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SUMMARY:4.5 Gyr of maturation of the Upper Continental Crust?  Evidence fr
 om stable isotope ratios. - Ed Tipper\, University of Cambridge
DTSTART:20100223T163000Z
DTEND:20100223T173000Z
UID:TALK22391@talks.cam.ac.uk
CONTACT:John Maclennan
DESCRIPTION:The average andesitic composition of the continental crust lea
 ves a number of outstanding questions concerning its formation. Contempora
 ry melting of the mantle generally forms melts of basaltic composition\, a
 nd so more exotic models have been proposed to generate crust of an andesi
 tic composition. One such model suggests that the crust has lost Ca and Mg
 \, two of the major components of the crust through chemical weathering. T
 hese two elements are highly soluble\, and two of the most concentrated ca
 tions in many low temperature aqueous fluids at the Earth’s surface\, ma
 king it potentially plausible that the crust that we observe today\, could
  differ from its pristine protolith. Such “far-fetched” models have na
 turally received little attention because there has been no method to begi
 n to test them. The stable isotope ratios of elements such as Mg (which sh
 ows one of the most important depletions in the crust compared to the mant
 le) could provide an opportunity to test such hypotheses through mass bala
 nce\, provided that data can be generated with sufficient precision and ac
 curacy. This talk will consider crustal recycling and review existing geoc
 hemical evidence for crustal alteration\, but in particular will show how 
 stable Mg isotope ratios could be well suited to tracking crustal evolutio
 n. Initial Mg isotope data from crustal materials will be compared that th
 at of the mantle and any discrepancies explored.\n
LOCATION:Harker 1 seminar room\, Department of Earth Sciences
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