Anders: Origin of Carbonaceous Chondrites 



519 



empirical abundance curves of Suess and Urey (1956) and Cameron (1959). 

 Other trace elements, including most chalcophile ones, do not conform to this 

 pattern. They occur in approximately their predicted abundances in car- 

 bonaceous chondrites, but are depleted by factors of up to 1000 in ordinary 

 chondrites (figure 4). If the carbonaceous chondrites were derived from 

 ordinary chondrites, as suggested by Urey, one would have to assume that 

 the depleted elements were somehow added to the carbonaceous chondrites 

 during the alteration process. In that case, it would be a remarkable coinci- 

 dence if 6 of the 7 elements happened to be restored to just their cosmic abun- 

 dances. (The seventh, mercury, may be exceptional because of its high 



Annealing of Mighei Glass 



• Almost Complete Anneal 

 — I Completion Observed 

 X Discontinued 



300 



o 



260 I 



0.1 



10 100 



Annealing Time (hrs) 



1,000 



Figure 3. .\nnealing of strained glass from Mighei carbonaceous chondrite. .\fter the 

 incorporation of the glass, the meteorite cannot have been heated to temperatures as high as 

 206° for as long as 48 hours, or the strain would have disappeared. (After DuFresne and 

 Anders, 1961.) 



volatility, but it should be noted that the point in figure 4 is based upon a 

 single measurement.) 



The olivine in carbonaceous chondrites has a highly variable iron content 

 (Ringwood, 1961), whereas it is of nearly constant composition in ordinary 

 chondrites (Mason, 1962). This factor, too, makes it difficult to derive car- 

 bonaceous chondrites from ordinary chondrites by any simple process. 



Another clue comes from the primordial noble gases which seem to be present 

 in all carbonaceous chondrites (figure 5). All meteorites contain noble gases 

 produced by cosmic rays or the decay of long lived radioactivities, but the car- 

 bonaceous chondrites also contain primordial noble gases that can be distin- 

 guished from cosmogenic or radiogenic noble gases by their isotopic and ele- 

 mental composition (Stauffer, 1961 ; Anders, 19626). With the exception of He^ 

 and Ar^", most of which is radiogenic, the noble gases in an ordinary chondrite 



