The concept of isotope thermometry, which has been the heart and soul of stable isotope geochemistry since its foundation more than half a century ago, has been constantly tested against the effect of other variables such as pressure, fluid composition and biological processes. Despite the fact that the effect of dissolved salts on isotope partitioning in aqueous systems (the isotope salt effect) was discovered in the early 1950s, soon after carbonate paleothermometry commenced, it took isotope geochemists decades to understand the detail and geochemical significance of the effects, particularly those at elevated temperatures. The effect of pressure, which is potentially large under subduction zone and mantle conditions, has been even more elusive. The 1990s witnessed several significant breakthroughs in experimental and theoretical developments for understanding the effect of these variables on equilibrium isotope partitioning. The controversy of high temperature (>100°C) isotope salt effects was finally resolved. It was demonstrated later that significant pressure effects exist for D/H fractionation between a hydrous mineral and water at 200-600°C and at pressures to 0.8 GPa. Theoretical advances in understanding the isotope pressure effects, on both minerals and water, were also made during this period. Finally, and unexpectedly, the effects of dissolved minerals were proved to be significant on isotopic distributions in aqueous systems at high temperature and pressure (750°C and 1.5 GPa). This article reviews historical development of these "other" effects in isotope thermometry, highlighting significant discoveries of the past decade.

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Mesozoic basalts occur widely in SE China, with two major episodes of activity during the Middle Jurassic and Early Cretaceous. The exact age and mantle source character for the first eruption of basaltic magma during the Jurassic are not well constrained. In this paper we report, for the first time, Re-Os isotope data on these basalts. We sampled the Fankeng basalts in the Yongding basin of southwestern Fujian, SE China and separated the Fe-Ti oxide concentrates in them. Six samples of the Fe-Ti oxide concentrates yield a Re-Os isochron age of 175.4 ± 3.1 Ma with an initial ¹⁸⁷Os/¹⁸⁸Os ratio of 0.124 ± 0.014, corresponding to an initial γ_Os value of -1.44 at 175.4 Ma. The age suggests that the Fankeng basalts are products of Middle Jurassic magmatism. Both (¹⁸⁷Os/¹⁸⁸Os)_i and γ_Os values are near chondritic. Together with Sm-Nd isotope data of these basalts, we conclude that the Fankeng basaltic magma might be derived from depleted asthenospheric mantle. The near chondritic γ_Os and εNd(T) values may suggest interactions between asthenosphere and lithosphere during early Mesozoic in the area.

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A combined hydrogen-carbon-isotope and microthermometric study has been carried out on CH₄-bearing fluid inclusions in high-pressure jadeitites from the famous jadeite tract Myanmar. Two types of fluid inclusions were found in jadeites, large H₂O-rich and CH₄-poor inclusions and small H₂O-poor and CH₄-rich inclusions, thus indicating a possible entrapment of CH₄-H₂O fluids under unmixing conditions. Microthermometric results yield lower temperature limits for the entrapment of these fluid inclusions of ca. 300 to 400°C. The bulk composition of the fluid inclusions is mostly H₂O (87 to 94 mol.% H₂O) and the isotopic composition of methane and water in the inclusions is characterized by δ¹³C(CH₄) values ranging from -30.1 to -25.5‰, and δD(H₂O) values ranging from -56.3 to -49.8‰. The stable isotope data would be indicative of an abiogenic mechanism of CH₄ formation; the occurrence of the jadeite veins in this paleo-subduction zone thus most likely point to the formation of these CH₄-bearing fluid inclusions by abiogenic thermal maturation of subducted organic carbon. These data not only provide evidence for cycling of organic carbon in paleo-subduction zones but also show that CH₄ not only occurs as shallow CH₄-rich plumes in accretionary prisms of recent subduction zones but also occurs in deeper portions of at least the upper 20 km of paleo-subduction zones.

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Many CO₂-rich springs are found in Mesozoic granitoids and surrounding rocks in South Korea. Their presence is locally restricted to three regions: the Kangwon region, the Chungcheong region and the Kyungpook region. Discharge of many CO₂-rich springs is mainly related to the geologic structures, i.e., the geologic boundaries, faults and dykes. The sixty-three CO₂-rich water samples can be classified into three chemical water types; Ca-HCO₃ water, Ca(Na)-HCO₃ water, and Na-HCO₃ water. Most of the soda waters show a high CO₂ concentration (P_CO2 0.12 atm to 5.21 atm), a slightly acid pH (4.8 to 6.76), and high ion concentrations. The microscopic observation and the chemical analysis of host rocks at CO₂-rich spring sites show that the carbonate minerals are secondary precipitates and interstitial fillings in Cretaceous sedimentary rocks that are the main sources of Ca, Mg, HCO₃ and Fe in the CO₂-rich waters of the Kyungpook region. The carbonate minerals locally present in the fractures of granite and gneiss would be one of the main sources of abundant Ca, Mg and HCO₃ in the CO₂-rich water of the Kangwon and the Chungcheong regions. The chemical composition of these CO₂-rich springs according to host rocks and discharge regions was compared by using the Box-Whisker diagram. Oxygen and hydrogen isotope data indicates that the CO₂-rich waters are of meteoric origin. The carbon isotope data (δ¹³C -6.6 to -0.9‰) suggest that the carbon of the soda waters is mainly derived from a deep-seated source, but is partly mixed with CO₂ derived from carbonate minerals. The formation process of the CO₂-rich springs can be summarized as follows. After the CO₂ gas derived from the deep-seated source enters the groundwater system along faults or geologic boundaries, the CO₂-rich water evolved into three chemical types depending on the aquifer rock types.

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The source of major and trace elements has been studied in the Arno river catchments, with repeated sampling of stream sediments in 73 stations within the basin. The study was performed for the inventory, survey, assessment and monitoring of metal pollution, and for geochemical mapping of the most representative elements. Chemical data displayed a wide dispersion, greater in the tributaries than in the Arno river, but in general, there was a good overlap between the stream sediments and the major geological units. SiO₂ (32-75 wt%) was high in the main portion of the Arno river and in the northern tributaries, whereas CaO (1.5-27 wt%) was enriched in the southern ones. High MgO values (up to 5.7 wt%) were related to the presence of ophiolitic masses and/or to the ultramafic fraction of Macigno and Cervarola geological formations, which affected the distribution of Ni and Cr. However, in the highly industrialized areas northwest of Florence, high Cr values were associated to Cu, Zn and Pb anomalies. Copper (and sulphur) anomalies also occurred where agricultural practices were widespread. Organic matter content was variable (Corg 0.19-8.97 wt%) with an average C/N ratio of 8.7 (range 3.2-12.4), which is consistent with other C/N ratios of river sediments in the world. The relationships between Corg and N, S, P₂O₅ and heavy metals indicated that the organic matter had a mixed origin (industrial, agricultural, urban) and that both natural and anthropogenic metals entered the Arno river catchment.

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The El Tatio geothermal field is located at an height of 4200-4300 m on the Cordillera de los Andes (Altiplano). Geysers, hot pools and mudpots in the geothermal field and local meteoric waters were sampled in April 2002 and analyzed for major and trace elements, δ²H, δ¹⁸O and ³H of water, δ³⁴S and δ¹⁸O of dissolved sulfate, δ¹³C of dissolved total carbonate, and ⁸⁷Sr/⁸⁶Sr ratio of aqueous strontium. There are two different types of thermal springs throughout the field, that are chloride-rich water and sulfate-rich water. The chemical composition of chloride springs is controlled by magma degassing and by water-rock interaction processes. Sulfate springs are fed by shallow meteoric water heated by ascending gases. In keeping with the geodynamic setting and nature of the reservoir rocks, chloride water is rich in As, B, Cs, Li; on the other hand, sulfate water is enriched only in B relative to local meteoric water. Alternatively to a merely meteoric model, chloride waters can be interpreted as admixtures of meteoric and magmatic (circa andesitic) water, which moderately exchanges oxygen isotopes with rocks at a chemical Na/K temperature of about 270°C in the main reservoir, and then undergoes loss of vapor (and eventually mixing with shallow water) and related isotopic effects during ascent to the surface. These chloride waters do not present tritium and can be classified as sub-modern (pre-1952). A chloride content of 5,400 mg/l is estimated in the main reservoir, for which δ²H and δ¹⁸O values, respectively of -78‰ and -6.9‰, are calculated applying the multistage-steam separation isotopic effects between liquid and vapor. From these data, the meteoric recharge (Cl≈0 mg/l) of the main reservoir should approach a composition of -107‰ in δ²H and -14.6‰ in δ¹⁸O, when a magmatic water of δ²H = -20‰, δ¹⁸O = +10‰ and Cl = 17,500 mg/l is assumed. The ⁸⁷Sr/⁸⁶Sr ratios of the hot springs are quite uniform (0.70876 to 0.70896), with values within the range observed for dacites of the Andean central volcanic zone. A water δ¹⁸O-⁸⁷Sr/⁸⁶ Sr model was developed for the main geothermal reservoir, by which a meteoric-magmatic composition of the fluids is not excluded. The uniform δ³⁴S(SO₄^2-) values of +1.4 to +2.6‰ in the chloride waters agree with a major deep-seated source for sulfur, possibly via hydrolysis in the geothermal reservoir of sulfur dioxide provided by magma degassing, followed by isotopic exchange between sulfate and sulfide in the main reservoir. This interpretation is supported by the largely negative δ³⁴S(SO₄^2-) value in steam-heated water sulfate (-9.8‰) and mass-balance calculation, which exclude leaching at depth of igneous iron-sulfides with δ³⁴S near zero per mill. All the δ¹³C values of total carbonate in the chloride waters are negative, with variable values from -9.2 to -20.1‰, pointing to an important proportion of biogenic carbon in the fluids. The interpretation of these data is problematic, and a number of alternative explanations are reported in the text.

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Based on the combination of petrologic characteristics of the deposits and carbon-14 dating of charcoal pieces, we determined the burial age of the ancient Roman villa, believed to belong to the first Roman Emperor Augustus, at the northern foot of Mt. Vesuvius. Volcanic deposits covering the site consist of three geological formations related to the eruptive activity of Mt. Vesuvius. Juvenile material of the lowest formation show the same whole-rock chemical composition as that of the AD472 eruption, and carbon-14 ages of charcoal in and below the deposits coincide with AD472, indicating that the villa was first buried by the AD472 eruption. The villa itself is thought to have been already abandoned, judging from the depositional relation of the Plinian-fall and pyroclastic surge deposits to the damaged building frames.

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