Terrestrial mineral samples

The following minerals are important in meteorites and other extraterrestrial samples. Some important classes of minerals in terrestrial rocks are not observed or are extremely rare in meteorites or planetary samples (e.g. micas, amphiboles) and will not be considered. 

There are also similar equations for both uranium-235 and thorium-232. Results embody three independent ages referring to the three decay series involved and ideally should agree. However, they will only do so if the mineral samples analyzed stayed closed throughout their geological history and also if the isotopic compositions of uranium and thorium were not modified in any way, for instance by fractionation. It is assumed that the values used for the initial lead isotopes are accurate and that no analytical or systematic errors occurred. The ratio [235u/238u] 1/137 gg for uranium of normal composition found in terrestrial minerals, lunar... 

Plutonium occurs in natural ores in such small amounts that separation is impractical. The atomic ratio of plutonium to uranium in uranium ores is less than 1 10 however, traces of primordial plutonium-244 have been isolated from the mineral bastnasite (16). One sample contained 1 x 10 g/g ore, corresponding to a plutonium-244 [14119-34-7] Pu, terrestrial abundance of 7 x 10 to 2.8 x 10 g/g of mineral and to <10g of primordial Pu on earth. The content of plutonium-239 [15117 8-3], Pu, in uranium minerals is given in Table 2. 

A representative sample of the isotopic data from terrestrial standards is given in Table 1 and plotted in figure 6 together with data from Mg-rich minerals (spinel and Ti-pyroxene) from Allende inclusions. Raw isotopic data are presented, corrected... 

Table 1. llnnormalized Mg Isotope Data from Terrestrial Samples and Mg-rich Minerals from Allende... 

Figure 6. Three-isotope correlation diagram for Mg using S-notation fsee text) for unnormalized data from terrestrial samples and Mg-rich Allende minerals.

Al/24Mg ratio for each sample. Data for Allende Ti-Al-pyroxene and spinel fall within the range of the terrestrial standards 625Mg = 0 7 permil. 626Mg = 0 14 permil. It is important to recognize that the spread in the data for Allende Mg-rich minerals due to instrumental fractionation is the same as that observed for... 

Oxygen 3-isotope plot showing excesses of 160 in minerals from calcium-aluminum inclusions (CAIs). All samples from Earth rocks plot along the terrestrial fractionation line. Mass-dependent fractionation processes cannot move a composition off of this line, so the excesses of 160 were clearly isotopic anomalies. After Clayton et al. (1977). 

It is essential to understand the isotopic variability within authigenic minerals that form the basis of terrestrial paleoclimate records and between such samples that are isochronous within an outcrop of a stratigraphic formation. Except for variability studies in biogenic materials (teeth, bone, shells) (e.g., Kohn et al. 2002), we know of no paleoaltimetry studies that have examined this natural variability in authigenic or pedogenic proxy materials. Such variability studies should be conducted before any quantitative estimates of paleoelevation can be made. 

Different evolutionary histories of other terrestrial planets have influenced the relative concentrations of the transition elements compared to their cosmic abundances, as suggested by geochemical data for surface rocks on the Moon, Mars and Venus (Appendix 1). Chemical analyses of lunar samples returned from the Apollo and Luna missions show that minerals and glasses occurring on the Moon contain high concentrations of Fe and Ti existing as oxidation states Fe(II), Ti(III) and Ti(IV). Some lunar minerals, notably olivine and opaque oxides, also contain significant amounts of Cr(H), Cr(III) and Mn(H). The lack of an atmosphere on the Moon simplifies interpretation of remote-sensed reflectance spectra of its surface. 

In the beginning of the nineteenth century, analytics of plant matter samples started with that of plant ashes. In addition, no methods were available then which could have enabled intact biological materials to be digested for complete, no-Ioss analyses without burning them before. Hence, volatile elements then could not be detected, let alone quantified in biomass. Elements then found in plant ashes (Fe, Na, K, Ca, etc.) were both abundant and had been discovered in other sources before. As, e.g., no spectroscopic methods whatsoever were at hand earlier than about 1860, technical prospects for trace analysis then were dim at best (there are very few instances of elements detected in environmental samples/spectra prior to their isolation on Earth helium (in 1868) and techne-tinm (in 1952) were found in stellar spectra before being isolated from or detected in terrestrial minerals... 

The oldest samples that provide direct constraints on the osmium isotopic composition of the upper mantle are rare spinel peridotites contained within the Early Archean Itsaq gneiss complex of southwest Greenland that are interpreted to be —3.81 Ga abyssal peridotites (Friend et al., 2002). The measured and initial compositions determined from low-Re/Os spinel and olivine mineral separates from these peridotites are the most primitive, in the sense of closest to solar-system initial compositions, Os isotopic compositions yet obtained on any terrestrial material (Bennett et al., 2002). This shows that at least some, if not all, of the Early Archean upper mantle was characterized by chondritic Os/ Os isotopic compositions. Osmium isotopic constraints from this time period (—3.8-3.9 Ga) are of particular interest as they provide a rough constraint on the timing of the addition of the late veneer of... 

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