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

tel-00344949, version 1 - 7 Dec 2008
3. Article soumis à GCA en révision
Table 3.1: Chemical composition for the major phases of our picrite ARP73‐10‐03.
Pillow
Rim
Olivine 4-11 Olivine 5-20
glass core rim inclusion core rim inclusion
n 18 - - 2 - - 4
SiO2 49,06 40,7 41,34 49,53 41,59 40,94 50,03
TiO2 0,68 n,d, n,d, 0,69 n,d, n,d, 0,63
Al2O3 16,22 n,d, 0,1 16 n,d, 0,11 16,27
Cr2O3 0,08 n,d, 0,12 n,d, n,d, 0,16 n,d,
FeO 8,12 10,24 10,43 7,9 8,34 9,79 7,11
MnO 0,1 0,27 0,15 0,19 0,1 0,14 0,19
MgO 9,79 48,72 48,75 9,04 50,26 49,61 8,01
CaO 13,43 0,39 0,32 14,19 0,29 0,35 14,98
Na2O 1,75 n,d, n,d, 1,58 n,d, n,d, 1,56
K2O 0,06 n,d, n,d, 0,12 n,d, n,d, 0,04
P2O5 0,05 n,d, n,d, n,d, n,d, n,d, 0,1
NiO 0,06 0,08 0,17 0,23 0,28 0,38 n,d,
Total 99,4 100,5 101,4 99,5 100,9 101,5 99
size
(µm) - - - 185 - - 265
Fo - 89,5 89,3 - 91,5 90 -
The temperature of melt‐olivine equilibrium calculated for the pillow natural
quenched glass is 1200°C �Jones, 2003� and the calculated composition of equilibrium
olivine is Fo90.1 for a Kd � 0.30 �Ford et al., 1983�. This value is close to the average of
olivines from this sample and suggests that crystals in this picrite are phenocrysts. This is
also suggested by the chemistry of the melt trapped by the phenocrysts in the ARP73‐10‐
03 picrite. Kamenetsky �1996� has shown that the compositions of the original melts
trapped in olivine and chromite phenocrysts are very close to the composition of the
quenched pillow rim glass. These observations indicate unambiguously that olivine
phenocrysts were transported to the surface by their parental magma.
4. LI ABUNDANCE AND ISOTOPIC COMPOSITION
IN ARP73‐10‐03 PHASES
4.1. Fine grained groundmass and glass
The microlitic groundmass has not been analyzed due to the large ion probe beam
compared to the size of the glass patches in this part of the section. Thus the measurements
reflect the proportions of each of the phases in the analyzed area. On the contrary, the glass
99