Stability and equation of state of post-aragonite BaCO3     

Joshua P. Townsend  Yun-Yuan Chang  Xiaoting Lou  Miguel Merino  Scott J. Kirklin  Jeff W. Doak  Ahmed Issa  Chris Wolverton  Sergey N. Tkachev  Przemyslaw Dera  Steven D. Jacobsen 《Physics and Chemistry of Minerals》2013,40(5):447-453

At ambient conditions, witherite is the stable form of BaCO₃ and has the aragonite structure with space group Pmcn. Above ~10 GPa, BaCO₃ adopts a post-aragonite structure with space group Pmmn. High-pressure and high-temperature synchrotron X-ray diffraction experiments were used to study the stability and equation of state of post-aragonite BaCO₃, which remained stable to the highest experimental P–T conditions of 150 GPa and 2,000 K. We obtained a bulk modulus K ₀ = 88(2) GPa with $K'$  = 4.8(3) and V ₀ = 128.1(5) ų using a third-order Birch-Murnaghan fit to the 300 K experimental data. We also carried out density functional theory (DFT) calculations of enthalpy (H) of two structures of BaCO₃ relative to the enthalpy of the post-aragonite phase. In agreement with previous studies and the current experiments, the calculations show aragonite to post-aragonite phase transitions at ~8 GPa. We also tested a potential high-pressure post–post-aragonite structure (space group C222 ₁ ) featuring four-fold coordination of oxygen around carbon. In agreement with previous DFT studies, ΔH between the C222 ₁ structure and post-aragonite (Pmmn) decreases with pressure, but the Pmmn structure remains energetically favorable to pressures greater than 200 GPa. We conclude that post–post-aragonite phase transformations of carbonates do not follow systematic trends observed for post-aragonite transitions governed solely by the ionic radii of their metal cations.  相似文献   

Diagenesis in tertiary sandstones from Kettleman North Dome. California—II. Interstitial solutions: Distribution of aqueous species at 100°C and chemical relation to the diagenetic mineralogy     

Enrique Merino 《Geochimica et cosmochimica acta》1975,39(12):1629-1645

Interstitial brines from the Temblor and the McAdams sandstones at Kettleman are essentially NaCaCl solutions with subsidiary SO₄ and the total salinities are roughly 30,000 and 10,000 ppm, respectively. Activities of H⁺ and all other aqueous species have been calculated for 100°C (the in situ temperatures of the brines) from chemical analyses of the brines and 100-degree dissociation constants alone. The brine alkalinities measured at surface temperature appear to be too low when comparing them against alkalinities calculated from the measured pHs of the brines. Consequently, alkalinities calculated for 25°C were substituted for the measured ones in the calculation of the distribution of aqueous species at 100°C.Although the brines are nearly neutral (pH 6·3–d7·9) at surface temperature, their pHs calculated for 100°C range from 8·1 to 8·7 (± 0·35). These pHs and the 100-degree activities of the other aqueous species permit graphic representation of the brines on activity diagrams. Most brines fall at or near the boundaries between the stability fields of quartz, albite, microcline, mica, montmorillonite and anhydrite. Because these minerals are present as authigenic phases in the sandstones, the calculations suggest that the minerals are in stable equilibrium with the brines. By contrast, the calculations suggest that the brines are supersaturated by about three orders of magnitude with respect to calcite, also present in the sandstones. One possible explanation for this is kinetic inhibition of calcite crystallization by Mg²⁺ and SO₄^2? ions in the brines. Phosphatic pellets, glauconite and probably dolomite, pyrite and some kaolinite are early authigenic minerals preserved in the sandstones and they are not now in equilibrium with the brines, which are supersaturated with respect to dolomite and pyrite. The chemical relationship between the brines and the diagenetic minerals laumontite and sphene, also present in the Temblor Formation, cannot be assessed reliably until the thermodynamic properties of laumontite and of aqueous titanium complexes are well known.  相似文献   

Extreme maximum temperature events and their relationships with large-scale modes: potential hazard on the Iberian Peninsula     

Merino  Andrés  Martín  M. L.  Fernández-González  S.  Sánchez  J. L.  Valero  F. 《Theoretical and Applied Climatology》2018,133(1-2):531-550

Theoretical and Applied Climatology - The aim of this paper is to analyze spatiotemporal distribution of maximum temperatures in the Iberian Peninsula (IP) by using various extreme maximum...  相似文献   

Mapping benthic faunal communities in the shallow and deep sediments of Las Perlas Archipelago, Pacific Panama     

James M. Mair  Sarah L. Cunningham  Hector M. Guzman  Daisi Merino 《Marine pollution bulletin》2009,58(3):375-383

Las Perlas Archipelago (LPA) is located off the Pacific Coast of Panama and was designated as a marine protected area (MPA) in 2007. This baseline study of the shallow and deeper sedimentary habitats of the islands partly informed the MPA designation. Ninety-two grab stations and twenty trawl stations were sampled. Sediment grab sample results were interpolated to produce a map that showed the area to be dominated by mud (1246 km², 40%) and sand/shell sediments (780 km², 25%). A total of 201 taxa were recorded and over 5800 individual specimens were processed, revealing that the sediments hold varying community compositions, with annelids being the dominant group (73%) followed by crustaceans (14%). Relationships were evident between community, feeding guilds, and sediment types, which give an indication of communities that can be expected in similar sediments in other areas of the Tropical Eastern Pacific. A study of this scale and level of detail is rare for this biogeographic region and provides a valuable, comprehensive appreciation of the LPA’s benthos.  相似文献   

Consistent floor response spectra for performance-based seismic design of nonstructural elements     

Roberto J. Merino  Daniele Perrone  Andre Filiatrault 《地震工程与结构动力学》2020,49(3):261-284

The achievement of adequate performance objectives for buildings under increasing seismic intensities is not only related to the performance of structural members but also to the behavior of nonstructural elements. The need to properly design nonstructural elements for earthquakes has been largely demonstrated in the last few years and has become an important objective within the earthquake engineering community. A crucial aspect in the proper design of nonstructural elements is the definition of the seismic demand in terms of both absolute acceleration and relative displacement floor response spectra. In the first part of this study, relative displacement and absolute acceleration floor response spectra were computed for four reinforced concrete moment-resisting archetype frames via dynamic time-history analyses and were compared with floor response spectra predicted by means of two recent simplified methodologies available in the literature. It was observed that one of the existing methodologies is generally unable to predict consistent absolute acceleration and relative displacement floor response spectra. An improved procedure is developed for estimating consistent floor response spectra for building structures subjected to low and medium-high seismic intensities. This new procedure improves the predictions of a relative displacement floor response spectrum by constraining its ordinates at long nonstructural periods to the expected peak absolute displacement of the floor. The resulting acceleration and relative displacement response spectra are then consistently related by the well-known pseudo-spectral relationship over the entire nonstructural period range. The effectiveness of the proposed methodology was appraised against floor response spectra computed from nonlinear time-history analyses.  相似文献   

A nonlinear model of parametric rolling stabilization by anti-roll tanks     

Marcelo A.S. Neves  Jorge A. Merino  Claudio A. Rodríguez 《Ocean Engineering》2009,36(14):1048-1059

The present paper describes a mathematical model in which the fluid motion inside a U-tank is nonlinearly coupled to the heave, roll and pitch motions of the ship. The main purpose of the investigation is centred on the control of roll motion in the case of parametric resonance in longitudinal waves. A transom stern small vessel, known to be quite prone to parametric amplification, is employed in the study. Four tank designs are employed in order to study the influence of tank mass, tank natural frequency and tank internal damping on the control of parametric rolling at different head seas conditions. Additionally, the influence of the vertical position of the tank is also investigated. The main results are presented in the form of limits of stability, with encounter frequency and wave amplitudes as parameters. Distinct dynamical characteristics are discussed and conclusions are drawn on the relevant parameters for the efficient control of the roll amplifications in head seas.  相似文献   

Electron microprobe monazite geochronology of granitic intrusions from the Montes de Toledo batholith (central Spain)     

David Orejana  Enrique Merino  Carlos Villaseca  Cecilia Prez‐Soba  Andrs Cuesta 《Geological Journal》2012,47(1):41-58

U–Th–Pb monazite dating by electron microprobe has been applied to three peraluminous granitic intrusions of the western Montes de Toledo batholith (MTB). Back scattered electron images of monazite crystals reveal a variety of internal textures: patchy zoning, overgrowths around older cores and unzoned crystals. On the basis of their zoning pattern and chemical composition, two monazite domains can be distinguished: (1) corroded cores and crystals with patchy zoning, exhibiting relatively constant Th/U ratios and broadly older ages, and (2) unzoned grains and monazite rims, with variable Th/U ratios and younger ages. The first monazite group represents inherited domains from metamorphic sources, which accounts for pre‐magmatic monazite growth events. Two average ages from Torrico and Belvís de Monroy granites (333 ± 18 and 333 ± 5 Ma, respectively) relate these cores to a Viséan extensional deformation phase. The second group represents igneous monazites which have provided the following crystallization ages for the host granite: 298 ± 11 Ma (Villar del Pedroso), 303 ± 6 Ma (Torrico) and 314 ± 3 Ma (Belvís de Monroy). Two main magmatic pulses, the first about 314 Ma and the second at the end of the Carboniferous (303–298 Ma), might be envisaged in the western MTB. While Belvís de Monroy leucogranite is likely a syn‐ to late‐tectonic intrusion, the Villar del Pedroso and Torrico plutons represent post‐tectonic magmas with emplacement ages similar to those of equivalent intrusions from nearby Variscan magmatic sectors. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Isotopic fingerprints of Milankovitch cycles in Pennsylvanian carbonate platform‐top deposits: the Valdorria record,Northern Spain          下载免费PDF全文

Valentin Chesnel  Óscar Merino‐Tomé  Luis Pedro Fernández  Elisa Villa  Elias Samankassou 《地学学报》2016,28(5):364-373

Sedimentary cyclic sequences deposited during the Late Palaeozoic Ice Age are widespread. Glacio‐eustatic control of the cyclic patterns is commonly accepted, and the durations of the cyclothems generally match the short‐ and long‐eccentricity Milankovitch orbital parameters. Nevertheless, geochemical fingerprints of orbital parameters are poorly documented in deep‐time sedimentary records. Here, we report on well‐exposed Bashkirian cyclothems of c. 123 ka and c. 400 ka durations from the Valdorria platform. The shorter‐term cyclothems can be grouped into longer‐term composite sequences that are consistent with generally accepted durations of c. 125 ka and c. 400 ka for Milankovitch eccentricity cycles. The stratigraphic pattern is mirrored by the isotope geochemical signals, which show distinct recurring trends. These trends are confirmed by statistical tests. Whereas intrinsic factors and/or subaerial exposure related to sea‐level lowstands might have truncated cycle patterns in tectonically stable basins, rapid subsidence of the Valdorria platform's foreland basin appears to have contributed to a faithful recording of cyclothems of different orders. The patterns and biostratigraphic constraint revealed in this study demonstrate the power of orbital forcing in imprinting sedimentary and geochemical signals in the rock record.  相似文献   

Internal consistency of a water analysis and uncertainty of the calculated distribution of aqueous species at 25°C     

Enrique Merino 《Geochimica et cosmochimica acta》1979,43(9):1533-1542

Many water analyses contain more than the minimum number of analytical determinations needed to calculate the distribution of species at ~ 25°C. The speciation of a water that contains $\text{n}$ cations and ligands other than H⁺ and OH^? can be calculated if just $\text{n}$ analytical determinations are available. In the frequent case where $\text{n + 1}$ (or more) determinations are available, one can calculate from the speciation a value for the ($\text{n + 1}$)th variable. The comparison between this computed value and its analytical counterpart (not used in calculating the speciation) constitutes a test for internal consistency among the $\text{n + 1}$ determinations that make up the whole analysis.Application of this test requires knowing the uncertainties of the calculated speciation and of the value computed for the ($\text{n + 1}$)th variable from the speciation. Such uncertainties have been ignored in previous algorithms, but have been determined herein by a Monte Carlo method of error propagation which is very well suited to systems of nonlinear algebraic equations.By comparing the titration alkalinity against the alkalinity calculated from the speciation, several published analyses for which the cation/anion balance is < 3% can be shown to be internally inconsistent. Such analyses may be unsuitable for geochemical calculations (water/rock interaction, estimation of reservoir temperatures, etc.).Several existing speciation algorithms disregard the possibility that the analytical data used as input are internally inconsistent.  相似文献   

Generation of evenly-spaced pressure-solution seams during (late) diagenesis: A kinetic theory     

Enrique Merino  Peter Ortoleva  Peter Strickholm 《Contributions to Mineralogy and Petrology》1983,82(4):360-370

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