Chondrites manganese/sodium

The bulk compositions of chondrites closely match the compositions of the solar photosphere, with the exception of a few highly volatile elements (hydrogen, carbon, nitrogen, helium) and lithium (see Chapter 1.03). The chondrite groups also show different levels of depletions in moderately volatile elements (e.g., manganese, sodium, potassium, gallium, antimony, selenium. 

The concentrations of four typical moderately volatile elements—manganese, sodium, selenium, and zinc—in the various classes of chondritic meteorites are shown in Figure 12, where elements are normalized to magnesium and CI-chondrites. Again there is excellent agreement between solar abundances and Cl-meteorites. A characteristic feature of the chemistry of carbonaceous chondrites is the simultaneous depletion of sodium and manganese in all types of carbonaceous chondrites, except Cl. Ordinary and enstatite chondrites are not or only slightly... 

The aubrites are the most reduced achondrites (Keil et al., 1989). Their silicates are essentially free of iron, and they contain minor metallic iron. A variety of unusual sulfides of calcium, chromium, manganese, titanium, and sodium - all usually lithophile elements -occur in aubrites. These unusual sulfides also characterize the highly reduced enstatite chondrites, which may have been precursors for these rocks. 

Figure 5 Concentrations of soluble elements in CM chondrites, illustrating the restricted compositional range of these elements in chondrites with variable degrees of alteration, (a) Sodium versus potassium and (b) manganese versus calcium (sources Kallemeyn and Wasson, 1981 Jarosewich, 1990).

Itqiy is distinct from chondritic meteorites in bulk composition. Aluminum, FREE, europium, sodium, potassium, vanadium, chromium, and manganese are aU depleted. Itqiy has La/Yb of 0. lOxCI, and Eu/Sm of 0.16 X Cl. Refractory siderophile elements are enriched —2-3 X Cl, while moderately volatile siderophile elements are at roughly Cl abundances. The bulk rock Mg/Si and Fe/Si ratios are greater than those of EH or EL chondrites. 

In Figure 13 the Earth s mantle seems to extend the trend of the moderately volatile elements to lower abundances, at least for sodium, manganese, and zinc (zinc behaves as a lithophile element in the Earth s mantle (see Dreibus and Palme, 1996)). The elements lithium, potassium, and rubidium which are not plotted here, show similar trends. The carbonaceous chondrite trend of iron is not extended to the Earth, as most of the iron of the Earth is in the core. The magnesium abundance of the Earth shows a slightly different trend. If the core had 5% silicon (previous section) and if that would be added to the bulk Earth silicon, then the bulk Mg/Si ratio of the Earth would be the same as that of carbonaceous chondrites (Eigure 10) and the silicon abundance of the Earth s mantle in Figure 13 would coincide with the magnesium abundance. 

Figures 12 and 16). The Mn/Na ratio of the Earth s mantle is also chondritic (Figures 12 and 16). Heating of meteorite samples to temperatures above 1,000 °C for a period of days will inevitably lead to significant losses of sodium and potassium but will not affect manganese... 

The minor amount of manganese in the core reflects the volatility model assumed for this element. O Neill and Palme (1997) argue that manganese and sodium have similar volatilities based on the limited variation in Mn/Na ratios in chondrites (see also Chapter 2.01). However, a plot of Na/Ti versus Mn/Na in chondrites (Figure 10) shows that indeed Mn/Na varies as a function of volatility this illustration monitors volatility by comparing titanium, a refractory lithophile element, with sodium, a moderately... 

---