Calculation of vapor-liquid equilibrium and PVTx properties of geological fluid system with SAFT-LJ EOS including multi-polar contribution. Part III. Extension to water-light hydrocarbons systems

International audienceThe SAFT-LJ EOS improved by Sun and Dubessy (2010, 2012) is extended to water-light hydrocarbon systems. Light hydrocarbons (including CH4, C2H6, C3H8 and nC(4)H(10)) are modeled as chain molecules without multi-polar moments. The contributions of the shape of molecules and main intermolecular interactions existing in water-light hydrocarbon systems (including repulsive and attractive forces between Lennard-Jones segments, the hydrogen-bonding force and the multi-polar interaction between water molecules) to the residual Helmholtz energy were accounted for by this EOS. The adjustable parameters for the interactions of H2O-CH4, H2O-C2H6, H2O-C3H8, and H2O-nC(4)H(10) pairs were evaluated from mutual solubility data of binary water-hydrocarbon systems at vapor-liquid equilibria. Comparison with the experimental data shows this SAFT-LJ EOS can represent well vapor-liquid (and liquid-liquid) equilibria of binary water-light hydrocarbon systems over a wide P-T range. The accuracy of this EOS for mutual solubilities of methane, ethane, propane and water is within the experimental uncertainty generally. Moreover, the model is able to accurately predict the vapor-liquid equilibria and PVTx properties of multi-component systems composed of water, light hydrocarbon as well as CO2. As we know, this EOS is the first one allowing quantitative calculation of the mutual solubilities of water and light hydrocarbons over a wide P-T range among SAFT-type EOSs. This work indicates that the molecular-based EOS combined with conventional mixing rule can well describe the thermodynamic behavior of highly non-ideal systems such as water-light hydrocarbons mixtures except in the critical region for which long range density fluctuations cannot be taken into account by this analytical model

Petrogenesis and its significance to continental dynamics of the Neogene high-potassium calc-alkaline volcanic rock association from north Qiangtang, Tibetan Plateau

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Geochronological, geochemical, and Nd-Hf isotopic studies of the Qinling Complex, central China: Implications for the evolutionary history of the North Qinling Orogenic Belt

The Qinling Complex of central China is thought to be the oldest rock unit and the inner core of the North Qinling Orogenic Belt (NQOB). Therefore, the Qinling Complex is the key to understanding the pre-Paleozoic evolution of the NQOB. The complex, which consists of metagraywackes and marbles, underwent regional amphibolite-facies metamorphism. In this study, we constrained the formation age of the Qinling Complex to the period between the late Mesoproterozoic and the early Neoproterozoic (ca. 1062–962 Ma), rather than the Paleoproterozoic as previously thought. The LA-ICP-MS data show two major metamorphic ages (ca. 499 and ca. 420–400 Ma) for the Qinling Complex. The former age is consistent with the peak metamorphic age of the high- and ultra-high pressure (HP-UHP) rocks in the Qinling Complex, indicating that both the HP-UHP rocks and their country rocks experienced intensive regional metamorphism during the Ordovician. The latter age may constrain the time of partial melting in the NQOB between the late Silurian and early Devonian. The Qinling Complex is mostly affiliated with subduction–accretion processes along an active continental margin, and should contain detritus deposited in a forearc basin. The available data indicate that the NQOB was an independent micro-continent at least prior to the Neoproterozoic, and included a portion of the Grenville orogenic belt during the period of 1.2–0.8 Ga. The NQOB has experienced a unique geological history, which is obviously different from that of the North China Craton (NCC) and the Yangtze Craton during the Precambrian. The Neoproterozoic granitoids that intruded the Qinling Complex can be interpreted as the products of assembly of the supercontinent Rodinia. The NQOB was separated from Rodinia at ca. 830–740 Ma. Subsequently, the NQOB moved closer to the northern margin of the NCC, and the initial accretion or collision with the NCC occurred from the late Cambrian to the early Ordovician

Data sets for "<b>The redox state of asthenospheric mantle and the onset of melting beneath mid-ocean ridges</b>"

The redox state of the convective asthenospheric mantle governs the speciation of volatile elements, such as carbon, therefore influences the depth at which (redox) melting can occur with implications for the seismic signals. Geophysical observations suggest the potential presence of carbonatite melts at depth of 200–250 km, however, thermodynamic models indicate the onset of (redox) melting would occur at 100–150 km for a mantle with 3–4 % of Fe3+/∑Fe. Here we present a new oxybarometer that based on the V/Sc exchange coefficient between olivine and melt, which is insensitive to surficial alteration, volatile degassing, electron exchange reactions and fractional crystallization. By applying this method to primary mid-ocean ridge basalts (MORBs) from Southwest Indian Ridge and East Pacific Rise, we demonstrate that the average oxygen fugacity (fo2) of MORBs corrected for the depth of formation is 0.78±0.26 (1) log units above the fayalite-magnetite-quartz (FMQ) buffer, which is slightly more oxidized than previously estimated (near FMQ buffer). Our findings indicate that the convective asthenospheric mantle exhibits a higher oxygen fugacity than continental lithospheric mantle. Along an adiabat, carbonatitic melts can form from a CO2-bearing source at depth of 200–250 km explaining, therefore, the electrical conductivity and seismic velocity anomaly of the asthenospheric mantle.</p

Evaluation of lead isotope compositions of NIST NBS 981 measured by thermal ionization mass spectrometer and multiple-collector inductively coupled plasma mass spectrometer

Because Pb isotopes can be used for tracing, they are widely used in many disciplines. The detection and analysis of Pb isotopes of bulk samples are usually conducted using thermal ionization mass spectrometer (TIMS) and multiple-collector inductively coupled plasma mass spectrometer (MC-ICP-MS), both of which need external reference materials with known isotopic compositions to correct for the mass discrimination effect produced during analysis. NIST NBS 981 is the most widely used reference material for Pb isotope analysis; however, the isotopic compositions reported by various analytical laboratories, especially those using TIMS, vary from each other. In this study, we statistically evaluated 229 reported TIMS analysis values collected by GeoReM in the last 30 years, 176 reported MC-ICP-MS analysis values, and 938 MC-ICP-MS analysis results from our laboratory in the last five years. After careful investigation, only 40 TIMS results were found to have double or triple spikes. The ratios of the overall weighted averages, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, obtained from 40 spiked TIMS reports and 1114 MC-ICP-MS results of NIST NBS 981 isotopes were 16.9406 ± 0.0003 (2s), 15.4957 ± 0.0002 (2s), and 36.7184 ± 0.0007 (2s), respectively