Metamorphic Transformations Research Articles

Late Precambrian Metamorphic Complexes of the Ulutau Massif (Central Kazakhstan): Age, Composition, and Formation Settings of Protoliths

This work presents the results of a study of metamorphic rocks of the Bekturgan and Balazhezdy groups of the Precambrian Ulutau massif (Central Kazakhstan), which have been traditionally identified with the most ancient Early Precambrian complexes, comprising the massif’s basement. The protoliths of the metamorphic rocks, represented by lavas and tuffs of basalt and rhyolite–trachyrhyolite composition, sandstones, and tuffaceous sandstones, comprise a contrasted volcanic-sedimentary sequence. The obtained U‒Th–Pb zircon ages (LA–ICP MS, SHRIMP II) demonstrate that the formation of this sequence occurred during a narrow (762–788 Ma) interval during the second half of Tonian (Neoproterozoic). The metamorphic transformations of the rocks were completed before an intrusion of the alkaline syenites of the Karsakpai complex (673 ± 2 Ma), which were not subject to metamorphism. The whole-rock Nd isotopic compositions of the metamorphic rocks indicate the origin of their protoliths due to erosion and partial melting of the more ancient complexes of the Precambrian continental crust of the Ulutau massif. The Hf isotopic compositions of zircons indicate that the main stages of formation and transformation of the Ulutau continental crust occurred during the Neoarchean–Neoproterozoic and coincided with the main stages of the Precambrian magmatism in the western part of the Central Asian Orogenic Belt.

Evolutionary and developmental considerations of the diet and gut morphology in ceratophryid tadpoles (Anura)

BackgroundBefore metamorphosis, almost all anuran tadpoles are omnivores. Larval carnivory occurs in some species and, it is associated with distinctive morphotypes. Obligatory carnivorous tadpoles exhibit structural changes in the gastrointestinal tract compared to larvae that are predominately omnivores. The most distinctive feature of the anuran family Ceratophyridae (three genera) overall is the enormous gape of adults. This feature increases their ability to capture extremely large and active prey. The larvae of Ceratophyrid genera are remarkably distinct from each other and carnivory has diversified in a manner unseen in other anurans. The larvae of one genus, Lepidobatrachus, has a massive gape like the adult. Herein, we report on larval developmental variation, diet, gross morphology of the gastrointestinal tract, and histology of the cranial segment of the gut before, during and after metamorphosis in larval series for the following ceratophryid species: Chacophrys pierottii, Ceratophrys cranwelli, Lepidobatrachus laevis and Lepidobatrachus llanensis.ResultsWe described patterns of larval development with variation in growth with consequence to the final size at the end of metamorphosis. These patterns seem to be influenced by food quantity/quality, and most predominant by animal protein. Prey items found in pre and post-metamorphic Lepidobatrachus spp. are similar. Tadpoles of Ceratophrys and Chacophrys (and other anurans) share a short cranial segment of the gut with an internal glandular, mucous secreting epithelium, a double coiled intestine and the sequence of metamorphic changes (tract is empty, the stomach differentiates and the intestine shortens abruptly). In contrast, Lepidobatrachus tadpoles have a true stomach that acquires thickness and increased glandular complexity through development. As larvae they have a short intestine without double coils, and the absence of intestine shortening during metamorphosis.ConclusionsThe larval development of the gastrointestinal tract of Lepidobatrachus is unique compared with that of other free-living anuran larvae. An abrupt metamorphic transformation is missing and most of the adult structural features start to differentiate gradually at the beginning of larval stages.

Mineralogical and geochemical aspects of rare-earth elements behavior during metamorphism (on the example of the Upper Precambrian structural-material complexes of the Bashkir megaanticlinorium, South Urals)

The article provides new data on geochemistry and mineralogy of rare-earth elements (REE) in rocks of structural-material complexes of the Bashkir megaanticlinorium, which underwent metamorphic transformations of various nature: contact metamorphism (Suran section); syn- and postgenetic contact-dislocation metamorphism (Shatak complex) and hydrothermal metamorphism (Uluelga-Kudashmanovo zone). It has been established that when a magmatic melt is exposed to sediments, the latter are enriched with REEs with the formation of rare earth minerals (monazite, allanite, xenotime et al.). The study of the chemical composition of monazites and allanites showed that all variations of oxides in the composition of the former are due to isomorphous Ce-Ca-Th substitutions in the structure of minerals, but redistribution of these elements was an independent process characteristic of each structural-material complex. The study of allanites made it possible to establish the presence of isomorphism according to the Ca↔Ce, La, Nd principle, as well as the sharp difference between the characterized minerals in the amount of MgO, Fe* and MnO from analogues from other regions, which indicates the presence of a regional component in the chemical compositions of minerals altogether, geotectonic settings of mineralization formation. The temperature regimes of mineral-forming processes with metamorphic transformations of rocks calculated from chlorite and muscovite compositions (344-450°C – Suran section, 402-470°C – Shatak complex, 390-490°C – Uluelga-Kudashmanovo zone) indicate the possibility of stable coexistence of the association monazite-allanite. It was established that when a magmatic melt on the sedimentary substrate of the frame, the lanthanides enrich the exocontact rocks with the formation of newly formed REE-mineral associations. At the same time, the processes of formation of rare-earth mineralization are largely determined by the physicochemical parameters and thermobaric conditions of the accompanying and subsequent metamorphism.

STUDIES OF THE ORGANIC ORIGIN CHEMICAL COMPOUNDS OF BROWN COALS AND CARBONIZED PLANT RESIDUES FROM NORTHERN TIMAN

The results of the physical and chemical studies of the organic matter of Devonian brown coals and rocks with carbonized plant residues from Northern Timan (Russian Arctic) are presented. We used a complex of physical and chemical methods, including IR spectroscopy, EPR spectroscopy, quantitative chemical analysis, pyrolytic gas chromato-mass spectrometry. For comparative studies we used Devonian (Middle Timan) and Jurassic (Griva, Komi Republic, Russia) carbonized plant residues and lignins, isolated from modern wood and non-wood plants. Organic structures of aromatic nature, which are products of the metamorphic transformation of lignins of coal-forming plants, were found in the investigated samples. It was shown that lignin’s relics show pronounced paramagnetic properties, mainly due to the presence of phenoxyl radicals. The concentration of paramagnetic centers reaches a value that is close to the maximum value nорг for carbonaceous substances. Based on quantitative analysis of phenolic products of pyrolysis the composition of lignin relics was calculated, taking into account the ratio of the main structural H, G and S units. Experimental data allowed to put forward the hypothesis that in the composition of Devonian coal-forming plants, as one of the first representatives of forest communities on the planet, included compositionally homogeneous protolignins of H-type, built mainly from p-coumaric structural units.

Process of Incorporation and Morphological Transformations of Rural Settlement Patterns in the Context of Urban Development. The Case Study of Łódź

AbstractThe subject of the research covers the problem of morphological changes in former villages incorporated into the city on the example of Łódź. The first objective of the article is to analyse the urban development of the city, taking into account the territorial changes and incorporation of villages. The second objective includes the analysis of morphological changes in former villages that have taken place after their incorporation into the city since the mid-twentieth century. The study required analysis of source materials in the form of preserved historical maps and today's plans, legal acts, planning documents and chosen statistical data. The analysis of changes in the spatial structure of villages incorporated into the city was possible mainly thanks to the retrogressive, as well as progressive method. The article also uses the method of morphological analysis of the city plan based on the Conzenian tradition of urban morphology. The study applies the typology of rural settlement patterns, taking into account the issue of morphological changes and relics of morphological features from the period before the incorporation into the city. It is characteristic that the transformation process of rural settlement patterns took place in different ways and with various intensity depending mostly on the scale of urbanisation processes. It was possible to distinguish the orthomorphic transformations, where all spatial modifications were mainly additions and did not destroy the morphogenetic core, so the former layouts have been preserved almost completely, semi-metamorphic transformations, where spatial reorganisation was considerable, but not total, and clear relics of the historical rural settlement pattern have been saved, and metamorphic transformations, in which almost all elements of the former morphological structure have been completely erased and the former layouts have been totally changed.

Late Paleozoic Age and Nature of Protolith of Metamorphic Rocks of the Djagdagle Formation, Bureya Terrane, Central Asian Fold Belt

The results of geological, geochemical, Sm–Nd isotopic geochemical studies of metamorphic rocks of the Djagdagle Formation and U–Pb geochronological studies of its zircons are presented. In correlation schemes of geological complexes of the Bureya Terrane, this formation is the oldest (conditionally, Late Archean) amid other formations of the terrane; thus, it is considered its basement. The biotite and two-mica garnet-bearing gneisses of the formation formed owing to transformation of primary sedimentary rocks. The maxima on the relative probability curve of zircon age correspond to 487, 541, 690, 778, and 896 Ma. Thus, the Djagdagle Formation is Paleozoic rather than Early Precambrian, as was considered before. The lower age boundary of the accumulation of the protolith is identified by the age of the youngest zircon population of ~487 Ma. Similar ages of some cores and rims of zircons indicate that the rocks of the protolith underwent structural metamorphic transformations under PT conditions of amphibolite facies. The results of Sm–Nd and Lu–Hf isotopic studies indicate that the geological complexes which originated by means of reworking of the Mesoproterozoic crust could have been the source of primary sedimentary rocks. Taking into account the lack of Mesoproterozoic (and older) rocks in the structure of the Bureya Terrane, it can be suggested that the sources included some amount of ancient recycled material. Similar geological evolution of the Bureya and Jiamusi terranes is suggested on the basis of similar age ranges of metasedimentary rocks of the Djagdagle Formation and Turan Group of the Bureya Terrane and the Kimkan Formation of the Jiamusi Terrane. This is also evident from their synchronous Neoproterozoic magmatism.

ON DETERMINING THE COAL CARBONIZATION INDICATOR FOR ESTABLISHMENT OF MINE FIRE HAZARD GROUPS

The article analyzes the dependence of endogenous fire hazards on the following factors: the degree of coalification, the total sulfur content, the thickness of the developed formations and their structure, the presence of tectonic disturbances. By the genetic propensity of coals to spontaneous combustion, three groups of coal sites are distinguished: І – Vdaf ≥ 41%, Сп ≤ 7, coals of marks D and partially G; ІІ – Vdaf = 40-30%, Сп ≤ 8, coals of marks D and partially F; ІІІ – Vdaf < 36%, Сп >8, coals of marks Zh, K, OS, T. Studies have shown that individual dependences of the decrease in the content of each component (Оo, Нo, No) significantly differ from each other. Decrease in oxygen content, as well as the sum of the main components, occurs with an increase in carbon content. The sum of the content of the main components decreases inversely to the increase in carbon content over the entire range of coal conversion from a small degree of their metamorphism (Со ≈ 70%) to anthracites (Со ≈ 98%). The dependence of decrease in oxygen content with increased carbon is nonlinear. With carbon content of more than 88%, there is a slight decrease in the rate of oxygen reduction in comparison to its decrease at earlier stages of metamorphism. Data analysis showed an almost functional dependence between the sum of the main components of the organic mass (0.995). A significant correlation of carbon with oxygen and hydrogen is observed. A significant scatter of points in experimental data is due to the diversity of composition of the source material, the conditions of its accumulation and transformation for different coal basins and individual coal sites. Studies have shown that the relationships between all the main components of the organic mass of coal during metamorphic transformations change significantly at different stages of these processes. The established dependence of the carbonization index on the carbon content at different stages of coalification allowed us to develop an engineering method for calculating the carbonization index for the entire range of coal metamorphism. The proposed method significantly clarifies the determination of the carbonization index, which is necessary not only for establishing the fire hazard of mine layers, but also for establishing other manifestations of the dangerous properties of coal sites during mining operations. Keywords: carbonization index, endogenous fire hazard, elemental composition, organic mass, metamorphism, coalification.

Fe-Ti Oxide Assemblages from the Contact-Metamorphosed Mafic-Ultramafic Rocks of the Sedova Zaimka Intrusion (Western Siberia, Russia): The Tracking of Metamorphic Transformations

Studies that track and compiled transformations of ilmenite and magnetite under conditions of different metamorphic grades are still very limited. The Sedova Zaimka intrusion in Western Siberia (Russia) is a good example to examine the effect of contact metamorphism from greenschist to low-amphibolite facies on magmatic Fe-Ti oxide minerals, as this small mafic-ultramafic body is located within contact metamorphic aureole of a large granite pluton. In the Sedova Zaimka, ilmenite with little to no magnetite is present as an accessory dissemination throughout metamorphosed rocks. Ilmenite is variably enriched in MnO (1 to 13.3 wt%) and depleted in MgO (less than 0.3 wt%), suggesting that its primary magmatic composition has been unevenly modified by diffusion re-equilibrium with coexisting metamorphic silicates. The elevated content of ZnO (up to 0.5 wt%) and NiO (up to 0.4 wt%) in ilmenite suggests that both ZnO and NiO, like MnO, must be strongly partitioned into ilmenite relatively to silicate minerals under the reducing contact metamorphic conditions, if chromite is absent. The textural observations of ilmenite–sulfide and ilmenite–titanite–sulfide relationships indicate that Ti-magnetite, in contrast to ilmenite, is an unstable phase in the presence of sulfur-rich reduced metamorphic fluids and is completely replaced by sulfides, with the development of specific “octahedral meshes” of ilmenite in sulfides.

Effect of Thyroid Hormones on the Development of Asymmetric Pigment Patterns in Teleost Fish: Experimental Data on the Example of Amatitlania nigrofasciata (Cichlidae) and Poecilia wingei (Poeciliidae)

Thyroid hormones (THs) are the most important regulators of coloration ontogeny in teleosts. It has been shown experimentally that alterations in the hormonal status due to prolonged treatment with a biologically active form of THs, triiodothyronine, causes changes in the development of adult pigment patterns in bilaterally symmetrical Amatitlania nigrofasciata and Poecilia wingei. Induced hyperthyroidism in experimental fishes leads to an acceleration of coloration ontogeny and an increase in the frequency of asymmetry in various elements of the melanistic pattern. The revealed dependence of the development of asymmetric pigment patterns on the activity of the thyroid axis in fishes with varying degrees of metamorphic coloration transformations offers the prospect for further experimental studies of the role of the TH-signaling pathway in the evolution of teleosts.

Mineralogical and isotope-geochemical (δ13C, δ34S and Pb-Pb) characteristics of the Krasniy gold mine (Baikal-Patom Highlands): Constraining ore-forming mechanisms and the model for Sukhoi Log-type deposits

Orogenic gold deposits localized in carbonaceous sedimentary (black-shale) complexes are major contributors to worldwide balance of gold extracted from the crust, though there is a limited consensus about the role of host sedimentary rocks, involvement of external (i.e., magma-derived) fluids and brittle deformations into ore remobilization and transport. This paper presents the original results of mineralogical, petrographic and isotope-geochemical studies of rocks and ores from the large Krasniy gold deposit (Baikal-Patom plateau, southern Siberian craton) given in comparison with the thoroughly studied giant Sukhoi Log deposit, with both deposits hosted by the Neoproterozoic carbonaceous metasedimentary rocks. The multi-stage ore process occurred discretely at 200–400 °C (greenschist-facies metamorphism) and included (1) low-P-T diagenetic formation of globular pyrite, (2) catagenetic (<200 °C, 1–2 kbar) formation of small euhedral pyrite, (3) high-temperature and high-pressure (300–380 °C, 5–6 kbar) crystallization of arsenopyrite and pyrrhotite related to metamorphic transformation, and (4) formation of the major ore assemblage (arsenopyrite, pyrrhotite, pyrite meta-aggregates, native gold, galena, sphalerite, fahl ores) during almost isothermal decompression (270–320 °C, 0.5 kbar). Gold is detected as nanoparticles unevenly distributed at the surface of the early globular pyrite (up to 0.4 ppm) and occurs as inclusions in later metamorphic pyrite. Relatively narrow ranges of sulfur (δ34S within −4.7 – −6.9‰) and lead isotopic composition (206Pb/204Pb = 18.33–18.65, 207Pb/204Pb = 15.65–15.68 and 208Pb/204Pb = 38.13–38.82) in sulfides from the ores was continuously inherited from earlier generation of sulfides to the later (associate with native gold) and is similar to the values obtained for sulfides from the host Neoproterozoic metasedimentary rocks of the Aunakit formation. The compositional inheritance together with geochemical evidence of no additional contribution of К, Na, Mg and Si into the ores and no correlation between gold and organic carbon content highlight the absence of the external metasomatic overprint of metal-bearing fluids. Instead, both the above facts and high Au content (up to 1 ppm) in bitumens derived from the host metasediments indicate a key role of the host carbonaceous substrate in the supply of metals through release and local transport of internally derived diagenetic/catagenetic carbon-rich fluids. Overall, the obtained results for the Krasniy deposit led to distinguishing the three key stages of the gold deposit formation, including 1) sedimentation of gold-specialized sediments in the spreading of the back-arc basin, where gold was associated with the scattered diagenetic pyrite mineralization (610–590 Ma), 2) catagenetic redistribution of sedimentary pore fluids from preconditioned sedimentary rocks into the vaulted parts of gentle anticlines with the formation of abnormally high concentrations of gold (~570 Ma), and 3) metamorphic-metasomatic redistribution of gold as a result of decarbonization of catagenic fluid with the formation of economically significant ore bodies (450–420 Ma). The compilation of the available geochemical and isotopic data allows to suspect this model as a general for the other Bodaibo region deposits, so that it can be used further for prediction and exploration purposes.

Proterozoic Granitoid Magmatism at the Southwestern Margin of the Siberian Platform in the Tectonic History of the Angara–Kan Block

The large massifs of ancient granitoids of the South Yenisei Ridge are divided into three complexes that differ in the geological, geochemical, and geochronological features. The Tarak massif consists of two complexes of different ages: the S–A-type porphyritic granitoids (collisional) of the Tarak complex (1.84 Ga) and the A-type subalkaline granites (anorogenic) of the Telkun complex (1.76 Ga). The magmatic crystallization of gneiss granites of the Posolnenskii complex is interrelated with the late stage of metamorphism and falls into the age interval between the above two complexes (1789.8 ± 8.9 Ma). Metamorphic transformations of the enclosing formations are recorded by the presence of small bodies of charnockitoids with dates of 1.84 and 1.73 Ga.

ABOUT POSSIBILITY TO CLASSIFY COAL LAYERS HAZARDOUS CHARACTERISTICS BY GENETIC AND PROCESS PARAMETERS OF COALS

&#x0D; &#x0D; &#x0D; &#x0D; The analysis of Ukrainian legal environment has been performed for solid fossil fuels production, which has shown existing of contradictories between parameters describing the accuracy of forecast to manifest the coal layers hazardous characteristics during independent of mining and does not exclude any possibility for emergency situation to occur, independent of the preventive measures full implementation. The base to determine the coal layers hazardous characteristics are: average reflectance of vitrinite, presence of some components in organic matter (С0, О0, Н0, N0), alteration of moisture and mineral impurities content. For these classificatory parameters, their quantitative assessment is available in the whole multiplicity of coals metamorphic transformation. The specific electrical resistivity logarithm and other proxy parameters may serve as additional classificatory parameters to reveal any hazardous characteristics of anthracites after grounding their using in some ranges of metamorphism series. It has been established that the existing wide range of vitrinite reflectance alteration for anthracites specifies significant alterations in the fossil fuel structure and properties. In their process of metamorphism, these peculiarities of anthracite alterations have almost not been classificatory established by their genetic and process parameters.&#x0D; &#x0D; &#x0D; &#x0D;

3D reconstruction of fabric and metamorphic domains in a slice of continental crust involved in the Alpine subduction system: the example of Mt. Mucrone (Sesia–Lanzo Zone, Western Alps)

Geological mapping, multiscale structural analysis, and estimations of the degree of fabric evolution and of reaction progress allow the construction of a 3D quantitative model of structural and metamorphic gradients in a portion of continental crust deeply involved in the Alpine subduction system and mainly structured under eclogite-facies conditions before the continental collision. The investigated and modelled rocks outcrop in the surroundings of Mt. Mucrone, in the central Sesia–Lanzo Zone. The Geomodeller® software allowed a quantitative 3D estimation of domains characterized by homogeneous fabric evolution and metamorphic reaction progress (DFE and DRP, respectively) for two of the seven structural and metamorphic imprints detected in this area: the D2-eclogitic and D5-greenschist stages, which are the most pervasive at km scale. Such a 3D modelling clarifies mutual relationships between fabric and metamorphic gradients and indicates that: (i) DFE and DRP are closely related regardless of the rock type; (ii) the syn-deformational thermal regime can influence the degree of metamorphic transformation, if DFE remains below the 60% threshold; (iii) the phase transitions can not be properly implemented in quantitative geodynamic modelling without considering the heterogeneity of reaction progress and fabric evolution.

Four Stages of the Thermal Evolution of Eclogites from the Maksyutov Complex (South Urals)

Abstract —Based on a detailed electron probe microanalysis of the composition and zoning of coexisting minerals (garnet, clinopyroxene, and plagioclase), we have studied the P–T conditions of formation of high-pressure (HP/UHP) rocks of the Maksyutov eclogite–blueschist complex in the South Urals. We have established its periodic evolution and have determined the specific thermodynamic parameters of mineral formation at each stage of its geodynamic history, from the conditions of crystallization of the protolith to the final stages of retrograde greenschist metamorphism. The new analytical data on the composition of coexisting phases confirm the high-pressure formation of eclogites present as numerous lenses, boudins, and interlayers among blueschist and feldspar–mica schists in the lower part of the complex. Thermobarometric calculations of metamorphism parameters were performed for the Grt + Cpx ± Pl + Qz paragenesis using a Grt–Cpx geothermometer and a Pl–Cpx–Qz geobarometer. Garnet in eclogites of the Maksyutov Complex, being conservative to changes in the P–T conditions, has a direct, reverse, or inverse chemical zoning. Under equilibrium of garnet with omphacitic clinopyroxene, this zoning records conjugate progressive and regressive P–T paths reflecting the thermodynamic conditions at the certain stages of the terrane evolution. Based on the data obtained, we have recognized at least four P–T stages of progressive metamorphic transformations of the Maksyutov Complex: (1) &amp;gt;800–910 °C/~2.5–3.5 GPa; (2) 540–790 °C/2.0–3.5 GPa; (3) 410–690 °C/1.1–2.5 GPa; and (4) 310–520 °C/1.0–1.2 GPa. The estimated P–T parameters of the conjugate regressive stages of metamorphism are as follows: (1) 870–625 °C/3.5–2.5 GPa; (2) 745–615 °C/3.5–2.0 GPa; (3) 690–550 °C/1.5–1.0 GPa; and (4) 590–460 °C/1.2–0.6 GPa, respectively. The age data for the certain stages, along with the parameters of metamorphism, form a single P–T–t path of the complex, which determines the position of the gradient of the metamorphic field during the complex exhumation.

Integrating X-Ray Computed Tomography With Chemical Imaging to Quantify Mineral Re-crystallization From Granulite to Eclogite Metamorphism in the Western Italian Alps (Sesia-Lanzo Zone)

Metamorphic transformations and fabric evolution are the consequence of thermo-dynamic processes, lasting from thousands to millions of years. Relative mineral percentages, their grain size distribution, grain orientation, and grain boundary geometries are first-order parameters for dynamic modeling of metamorphic processes. To quantify these parameters, we propose a multidisciplinary approach integrating X-ray computed microtomography (µ-CT) with X-ray chemical mapping obtained from an Electron MicroProbe Analyzer (EMPA). We used a metapelitic granulite sample collected from the Alpine HP-LT metamorphic rocks of the Mt. Mucrone (Eclogitic Micaschists Complex, Sesia-Lanzo Zone, Western Alps, Italy). The heterogeneous Alpine deformation and metamorphism allowed the preservation of pre-Alpine structural and mineralogical features developed under granulite-facies conditions. The inferred granulitic mineral association is Grt + Bt + Sil + Pl + Qtz ± Ilm ± Kfs ± Wm. The subsequent pervasive static eclogite-facies re-equilibration occurred during the Alpine evolution. The inferred alpine mineral association is Wm + Omp ± Ky + Qtz+ Grt though local differences may occur, strongly controlled by chemistry of microdomains. X-ray µ-CT data extracted from on centimeter-sized samples have been analyzed to quantify the volumetric percentage and shape preferred orientation for each mineral phase. By combining tomographic phase separation with chemical variation and microstructures (i.e., different grain-size classes for the same phase and morphology of different pre-Alpine microdomains) the pre-Alpine mineralogical phases from the Alpine overprint have been distinguished and quantified. Moreover, the sample preserves 100% of the pre-Alpine granulite fabric, which surprisingly corresponds to less than 22% of the corresponding pre-Alpine metamorphic assemblages, while the Alpine eclogitic static assemblage corresponds to 78% though no new fabric is developed. This contribution demonstrates that the combined use of EMPA X-ray chemical mapping with the X-ray µ-CT shape analysis permits a dynamic approach to constrain the chemistry of the mineral phases linked to the development of metamorphic-related static and dynamic fabrics.

The relationship between crust-lithosphere structures and seismicity on the southeastern edge of the Tibetan Plateau

The crust-lithosphere structure, especially the discontinuities such as Moho and lithosphere-asthenosphere boundary (LAB), is important in the investigation of geodynamic process implications and tectonic evolution of the lithosphere and regional seismic activity. We stacked the S receiver functions from 51 permanent broad-band stations to investigate the crust-lithosphere structures beneath the southeastern edge of the Tibetan Plateau and further discussed the mechanism of lower-crust earthquakes, the regional tectonics deformation characteristics, and the relationship between the two discontinuities and seismicity in this region. The results show that the Moho depth increases from 40 to 52km beneath the Sichuan Basin to 56–74km on the both western side of the Longmenshan (LMS) fault and Anninhe-Zemuhe fault. The LAB depth ranges from 130 to 170km beneath the Sichuan Basin, and a shallow belt ranges from 100km to 130km around the Sichuan Basin. On the Moho depth contour map, 374 moderate earthquakes that accounted for 72.2%, corresponding to the depth range of 44–52km and 60–68km on the both sides of a narrow strip (longitude 102°~104°). On the LAB depth contour map, 321 earthquakes accounted for 62.15% in the depth range of 130–150km. The variation of LAB corresponds to the increasing crustal thickness, intensive lower crustal earthquakes (hypocenters about 60km and magnitude 4.0≤Ms.≤4.9) and surface abrupt elevations. It implied that Normal strong earthquakes generate the lower crustal earthquakes or aftershocks that resulted in the shear zones where fluid-induced metamorphic transformations, the eclogitization of dry granulite, and further affect the crustal thickness and deformation to control the spatial distribution of deep faults and seismicity.

Post-transcriptional regulation of insect metamorphosis and oogenesis.

Metamorphic transformation from larvae to adults along with the high fecundity is key to insect success. Insect metamorphosis and reproduction are governed by two critical endocrines, juvenile hormone (JH), and 20-hydroxyecdysone (20E). Recent studies have established a crucial role of microRNA (miRNA) in insect metamorphosis and oogenesis. While miRNAs target genes involved in JH and 20E-signaling pathways, these two hormones reciprocally regulate miRNA expression, forming regulatory loops of miRNA with JH and 20E-signaling cascades. Insect metamorphosis and oogenesis rely on the coordination of hormones, cognate genes, and miRNAs for precise regulation. In addition, the alternative splicing of genes in JH and 20E-signaling pathways has distinct functions in insect metamorphosis and oogenesis. We, therefore, focus in this review on recent advances in post-transcriptional regulation, with the emphasis on the regulatory role of miRNA and alternative splicing, in insect metamorphosis and oogenesis. We will highlight important new findings of miRNA interactions with hormonal signaling and alternative splicing of JH receptor heterodimer gene Taiman.

Metamorphic transformations of nitrogen functionalities: Stabilization of organic nitrogen in anthracite and its effect on δ15N parameter

Abstract The coal metamorphism, as it evolves the microstructure of the coals, would also have significant influences on the structural transformations and isotopic discriminations of the primary chemical moieties. The present study aims to illustrate the nitrogen functionalities present within the chemical framework of the bituminous coal samples from the Raniganj and the Jharia Basins and anthracite A samples of the fold-thrust belts of the Sikkim Himalayas as well as to document the metamorphic transformations of these nitrogenous moieties with the advent in the degree of the coalification. The stable carbon (−24.08 to −21.67‰ for bituminous coal samples and −23.91 to −21.39‰ for anthracite A samples) and nitrogen isotopes (1.64–2.81‰ for the bituminous coal samples; 1.07–3.44‰ for the anthracite A samples) do not show any significant variation with the vitrinite reflectance and, therefore, correspond to the terrestrial higher plant sources of the organic matter. Further, the weak shifts of stable nitrogen isotope values in the anthracite A samples may be attributed to the preservation of the organic nitrogen in the thermally stable aromatic and heterocyclic structures. The total organic carbon to total nitrogen (TOC/TN) ratio may represent the vascular organic matter input into the mire in the case of bituminous coal samples (33.49–43.69), while for the anthracite A samples, this ratio may be an indication of the preservation of the organic nitrogen in the stable chemical framework within the microstructure. The primary alteration of the labile nitrogen-containing groups including the pyrrolic structures would have been initiated by the aqueous fluid entering into the reactive chemical framework during hydrothermal metamorphism. During these processes, most of the nitrogen atoms would have been quaternarized, which is evidenced by strong correlation (r = 0.96) between the relative area ratio of the graphitic to pyrrolic nitrogen and the mean random vitrinite reflectance. Moreover, the intensity and relative area ratio of the pyridinic to pyrrolic nitrogen are strongly correlated with the mean random vitrinite reflectance (r = 0.92 and 0.89, respectively) suggesting entanglement of the nitrogen atoms within the pyridinic forms as well with increasing metamorphic temperature. These structural rearrangements would have intensified the cyclazine structures and preserved the pyridinic forms in the anthracite A samples. Due to the increase in aromaticity and consequent increase in surface hydrophobicity and decrease in the interlayer spacing, the fluid would have lost its mobile phase and could not invade the relatively inert aromatic clusters. Thus, the organic nitrogen atoms were preserved within the thermochemically stable functionalities without showing any substantial isotopic variation. The scientific contribution of this present investigation, hence, lies in depicting the transformation of organic nitrogen among the pyrrolic, pyridinic and the cyclazine moieties with insignificant shifts in stable nitrogen isotope during coalification.

Dirt in the Lens

Responding to the theme of ‘Animism and the Elemental’ Dirt in the Lens explores two historic image-series Claude Cahun’s Je tends le bras (1932) and Ana Mendieta Siluetas (1973-1980) alongside a contemporary work, Cassils’ Becoming an Image (2013): Cahun’s arms extending from within a hollowed rock; Mendieta’s relief hollowed in a bed of earth; Cassils punching and kicking a 2,000-Lb block of clay in memory of murdered transgender persons.Each work unites the photographic, the sculptural and the performative. The paper discusses Cahun, Mendieta and Cassils in relation to Stengers’ conception of the ‘animate earth’ (2012: 6). The photographic performance becomes an assemblage (agencement) which ‘lures us into feeling’, generating ‘metamorphic transformations in our capacity to affect and be affected’ (9). The performances bear out ‘that we are not alone in the world’ (ibid.). Perceptual changes are understood as a function of molecular movements (Bergson 1896: 8); flesh and thought are understood in term of images. After Stengers, we may ‘freely speak of magic’ (7), since the artists change everything [they] touch’ (8) — but the change belongs, first of all, to the earth. Whilst the performances may remain ultimately anthropocentric works, each proposes that there are only ‘nonhuman becomings’ (Deleuze and Guattari 1994: 169). Each connects the ‘phenomenological body with cosmological forces’, testifying to the ‘body's immersion and participation in nature, chaos, materiality’ (Grosz 2008: 3).

The Effects of Earthquakes and Fluids on the Metamorphism of the Lower Continental Crust

AbstractRock rheology and density have first‐order effects on the lithosphere's response to plate tectonic forces at plate boundaries. Changes in these rock properties are controlled by metamorphic transformation processes that are critically dependent on the presence of fluids. At the onset of a continental collision, the lower crust is in most cases dry and strong. However, if exposed to internally produced or externally supplied fluids, the thickened crust will react and be converted into a mechanically weaker lithology by fluid‐driven metamorphic reactions. Fluid introduction is often associated with deep crustal earthquakes. Microstructural evidence, suggest that in strong highly stressed rocks, seismic slip may be initiated by brittle deformation and that wall‐rock damage caused by dynamic ruptures plays a very important role in allowing fluids to enter into contact with dry and highly reactive lower crustal rocks. The resulting metamorphism produces weaker rocks which subsequently deform by viscous creep. Volumes of weak rocks contained in a highly stressed environment of strong rocks may experience significant excursions toward higher pressure without any associated burial. Slow and highly localized creep processes in a velocity strengthening regime may produce mylonitic shear zones along faults initially characterized by earthquake‐generated frictional melting and wall rock damage. However, stress pulses from earthquakes in the shallower brittle regime may kick start new episodes of seismic slip at velocity weakening conditions. These processes indicate that the evolution of the lower crust during continental collisions is controlled by the transient interplay between brittle deformation, fluid‐rock interactions, and creep flow.