Re: extinction

["Dewey M. McLean" <dmclean@vt.edu>]

Response to Phil Bigelow's Wed, 14 Jan 2004 02:30:52 post.

Phil wrote: "as I understand it,  iridium does 
not aerosolize out of basalt flows. In fact, 
iridium doesn't aerosolize at all.  The 
chlorides, fluorides, and oxides of iridium 
(which have to be produced under laboratory 
conditions)
are all dense solids."

In 1983, Bill Zoller, Josef Parrington, and Janet 
Phelan Kotra published a milestone paper titled 
"Iridium enrichment in airborne particles from 
Kilauea volcano: January 1983" (Science, 1983) in 
which it was shown for the first time that 
volcanos can release iridium into the atmosphere. 
The authors stated, "The iridium enrichment 
appears to be linked with the high fluorine 
content of the volcanic gases, which suggest that 
the iridium is released as a volatile IrF6." 
Fluorine gases are found only in volcanoes fed by 
a deep magma source, possibly the mantle. And, 
"The calculated mass of Ir in the K/T boundary 
layer is approximately 200 kilotons and would 
require an eruption much larger...than 
Kilauea...the Deccan flood basalts...were of 
sufficient magnitude to have introduced the Ir 
found in the K-T layer."

In 1989, Toutain and Meyer published a paper 
titled "Iridium-bearing sublimates at a hot-spot 
volcano (Piton de la Fournaise, Indian Ocean)" 
(Geophysical Research Letters, 1989). They 
pointed out that iridium seems to be 
preferentially released by hot-spot type 
volcanoes. They also noted that Piton de la 
Fournaise is related to the hot-spot track which 
generated the Deccan Traps, and that volcanic 
gaseous iridium can be related to the KTB. And, 
that if investigations of the Deccan volcanics do 
not evidence significant iridium contents, it has 
been calculated that Ir amounts about three times 
less than iridium in lavas of Piton de la 
Fournaise (0.25±0.03 ppb) are sufficient to 
produce the KTB iridium anomaly (Rocchia et al. 
1988).

In 1986, Olmez, Finnegan, and Zoller published a 
paper titled "Iridium emissions from Kilauea 
volcano" (Journal of Geophysical Research, 1986). 
Following is a direct quotation from the paper:

"...Kilauea is a small volcano with insignificant 
eruptions....To estimate the importance for the 
mass extinction hypothesis, one must consider 
eruptions of a much larger scale, such as 
those...65 m.y. ago. One such eruption has been 
discussed by McLean [1982], who believes that the 
Deccan Traps basalts were a likely 
candidate....The Deccan probably did not occur on 
a short time scale, but let us estimate the 
quantity of Ir that could be emitted if the 
emissions were Kilauea-like in nature. Since 
approximately 10 x 10^6 km^3 of magma were 
emitted by the Deccan, the Ir emissions would be 
expected to be of the order of 30,000 tons, a 
little less than the mass believed to be 
contained in the KT boundary layer."

Cordially,
Dewey McLean