Chicxulub batholite

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Dear Paleonet readers,

	In the almost endless discussion about the eventual relation 
between a collision with a celestial body and the massextinction at the 
K/T-limit, very little attention seems to have been paid to the nature 
of the magmatic intrusion, underlying the Chicxulub-structure.

	Yet, it seems to me that this issue may be of some importance.  
Let us first assume that the Chicxulub structure is indeed an astrobleme 
(an impact crater), as postulated by main stream science and popular 
"belief".  The impact of a celestial body, capable of excavating an 
astrobleme with a diameter up to 150 km or more, would almost certainly 
shatter the earth's crust to an equally considerable depth.  It is thus 
perfectly conceivable that the shattering penetrates the earth's mantle 
and the asthenosphere.  The intrusion of asthenospheric magma's into the 
crust might then be the unavoidable result of such a cataclysm.  In that 
case, one would expect to find a batholite underlying the Chicxulub 
structure, consisting of alkaline of very alkaline rocks, such as a 
gabbro, a theralite, an essexite, or maybe even some peridotite.

	I remember having read somewhere (but I unfortunately forgot 
where and when), that the Chicxulub batholite is actually granitic in 
composition, and thus acid, rich in silica.  Granitic intrusions are 
mainly the result of the melting and injection of molten crustal 
material, such as happens in subduction zones.  Mexico is indeed 
situated in a very active subduction zone and has been so since the 
before the Upper Cretaceous.  The presence of granitic batholites in the 
country can thus be no great surprise.  Yet, the granitic nature of the 
Chicxulub batholite seems very difficult to concile with an impact 
nature of the structure.  Being underlain by a granitic batholite, the 
Chicxulub structure is much more likely to be no more than a caldeira.  
A large one, admitted, but yet a caldeira !  If this is true, where is 
the "smoking gun", pointed out by many impactists ?
	
	Because of the potential importance of this issue, I'ld like to 
post the following question.

	CAN ANYONE HELP ME FINDING SOME REFERENCES ABOUT THE PETROGRAPHY 
OF THE BATHOLITE, UNDERLYING THE CHICXULUB STRUCTURE IN YUCATAN, MEXICO ?


	Thank you very much in advance.

	J. F. Geys
	Dept. of Biology
	State University Antwerpen (RUCA)
	Groenenborgerlaan 171
	B-2020  Antwerpen, Belgium