56 
A.W.R. Bevan, E.M. Shoemaker, C.S. Shoemaker 
DISCUSSION 
In Veevers fragments, transformation of kamacite 
to ragged a, indicates a transient, but severe re¬ 
heating to temperatures above the a to y 
transformation temperature, followed by rapid 
cooling (Brentnall and Axon 1962; Axon et al. 1968; 
Lipschutz 1968). Reaction haloes between 
schreibersite and metal indicate incipient 
resorption of the phosphide and are also consistent 
with a brief, but severe re-heating event. This re¬ 
heating event is superimposed on earlier formed 
structures in Veevers and appears to be the most 
recent thermal event in the history of the meteorite. 
There are several possible explanations for the 
cause of the re-heating in Veevers that include; pre¬ 
terrestrial cosmic shock reheating, frictional 
heating during atmospheric passage, shock 
reheating on impact, and contact with hot impact 
ejecta. However, there are a number of significant 
features of the microstructure of Veevers indicating 
that the observed effects of transient re-heating 
were associated with the impact event. 
As shown for Canyon Diablo by Heymann et al. 
(1966), the localised occurrence of severe thermal 
effects observed in the interiors of some of the 
Veevers fragments indicates steep temperature 
gradients that exclude conductive heating (e.g., 
atmospheric passage and contact with hot ejecta) 
as a mechanism for re-heating. In Veevers, the 
superimposition of thermal alteration on earlier 
structures, and its clear association in at least one 
fragment with intense shear deformation, suggests 
that heating in that case was caused by shock¬ 
loading during the formation of the crater and tire 
disruption of the impacting projectile. However, in 
the largest fragment recovered (WAM 13761) the 
general transformation of metal to a 2 -kamacite that 
is not obviously associated with mechanical 
deformation does not exclude the possibility of 
conductive re-heating. Notwithstanding, the 
similarity of the condition of the schreibersite and 
rhabdites in all three fragments examined is 
consistent with re-heating for short (seconds) 
duration rather than prolonged (minutes/hours) 
heat-treatment in a hot ejecta blanket. 
Comparison with experimentally heated and 
shock re-heated samples of iron meteorite allows 
the magnitude and duration of thermo-mechanical 
treatment of Veevers to be determined more 
accurately. The thermal effects observed in 
kamacite and schreibersite in lightly shocked 
samples of Canyon Diablo experimentally heat- 
treated in air for 10 and 100 seconds at 800 - 850 
°C (Figure 5a and b) and allowed to cool by 
radiation are very similar to the range of structures 
observed in Veevers fragments. In these samples, 
metal is partially or wholly transformed to a 2 - 
kamacite comprising 10 - 200 pm units, and 
a 
incipient reaction schreibersite [s] with 
surrounding metal, degenerated Neumann 
bands and a 2 transformations. Scale bars 100 
pm (2% nital etch). 
phosphides show incipient, ragged reaction haloes 
with surrounding metal. In samples heated to the 
same temperatures but for longer (100 - 1000 secs) 
periods, the reaction haloes around phosphides 
become more prominent, and thorn-like 
protuberances penetrate the metal from the 
phosphide metal interface. These features were not 
observed in the Veevers fragments examined. 
The peak temperature to which Veevers 
fragments were subjected during terrestrial impact 
is more difficult to determine. Samples of Canyon 
Diablo experimentally heated to 1000°C for shod 
duration (300 secs) by Brentnall and Axon (19621 
showed extensive eutectic melting and resorption 
of schreibersite. Widespread melting of 
schreibersite was not observed in the Veevers 
fragments examined, suggesting that overall re¬ 
heating of the surviving fragments was 
considerably less than 1000°C. However, to 
