Minerals terrestrial, isotope

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.

The isotopic studies of terrestrial minerals and Allende inclusions have clearly established the capabilities of the Chicago ion probe to perform precise isotopic measurements on femtogram... 

Similar equations can be written for Pb and Pb using their appropriate radioactive parents and decay constants. If t = 0 is taken to represent the time of the formation of the Earth s crust, then these three equations describe the trajectory of the isotopic composition of terrestrial lead from that time. If T is the time elapsed since the formation of the Earth, (i.e., the age of the Earth), and tm is the time before present at which the lead minerals were formed, then, using the assumptions of the Holmes Houtermans model given above, the isotopic composition of a common lead deposit formed tm years ago is given as follows ... 

The observed range of natural variations of 5 Ca is about 4 to 5%o in terrestrial materials and up to 50%o in high temperature condensate minerals in carbonaceous chondrites. The typical reproducibility of measurements is about +0.15%o. Broader application of Ca isotope measurements in geochemistry may be possible, particularly if the reproducibility can be improved to 0.05%o to 0.03%o. There is hope that this can be achieved either with inductively coupled plasma source mass spectrometry (Halicz et al. 1999) or with a new generation of multi-collector thermal ionization mass spectrometers (Heuser et al. 2002). 

Isotopic reconstruction of climatic conditions on the continents is difficult, because land ecosystems and climates exhibit great spatial and temporal heterogeneity. The most readily determined terrestrial climatic parameter is the isotopic composition of precipitation, which is in turn dependent largely but not exclusively on temperature. Relevant climatic information from meteoric precipitation is preserved in a variety of natural archives, such as (1) tree rings, (2) organic matter and (3) hydroxylbearing minerals. 

In Stable Isotope Geochemistry. Rev Miner Geochem 43 415 67 Beard BL, Johnson CM (1999) High-precision iron isotope measurements of terrestrial and lunar materials, Geochim Cosmochim Acta 63 1653-1660 Beard BL, Johnson C (2004) Fe isotope variations in the modem and ancient Earth and other planetary bodies. Rev Miner Geochem 55 319-357 Beard BL, Johnson CM, Cox L, Sun H, Nealson KH, Aguilar C (1999) Iron isotope biosphere. Science 285 1889-1892... 

Tomascak PB, Ryan JG, Defant MJ (2000) Lithium isotope evidence for light element decoupling in the Panama subarc mantle. Geology 28 507-510 Tomascak PB, Widom E, Benton LD, Goldstein SL, Ryan JG (2002) The control of lithium budgets in island arcs. Earth Planet Sci Lett 196 227-238 Tomaszak PB (2004). Lithium isotopes in earth and planetary sciences. Rev Miner Geochem Trofimov A (1949) Isotopic constitution of sulfur in meteorites and in terrestrial objects. Doki Akad Nauk SSSR 66 181... 

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). 

The isotopes of thorium include mass numbers 223-234. 232Th has a half-life of 1.39 x 1010 years, See also Radioactivity. It emits an alpha-particle and forms meso-thorium 1 (radium-228), which is also radioactive, having a half-life of 6.7 years, emitting a beta-particle. Since 2 2Th captures slow neutions to form, by a series of nuclear reactions, >>U which is fissionable, thorium can be used as a fuel for nuclear reactors of the breeder type. Thorium occurs in earth minerals, an average content estimated at about 12 ppm. Findings of hc Apollo 11 space flight indicated that thorium concentrations in some lunar rocks are about the same as the concentrations in terrestrial basalts. 

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. 

Kouwenberg LLR, Kiirschner WM, McElwain JC (2007) Stomatal frequency change over altitudinal gradients prospects for paleoaltimetry. Rev Mineral Geochem 66 215-242 Lai D (1988) In situ-produced cosmogenic isotopes in terrestrial rocks. Ann Rev Earth Planet Sci 16 355-388 Lai D (1991) Cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models. Earth Planet Sci Lett 104 424-439... 

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