Géochimie isotopique du lithium dans les basaltes-Géochimie des ...

tel-00344949, version 1 - 7 Dec 2008
4. Article soumis à G3
where Sr isotopic values vary from 0.702492 to 0.702462 with a coherent variation of
�La/Sm�N from 0.63 to 0.52. This discussion holds true when considering Nd isotopic ratios
shown in figure 4.12 where external error bars are indicated. The existence of these co‐
variations suggests �1� that the conventional statistics for external reproducibility may not
be applicable for small sub‐populations such as these �2� that it is very probable likely that
the described geochemical variations would be similar with a smaller sampling interval.
These variations being recognized, it is important to note that the most depleted
samples �in trace element ratios or isotopic composition� are found at segment ends, i.e.
DR4, DR34 �figure 4.12�. These intra‐segments geochemical variations are correlated with
the evolution of the ridge morphology along axis as expressed by the variation of the cross‐
150
Figure 4.13: Correlation of depth �m� and cross‐section
�km2� with �Nb/Zr�N together with illustrations of segment
center and segment end morphologies �from Klingelhöfer et
al., 2006�. The regression line is shown as a doted line with
corresponding correlation coefficients.