Elements, isotopic composition between

The variable compositions of mafic rocks at likely reflect the occurrence of different types of parental liquids, which are characterised by distinct enrichment in potassium and incompatible elements. The positive correlation of potassium vs. incompatible elements and the lack of systematic differences in isotopic compositions between potassic and ultrapotas-sic rocks are suggestive of a magma genesis by different degrees of partial melting in a broadly common mantle source. This is supported by the similar REE and incompatible element patterns of all the mafic rocks (Fig. 4.8). Also the melilite-bearing rocks from Montefiascone share these... 

Earlier work on the isotopic compositions of pyrite, elemental sulfur, and organic sulfur in coals from Japan, Australia, and Germany (107-110) was summarized by Nielsen (102). Smith and Batts (110) showed that organic sulfur in Australian coals ranging in age from Permian to Tertiary has a large isotopic variation (+2.9 to +24%c) in coals with more than % sulfur, whereas organic sulfur in low-sulfur coals (less than 1% sulfur) has a narrow isotopic composition between +4.6 and +7.3%o. The relatively uniform isotopic... 

For most other elements there is no difference between the isotopic composition of carbonaceous chondrites and the Earth. As of early 2000s, only two exceptions, chromium and titanium, are known for these two elements very small differences in the isotopic composition between carbonaceous chondrites and the Earth were found. Bulk carbonaceous chondrites have isotope anomalies in chromium and titanium. Isotopically unusual material may have been mixed to the CC-source after proto-earth material has accumulated to larger objects. 

In elemental analysis by ICP-MS, a difference in the isotopic composition between the sample and the calibration standard leads to a bias in the measurement result, that is, the elemental content determined. In serious routine analysis, the isotopic variation of certain elements therefore needs to be considered. For lead determination, often the ion currents of the isotopes ° Pb, Pb, and Pb are summed and this sum is used for the calculations, because the sum of all isotope amount fractions is one and therefore is not susceptible to isotopic variations. However, two approximations are included first, the ion current of Pb is not used owing to its low isotope amount fractions and the interference from... 

Calcium carbonate is also the main constituent of the shells of sea animals, which make their shells from elements acquired from the surrounding waters. Now, the degree of fractionation of the oxygen isotopes as well as the formation of mineral carbonates and of animal shells in sea waters are determined on the basis of the temperature-dependent fractionation of the isotopes of oxygen the oxygen isotope composition of these materials reflects, therefore, the temperature at the time of their formation. Thus determining the isotope ratio between the stable isotopes of oxygen... 

The exact mass of an ion (4 to 6 decimal points) reliably defines its elemental and isotopic composition, while the method is called high resolution mass spectrometry. The measurements are conducted manually or automatically (computerized). Manual measurements are based on the parallel acquisition of the peak of interest with the closest peak of an ion with the known composition. Any compound with an intense ion peak with m/z value in the region +10% may serve as a marker. The most widespread markers are perfluorokerosene, perfluorotributylamine, and other polyfluorinated compounds. The use of these compounds is based on their volatility, as well as on the fact that fluorine is a monoisotopic element. In the spectra of these compounds intense ion peaks randomly cover all the range between m/z 19 and M+. ... 

For lithium, as for a few other elements (noble gases), modified isotopic compositions may be found in commercially available material because it has been subject to undisclosed isotopic fractionation commercially available lithium specimens have atomic weights that range between 6.939 and 6.996 if a more accurate value is needed it must be determined for the specific material. 

The significant relative mass difference (c. 16%) between the two stable isotopes of Li (approximately Li 7.5%, Li 92.5%), coupled with broad elemental dispersion in Earth and planetary materials, makes this a system of considerable interest in fingerprinting geochemical processes, determining mass balances, and in thermometry. Natural mass fractionation in this system is responsible for c. 6% variation among materials examined to date (Fig. 1). Although the modem era of Li isotope quantification has begun, there are still many questions about the Li isotopic compositions of fundamental materials and the nature of fractionation by important mechanisms that are unanswered (e.g., Hoefs 1997). 

James et al. (2003) performed laboratory experiments in which aqueous fluids were reacted with natural samples of unaltered MORE (5 Li = +4.6) and a quartzofeldspathic mud/turbidite mixture (5 Li = +1.3). The starting fluids had elemental compositions generally intermediate between seawater and hydrothermal fluids, and were isotopically light (5 Li = -5.5). The initial fluid/solid was 4. Fluid samples were extracted as the experiments were raised to 350°C over 400-500 h, and then during cooling (c. 740 h total). In both experiments Li was removed from solution at low temperatures, but the isotopic composition of the fluids... 

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