma, ~820 Ma, ~850 Ma, ~1.84 Ga and 2.48 Ga. Metamorphosed calc-silicates of the Wanyuan Formation show similar detrital zircon age peaks of 624 Ma, 780–790 Ma, ~810 Ma, 840–850 Ma, 1.8–1.98 Ga and ~ 2.48 Ga, and a Paleozoic metamorphic age of ~447 Ma. The Cizhu pluton is a composite granitoid body intruding the Zhoutan and Wanyuan formations, with emplacement ages ranging at least from 485 Ma to 446 Ma. εHf(t) values of zircons from the mafic granulite range from −10.9 to +8.5, indicating its protolith derived from enriched mantle sources with or without crustal contaminations. The Cizhu magmatic event is a crustal reworking event as indicated by the coherently negative zircon εHf(t) values and ancient Hf crustal model ages of 1530–1830 Ma. Zircon εHf(t) values of the metamorphosed calc-silicates show large variations, ranging from −21.2 to +11, consistent with its complex provenances. The deposition of the sedimentary rocks of the Zhoutan and Wanyuan formations is consistent with the development of the Neoproterozoic-Paleozoic Nanhua Rift. The development of continental margin sequences like the Zhoutan and Wanyuan formations, the evolution of the Paleozoic metamorphism from early higher P/T metamorphic stage to later lower P/T stage, as well as the generation of the Paleozoic mafic-ultramafic rocks and the intermediate Cizhu pluton, are best explained by collision to post-collision settings. We, therefore, conclude that the Zhuotan terrane (as well as other high-grade terranes) witnessed a whole geological cycle, from early rifting to the closure of a rifted basin (Nanhua Basin), and the final lithospheric delamination following the rejoining of continental blocks flanking the rift.

Multi‐stage metamorphism by progressive accretion of continental blocks, example from the Western Hindu Kush

AbstractBasement rocks from the Western Hindu Kush preserve evidence of multiple metamorphic and magmatic events that occurred along the boundary between the Archean–Proterozoic Afghan Central and Afghan–Tajik Blocks. To verify the different metamorphic stages or events, mineral textures and phase equilibria in metamorphic basement rocks and their age relations to magmatic episodes have been investigated. Quartzofeldspathic gneiss and migmatite with lenses of amphibolite (with assumed Proterozoic age for their metamorphism) are intruded by the Triassic Hindu Kush granitoid batholith and small Cretaceous and Oligocene granite intrusions. The age of thermal overprint (210–170 Ma) by the Triassic batholith is confirmed by new monazite data. Both Triassic and Cretaceous granitoids and surrounding basement rocks underwent subsequent metamorphism up to epidote–amphibolite facies. The degree of this metamorphism increases southward at the contact to the Kabul Block, which under‐plates the Western Hindu Kush from the south. An early Miocene age was obtained by Pb–Th analyses in thorite and huttonite, which are close or slightly younger than the Oligocene granite in this area. The Cretaceous meta‐granodiorite near the border with the Kabul Block contains xenoliths of granulite facies rocks that could come from the Neoarchean granulite facies basement of the Kabul Block. The multi‐stage metamorphic and magmatic evolution classifies the Hindu Kush mountain belt as a long‐lived suture zone that was active since the early Palaeozoic. The results of this study support the interpretation about possible relations of the Afghan Central Blocks to the southern margin of Eurasia during the evolution of Para‐ and Neotethys.

P-T path of metamorphism and U-Pb monazite and zircon age of the Kitoy terrane: Implication for Neoarchean collision in SW Siberian Craton

The first data on P-T metamorphic conditions coupled with U-Pb monazite and zircon age obtained for the Neoarchean Kitoy granulite-gneiss terrane (SW Siberian Craton). Alumina gneisses of the Kitoy terrane indicate two-staged metamorphic evolution. The first stage of regional metamorphism (M1) occurred at high-amphibolite facies conditions at T ​= ​780–800 ​°C and P ​= ​8–9 ​kbar. The second stage (M2) belongs to MT-HT/LP type of metamorphism with the wide temperature interval 600–750 ​°C and pressure 2–4 ​kbar. Two age peaks were established on the basis of U-Pb monazite and zircon dating in garnet-anthophyllite gneisses. Both of them correspond to the Neoarchean age: the age of M1 falls into the interval of ca. 2489–2496 ​Ma, the age of M2 – ca. 2446–2456 ​Ma. The high-temperature metamorphism of the Kitoy block and nearly coeval granitoid magmatism can be an evidence for the Neoarchean collision in SW Siberian craton.

Subduction and exhumation of Luliangshan eclogite in the North Qaidam, northern Tibet: Constraints from petrology, geochemistry and phase equilibrium modelling

Eclogites in the high‐pressure (HP) and ultrahigh‐pressure (UHP) belt record important information about the subduction process and evolution history of the orogenic belt. The Luliangshan eclogites surrounded by granitic gneiss or paragneiss as lenses are exposed in the western segment of the North Qaidam UHP metamorphic belt, northwestern China. Petrology, mineral chemistry, and P–T pseudosection modelling show that the eclogites have experienced a multi‐stage metamorphic process. The peak eclogite‐facies metamorphic stage, is characterized by omphacite in matrix and as inclusion in garnet, with the peak mineral assemblages of garnet + omphacite + rutile + quartz atT > 790°C andP > 25.5 kbar. The initial HP granulite‐facies retrogression is characterized by the symplectite of diopside + plagioclase around omphacite, with P–T conditions of 911°C and 16.9 kbar. The subsequent amphibolite‐facies stage is characterized by amphibole + plagioclase symplectite around the clinopyroxene, with the metamorphic conditions of 674–686°C and 6.4–6.9 kbar. Zircon U–Pb analyses yielded two metamorphic age clusters: (a) HP granulite‐facies metamorphic age of 422–425 Ma, and (b) amphibolites‐facies retrograde age of 397–420 Ma. The protolith of eclogite have geochemical characteristics similar to those of normal mid‐ocean ridge basalt (N‐MORB); and the varyingεNd(t) values (−6.3 to 2.1) indicate that the Luliangshan eclogites were derived from a mantle source with rare crustal contamination. Combining these data with previous studies, a multi‐stage tectonic model can be proposed: In the Early Neoproterozoic, the protolith of the Luliangshan eclogites were emplaced into ancient continental crust; during 460–430 Ma, following the oceanic subduction, the subduction of continental crust was dragged by the oceanic slab and continue to subduct towards the Qilian Block, and metamorphosed at the depth of at least 75 km. After a long and slow exhumation process, it returned to the shallow crust.

Eocene migmatite formation and diachronous burial revealed by petrochronology in NW Himalaya, Zanskar

AbstractIn this contribution, we highlight the importance of in‐situ monazite geochronology linked to P−T modelling for identification of timescales of metamorphic processes. Barrovian‐type micaschists, migmatites and augengneiss from the Gumburanjun dome in the southeastern extremity of the Gianbul dome, NW Himalaya, have been studied in order to correlate the early stages of Himalayan metamorphism at different crustal levels and infer the timing of anatexis. P−T−t paths are constrained through combined pseudosection modelling and in‐situ and in‐mount monazite and xenotime laser ablation–split‐stream inductively coupled plasma‐mass spectrometry. Petrography and garnet zoning combined with pseudosection modelling show that garnet‐staurolite schists record burial from ~530 to 560°C and 5.5 kbar to ~630 to 660°C and 7 kbar; staurolite‐kyanite schists from ~530 to 560°C and 5 kbar to ~670 to 680°C and 7−9 kbar; and garnet‐kyanite migmatites from 540−570°C and 5 kbar to ~680 to 750°C and 7−10 kbar, probably also to >750°C and >9 kbar above the muscovite stability field. The decompression paths of garnet‐staurolite schists indicate cooling on decompression, while garnet rim chemistry and local sillimanite growth point to a stage of re‐equilibration at ~600 to 670°C and 4−6 kbar in some of the staurolite‐kyanite schists, and at ~670 to 700°C and 6 kbar in garnet‐kyanite migmatites. Some of the staurolite‐kyanite schists and garnet‐kyanite migmatites also contain andalusite or andalusite‐cordierite. Monazite and xenotime were analysed in thin sections in garnet, staurolite and kyanite, and in the matrix; and in mounts. BSE images and compositional maps of monazite (xenotime was too small) show variable internal structures from homogeneous through patchy zoning with embayed to sharp boundaries. Two groups of samples can be identified on the basis of the presence or absence of c. 44 − 37 Ma ages. The first group of samples—two garnet‐staurolite schists—recorded only c. 31 − 27 Ma ages in porphyroblasts and no c. 40 Ma ages. The second group (samples of staurolite‐kyanite schist, garnet‐kyanite migmatites, augengneiss) have both the older, c. 44 − 37 Ma monazite ages in porphyroblasts and younger ages down to c. 22 Ma. These significantly different ranges of ages from porphyroblasts of 44−37 Ma, and 31−27 Ma, are interpreted as the duration of prograde P−T paths in Eocene and Oligocene, and indicate diachronous two‐stage burial of rocks. Early migmatization occurred at 38 Ma. The c. 29 Ma is interpreted as the time when rocks from the lower and middle crustal levels were partially exhumed and came in to contact with rocks that were downgoing at this time. Localized monazite recrystallization is as young as 26−24 Ma. The youngest ages of 23−22 Ma are related to leucogranite emplacement.

Tectono-metamorphic evolution of the Calabria continental lower crust: the case of the Sila Piccola Massif

A combined structural and petrological study focuses on the Sila Piccola Massif to obtain new constraints on the exhumation history of a relic fragment of the intermediate to deep portion of the Variscan basement, which now belongs to the northern Calabria Peloritani Orogen. The timescale of the early (i.e. late-Variscan) shear-assisted exhumation stage is determined by diffusion-modelling and the strain rate of the latest (i.e. Alpine) shear event is determined by microstructurally derived paleopiezometry. The intermediate to deep portion of the Sila basement is characterised by a pervasive mylonitic horizon involving orthogneiss and, to a lesser extent, garnet paragneiss. Such a pervasive mylonitic foliation widely obliterated an older metamorphic fabric, which is preserved as relics in low-strain domains. The pre-mylonitic relics consist of plagioclase, biotite, white mica, sillimanite, quartz and the first generation of chemically homogeneous garnet. Our results show that the later mylonitization can be ascribed to two metamorphic stages. The first stage is associated with a late-Variscan extensional shearing, which shows a syn-kinematic growth of a second-generation garnet with plagioclase, biotite and quartz developed in the pressure shadows of garnet porphyroclasts likely during an early retrograde metamorphic stage. The second stage, characterised by a syn-shearing growth of chlorite, white mica, plagioclase and quartz, observed along the C-planes, is interpreted as a late Alpine mylonitic overprint in compressional regime.

Multiple sulfur sources for the volcanic hosted massive sulfides in Betul Belt, Central India: Evidence from the sulfide ore chemistry and sulfur isotope geochemistry

This work provides an overview of the geological, petrological, and geochemical data available on the three volcanic-hosted massive sulfides (VHMS) deposits (Ghisi, Biskhan, and Jangaldehri) in Betul Belt, Central Indian Tectonic Zone. Sulfur isotope geochemistry was used for the first time from the Betul Belt to constrain the source of sulfur for a better understanding of the ore genesis process. Mineralization is hosted in a felsic dominant bimodal volcano-sedimentary sequence associated with syn-genetic hydrothermal alteration, i.e., intense Mg–Ca alteration (actinolite-tremolite-anthophyllite) and Al–Fe alteration zone (gahnite-garnet-biotite-staurolite) followed by regional metamorphism. Field observations, drill core logging, and petrography studies reveal different modes of mineralization, i.e., dissemination, stringers, and semi-massive sulfides vein, comprises of chalcopyrite, sphalerite, pyrite, galena with lesser pyrrhotite, are paragenetically distinct in three deposits. The petrography, SEM-EPMA studies show the presence of chalcopyrite disease in Fe-rich sphalerite at Biskhan and Jangaldehri in the east and absence of the same texture at Ghisi in the west. This difference reveals the variable physio-chemical nature of the hydrothermal fluid and partial melting of sulfides during subsequent metamorphism.Cu–Fe mineralization was deposited from high-temperature hydrothermal fluids with less sulfur activity at Biskhan-Jangaldehri. Later Zn–Cu–Pb mineralization was formed from lower temperature hydrothermal fluids with higher sulfur activity. The δ34S values of sulfides (sphalerite, chalcopyrite, and pyrite) from three deposits show a wide range of sulfur values (δ34S) from −12.87 to + 19.31‰ (n = 27), consistent with heterogeneous sourcing of S, probably combining magmatic source along with the reduction of seawater sulfate. Variation in the sulfur isotopic compositions of sulfide was the result of dilution and cooling of the metalliferous fluid at different stages after interaction with meteoric, seawater and hydrothermal fluids, which caused the deposition of base metal sulfides.Sulfides from Ghisi in the west display both +ve and −ve values (−12.88 to + 0.38‰; n = 10), suggest sulfur predominantly derived by thermochemical reduction of seawater sulfate with minor input of magmatic sulfur reduction lead to polymetallic Zn–Cu–Pb mineralization. The gradual increasing in the δ34S values (more + ve values +18.65 to +19.31‰; n = 8) from west to east at Biskhan and Jangaldehri (+ 5.01 to + 8.3‰, n = 9) may be due to involvement of both the leaching of igneous basement rocks and chemical process of seawater sulfates by thermochemical reduction (TSR) from deep water levels lead to Zn–Cu mineralization. This δ34S variation occurs in three deposits of the Betul Belt due to modifications of the primary mineralization during subsequent stages of ore formation and metamorphism, indicating a complex fluid evolution history for VHMS deposits in Betul Belt, Central India, where S derived from a heterogeneous source by multiple geological processes. This situation is more akin to many established VHMS deposits of ancient and modern submarine hydrothermal systems.

Engineering equations for determining coal-water fuel combustion stages

Research on the combustion of coal-water fuel has grown significantly in recent years. Many experimental and numerical calculated data are available in the scientific literature. Nowadays, a large number of different models of the combustion of coal-water fuel have been developed for numerical research. However, there is no systematic generalization of all these data in the published results.This article is an attempt to fill the gap in the field of such a generalization. Simple equations are obtained based on a generalization of experimental data on the combustion of coal-water fuel for engineering applications, as well as to verify already existing and new mathematical models being developed. Those equations are basic for calculation of each stage duration of “pure” coal-water fuel (without any additions) combustion parameters in still air; they take into account all metamorphic stages of source coal, the different water content in the range of 25–50% and mineral impurities content (ash) 0.5–60% in the temperature range of the oven medium 550–1000 °C.