Three-Isotope Diagrams

Here / , and R2 are the compositions of reservoirs 1 and 2, respectively /, is the fraction of the reference isotope JA, which is contributed by component 1, and likewise for/. This equation is applicable to both the abscissa ratio X and the ordinate ratio Y  

In noble gas studies, it may often be the case that a correlation line is only a mixing line reflecting variable admixture of a single sample source component with 

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It is clear from figure 6 that the terrestrial data do not cluster about a single point but instead lie along a line of slope 0.5 on the three-isotope diagram, indicating isotopic variation due to mass-dependent fractionation. Since mass fractionation effects in Mg have not been observed in terrestrial materials [30,31], this distribution of observed isotope ratios must be due to fractionation in the ion probe. The physical process which produces the... 

RESOLVING MECHANISMS OF ISOTOPE FRACTIONATION WITH THREE ISOTOPE DIAGRAMS... 

Oxygen isotopic compositions of minerals in CAIs on an oxygen three-isotope diagram. Axes are given in delta notation 81S0 =[((180/160)sampie/(180/160)s,andard)-1] x 1000, and similarly for S170. After Clayton et al. (1977). 

Figure 1.2 Schematic illustration of a three-isotope diagram. The abscissa is any isotope ratio A/ A, the ordinate is another ratio kAPA involving a third isotope in the numerator and the same (reference) isotope in the denominator. The points labeled 1 and 2 represent any two components of distinct composition. The locus of all mixtures of components 1 and 2 is the straight line connecting these points. Point M represents any mixture composition the ratio of the line segment lengths AL and L, measured from 1 to M and from 1 to 2, respectively, is the fractional contribution that component 2 contributes to the reference isotope (illustrated for 65%).

As in Section 1.4, a component is any uniform reservoir with well-defined composition. A component reservoir with at least three isotopes, and therefore two isotope ratios, thus defines a point on a three-isotope diagram (e.g., as labeled 1 on Figure 1.2). A second reservoir with a distinct composition then defines a distinct point (e.g., 2 on Figure 1.2). For any two isotopes A and A, and their ratio R = A/ A, mixing of components 1 and 2 produces an intermediate ratio R, which is given by... 

Figure 3 Oxygen-isotopic compositions of CM2 carbonaceous chondrites plotted in a three-isotope diagram. The CM2s form a linear array with a slope of 0.7, with enrichments in the heavy isotopes that show a general increase as a function of increasing alteration. Nogoya (NG) and Cold Bokkeveld (CB) are the most heavily altered CMs and Murchison (MC) is one of the least altered. Chondrites with intermediate degrees of alteration are not well resolved in this diagram (after Browning et al., 1996 source Clayton, 1993).

Figure 6 Oxygen-isotopic compositions of CV chondrites and their dark inclusions plotted on a three-isotope diagram. Bulk CVS chondrites plot close to the CCAM line defined by the isotopic composition of anhydrous minerals from CAIs in Allende. The reduced CV chondrites are isotopically lighter than the oxidized CV chondrites such as Allende. Dark inclusions from Allende also plot on the CCAM line, whereas inclusions from the reduced CV chondrites, Vigarano, Leoville, and Efremovka have oxygen-isotopic compositions that show significant heavy isotope enrichments, indicative of aqueous alteration (source Krot et al., 1999).

A common tool for visualization of isotopic variations is the so-called three-isotope diagram, in which two isotope ratios, each with the same reference (denominator) isotope, are... 

Figure 2 A three-isotope diagram illustrating compositional variations in lunar samples and meteorites, as observed in stepwise in vacuo etching and pyrolysis. Since the observed isotopic compositions do not lie on a single straight line, at least three isotopically distinct components must contribute in variable proportions. These data are interpreted as superposition of solar wind (SW), solar energetic particles (SEP), and galactic cosmic ray, i.e., spallation (GCR)...

Figure 5 A display of prominent exotic (presolar) noble-gas compositions (from Anders and Zinner, 1993). In the left two panels, for each isotope on the abscissa the ordinate is the ratio (to °Xe) in the HL component (left panel) or the G (formerly termed Xe-S) component (center panel), divided by the equivalent ratio in solar xenon (i.e., solar xenon would plot with all isotopes at unity on the ordinate). The HL component shows the defining characteristics of enriched heavy and light isotopes. For the G-component, the pattern is that expected for s-process (slow neutron capture) nucleosynthesis. The right panel is a three-isotope diagram analogous to Figure 4, except that both scales are logarithmic. It shows experimental limits for the R-component (formerly Ne-E(L)) and the G-component (formerly...

Figure 1. Oxygen three-isotope diagram showing isotopic compositions of minerals from Allende CAIs (CCAM = carbonaceous chondrite anhydrous minerals). The other line, labelled TF (terrestrial fractionation) is the locus of data points for terrestrial rocks and waters (data not shown). The bulk oxygen isotopic composition of the Earth is indicated by point E the expected oxygen isotopic composition of the Sun is indicated by point S. The S-notation on the...

In comparison to MORBs, some OIBs show a much steeper correlation in the Ne three-isotope diagram (Fig. 11). This is especially true for the cases of Hawaii, Iceland and Reunion (Fig. 11 Honda et al. 1991 Valbracht et al. 1997 Trieloff et al. 2000 Dixon et al. 2000 Moreira et al. 2001 Hanyu et al. 2001). These steep trends reveal that these OIB mantle sources have less nucleogenic Ne (lower Ne/ Ne) than the MORB mantle source. Because MORBs also show more radiogenic He than OIBs from Hawaii, Iceland and Reunion, the mantle source for MORBs must be characterized by lower time-integrated He/(U+Th) and Ne/(U+Th) than the mantle source for those OIBs. Because the MORB mantle source is also trace element-depleted compared to the source for many OIBs, the OIB mantle source, at least for cases such as Hawaii, Iceland and Reunion, must be less degassed (i.e., it has higher He and Ne concentrations) than the upper mantle source ofMORBs. 

Figure 14. Neon three-isotope diagram ( Ne/ °Ne vs. Ne/ °Ne) showing the compositions and trends of various Ne components. Mixtures of atmospheric and cosmogenic Ne plot on the spallation line, the slope of which has been experimentally determined for quartz and pyroxene (Table 8). Contributions from nucleogenic Ne and Ne are characterized by shifts in horizontal and vertical directions, respectively. The trends for crustal Ne (Kennedy et al. 1990) and MORB-type Ne (Sarda et al. 1988) are also given. The dotted line labeled mfl is the mass fractionation line.

A rubidium/strontium Three-isotope diagram showing the time-dependent isotopic evolution of rock systems after they crystallize from a homogeneous magma... 

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