Geoscience Reference
In-Depth Information
41
HIMU
40.5
40
C
39.5
EM I
39
38.5
38
DM
37.5
37
17
18
19
20
21
22
206
Pb/
204
Pb
15.9
15.85
HIMU
15.8
15.75
15.7
C
15.65
15.6
EM I
15.55
15.5
15.45
DM
15.4
17
18
19
20
21
22
206
Pb/
204
Pb
Figure 11.11
Two-dimensional histogram of Pb isotope compositions of oceanic basalts showing the high
238
U/
204
Pb ratio of the mantle source of HIMU basalts (St Helena, Mangaia).
of trace elements, the most incompatible of which are normally greatly enriched in our
understanding of oceanic basalt genesis.
With the new emphasis of some isotopic systems since the mid 1990s, notably the
oxygen isotopes and the
176
Lu-
176
Hf and
187
Re-
187
Os systems, the complex geochemical
landscape of the source of OIB is coming into sharper focus. Isotopic variations of oxy-
gen indicate that mantle material that had experienced low-temperature sea-floor alteration
is involved in the source of the Hawaiian basalts. Isotopic compositions of osmium and
hafnium show that we find all the components of the ancient oceanic lithosphere recycled,
