QUOTE (edstrick @ Mar 7 2006, 03:37 PM)
but there's no sign of a source crater anywhere
Yeah a bit of a mystery there...
Australites (and Indochinites which are indistinguishable from each other) have been dated to about 710,000 years using fission track and potassium-argon (K-Ar) dating methods; However the stratigraphic positions indicates an age of 7000 to 20,000 years BP.
From their chemical composition, both belong to the same impact event...!
The evidence seems to show a least two episodes of australite falls - one relatively recent (24,000 and 16,000 years ago) and at 710,000years. (It could be influenced by sorting by ie Early man)
Australites are also unusual in that some show that they were remelted; this may show different trajectories - sending some material into orbit...
Darwin glass from South West Tasmania has a combined K-Ar and fission track age of 730,000 +/- 40,000 years. It seems that Darwin crater was the source of both.
I would also add that it is possible that the impact crater may be part of two or more events that occurred together. Another associated impact crater could have been formed in the Indonesian region.
A larger impact crater that still has to be found...
Darwin Crater has a diameter of 1 kmExpand
(This is a possible location - can someone confirm?)-42.249599° 145.555629°
(i`ve posted another location (42°18.39'S, 145°39.41'E) at googlehacks though)http://www.grisda.org/origins/04076.htm