Metamorphic Phenomena Research Articles

Revelation of metamorphic phenomenon through the equivalent mechanisms and development of the novel metamorphic epicyclic gear trains

Epicyclic gear train, a typical higher pair mechanism with one-wheel axis that revolves around another fixed axis, has been widely used in mechanism design. However, applying the metamorphic mechanisms to the epicyclic gear trains remains a challenge. This paper analyses the metamorphic phenomenon of epicyclic gear trains using the equivalent mechanism approach and presents for the first time a set of novel metamorphic epicyclic gear trains with variable motion branches and changed configurations. Three 5-bar equivalent mechanisms of typical epicyclic gear trains and their equivalent geometrical relationships are introduced based on the instantaneous screw axes of the gear pairs. First- and second-order kinematic models of the equivalent mechanisms are established to obtain motion branches and their corresponding constraint conditions. With the equivalent geometrical relationship, the configurations and the motion branches of the epicyclic gear train are identified, and the constraint conditions are obtained. A set of novel metamorphic epicyclic gear trains are therefore designed by implementing the metamorphosis technique that can realize the configuration transformation of an epicyclic gear train under constraint conditions. A metamorphic epicyclic bevel gear clamping mechanism is further designed as an example to demonstrate the application of the metamorphic epicyclic gear mechanisms.

U-Pb, Hf isotope and REE constraints on high-pressure acid migmatites from the Cabo Ortegal Complex (NW Spain): New evidence of short-duration metamorphism in a Variscan subduction channel

Paired LA-ICP-MS UPb and LuHf isotopic data and trace element data are reported on zircon in thin section from poorly known acid migmatites exposed in the Cabo Ortegal Complex, Western Variscides, NW Spain. The migmatites are part of the high-pressure granulite unit, tectonically placed between the eclogite and ultramafic units. Large oscillatory zoned zircon cores date the felsic igneous protolith at 459 ± 7 Ma as a minimum age reflecting a protracted basic magma differentiation in a Cambro-Ordovician arc setting. Lower Th/U, weakly- to un-zoned overgrowth rims are attributed to partial melting at 392 ± 5 Ma during high-pressure metamorphism. The distinctly lower epsilon Hf (+4.0) of the rim relative to the core (+8.2) implies an open-system behavior metamorphism and mass transfer between different units in deep parts of a subduction channel during the Variscan Orogeny. Tiny xenomorphic zircon crystals devoid of internal microstructures dated at 355 ± 4 Ma and with nearly flat REE patterns are interpreted as product of metamorphic overprint driven by hot fluids. The latter is envisaged as a subduction channel short-duration metamorphic phenomenon.

Short-duration regional metamorphic event recorded in a Variscan subduction channel (Malpica–Tui eclogites, NW Iberia)

An isotopic resetting event is disclosed at ca. 350 Ma, based on Rb–Sr isotopic analyses (whole rock, garnet, clinopyroxene and phengite fractions) of eclogites with coronitic garnet and planolinear eclogites from the Malpica–Tui Allochthonous Complex (NW Iberia). The eclogites were buried, deformed/recrystallized and subsequently exhumed in a Late Devonian subduction channel. Lu–Hf and Sm–Nd isotopes date a ca. 375-Ma metamorphic peak of the subduction–exhumation cycle that occurred under ~ 2.6 GPa and 610–640 °C and was overprinted by the 350-Ma event, which occurred still under high-pressure conditions. The latter resetting is interpreted as a very short-duration regional metamorphic phenomenon recorded by high-pressure rocks in the west European Variscan belt at time scales shorter than those characteristic of orogenic lithosphere in subduction/collision cycles.

Eclogites in the interior of the Tibetan Plateau and their geodynamic implications

Eclogites have been recently reported in the interior of the Tibetan Plateau, including in the central Qiangtang metamorphic belt, in the Basu metamorphic massif of the eastern Bangong-Nujiang suture zone, and at Songdo and Pengco in the eastern Lhasa terrane. Some typical ultrahigh-pressure (UHP) metamorphic phenomena, e.g., garnet exsolution from clinopyroxene, were documented in the Basu and Pengco eclogites. The UHP metamorphism in the interior of the Tibetan Plateau marked by these eclogites generally took place in the Early Mesozoic. Along with exhumation of these eclogites, (post-) collision-related magmatism extensively occurred around the central Qiangtang belt, the eastern Bangong-Nujiang suture zone, and the eastern Lhasa terrane. The occurrence of these Early Mesozoic eclogites manifests an out-of-sequence evolution of the Tethys, and they could be a product of diachronous collision between the eastern Qiangtang terrane and the irregular continental margin of the united western Qiangtang-Lhasa plate, along the linked eastern Bangong-Nujiang-central Qiangtang zone. The collision-related magmatic rocks could have been originated from lithospheric thickening, melting, or detachment due to the collision. The presence of UHP metamorphic rocks in central Qiangtang and Basu implies likely continental deep-subduction, and the denudation of these two metamorphic zones could have served as the source of the Triassic turbidites in the Songpan-Garze complex and the Jurassic turbidites in the western Bangong-Nujiang zone, respectively. However, studies of the eclogites in the interior of the Tibetan Plateau just began, and many principal aspects still remain to be explored, such as their distributions, typical lithologies and minerals, temperature-pressure conditions, timing of formation and exhumation, protoliths and tectonic setting, and relationship with the evolution of the Tethys and large-scale basins in Tibet.

Larval arm resorption proceeds concomitantly with programmed cell death during metamorphosis of the sea urchin Hemicentrotus pulcherrimus

Sea urchins are excellent models to elucidate metamorphic phenomena of echinoderms. However, little attention has been paid to the way that their organ resorption is accomplished by programmed cell death (PCD) and related cellular processes. We have used cytohistochemistry and transmission electron microscopy to study arm resorption in competent larvae of metamorphosing sea urchins, Hemicentrotus pulcherrimus, induced to metamorphose by L-glutamine treatment. The results show that: (1) columnar epithelial cells, which are constituents of the ciliary band, undergo PCD in an overlapping fashion with apoptosis and autophagic cell death; (2) squamous epithelial cells, which are distributed between the two arrays of the ciliary band, display a type of PCD distinct from that of columnar epithelial cells, i.e., a cytoplasmic type of non-lysosomal vacuolated cell death; (3) epithelial integrity is preserved even when PCD occurs in constituent cells of the epithelium; (4) secondary mesenchyme cells, probably blastocoelar cells, contribute to the elimination of dying epithelial cells; (5) nerve cells have a delayed initiation of PCD. Taken together, our data indicate that arm resorption in sea urchins proceeds concomitantly with various types of PCD followed by heterophagic elimination, but that epithelial organization is preserved during metamorphosis.

Gene expression profiling between embryonic and larval stages of the silkworm, Bombyx mori

To elucidate the molecular mechanisms associated with metamorphic phenomenon relating to Bombyx mori, an important organism in the sericulture industry, we identified genes that are expressed in the different developmental stages, specifically the embryonic (ES) and larval (LS) stages of B. mori. Of 8230 high-quality ESTs from two full-length enriched cDNA libraries, 3442 of the ES ESTs were coalesced into 1325 clusters, while 4788 were coalesced into 927 clusters. The functional classification of these ESTs based on Gene Ontology showed that the types of genes that are associated with oxidoreductase activity, enzyme inhibition, and larval development were highly observed in LS, whereas the types of genes that are involved in nucleotide binding, enzyme activity, and protein transport activity were highly observed in ES. In addition, when the gene expression profile between ES and LS was examined by counting the EST frequencies in each library, 69 genes were identified as being either up- or down-regulated in the larval stage compared to the embryonic stage ( P > 0.99) and this was confirmed by semi-quantitative RT-PCR. The results show that genes involved in proteolysis and peptidolysis, and lipid and carbohydrate metabolism were dramatically up-regulated in LS, while those related to protein metabolism, DNA/RNA, and coenzymes were highly down-expressed. In particular, a GO analysis of these genes revealed that genes that are involved in hydrolase activity were observed to be highly expressed in amount as well as diversity in LS, while those involved in nucleic acid binding were highly expressed in ES. These data may contribute to elucidating genetic events that distinguish the developmental stage and to our understanding of the metamorphosis of B. mori.

EVOLUÇÃO PETROLÓGICA E ESTRUTURAL DA PORÇÃO ORIENTAL DO ESTADO DE MINAS GERAIS E SUAS IMPLICAÇÕES GEOTECTÔNICAS

A metamorphic terrain with high-grade rocks of the Atlantic Metamorphic Belt underlies the eastern part of Minas Gerais State, from south of the town of Manhuaçu to Caratinga. This terrain comprises peraluminous gneisses, igneous and meta-igneous rocks. Granulites occur as small nucleus and vary in composition between peraluminous and basic to intermediate, the latter represented by enderbitic mobilizate. Their formation, as well as that of migmatites of granitic composition, is considered to be related to mafic and ultramafic intrusions. In basic granulites, garnet-bearing mineral assemblages, with the development of corona textures, attest the effects of granulite facies metamorphism, although igneous assemblages and textures are still well preserved. Retrograde alteration assemblages are locally preserved. Despite of the diversity of metamorphic phenomena in this area, T and P calculations reveal consistent results. Temperature and pressure calculations were undertaken in basic granulites slightly affected by the retrograde process. Using Fe +²/Mg exchange between garnet and ortopyroxene as geothermometers and the exchange reaction: An +En = 2/3Pyr + 1/3Grs + Qz as geobarometers peak metamorphic temperatures in the range of 660 to 760°C, at 4,8 to 6,6 Kbar are obtained. Mineral, textural and geochemical evidences indicate that the metamorphic conditions have changed with time and suggest that the formation of the granulites is caused by the underplating of magmas, probably mantle-derived, at the base of the crust. Several rations between major, trace and rare earth elements have been employed. The basic rocks are similar in composition to tholeiites generated in within-plate tectonic settings. Positive correlations netween K2O and SiO2 and negative between MgO and SiO2 in fresh gabbro-noritic rocks and enderbites indicate magmatic differentiation. The geochemical character of altered basic rocks displays an unsystematic dispersion in correlations diagrams. This lack of correlation coupled with field and petrographic suggest the effects of a late metasomatic event on these rocks. This metasomatism comprises the dispersed development of charnockitic rocks with large K-feldspars and quartz crystals. Later dynamic processes gave place to subvertical shear zones with a well defined foliation.

Examples and genetic significance of the formation of iron oxides in the Nigerian banded iron-formations

Ore microscopic studies reveal two main parageneses in the banded iron-formations of Nigeria. In the low-grade metamorphic schist belts of northern Nigeria, a magnetitic paragenesis comprising magnetite, silicates (grunerite and garnet), and quartz is developed. Magnetite which sometimes contains carbonate inclusions is markedly martitized. In contrast, the higher-grade metamorphic terrains of central Nigeria exhibit a different paragenesis consisting of hematite (including specularite) and quartz. Here, minerals of the magnetitic paragenesis only occur as relics. The protolith of these banded iron-formation occurrences envisioned as carbonate-containing sediments, with high concentrations of Fe and Si, and lower contents of Ca, Mg, Al (and also Mn where they are associated with gondite) underwent both submarine weathering and metamorphic changes in their evolution. During submarine weathering, sheet silicates and porphyroblasts of Fe-Mn-(Mg-Ca)-carbonate solid solutions, were formed. At the outset of a regional metamorphic episode, grunerite, garnet and porphyroblastic magnetite were developed. Magnetite formed at the expense of carbonate and sheetsilicates but was later martitized under post-metamorphic conditions. In the course of a later heterogeneous tectono-metamorphic event, martitized magnetite was transformed as follows: under low-grade metamorphism, as observed in the northern Nigerian schist belts, recrystallization into coarse-grained martite occurred, while at the higher grades of metamorphism in central Nigeria, recrystallization into hematite and, ultimately, specularite, took place. This relationship between magnetite and hematite has also been observed in many other banded iron-formations from different parts of the world, thus underscoring its widespread significance. Magnetite crystallizes first at the expense of carbonate and silicate minerals and hematite is subsequently derived from it directly or generally through martitization. This metamorphic phenomenon contradicts the common assumption that magnetite and hematite in banded iron-formations are invariably the products of direct precipitation from solution, in response to changes in environmental Eh/pH or different (reducing/oxidizing) diagenetic alterations of precipitated ferric hydroxide.

Genesis of the Olympias carbonate-hosted Pb-Zn (Au, Ag) sulfide ore deposit, eastern Chalkidiki Peninsula, northern Greece

Genesis of the Olympias carbonate-hosted Pb-Zn (Au, Ag) sulfide ore deposit, eastern Chalkidiki Peninsula, northern Greece

Achievement in Isolation: A.W. Howitt, Pioneering Investigator of Metamorphism in Australia

The earliest coherent observations of metamorphic phenomena in Australia were made by a policemagistrate, stationed in a remote part of Victoria and largely self-taught in geology. In a series of reports and papers issued between 1875 and 1892 that magistrate, Alfred William Howitt, recorded details of metamorphic progressions found in the mountains of eastern Victoria - from folded Palaeozoic strata to crystalline schists and gneisses, and of different sorts of granitic bodies in the regional metamorphic association.Howitt worked at a time when the metamorphic status of crystalline schists was far from generally accepted in Europe and America; some still regarded them as portions of unchanged Primitive crust. Like George Barrow in Scotland - whose work in some ways he anticipated, Howitt, however, through the influence of Lyell's writings, began as a believer in metamorphism. But whereas Barrow is respected for innovative contributions to metamorphic thought and method, Howitt's isolation in Australia kept his work little known. In fact, as recent studies show, Howitt was investigating a regional metamorphism different in style from that of Barrow. Howitt not only pioneered metamorphic petrology in Australia, he really began the study of what is now termed low-pressure regional metamorphism.This paper seeks to set Howitt's metamorphic investigations in the contexts of his career and the then condition of his chosen subject. The principal influences on his approaches to petrography and metamorphism are seen to be German in origin. Howitt may have had no formal training in science but as a boy he lived in Germany for some years and learned the language. It was to be a most useful acquisition.

Regional metamorphism of the Vassalboro Formation, south-central Maine, USA: a case study of the role of fluid in metamorphic petrogenesis

Progressively metamorphosed carbonate rocks of the Vassalboro Formation serve a′ natural laboratory for the investigation of fluid/rock interactions during metamorphism. An integrated study of their whole-rock chemistry, mineralogy, mineral chemistry and mineral abundances has led to the following results. (a) Prograde mineral reactions involved hydrolysis as well as dehydration and decarbonation. The hydrolysis reactions have resulted in an almost quantitative extraction of K and Na from high-grade metacarbonates. (b) Prograde mineral reactions buffered the X CO 2 of coexisting metamorphic fluid during almost all of the rocks’ metamorphic history. (c) The carbonate rocks were infiltrated by large volumes of H 2 O-rich fluid while the buffering reactions progressed during the metamorphic event. Some high-grade metacarbonates were infiltrated by at least 3 rock volumes of fluid. Combined buffering and infiltration appears to be a general metamorphic phenomenon in carbonate-bearing rocks to depths of ∼30 km in the crust. (d) There is an excellent positive correlation between the heat budget of individual metacarbonate rock samples and calculated fluid/rock ratios. Convective heat transfer by metamorphic fluids is therefore likely to be an important item in the heat budget of metamorphic terrains. Consideration of these results leads to a model of regional metamorphism which involves infiltration of rock by large volumes of acid, H 2 O-rich fluid (large-scale acid infiltration metasomatism?). In this model, the infiltrating fluid exerts enormous control over the mineralogical evolution of the carbonate rocks during the metamorphic event: it drives mineral reactions, it changes whole-rock chemistry and it supplies heat.

Larval-specific protein in the order dictyoptera—II. Antagonistic effects of ecdysone and regeneration on LSP concentration in the hemolymph of the oriental cockroach, Blatta orientalis

1.1. Larval-specific protein, LSP, reaches a peak concentration in cockroach hemolymph 24–48 hr prior to ecdysis.2.2. When ecdysis is delayed by autotomy-induced leg regeneration, LSP continues to accumulate and reaches a higher than normal peak concentration 24–48 hr prior to the delayed ecdysis.3.3. Ecdysone inhibits the regeneration-induced delay and returns the normal pattern of ecdysis and LSP accumulation.4.4. By using single and multiple autotomies it was demonstrated that the amount of accumulated LSP is proportional to the length of molting cycle delay rather than the amount of regenerating tissue.5.5. It is suggested that the greater peak concentration of LSP seen in metamorphic molting cycles (Kunkel & Lawler, 1974) is a function of the greater length of metamorphic molting cycles rather than being specifically a metamorphic phenomenon.

Earthquake processes in a micromorphic continuum

The paper introduces a new model earthquake process based on the theory of micromorphic continua. The processes in a focal region are described by deformations of microstructure in time. It is assumed that the fracturing processes as well as phase transformation of metamorphic phenomena have caused in the past certain non-reversible changes which determine the microstructure of focal region. These internal microstructural elements form the attaching points around which the couple stresses arise. The properties of focal region are determined by the constitutive equations. The micromorphic mechanics considers the existence of body couples as determined by a regional stresses and looks after a response field of stresses, stress moments and strains in the focal region. Further, it is explained how microdislocation field is connected with microdeformations and micromorphic structure. In the considered earthquake structure model a microanisotropy is assumed through the tensor of microinertia. This tensor describes a distribution of microelements. Simple solutions of wave processes in a focal region are presented. The dispersion of waves is discussed.

Rejection of skin homografts in larvae of Rana pipiens.

AbstractLarvae of the leopard frog, Rana pipiens, regularly reject skin homo‐grafts. Grafts from sibling larvae show initial signs of necrosis later than grafts from non‐siblings; grafts between very young feeding larvae also show initial necrosis later than those between older larvae. Homograft rejection pattern is essentially the same in larvae of stage IV and older, in hypophysectomized larvae, and in larvae immersed in thyroxine for two weeks after grafting. Second grafts from the same donor are necrotic 4 to 5 days before first grafts are. The conclusion is drawn that destruction of skin homografts in frog larvae is independent of metamorphic phenomena, and is an immunologic reaction, possibly involving the thymus gland. The weakened response of very young larvae may reflect an immunologic mechanism that is not yet mature.

Certain aspects of basaltoid metallogeny of Urals

New data on the dependence of endogenic formation of ores from the region's tectonic history and its magmatic and metamorphic phenomena were obtained in the Urals in recent years. This article is a discussion of certain aspects of the relationship between pyritic as well as, to some extent, contact-metasomatic ore deposition, and developments of geosynclinal magmatism with the accompanying regional metamorphic and metasornatic alterations.--Author.

CORONITES FROM INDIA AND THEIR BEARING ON THE ORIGIN OF CORONAS

Detailed petrographic and mineralogic studies of some coronites from India confirm observations of previous workers on similar rocks. The first rhombic pyroxene corona is formed by replacement of olivine, and the second corona of amphibole, amphibole-spinel, and/or garnet develops by replacement of plagioclase. Certain features such as the clouding of plagioclase, pyroxenes, and olivines and the recrystallization of primary minerals ( e.g., pyroxene) and the development of garnet are commonly noted in coronites. Their significance as metamorphic phenomena and their relationship with corona formation is stressed. From a crystallochemical examination of the reacting minerals and the resulting corona minerals, the writer concludes that the first corona of rhombic pyroxene is formed from olivine by rearrangement of the independent SiO 4 tetrahedra of the nesosilicate into chains in the inosilicate rhombic pyroxene. During metamorphism this reaction is favored along the olivine-plagioclase interface where disorder and chemical potential are high and is inhibited along the olivine-pyroxene interface where disorder and chemical potential are low. The reaction is initiated by an intergranular film of water which is effective in breaking bonds in olivine. For formation of the second corona minerals, disruption of the plagioclase structure is essential. Inosilicate amphibole is the simplest structural change from plagioclase and is presumably formed in the presence of lower concentrations of water. The formation of nesosilicate garnet requires complete disruption of plagioclase and a change in the co-ordination of Al +3 , which probably occurs as a result of greater concentrations of water. Biotite, amphibole, amphibole-spinel, and garnet coronas around iron ore and spinel are also metamorphic and are formed in part by replacement of plagioclase. Regional metamorphism at comparatively high temperatures, under water-deficient conditions and with little shearing stress, gives rise to coronas; the degree of development is partly a function of time. Data and observations are given in support of these conclusions.

A Possible Connection between Certain Metamorphic Phenomena and Anomalies in the Earth's Magnetic Field

A Possible Connection between Certain Metamorphic Phenomena and Anomalies in the Earth's Magnetic Field

A Metamorphic Phenomenon of Ultrabasic Rocks Caused by Intrusion of Granodiorite in Miyamori District, Iwate Prefecture ------ Metamorphism of Diopside-Hornblende Rock

Ultrabasic rocks exposed in Miyamori district, 16km E of Hanamaki-machi, Iwate Prefecture, is intruded by granodiorite on its western side., The metamophic effect of the acid intrusive is seen in a zone about 24km wide along the contact., In this zone, diopside-hornblende rock, a member of the ultrabasic complex, occurs as parallel dikes cutting serpentinized dunite., In the latter rock, porphyroblasts of tremoliteactinolite have been formed by the metamorphism, while the former rock has been converted to the following rock types : 1, Grossularite-basic plagioclase rock (sometimes with epidote and hedenbergite) 2, Bluish green amphibole-biotite rock 3, Biotite-bluish green amphibole-acidic plagioclase rock The first type is characterized by richness in Ca, the second by that in K, Mg and Fe, while the third by that in Na, Fe and Mg (see Fig 6)., It is concluded that these changes have been brought about by combined metasomatism and metamorphic differentiation ; Al, K, Na and Si having been introduced to the diopside-hornblende rock while Fe, Mg and Ca having migrated within the same rock mass.,

Some Metamorphic Phenomena Produced by Gabbroic Intrusion

Locally, metamorphism by the Duluth gabbro has caused progressive changes in texture and mineralogy of the Knife Lake slate, producing a granulitic and granoblastic rock very similar to the gabbro in composition. Several metamorphic zones may be roughly delineated. These zones are characterized by mineral suites different from those developed in zones surrounding granite and especially by the rather abundant development of orthopyroxene in some zones. This mineral development is attributed to the influence of the gabbroic magma and is thought to represent a characteristic type of metamorphism produced in argillaceous rocks by such magma.

XIV.—The Igneous and Metamorphic History of Cromar, Deeside, Aberdeenshire

Middle and Lower Deeside lie within the belt of injection and high-temperature metamorphism made famous by the pioneer researches of Mr George Barrow. In this paper are recorded the results obtained from a study of Cromar, an area small enough to admit of detailed petrographical treatment and yet large enough to exhibit a considerable variety of igneous and metamorphic phenomena. Of the three great phases of igneous activity there displayed, one is older than the epoch of maximum crustal movements, the second is closely connected with these, and the third is later; the rocks of each period have their own quite definite chemical, petrographical, and geological characteristics. Whilst here most attention will be directed towards the second group, that associated with the movements, an account of the other two groups will be given adequate for a discussion of the full igneous history of the area.