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Different P (different + p)
Selected AbstractsExhumation paths of high-pressure metapelites obtained from local equilibria for chlorite,phengite assemblagesGEOLOGICAL JOURNAL, Issue 3-4 2000O. Vidal Abstract The compositional variation of phengite and chlorite pairs in rocks sampled across the metamorphic zonation of three different blueschist belts (Cycladic, Sambagawa and Schistes Lustrés) is characterized from the regional to the thin-section scale. The different sample suites show different compositional trends, but similar trends are observed at the regional and thin-section scale in the same unit. At the thin-section scale, several local chlorite,phengite equilibria involving minerals of different compositions can be identified. These observations suggest that at temperature T <,,550°C, equilibration of chlorite and phengite compositions with varying pressure and temperature is controlled by crystallization/recrystallization processes rather than by changing the composition of older grains by lattice diffusion. In some instances, the relative time of growth of the different phyllosilicate generations can be determined using microstructural criteria. The observed compositional variations are interpreted and quantified in terms of pressure (P) and temperature (T) variations using new thermodynamic solution models accounting for the Tschermak, di/trioctahedral, and pyrophyllitic substitutions. Chlorite,phengite local equilibria constrain the shape of the exhumation P,T paths of the rocks under consideration. The assemblage chlorite,phengite,paragonite,albite,quartz,H2O can be used to constrain different P,T paths for Tinos and Sambagawa blueschists. Copyright © 2000 John Wiley & Sons, Ltd. [source] Constrained tomography of realistic velocity models in microseismic monitoring using calibration shotsGEOPHYSICAL PROSPECTING, Issue 5 2010T. Bardainne ABSTRACT The knowledge of the velocity model in microseismic jobs is critical to achieving statistically reliable microseismic event locations. The design of microseismic networks and the limited sources for calibration do not allow for a full tomographic inversion. We propose optimizing a priori velocity models using a few active shots and a non-linear inversion, suitable to poorly constrained systems. The considered models can be described by several layers with different P- and S-wave velocities. The velocities may be constant or have 3D gradients; the layer interfaces may be simple dipping planes or more complex 3D surfaces. In this process the P- and S- wave arrival times and polarizations measured on the seismograms constitute the observed data set. They are used to estimate two misfit functions: i) one based on the measurement residuals and ii) one based on the inaccuracy of the source relocation. These two functions are minimized thanks to a simulated annealing scheme, which decreases the risk of converging to a local solution within the velocity model. The case study used to illustrate this methodology highlights the ability of this technique to constrain a velocity model with dipping layers. This was performed by jointly using sixteen perforation shots recorded during a multi-stage fracturing operation from a single string of 3C-receivers. This decreased the location inaccuracies and the residuals by a factor of six. In addition, the retrieved layer dip was consistent with the pseudo-horizontal trajectories of the wells and the background information provided by the customer. Finally, the theoretical position of each calibration shot was contained in the uncertainty domain of the relocation of each shot. In contrast, single-stage inversions provided different velocity models that were neither consistent between each other nor with the well trajectories. This example showed that it is essential to perform a multi-stage inversion to derive a better updated velocity model. [source] Phosphorus heterocycles from 2-(2-hydroxyphenyl)-1H -benzimidazoleHETEROATOM CHEMISTRY, Issue 4 2004Julio Hernández-Díaz Sixteen different P(III) and P(V) heterocycles derived from 2-(2-hydroxyphenyl)-1H-benzimidazole (1) are reported. In these heterocycles the phosphorus atom is part of a six-membered unsaturated ring. They were mainly studied by multinuclear NMR. The X-ray diffraction of 3,4- benzimidazole-5,6-benzo-2-dimethylamino-2-seleno- 1,3,2-oxazaphosphorinane is reported. Phosphoranes derived from 1 and 3,5-di-tert-butylcatechol, and bearing Cl, NMe2, or phenyl as substituent at phosphorus are presented. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:307,320, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20021 [source] Microstrain and grain-size analysis from diffraction peak width and graphical derivation of high-pressure thermomechanicsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008Yusheng Zhao An analytical method is presented for deriving the thermomechanical properties of polycrystalline materials under high-pressure (P) and high-temperature (T) conditions. This method deals with non-uniform stress among heterogeneous crystal grains and surface strain in nanocrystalline materials by examining peak-width variation under different P,T conditions. Because the method deals directly with lattice d spacing and local deformation caused by stress, it can be applied to process any diffraction profile, independent of detection mode. In addition, a correction routine is developed using diffraction elastic ratios to deal with severe surface strain and/or strain anisotropy effects related to nano-scale grain sizes, so that significant data scatter can be reduced in a physically meaningful way. Graphical illustration of the resultant microstrain analysis can identify micro/local yields at the grain-to-grain interactions resulting from high stress concentration, and macro/bulk yield of the plastic deformation over the entire sample. This simple and straightforward approach is capable of revealing the corresponding micro and/or macro yield stresses, grain crushing or growth, work hardening or softening, and thermal relaxation under high- P,T conditions, as well as the intrinsic residual strain and/or surface strain in the polycrystalline bulk. In addition, this approach allows the instrumental contribution to be illustrated and subtracted in a straightforward manner, thus avoiding the potential complexities and errors resulting from instrument correction. Applications of the method are demonstrated by studies of ,-SiC (6H, moissanite) and of micro- and nanocrystalline nickel by synchrotron X-ray and time-of-flight neutron diffraction. [source] Metastable persistence of pelitic metamorphic assemblages at the root of a Cretaceous magmatic arc , Fiordland, New ZealandJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2009N. R. DACZKO Abstract Four aluminosilicate-bearing, amphibolite facies pelitic schists sampled from the root of the long-lived eastern Gondwana continental magmatic arc now exposed in southwest Fiordland, New Zealand, record remarkably different P,T,t histories. The four samples were collected from within 20 km of each other within the Fanny Bay Group and Deep Cove Gneiss near Dusky Sound. Integrated petrography, mineral chemistry, mineral equilibria modelling and in situ electron microprobe chemical dating of monazite shows that the sample of the Fanny Bay Group south of the Dusky Fault records a Carboniferous history with peak conditions of 4,4.5 kbar at 570,590 °C, while one sample of the Deep Cove Gneiss from Long Island records a Cretaceous history with apparent peak conditions of 7.5 kbar at 650 °C. Two other samples of the Deep Cove Gneiss from Resolution Island record mixed Carboniferous and Cretaceous histories with apparent peak conditions of 7 kbar at 650 °C and 3,7 kbar at 640,720 °C. The metapelitic schists on Resolution Island were intruded by arc magmas including the voluminous high- P Western Fiordland Orthogneiss, yet they lack mineralogical evidence of the Cretaceous high- P (>12 kbar) event. Analysis of water isopleths in a model system shows that the amount of water accommodated in the rock mineral assemblage increases with pressure. With the exhaustion of all free water, and without the addition of external water, these rocks persisted metastably within the deep arc during the high- P event. The emplacement of large volumes of diorite (i.e. the Western Fiordland Orthogneiss) into the root of the Early Cretaceous continental magmatic arc did not lead to regional granulite facies metamorphism of the country rock schists, as large volumes of amphibolite facies rock metamorphosed under medium- P conditions persisted metastably in the deep arc crust. [source] Variation in peak P,T conditions across the upper contact of the UHP terrane, Dabieshan, China: gradational or abrupt?JOURNAL OF METAMORPHIC GEOLOGY, Issue 9 2006Y. SHI Abstract The Southern Dabieshan Terrane (SDT) has previously been divided into high-pressure (HP) and ultrahigh-pressure (UHP) terranes, and its regional extent and the tectonic nature of its boundaries are hotly debated topics. In this study, an eclogite-bearing area of 100 km2 near Taihu is mapped in detail, and divided into Northern, Middle and Southern Zones on the basis of lithological characteristics. The Northern Zone consists of epidote-biotite gneiss and eclogite blocks, the Middle Zone includes granitic gneiss, biotite gneiss, eclogites and amphibolite, and the Southern Zone is composed mainly of garnet-bearing mica schist. The eclogites occur mainly as lens or blocks in the Northern and Middle Zones. The peak P,T conditions for 61 eclogite samples across the area are estimated using the Grt-Cpx Fe2+ -Mg thermometers and the Grt-Cpx-Phe barometers. The results indicate three different P,T regions: 2.82,4.09 GPa/759,942 °C in the Northern Zone, and 2.00,3.54 GPa/641,839 °C in the granitic gneiss and 1.38,2.36 GPa/535,768 °C in the biotite gneiss from the Middle Zone. Combined with the spatial distribution of eclogites across the area, the P,T values for eclogites increase continuously from the south to the north, defining a reference ,geotherm' of 5 °C km,1. However, some unreasonable apparent gradients can be established along two south,north profiles across the area, and display a P,T difference between the Northern and Middle zones. On the basis of the average P,T data for eclogites across the area, a gap of at least 0.3 GPa/20 °C exists between the Northern and Middle zones. By contrast, the P,T values of eclogites from the Middle zone show a coherent pattern with transitional characteristics from HP in the south to UHP in the north. We suggest that the SDT was a coherent slab during subduction, and was broken up by a major fault during exhumation, which was formed under UHP metamorphic conditions. [source] Petrogenesis of lawsonite and epidote eclogite and blueschist, Sivrihisar Massif, TurkeyJOURNAL OF METAMORPHIC GEOLOGY, Issue 9 2006P. B. DAVIS Abstract The Sivrihisar Massif, Turkey, is comprised of blueschist and eclogite facies metasedimentary and metabasaltic rocks. Abundant metre- to centimetre-scale eclogite pods occur in blueschist facies metabasalt, marble and quartz-rich rocks. Sivrihisar eclogite contains omphacite + garnet + phengite + rutile ± glaucophane ± quartz + lawsonite and/or epidote. Blueschists contain sodic amphibole + garnet + phengite + lawsonite and/or epidote ± omphacite ± quartz. Sivrihisar eclogite and blueschist have similar bulk composition, equivalent to NMORB, but record different P,T conditions: ,26 kbar, 500 °C (lawsonite eclogite); 18 kbar, 600 °C (epidote eclogite); 12 kbar, 380 °C (lawsonite blueschist); and 15,16 kbar, 480,500 °C (lawsonite-epidote blueschist). Pressures for the Sivrihisar lawsonite eclogite are among the highest reported for this rock type, which is rarely exposed at the Earth's surface. The distribution and textures of lawsonite ± epidote define P,T conditions and paths. For example, in some lawsonite-bearing rocks, epidote inclusions in garnet and partial replacement of matrix epidote by lawsonite suggest an anticlockwise P,T path. Other rocks contain no epidote as inclusions or as a matrix phase, and were metamorphosed entirely within the lawsonite stability field. Results of the P,T study and mapping of the distribution of blueschists and eclogites in the massif suggest that rocks recording different maximum P,T conditions were tectonically juxtaposed as kilometre-scale slices and associated high- P pods, although all shared the same exhumation path from ,9,11 kbar, 300,400 °C. Within the tectonic slices, alternating millimetre,centimetre-scale layers of eclogite and blueschist formed together at the same P,T conditions but represent different extents of prograde reaction controlled by strain partitioning or local variations in fO2 or other chemical factors. [source] Hetero-Seeding and Solid Mixture to Obtain New Crystalline FormsCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2009Dario Braga Prof. Abstract Para -methyl benzyl alcohol (p -MeBA,II) and para -chloro benzyl alcohol (p -ClBA) are quasi-isostructural and share the same hydrogen-bond patterns, but their crystals are not isomorphous. No new polymorphs could be obtained by conventional polymorph screening based on different solvents and different crystallization conditions. Formation of a new polymorph of p -MeBA named p -MeBA,I, isomorphous with the crystal of p -ClBA, was induced by hetero-seeding with a small quantity of powdered p -ClBA added to a supersaturated solution of p -MeBA in hexane, while seeding of p -ClBA with p -MeBA,II failed to give a new phase of p -ClBA isomorphous with known crystalline p -MeBA,II. Mixed crystals of p -MeBA and p -ClBA were also prepared with different p -MeBA/p -ClBA ratios to understand the role of the different functional groups in the crystal structure. Crystal phases were characterized by combined use of single-crystal and powder X-ray diffraction, differential scanning calorimetry, and solid-state NMR spectroscopy. [source] | |||||||||||||