139
Fig. 7.4
Calculation of bulk D values in logarithmic diagrams. (
a ) Example of logarithmic dia-
grams. Symbols as in Figs.
7.1
and
7.2
. Lines are regression lines of slopes
Δ^ i
with
Δ
~1–Di. i
Comparison between Chaîne des Puys (stricto sensu) and Pavin group magmas evidence a step-wise differentiation process, each step being characterized by approximately constant D
values. i
( b
) Bulk D values of some incompatible elements, comparison with amphibole and clinopyroxene/
melt partition coeffi
cients. Zr, Hf, Nb, Ta and REE partition coeffi
cients calculated for Basalt-
Hawaïte and Hawaïte-Benmoreite differentiation steps in Pavin group (Dg Pav) and Chaîne des
Puys (stricto sensu; Dg CP) differentiation series. Mineral/melt partition coeffi
cients for clinopy-
roxene (d CPx) and amphibole (d Amph) in alkaline series are from Lemarchand et al. (
1987
). For
Basalt-Hawaïite differentiation step, mineral/melt partition coeffi
cients vary in a relatively large
range: extreme values are represented). Notice the large differences in bulk D values of LREE in basalt-hawaïite differentiation steps in Pavin and Chaîne des Puys series. The mineral/melt parti-tion coeffi
cients of amphibole and clinopyroxene are generally close for all elements (‘parallel D
values patterns’), except Nb and Ta which are much more effi
ciently partitioned into amphibole
2.8 2.6 2.4 2.2 2.0
0.4
0.6
0.8
1.0
1.2
1.4
log Zr
log Th
3.2 3.0 2.8 2.6 2.4
0.4
0.6
0.8
1.0
1.2
1.4
log Ba
log Th
1.2 1.0 0.8 0.6 0.4 0.2
0.4
0.6
0.8
1.0
1.2
1.4
log Ta
log Th
2.5 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0
0.4
0.6
0.8
1.0
1.2
1.4
log Co
log Th
7 Magmatic Evolution of Pavin’s Group of Volcanoes: Petrology, Geochemistry...