Géochimie isotopique du lithium dans les basaltes-Géochimie des ...
Géochimie isotopique du lithium dans les basaltes-Géochimie des ...
Géochimie isotopique du lithium dans les basaltes-Géochimie des ...
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tel-00344949, version 1 - 7 Dec 2008<br />
3. Article soumis à GCA en révision<br />
Figure 3.12 : Calculated standard deviation of the Li isotopic composition<br />
of aliquots of samp<strong>les</strong> in function of their mass. The three curves<br />
correspond to three characteristic sizes of the possible Li isotopic<br />
heterogeneities pro<strong>du</strong>ced in a magmatic rock which was initially perfectly<br />
homogeneous in δ 7Li and in which Li diffusion took place <strong>du</strong>ring cooling<br />
�see text�.<br />
8. CONCLUSIONS<br />
Different Li isotopic profi<strong>les</strong> were found for olivine phenocrysts from different<br />
locations within the same lava pillow. Diffusion‐in<strong>du</strong>ced <strong>lithium</strong> isotopic fractionation can<br />
perfectly explain �i� the low δ 7 Li edges shown by olivines that have experienced the<br />
slowest cooling rate, �ii� the lack of detectable δ 7 Li zoning in olivines embedded in the<br />
glassy rim of the pillow, and �iii� the heavier <strong>lithium</strong> isotopic composition found in melt<br />
inclusions<br />
hosted by olivines.<br />
The quantification of the diffusion of Li in olivine is not straightforward to model.<br />
Experimental determinations of specific diffusion parameters for Li in olivine have still not<br />
yet been determined and this must be the next step. Our data suggest that the β parameter<br />
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