Academic literature on the topic 'Earth internal structure'

Quartz and orthopyroxene in mafic rocks are commonly observed to be surrounded by fringes of granular pyroxene, and of olivine and clinopyroxene, respectively. This study reproduces the conditions of formation of these textures, and investigates their origins, kinetics and phase relations. Pieces of silica glass or crystals of orthopyroxene were dissolved into tholeiitic and slightly alkaline basalts, suspended from wire loops in an atmospheric pressure quenching furnace, and run for 10 minutes to 32 days at subliquidus temperatures between 1120° and 1190°C and oxygen fugacities close to the QFM buffer. Polished sections of charges were examined primarily by backscattered electron imagery and by microprobe analysis. The textures developed in silica dissolution experiments consist of fringes of elongate skeletal pyroxenes radially arranged around the silica. The pyroxenes first nucleate on the surface of the silica. As dissolution continues, growth continues mostly on existing crystals, rather than by the nucleation of additional crystals. Dissolution rates for silica range from 2.8*10⁻¹¹ to 4.4*10⁻¹⁰ms⁻¹, and are time-independent until growth of the pyroxene fringe hinders transport processes in the melt. This causes dissolution to slow down, until it ceases altogether after 3 to 8 days. A silica-rich layer of melt forms around the surface of charges run at higher temperatures, suggesting that convection driven by variations in surface tension may operate in the charges. The textures developed in orthopyroxene dissolution experiments consist of granular olivines, some of which nucleate on the pyroxene surface, whereas others nucleate within the pyroxene as a result of the decomposition of included phases. With time, olivine crystals become connected and form complex grain shapes. Dissolution rates for orthopyroxene range from 1.7*10⁻¹¹ to 1.2*10⁻⁹ ms⁻¹. At higher temperatures dissolution rates are constant, but at lower temperatures dissolution is time-dependent. Unlike silica dissolution, orthopyroxene dissolution does not cease as a result of continued neocryst growth hindering melt transport, indicating that the fringe remains permeable. For both systems, the neocryst compositions are strongly dependent on the chemistry of the melt formed at the interface between the dissolving crystal and the bulk melt, and the neocrysts may be metastable with respect to the bulk melt. Chemical equilibration of olivine neocrysts with time is observed for longer experiments. Textural equilibration of olivine grains occurs by the processes of liquid-phase sintering in runs longer than 12 hours. Subliquidus dissolution data are applied to textures from natural samples collected from dykes, lava flows and lava lakes, to estimate the residence time of reacted crystals; values range from 0.6 to 208 days for reacted quartz, and from 0.7 to 462 days for reacted orthopyroxenes. The rates of cooling of the magma and the size of the magma body in which the reaction occurred are also estimated.

This PhD is about the serpentinitic matrix, mafic crust and exotic ultramafic blocks of the Villa Clara serpentinitic mélange (VCSM) in central Cuba in an attempt to evaluate the evolution of oceanic lithosphere. Each of these units bears witness of mantle source composition, origin of oceanic crust and its relation to the mantle, ocean floor metamorphism, metasomatism and fluid flux in the subduction zone. The study of the serpentinitic matrix allowed the identification of two peridotite protoliths. Group A, with fertile compositions (high Al2O3 and low Cr# in pyroxene and spinel and enriched in heavy rare earth elements) and group B, displaying refractory compositions (low Al2O3 and higher Cr# in pyroxene and spinel compositions and depleted in middle and heavy rare earth elements). Group A can be related to typical abyssal/fracture zone peridotite, whereas group B is typical of forearc peridotite. Melting modelling shows that, group A resulted from low melting degrees (c. 4-8%) of a depleted mantle source, whereas group B reached up to c. 14-22% melting upon a two-stage melting of a depleted mantle followed by melting of a protolith similar to group A. The studied mafic crust includes rocks of sub-volcanic (diabase and microgabbro) and plutonic origin (cumulate gabbro and olivine gabbro). The sub-volcanic unit attests for two types of mafic magma: group 1 displays forearc basalts signature (FAB; low Ti/V ratio) and group 2 island arc tholeiite composition (IAT; medium Ti/V ratio), both with positive Th and negative Nb anomalies in comparison to N-MORB compositions. These compositions as well as the isotopic signature of the plutonic unit (low 143Nd/144Nd and low 87Sr/86Sr) point to a subduction-related imprint. Geochemical evidence supports a genetic relationship between the protoliths of the serpentinitic matrix rocks and the sub-volcanic mafic crust. An indirect evidence is the light rare earth element enrichment of group B peridotites, which is commonly interpreted as a result of re-equilibration with percolating basaltic melts like those represented by the sub-volcanic mafic crust. Also, melting modelling of primitive melts of the mafic crust (group 1-FAB related) results in c. 8-10 % melting of an abyssal mantle source like group A peridotites that produced a residue like group B peridotites. On the other hand, ocean floor metamorphism affected the mafic crust, which displays greenschist to amphibolite facies assemblages that attest for low pressure/low to medium temperature at shallow depths. This process had an impact on the concentration of mobile elements. A different metasomatic/enrichment process is recorded by trace element geochemistry and stable and radiogenic isotopes (B, Nd, Sr and Pb) in the serpentinitic matrix. The isotopic relations point to a slab fluid formed after devolatilitzation of the subducting plate as the source of metasomatic agent. The slab fluid is composed of diverse proportions of altered oceanic crust fluid (AOCF), global subducting sediment fluid (GLOSSF) and terrigenous fluid (TERF). The combination of these three isotopic reservoirs with an already serpentinized mantle related to ocean floor hydration reproduces the isotopic signature of the serpentinitic matrix of the VCSM. This result is in agreement with evidence provided by the high-pressure exotic ultramafic block of the VCSM, which showssimilar isotopic composition indicating interaction with a similar fluid in a context of subduction. The petrological and geochemical characteristics of the exotic ultramafic block allow distinguishing two types of serpentinite: i) antigorite-serpentinite and ii) dolomite-bearing antigorite serpentinite. Both represented a subducted peridotite that derives from a peridotite protolith locally CaO-enriched as a result of infiltration of a H2O-CO2 fluid mixture. Fluid infiltration in the subduction channel triggered serpentinization /carbonation and formation of tremolite veins and associated blackwalls developed in host antigorite-serpentinite. Mineralogical and chemical zoning in the blackwall (Atg + Chl + Tr towards the host serpentinite and Chl + Tr towards the vein) attest for metasomatic changes in fluid composition during fluid-rock interaction. The differences in chemical composition between blackwall and antigorite-serpentinite show that the infiltrating fluid was enriched in Ca, Al, LILE and LREE. Pseudosection modelling in the vein structure indicates that their formation took place at c. 4S0QC and c. 10 kbar. All these findings allow constraining the geodynamic evolution of the Villa Clara serpentinitic mélange in the context of the Caribbean realm. The serpentinitic matrix attests for two contrasting geodynamic settings. Group A peridotites formed at an abyssal/fracture zone setting in the Proto-Caribbean oceanic basin, whereas group B peridotites, exotic ultramafic block and mafic crust are pointing to a forearc setting. Both scenarios are reconciled in a geodynamic model of Upper Jurassic-Lower Cretaceous oceanic lithosphere formation upon break-up of Pangea followed by subduction initiation, likely at a fracture zone setting, during the early Cretaceous, and further development of a serpentinized forearc mantle and associated subduction channel during Lower-Upper Cretaceous time until final emplacement of the ensemble (serpentinitic mélange) during the latest Cretaceous-Eocene.<br>Aquesta tesi doctoral tracta sobre la matriu serpentinítica, escorça màfica i els blocs exòtics ultraàafics de la mélange serpentinítica de Villa Clara situada a Cuba Central. El propòsit és avaluar l'evolució de la litosfera oceànica. Cadascuna d'aquestes unitats proporciona informació sobre la composició original del mantell, l'orígen de la escorça oceànica i la seva relació amb el mantell, el metamorfisme de fons oceànic, el metasomatisme i el flux de fluids en la zona de subducció. L'estudi de la matriu serpentinítica ha permès l'identificació de dos protòlits de peridotita. El grup A, amb composicions fèrtils (alt Al2O3 i baix Cr# en piroxens i espinela, així com un enriquiment dels elements de les terres rares pesades) i el grup B, que mostra composicions refractàries (baix Al2O3 i alt Cr# en piroxens i espinela, així com un empobriment en els elements de les terres rares mitjanes i pesades). El grup A es pot relacionar amb peridotites abissals / zona de fractura, mentre que el grup B té composicions típiques d'avantarc. Els models de fusió mostren que el grup A és el resultat de la fusió a graus de fusió baixos (c. 4-8%), mentre que el grup B pot arribar fins a c. 14-22% de fusió després d'una fusió en dos passos, la primera a partir d'un mantell empobrit i la segona per una fusió d'un protòlit similar a les roques del grup A. L'escorça màfica aquí estudiada inclou roques d'origen subvolcànic (diabasa i microgabre) i plutònic (acumulats de gabre i gabre olivínic). La unitat subvolcànica mostra que hi ha dos tipus de magma màfic; grup 1 mostra una signatura típica de basalts d'avantarc (FAB; baix ratio Ti/V) i el grup 2 amb una composició de toleiites d'arc d'illes (IAT; ratio intermedia Ti/V), ambdòs amb anomalia positiva de Th i negativa de Nb en comparació a composicions N-MORB. Aquestes composicions a més de la composició isotòpica de la unitat plutonica (baix 143Nd/144Nd i 87Sr/86Sr) indica la presència d'un component subductiu. Hi ha evidències geoquímiques que recolzen una relació genètica entre els protòlits de la matriu serpentinítica i la unitat subvolcanica de l'escorça màfica. Una evidencia indirecta és l'enriquiment de terres rares lleugeres en les peridotites del grup B. Aquest enriquiment s'interpreta com a resultat de la reequilibració de fosos basàltics que percolen en el mantell, aquests podrien estar representats per la unitat subvolcànica de l'escorça màfica. També els models de fusió dels fosos primitius de la escorça màfica (grup 1- FAB) prediuen el c. 8-10 % de fusió d'un mantell abissal, com el de les peridotites tipus A que produeix un residu equivalent al de les peridotites tipus B. D'altra banda, el metamorfisme de fons oceànic afecta a l'escorça màfica, que mostra associacions minerals típiques de fàcies d'esquistos verds i amfibolites. Aixà permet establir una pressió baixa i una temperatura baixa a intermèdia típica de condicions someres. Aquest procés té un impacte directe en la concentració dels elements mòbils. Diferents processos metasomàtics/enriquiment es veuen registrats en la geoquímica dels elements traça i els isòtops estables i radiogènics (B, Nd, Sr i Pb) de la matriu serpentinítica. Les relacions isotòpiques apunten a la presència de fluids provinents de la desvolatilització de la placa subduent on es forma l'agent metasomatizador. Aquests fluids estan compostos per diferents proporcions de fluids provinents de l'escorça oceànica alterada, sediments subduïts i sediments terrígens. La combinació d'aquests tres reservoris isotòpics amb un mantell ja hidratat en el fons oceànic reprodueix la signatura isotòpica de la matriu serpentinítica de la mélange serpentinítica de Villa Clara. Aquest resultat està en consonància amb l'evidencia proveïda pels blocs exòtics ultramàfics d'alta pressió de la mélange serpentinítica de Villa Clara, ja que aquests mostren composicions isotòpiques similars indicant la interacció amb un fluid similar en un context de subducció. Les característiques petrològiques i geoquímiques dels blocs exòtics ultramàfics permeten distingir dos tipus de serpentinites: i) antigoritita i ii) antigoritita amb dolomita. Ambdues representen peridotites subduïdes que deriven d'un protòlit localment enriquit en CaO com a resultat de l'infiltració d'una mescla de fluids amb H2O-CO2. L'infiltració de fluids en el canal de subducció és el detonant per la serpentinització/carbonatació i formació de dominis de reemplaçament i venes de tremolita en la antigoritita. El zonat mineralògic i químic observat en els dominis de reemplaçament (domini de Atg + Chl + Tr en direcció a la antigoritita i el domini Chl + Tr en direcció a la vena) confirmen els canvis metasomàtics de la composició del fluid durant l'interacció fluid-roca. Les diferències de composició química entre els dominis i la antigoritita mostren que el fluid que s'infiltra estava enriquit en Ca, Al, elements litòfils de gran radi ionic i terres rares lleugeres. La modelització de la pseudosecció realitzada en el domini Atg + Chl + Tr indica que la seva formació va tenir lloc a c. 4S0QC i c. 10kbar. Tots aquests resultats permeten constrènyer l'evolució geodinàmica de la mélange serpentinítica en el context de la regió del Carib. La matriu serpentinítica demostra la presència de dos ambients geodinàmics diferents. Les peridotites del grup A format en un ambient abissal/zona de fractura en la conca oceànica del Proto-Carib, mentre que les peridotites del grup B, els blocs exòtics ultramàfics i l'escorça màfica apunten cap a un ambient d'avant arc. Els dos escenaris coexisteixen en un model geodinàmic del Juràssic Superior- Cretaci Inferior amb la formació de litosfera oceànica després del trencament de Pangea i el posterior inici de la subducció, en un ambient de zona de fractura. L'inici de la subducció en el Cretaci inferior i posterior desenvolupament de la serpentinització de la zona d'avantarc i el canal de subducció durant el Cretaci Inferior- Superior fins al final emplaçament del conjunt (mélange serpentinitic) durant Cretaci Superior-Eocè.

Current design codes of Mechanically Stabilized Earth (MSE) Walls allow the use lower lateral earth pressure coefficient (K value) for designing geosynthetics walls than those used to design steel walls. The reason of this is because geosynthetics walls are less rigid permitting the wall to deform enough to work under active pressures instead of at rest pressures as in steel walls. A new concept of crimped steel bars was recently introduced. This new type of bar was tested for tension and pullout behavior. Results on tests made on crimped bars show that putting those crimps in the steel bar will give us a better pullout behavior and a more flexible tensile behavior. This new type of steel bar will behave more like geosynthetics, allowing the wall to deform sufficiently to reach the necessary deflection to reach the active condition. The use of steel by current design codes is pushing MSE walls to be designed with more steel than needed. Measurements of the force in different walls showed that the steel is not being used even close to the maximum stress allowed by the code which is 50%. The proposed design methodology using crimped bars will help us save around 52% of steel volume compared to the actual design procedures. This means a huge improvement in the usage of steel versus actual designs. This improvement is obtained because of the efficient behavior of rounded bars under corrosion and because of the flexibility in the bars obtained with the crimps that will allow us to reach the active condition.

The aim of the diploma thesis is static solution of selected parts of the residental house with formwork drawings and reinforcement drawings of designed structures included. Project describes the design and assessment of the monolitic slab structure, precast stair flights, basement loadbearing wall and retaining wall. For calculation of the internal forces was used software Scia Engineer.

碩士<br>國立臺中教育大學<br>自然科學教育學系碩士班<br>94<br>The purpose of this study is to investigate why 9th graders in junior high have a misconception of the earth internal structure and the plate movement and to analyze the relation between gender and misconception. The result of this study would be useful for earth science teachers to upgrade their teaching quality. Samples are 899 9th graders, selected from three junior high schools in Chiayi City, Nantou City and Yunlin County with purposive sampling. The research is conducted by two-tier diagnostic instrument which is developed by researcher and the data collected would be analyzed by SPSS 10.0 to compare the difference between genders. The following is the major results of the study： 1.Students have many misconceptions about the earth internal structure, the plate movement and so on, especially why the geological phenomenon formed in the the edge of tectonic plates and the concrete range of plates. 2.The Independent-Samples T Test tool is used on this study to analyze the relation of the gender with misconception of the earth’s internal structure and plate movement. There was significant difference between the mean scores of male and female junior high school students, which indicates both male and female junior high school students have different patterns of misconceptions about the earth’s internal structure and plate movement. Finally, the study offers some suggestions for those who will teach or study the earth internal structure and plate movement.

碩士<br>國立臺灣科技大學<br>營建工程系<br>100<br>Geosynthetic-Reinforced Soil (GRS) structures are conventionally designed using the deterministic approach to calculate factor of safeties. This approach, however, is not able to consider variability and uncertainty from design variables and prediction models. On the other hand, the reliability approach considers the possible variations in the design parameters and gives more realistic estimates of the safety of the structure and the possible risk of failure. Therefore, this study presents reliability-based design (RBD) for internal stability of GRS structures. Two prediction methods (i.e., lateral earth pressure and K-stiffness methods) were used to predict reinforcement tensile loads and their model uncertainty on RBD results was investigated. This study first compared failure probabilities and reliability indices calculated by different reliability methods: Monte Carlo simulation (MCS), first-order reliability method (FORM), first-order second-moment method (FOSM). Afterward, a sensitivity study was conducted using MCS to identify design variables that affect the probability of internal failure of GRS structures. Based on the results of the sensitive study, a series of additional simulations were conducted where the significant variables were varied over a broad range. The results of these simulations were used to develop a series of RBD charts. A design example was provided to illustrate the RBD procedure and to validate the proposed RBD charts. Last, the effect of model uncertainty on RBD results was evaluated. The model uncertainty was statistically quantified using a model factor, defined as the measured reinforcement load divided by the predicted reinforcement load. The impact of the model factor and its potential correlation with the predicted reinforcement tensile loads on RBD results was discussed. This study demonstrates the RBD results using two prediction methods become more consistent when the model uncertainty is considered. The results obtained from this study provide insightful information for RBD for internal stability of GRS structures.