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11.
Homogenisation techniques have been successfully used to estimate the mechanical response of synthetic composite materials, due to their ability to relate the macroscopic mechanical response to the material microstructure. The adoption of these mean-field techniques in geo-composites such as shales is attractive, partly because of the practical difficulties associated with the experimental characterisation of these highly heterogeneous materials. In this paper, numerical modelling has been undertaken to investigate the applicability of homogenisation methods in predicting the macroscopic, elastic response of clayey rocks. The rocks are considered as two-level composites consisting of a porous clay matrix at the first level and a matrix-inclusion morphology at the second level. The simulated microstructures ranged from a simple system of one inclusion/void embedded in a matrix to complex, random microstructures. The effectiveness and limitations of the different homogenisation schemes were demonstrated through a comparative evaluation of the macroscopic elastic response, illustrating the appropriate schemes for upscaling the microstructure of shales. Based on the numerical simulations and existing experimental observations, a randomly distributed pore system for the micro-structure of porous clay matrix has been proposed which can be used for the subsequent development and validation of shale constitutive models. Finally, the homogenisation techniques were used to predict the experimental measurements of elastic response of shale core samples. The developed methodology is proved to be a valuable tool for verifying the accuracy and performance of the homogenisation techniques. 相似文献
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Ćwiek Mateusz Matusiak-Małek Magdalena Puziewicz Jacek Ntaflos Theodoros 《International Journal of Earth Sciences》2018,107(5):1731-1753
International Journal of Earth Sciences - The Oligocene/Miocene basanite from Pilchowice (Sudetes Mts., SW Poland) carries numerous small xenoliths of mantle peridotite, mostly harzburgite. The... 相似文献
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Renata??opjakováEmail authorView authors OrcID profile Jana?Kotková 《Contributions to Mineralogy and Petrology》2018,173(12):106
Multiphase solid inclusions in minerals formed at ultra-high-pressure (UHP) provide evidence for the presence of fluids during deep subduction. This study focuses on barian mica, which is a common phase in multiphase solid inclusions enclosed in garnet from mantle-derived UHP garnet peridotites in the Saxothuringian basement of the northern Bohemian Massif. The documented compositional variability and substitution trends provide constraints on crystallization medium of the barian mica and allow making inferences on its source. Barian mica in the multiphase solid inclusions belongs to trioctahedral micas and represents a solid solution of phlogopite KMg3(Si3Al)O10(OH)2, kinoshitalite BaMg3(Al2Si2)O10(OH)2 and ferrokinoshitalite BaFe3(Al2Si2)O10(OH)2. In addition to Ba (0.24–0.67 apfu), mica is significantly enriched in Mg (XMg ~ 0.85 to 0.95), Cr (0.03–0.43 apfu) and Cl (0.04–0.34 apfu). The substitution vector involving Ba in the I-site which describes the observed chemical variability can be expressed as BaFeIVAlClK?1Mg?1Si?1(OH)?1. A minor amount of Cr and VIAl enters octahedral sites following a substitution vector VI(Cr,Al)2□VI(Mg,Fe)?3 towards chromphyllite and muscovite. As demonstrated by variable Ba and Cl contents positively correlating with Fe, barian mica composition is partly controlled by its crystal structure. Textural evidence shows that barian mica, together with other minerals in multiphase solid inclusions, crystallized from fluids trapped during garnet growth. The unusual chemical composition of mica reflects the mixing of two distinct sources: (1) an internal source, i.e. the host peridotite and its garnet, providing Mg, Fe, Al, Cr, and (2) an external source, represented by crustal-derived subduction-zone fluids supplying Ba, K and Cl. At UHP–UHT conditions recorded by the associated diamond-bearing metasediments (c. 1100 °C and 4.5 GPa) located above the second critical point in the pelitic system, the produced subduction-zone fluids transporting the elements into the overlying mantle wedge had a solute-rich composition with properties of a hydrous melt. The occurrence of barian mica with a specific chemistry in barium-poor mantle rocks demonstrates the importance of its thorough chemical characterization. 相似文献
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John?W.?Faithfull Tim?J.?DempsterEmail author John?M.?MacDonald Monica?Reilly EIMF 《Contributions to Mineralogy and Petrology》2018,173(12):99
Zircon megacrysts are locally abundant in 1–40 cm-thick orthopyroxenite veins within peridotite host rocks in the Archaean Lewisian gneiss complex from NW Scotland. The veins formed by metasomatic interaction between the ultramafic host and Si-rich melts are derived from partial melting of the adjacent granulite-facies orthogneisses. The interaction produced abundant orthopyroxene and, within the thicker veins, phlogopite, pargasite and feldspathic bearing assemblages. Two generations of zircon are present with up to 1 cm megacrystic zircon and a later smaller equant population located around the megacryst margins. Patterns of zoning, rare earth element abundance and oxygen isotopic compositions indicate that the megacrysts crystallized from crustal melts, whereas the equant zircon represents new neocryst growth and partial replacement of the megacryst zircon within the ultramafic host. Both zircon types have U–Pb ages of ca. 2464 Ma, broadly contemporaneous with granulite-facies events in the adjacent gneisses. Zircon megacrysts locally form?>?10% of the assemblage and may be associated to zones of localized nucleation or physically concentrated during movement of the siliceous melts. Their unusual size is linked to the suppression of zircon nucleation and increased Zr solubility in the Si-undersaturated melts. The metasomatism between crustal melts and peridotite may represent an analog for processes in the mantle wedge above subducting slabs. As such, the crystallization of abundant zircon in ultramafic host rocks has implications for geochemistry of melts generated in the mantle and the widely reported depletion of high field strength elements in arc magmas. 相似文献
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Renata M. Wentzcovitch D. A. Hugh-Jones R. J. Angel G. D. Price 《Physics and Chemistry of Minerals》1995,22(7):453-460
We have used a newly developed ab initio constant-pressure molecular dynamics with variable cell shape technique to investigate the zero temperature behaviour of high pressure clinoenstatite (MgSiO3-C2/c) from 0 up to 30 GPa. The optimum structure at 8 GPa, as well as structural trends under pressure, compare very well with experimental data. At this pressure, we find noticeable “fluctuations” in the chain configuration which suggests the structure is on the verge of a mechanical instability. Two distinct compressive behaviours then appear: one below and another above 8 GPa. This phenomenon may be related to the observed transition to a lower symmetry P21/c phase which involves a reconfiguration of the silicate chains, and suggests that the C2/c structure at low pressures found here, may be an artifact of the dynamical algorithm which preserves space group in the absence of symmetry breaking fluctuations. Comparison with calculations in other magnesium silicate phases, indicates that the size and shape of the silicate units (isolated and/or linked tetrahedra and octahedra) are generally well described by the local density approximation; however, the weaker linkages provided by the O-Mg-O bonds, are not as well described. This trend suggests that, as in the recently studied case of H2O-ice, the structural properties of more inhomogeneous systems, like enstatite, may be improved by using gradientcorrected density functionals. 相似文献
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C.?E.?Suh S.?N.?Ayonghe R.?S.?J.?SparksEmail author C.?Annen J.?G.?Fitton R.?Nana A.?Luckman 《Bulletin of Volcanology》2003,65(4):267-281
Mount Cameroon (4,095 m high and with a volume of ~1,200 km3) is one of the most active volcanoes in Africa, having erupted seven times in the last 100 years. This stratovolcano of basanite and hawaiite lavas has an elliptical shape, with over a hundred cones around its flanks and summit region aligned parallel to its NE--SW-trending long axis. The 1999 (28 March–22 April) eruption was restricted to two sites: ~2,650 m (site 1) and ~1,500 m (site 2). Similarly, in the eruption in 2000 (28 May–19 June), activity occurred at two sites: ~4,095 m (site 1) and ~3,300 m (site 2). During both eruptions, the higher vents were more explosive, with strombolian activity, while the lower vents were more effusive. Accordingly, most of the lava (~8×107 m3 in 1999 and ~6×106 m3 in 2000) was emitted from the lower sites. The 1999–2000 lavas are predominantly basanites with low Ni (5–79 ppm), Cr (40–161 ppm) and mg numbers (34–40). Olivine (Fo77–85, phenocrysts and Fo68–72, microlites), clinopyroxene (Wo47En41Fs10 to Wo51En34Fs15), plagioclase (An49–67) and titanomagnetite are the principal phenocryst and groundmass phases. The lavas contain xenocrysts of olivine and clinopyroxene, which are interpreted as fragments of intrusive rocks disrupted by magma ascent. Major and trace element characteristics point to early fractionation of olivine. The clinopyroxenes (Al2O3 1.36–7.83 wt%) have high Aliv/Alvi ratios (1.3–1.8) and are rich in TiO2, characteristics typical of low pressure clinopyroxenes. Geochemical differences between the 1999–2000 lavas and those from previous eruptions, such as higher Nb/Zr of the former, suggest that different eruptions discharged magmas that evolved differently in space and time. Geophysical and petrological data indicate that these fractionated magmas originated just below the geophysical Moho (at 20–22 km) in the lithospheric mantle. During ascent, the magmas disrupted intrusions and earlier magma pockets. The main ascent path is below the summit, where newly arrived magma degasses. Degassed magma simultaneously intrudes the flank rift zones where most lava is extruded.An erratum to this article can be found at 相似文献