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L. A. J. MARTIN M. BALLÈVRE P. BOULVAIS A. HALFPENNY O. VANDERHAEGHE S. DUCHÊNE E. DELOULE 《Journal of Metamorphic Geology》2011,29(2):213-231
The analysis of texture, major element and oxygen isotope compositions of cloudy garnet crystals from a metapelite sampled on Ikaria Island (Greece) is used to assess the model of growth and re‐equilibration of these garnet crystals and to reconstruct the pressure–temperature–fluid history of the sample. Garnet crystals show complex textural and chemical zoning. Garnet cores (100–200 μm) are devoid of fluid inclusions. They are characterized by growth zoning demonstrated by a bell‐shaped profile of spessartine component (7–3 mol.%), an increase in grossular from 14 to 22 mol.% and δ18O values between 9.5 ± 0.3‰ and 10.4 ± 0.2‰. Garnet inner rims (90–130 μm) are fluid inclusion‐rich and show a decreasing grossular component from 22 to 5 mol.%. The trend of the spessartine component observed in the inner rim allows two domains to be distinguished. In contrast to domain I, where the spessartine content shows the same trend as in the core, the spessartine content of domain II increases outwards from 2 to 14 mol.%. The δ18O values decrease towards the margins of the crystals to a lowest value of 7.4 ± 0.2‰. The outer rims (<10 μm) are devoid of fluid inclusions and have the same chemical composition as the outermost part of domain II of the inner rim. Garnet crystals underwent a four‐stage history. Stage 1: garnet growth during the prograde path in a closed system for oxygen. Garnet cores are remnants of this growth stage. Stage 2: garnet re‐equilibration by coupled dissolution–reprecipitation at the temperature peak (630 < T < 650 °C). This causes the creation of porosity as the coupled dissolution–reprecipitation process allows chemical (Ca) and isotopic (O) exchange between garnet inner rims and the matrix. The formation of the outer rim is related to the closure of porosity. Stage 3: garnet mode decreases during the early retrograde path, but garnet is still a stable phase. The resulting garnet composition is characterized by an increasing Mn content in the inner rim’s domain II caused by intracrystalline diffusion. Stage 4: dissolution of garnet during the late retrograde path as garnet is not a stable phase anymore. This last stage forms corroded garnet. This study shows that coupled dissolution–reprecipitation is a possible re‐equilibration process for garnet in metamorphic rocks and that intra‐mineral porosity is an efficient pathway for chemical and isotopic exchange between garnet and the matrix, even for otherwise slow diffusing elements. 相似文献
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D. LE GOURIÉRÈS 《水文科学杂志》2013,58(3):301-313
ABSTRACT In this paper, the author relies on Darcy's law and on an hypothesis formulated from experimental considerations to establish a semi-empirical formula for the calculation of the discharge of partially penetrating wells of free aquifer sunk in isotropic soils. This relatively simple relation applied to 27 cases studied under an experimental design or numerical computations, reveals itself to have an unexpected accuracy. Starting from previous formula, the author establishes another one for partially penetrating wells bored in anisotropic soils. 相似文献
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The actinic flux is the only radiometric quantity suitable for photolysisfrequency determination. It is derived from solar spectral irradiancemeasurements performed by a portable spectroradiometer in the 300–850nm wavelength range. The spectral irradiance is first divided into a directpart and a diffuse part, according to the atmospheric conditions, and thenconverted into the corresponding actinic flux quantity. As an intermediary,the ratio
of diffuse actinic flux to diffuseirradiance is calculated by the spherical harmonics radiative code withrespect to wavelength, solar zenith angle, surface albedo, and aerosolproperties.The results of extensive sensitivity studies of
asa function of the main atmospheric parameters are discussed and lead to theconclusion that aerosol optical depth is the major critical value for aprecise
determination. The global algorithm totransform spectral irradiance into actinic flux is finally applied forphotodissociation rate calculations by convolution of the obtained actinicflux spectra with the absorption cross-sections and quantum yields of themolecule studied. Photolysis rates of different atmospheric photooxidants havebeen measured with this spectroradiometric method during the summers of 1993and 1994 in Brittany and in Portugal. The ozone and nitrogen dioxidephotodissociation rates obtained present a good agreement with thej(O3) and j(NO2) actinometerresults, for the same experimental conditions in Brittany. 相似文献
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JEAN‐JACQUES CORNÉE JEAN‐LÈN LÉTICÉE PHILIPPE MÜNCH FRÉDÉRIC QUILLÉVÉRÉ JEAN‐FRÉDÉRIC LEBRUN PIERRE MOISSETTE JUAN‐CARLOS BRAGA MIHAELA MELINTE‐DOBRINESCU LYVANE DE MIN JULIEN OUDET AURAN RANDRIANASOLO 《Sedimentology》2012,59(5):1426-1451
Pliocene and Pleistocene deposits from Grande‐Terre (Guadeloupe archipelago, French Lesser Antilles) provide a remarkable example of an isolated carbonate system built in an active margin setting, with sedimentation controlled by both rapid sea‐level changes and tectonic movements. Based on new field, sedimentological and palaeontological analyses, these deposits have been organized into four sedimentary sequences (S1 to S4) separated by three subaerial erosion surfaces (SB0, SB1 and SB2). Sequences S1 and S2 (‘Calcaires inférieurs à rhodolithes’) deposited during the Late Zanclean to Early Gelasian (planktonic foraminiferal Zones PL2 to PL5) in low subsidence conditions, on a distally steepened ramp dipping eastward. Red algal‐rich deposits, which dominate the western part of Grande‐Terre, change to planktonic foraminifer‐rich deposits eastward. Vertical movements of tens of metres were responsible for the formation of SB0 and SB1. Sequence S3 (‘Formation volcano‐sédimentaire’, ‘Calcaires supérieurs à rhodolithes’ and ‘Calcaires à Agaricia’) was deposited during the Late Piacenzian to Early Calabrian (Zones PL5 to PT1a) on a distally steepened, red algal‐dominated ramp that changes upward into a homoclinal, coral‐dominated ramp. Deposition of Sequence S3 occurred during a eustatic cycle in quiet tectonic conditions. Its uppermost boundary, the major erosion surface SB2, is related to the Cala1 eustatic sea‐level fall. Finally, Sequence S4 (‘Calcaires à Acropora’) probably formed during the Calabrian, developing as a coral‐dominated platform during a eustatic cycle in quiet tectonic conditions. The final emergence of the island could then have occurred in Late Calabrian times. 相似文献
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Matthew S. HUBER Ludovic FERRIÈRE Anna LOSIAK Christian KOEBERL 《Meteoritics & planetary science》2011,46(9):1418-1424
Abstract– Planar deformation features (PDFs) in quartz, one of the most commonly used diagnostic indicators of shock metamorphism, are planes of amorphous material that follow crystallographic orientations, and can thus be distinguished from non‐shock‐induced fractures in quartz. The process of indexing data for PDFs from universal‐stage measurements has traditionally been performed using a manual graphical method, a time‐consuming process in which errors can easily be introduced. A mathematical method and computer algorithm, which we call the Automated Numerical Index Executor (ANIE) program for indexing PDFs, was produced, and is presented here. The ANIE program is more accurate and faster than the manual graphical determination of Miller–Bravais indices, as it allows control of the exact error used in the calculation and removal of human error from the process. 相似文献
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The Middle Oxfordian of the eastern Paris Basin constitutes a remarkable example of the growth and demise of a carbonate platform. Fischer plots, sedimentary and diagenetic features allow the identification of four depositional cycles (S5 to S8) in the Transversarium Zone; they are inserted in a lower frequency cycle of increased/decreased accommodation space (SoIII). The long‐term period of accommodation creation occurred during the older S5 and S6 cycles, the maximum accommodation zone being located in the lower part of the S6 cycle. This high accommodation period was tectonically controlled and was coeval with local distensive activity of a Hercynian fault. A major minimum accommodation zone exists during the S8 cycle. At that time, the platform was isolated and presented both a windward and a leeward margin. The growth of the platform was favoured by a warm and arid climate, oligotrophic conditions and reduced siliciclastic input during a highstand in relative sea‐level. These palaeoenvironmental features favoured the proliferation of phototrophic organisms producing carbonate material. The death of the platform was generated by a reduction in the carbonate production surface during a lowstand in relative sea‐level and by the appearance of mesotrophic conditions induced by the increase in siliciclastic inputs at the beginning of a period with a cooler and more humid climate. In the eastern Paris Basin, during the Middle Oxfordian, the parasequences are ordered and present ‘greenhouse’ characteristics. In contrast, at the beginning of the S8 cycle, the randomness in the thickness of contiguous parasequences increased. Decreased carbonate production during the lowstand caused by a transition from photozoan to heterozoan benthic communities certainly favoured this randomness and the appearance of catch‐down parasequences. 相似文献