OXYGEN
ISOTOPE
CONTRAINTS
ON
THE
SOURCES
OF
OCEAN
ISLAND
BASALTS
J.M
.
Eiler
1
,
K.
Farley1,
J.W
. Valley
2
,
A.W.
Hofm
ann
3
,
E.M.
Stolper
1
'
Di
vison
of
Geol
ogical
and
Pla n
etary
Scie
nce s. Cal
i forn
ia Ins titute
of
Tec
hn
ology,
Pasade
na
,
CA
91125
,
USA
2
D epa
rtm
ent
of
Geology
an
d
Geophy
sics.
Unive
rsit y
o f Win
co ns in , Madison
,
WI
, USA
·
'A
bt
e ilun
g
Geoc
h
emie
, Max
-Planck-Institut
fi.ir
Chemie,
Po
s tfach
3060
, D-5502
0
Main
z,
German
y
Oxygen
isotope
ratios
in
phenocrysts
from
ocean
island
basalts
(OIB)
can
place
constraints
on
the
origins
of
their
mantle
sources.
Values
of
()180
in
olivines
from
alkali
basalts
from
Pitcairn
Island
(which
have
the
extreme
"EMl"
signature
based
on
radiogenic
isotopes)
are
equal
to
those
of
olivines
from
average
mantle
peridotite
(based
on
studies
of
mantle
xenoliths
and
the
MORB
source
region)
.
This
result
suggests
that
the
amount
of
recycled
continental
sediment
in
Pitcairn
Island
EMl
sources
is less
than
-0.75%.
Based
on
studies
of
olivine
phenocrysts
,
the
sources
of
both
the
plume
component
of
Hawaiian
lavas
and
of
all
measured
Juan
Fernandez
("PHEM")
samples
also
have
oxygen
isotope
compositions
indistinguishable
from
average
upper
mantle
peridotite.
If
these
OIB
sources
come
from
the
lower
mantle,
it
is
implied
to
have
an
oxygen
isotope
ratio
similar
to
the
upper
mantle
. Low
18Q/160
olivines
from
some
Hawaiian
lavas
are
associated
with
a
more
MORB
-lik
e He
and
radiogenic
isotope
component,
possibly
recycled
but
also
consistent
with
contaminat
ion
from
the
base
of
the
modern
Pacific
plate.
INTRODUCTION
Oxygen
isotope
ratios
in
mantle-derived
lavas
can
provide
important
cons
traints
on the
nature
and
origin
of
mantle
reservoirs.
Du
e to
the
large
18
0-enrichments
(or
depletion
s)
caused
by
weatheri
ng (
or
high-temperature
water/rock
interaction
),
()1
8Q
can
be a sensitive
indicator
of
crusta
l and
surfi
cial
processes.
For
this
rea
son,
oxygen
isotope
s can
help
to
discriminate
between
models
for
the
genesis
of
OIB
sourc
e region
s;
e.g.
between
enrichments
ca
used by
intr
ama
ntle
meta
somatism
and
by
recycling
of
cru
stal
sediments.
We
present
here
the
resu
lts
of
mea
sure
ments
of
oxygen
isotope
ratio
s
of
phenocrys
ts from
basaltic
rock
s from
four
4
OIB
volcanic
centers
(Pitcairn,
Hawaii
, Juan
Fernandez
, and
Gambier
). Th
ese
place
constraints
on
the origin
s
of
the
"EMl"
(enriched)
an
d
"PHEM"
(pr
imiti~e
,
high
3He/4He
) mantle
end
members
,
and
preliminary
information
on
the
sources
of
lava
s carrying
highly
radiogeni
c
Pb
1.
ANALYTICAL
TECHNIQUE
Approximately
5-20
mg
of
olivine
and/or
plagioclase
(c
a.
10
-20
fragments
)
were
separated
from
sa
mple
s by
hand
- picking
under
a binocular
micro
sco
pe
(after
crushi
ng, washing
and
sieving),
preferentially
choosi
ng fragments
with
the
smal
lest
content
s
of
visi
ble
inclu
sion
s and
alteration.
Mineral
separate
s were
analyzed
by
laser
fluorination
at
the
University
of
Wi
sconsin2.
The
mean
and
standard
deviation
(1
cr
)
for
a Gore
Mountain
garnet
standard
(UWGMT
-2)
analyzed
concurrently with
sample
s was
5.74±0.07
(n=
35),
within
uncertainty
of
th
e accepted
value
of
()
18QsMow=5.8±0.
l.
The
average
de
viation
from
the
mean
of
replicated
analyse
s
(±0.06
%
0)
is comparable
to
thi
s nomina
l precision
, s
uggesting
that
oxygen
isotopic
variability
between
grain
s
within
a give
n sampl
e
is
minimal
(eac
h ana
lys is is
of
1-5
grain
fragments
).
Multiple
analyses
of
fragment
s from
a singl
e grain
of
San
Carlos
olivine
yielded
a
8
1
80
value
of
5.25±0.07
30
(n=l3)
, comparab
le to
the average
of
-5.2
for
olivine
from
mantle
peridotite
xenolith
s 3.
34
PITCA
I
RN
The
Pitcairn
hot
s
pot
(s outheas
t P
acific
Ocean)
carries
the
stronge
st
EM
1
signature
known
in
oceanic
lava
s,
and
thi
s characteristic
is found
in
rocks
from
both
Pitcairn
Island
and
from
the
nearb
y Pitcairn
seamounts4.
Oxygen
isotope
ratios
of
oliv
ine
ph
enocry
sts from
8 sam
ples
are
within
ana
lytical
uncertainty
of
eac
h other,
averaging
5.21±0
.0
8%0
(Figure
l
).
Pla
giocla
se o 180
values
(n=5;
4 from
rock
s in
wh
i
ch
o
li
vine
was
also
ana l
yzed)
average
6.05±0.15%0,
re
s
ulting
in
a
pJagioc
lase/o
livi ne frac
tiona
ti
on equa
l to
the expecte
d m
agmat
ic val
ue
(- 0.9
-
1.0
%0
for
An65
at
l
100
- 1
200
°C5)
,
suggesting
that
olivine
and
plag
i
ocla
se
were
in
isotop
ic
equilibrium
at
magmatic
temperature
s.
The
ave
rage
o180
value
of
5.2
1±0.08%0
for
Pit
cairn
Island
olivin
e phenocryst
s
is indi
stin
guis h
ab
le
from
the
average
va
l
ue
for
olivine
from
xenoliths
of
mant
le
peridotite3
(5.
1
9±
0.1
4%0),
0.5
%o
lower
than
the
average
for
mid-ocean
ridge
basalt
(M
ORB
)
glasses6
(
5.
7±
0.2
%0),
co
nsistent
with
the fract
ionation
between
olivin
e and
basa
ltic
liquid
previou
sly
esti mated
in
ex
perime
ntal and natural
studies?,
and
equa
l to
the
o
I
80
va
lue
of
ol ivine
in lunar
ba
sa
lts 8.
Pit
cairn
island
olivines
are therefore
indi
stingu
ishable
in thei
r oxygen
isotope ratio
from
the
best estimate
s
of
olivine
s in
the
upper
mantle
and
the
bulk
mantle
. The
se
resul
ts
·stron
gly
sugges
t tha
t the
enrich
ed
EMl
mantle
source
sampled
by
Pitcairn
Island
basalt
s
co
ntain
s little
,
if
any,
dir
ectly
added
1
80-r
ich
sediment
(:S;0.75%
if
sedim
ent
is assumed
to
have a
o
18Q
value
of
25%
0)
.
Submarine
glasses
from
the
Pit
cairn
seamo
unts have
been
reported
to
have
high
o
18Q
va
lu
es
(up to
6.8-
7.4%0);
these have
bee
n in terpreted
as ev
idence
of
subd
ucted
sediment
s in
the
EMl
- rich
mantle
sources
of
these
lava
s9,
in
co
nsistent
wit
h our res
ul
t
s.
Many
of
the sea
moun
t samp
les
are
chemically
evo
lved,
and
major
element
composition
is
highly
co
rr
elated
with
rad
iogenic
isotope
ratios
(i.e.,
the
chemicall
y evo
lved
end
member
is associated
with
the
EM
l sig
natur
e4).
Values
of
o 180
in
evo
lved
ocean
ic
magmas
are ofte
n e leva
ted
by
0
.6-
1.
5%0
above
values in
relat
ed
basalt
s,
con
sistent
with
isotopic
fra
ctionat
ion
during
melting
or
crystallization
IO.
Mix
ing betw
ee
n an evo
lved,
high-ol8o,
EMl
e nd member
and
alka
li basalt
s havi
ng less
of
the
EM
l signatu
re can
exp
lain
both
the
chemical
and
isoto
pic var
iatio
ns in
the
Pit
cairn
seamount
s .
HAWA
II
Hawaiian
lavas
are
co
nsiste
ntl
y low
in
o
18Q
re lative
to mo
st
o th er
OIB
11
(the
on
ly
co
mpara
ble vo
lcanic center
is Iceland
, where
l
8Q
dep
le tion
is associated
with
melting
and
ass
imilation
of
hydrothermall
y altered
crust
l
2)
.
The
fact
that
low
o
18Q
va
lu
es
and
high
3He/4
He
ratio
s are
both
observed
in Haw
aiia
n l
avas
has
led
to the
hypoth
esis that
180 - depletion
re
lativ
e to t
he
MORB
source
regio n i
s eithe
r a ge
nera
l
fea
ture
of
the un
deg
asse
d lower
ma
n
tl
e, or
of
the portion
of
the deep
man
tle samp
l
ed
by
the
H aw
aiian
plum
e
10.
We
ha
ve
analyze
d oxygen
isotope
ratio
s in
ph
eno
crys
ts (
princip
ally o
li vine)
from
over
80
sa
mp
les
of
Hawa
iian
lavas
in
or
der
to con
strain
the
sour
ce
of
the
l
8
Q-
dep
leted
sig natur
e.
Values
of
ol
80
in
olivine
phenocry
sts are
co
rre late
d with whole
rock
radioge
nic isotope
ratio
s, such th at samples
containin
g olivine
with
8
I
8Q
value
s in
the range
of
the
mantl
e av
erag
e
(-5.2)
are assoc
iat
ed
with
hig h 3
He
/
4
He
and more
"enriched
"
or
"primiti
ve"
Nd and
Sr
isotope
ratios,
whi
le olivines
fro
m
lavas
having
more
MORE-like
radiogen
ic and
He isot
ope
signatur
es
are
low
in
8
1
80
(do
w n to
4.6%0).
Thi
s relation
ship
is most
clea
rl
y expressed
in
plots
of
o 180
vs.
radi
oge
nic
isotop
e rat
ios fo r
sa
mpl
es
of
Mauna
L
oa
and
Maun
a Ke
a from
th e H awai
ian
Scie
ntific
D rillin
g
Proj
ec
t
co
re (Figure 2).
Low
o 180
val
u
es
(<5
.0
%o)
are
a
lmo
st
excl
us ivel
y
found
in
o
livin
es
from
"Ke
a trend
"
volcanoes
(Ha
l
ea
kal
a,
Koha
la,
Maun
a
Kea,
Ki
lauea)
, the
only exce
ption
being
the
mos
t r
ece
nt
histor
ic Mauna
Loa
lava
s .
Th
ese
35
result
"prim
mantl
plume
res
en
possit
Pacifi
Nd
a1
87
Sr/
8
interp
res
en
re pre
s
simil
e
sour
ce
Olivir
alkali
frac
tic
rep
res
suit
es
th at
b1
5.3%o
not
s i
sampl
Pa
cifi
twos<
most
ther
ef.
been s
two
~
in dist.
sou
rce
sig
ni
fi
0
18
0
ha
vin~
1 :
Zind
Min
era
EPSL,
(
1971
);
8:
Cla:
Mat
s
uh
Harris,
Garcia
al.,
CM
EMl
I
both
OS
of
)th
er,
.
ks
in
rn
a
1iio
for
>topic
:rysts
1antle
>asalt
~an
d
ml
to
·
efore
.n
the
EMl
1dded
hi
gh
JCted
suit
s.
;ition
l e
nd
~anic
with
lved,
!
can
(the
with
5180
) the
neral
~
d
by
vine)
l
80-
1hole
es
in
no
re
1
vmg
m
to
~e
m
c
itifi
c
tvely
Kea,
'h
ese
results
suggest
that
the
Hawaiian
plume
(wi
th
its
high
3
He
/4He
more
"enric
h
ed"
or
"primitive"
radiogenic
i
so
tope
ratios)
is indi
sting
uis habl
e in
o 1
80
from
the
upper
mantle/xenolith
average,
and
that
anomalous,
low
ol80
values
are
only
seen
when
this
pl
um
e
com
p
onent
has
been
diluted
by
a
more
depleted
reservoir.
This
deple
ted
r
ese
r voir
is
plausibly
assoc
iated
with
h
ydro
ther
mally
a
lt
er
ed
lower
oceanic
crust,
possibly
r
ecycled
but
also
consis
tent
with
co
ntamina
t
ion
from
the
ba
se
of
the
modern
Pacific
plate.
JUA
N
FERNANDEZ
The
Juan
Fernand
ez
islands
(so
uth
Pacific)
co
nta
in
ba
sal
ts
and
basanite
s having
Nd
and
Sr
isotop
e
ratios
coveri
n g a
relative
l y
restricted
range
(£N
d
=+3.3-4
.9;
87Sr/86Sr
=
0.7034-0.7037)
,
but
a w
ide
range
of
3
He
/4He
ra
tios
( 1
8.0-7.8
RA
),
interpreted
to
reflect
mixing
between
a plume
co
mpon
e nt from
a
primitive,
undegassed
r
ese
r voir
("
PHEM"
)
1,
and
an
ast
hen
ospheric
or
lithospheric
component
,
dominantly
represented
in
the
post-shield
lavasl3.
Oli
v
ines
from
lavas
carry
ing both
signatures
are
s imil
ar in
ol
8Q,
the
entire
population
averaging
5 . 1±0.
l
%0
(
n=
9),
consistent
w
ith
sources
having
oxygen
isotope
ratio
s
comparab
le
to
average
upper
mantle
peridotite.
Olivines
from
ba
san
ites
are
s
li
ght
ly
18Q
enr
i
ched
relative
to
those
from
transitional
and
alkali
basalts
(by
-0.2
%0),
poss
ibl
y reflecting
chemical
and/or
temperature
dependent
fract
ionations
during
melting
and
magmatic
evolution.
The
Juan
Fernandez
samp
le
s
represent
an
impo
rta
nt
com
pl
ement
to
the
Hawaiian
lavas
we
have
stud
ied,
in
that
both
suites
co
nta
in
shield-bu
ildin
g basalts
wi
th
elevated
3H e/4
He
ratios.
The
observation
that
both
island
gro
up
s contain
a
plume
componen
t with
a
8
l 8 Q
va
lu
e in
the
range
5.1-
5 .
3%0
sugge
s ts that
the relativ
e
ly
"primitive",
undegassed
mantle
sample
d in
plumes
is
not
si
gn
ificantl
y
different
in
oxygen
i
sotope
ratio
from
the
average
sha
llow
mantle
samp
l
ed
by
MORE
and
peridotite
xenoliths.
GAMBIER
Ol
ivines
from
two
samp
l
es
of
alka
li
basalt
from
Gambier
i
sla
nd
s,
southeast
Pa
c ific
ocean,
have
been
analyze
d.
Both
have
818Q
val
u
es
of
5.2
%0
.
Although
only
two
sa
mpl
es
have
been
analyzed,
these
resu
lts are
significant
because
they
conta
in
the
most
radiogenic
Pb
of
any
s
ample
s
de
sc
ribed
in
this s
tud
y
(206
pb
/204
pb
>
19),
and
therefore
may
provide
constraints
on
the
or
igin
of
the
"HIMU"
component,
which
ha
s
been
sugges
t
ed
to
be
associated
with
recycled
oceanic crust
1
4.
Value
s
of
o 180
in
these
tw
o
sa
mple
s
are
consistent
w
ith
derivation
from
sources
with
o
l8Q
va
lu
es
indistinguishable
from
average
upper
mantle
peridotite
xenol
i ths
and
the
MORB
source;
in
particular,
they
s u
ggest
that
the
sources
of
these
lavas
do
not
con
tain
significan
t quantities
of
low-o
18Q
hydrothermally
altered
lower
oceanic
crust
or
high-
8
l
8Q
upper
crust
and
se
dim
ents .
The
presence
of
a mixture
of
the
two
compone
nts
havin
g the
average
MORB
oxygen
isotop
e composition
can
n
ot
be
excluded.
1:
Zind
ler
and
Hart,
An nu.
Rev
. Earth
Planet.
Sci.
( 1986
);
Farley
et
al.,
EPSL
( 1992)
2:
Kohn
et
al.
, Am.
Min
era
l.
( 1993)
3:
Matt
ey
e t al.
,
EPSL
(1994)
4 : Woodhead
e t al
.,
EPSL(
l9
89
);
Wo
odhead
&
Deve
y,
EPSL,
(1993)
5:
Chiba
et
al
.,
GCA
, ( 1989)
6: Ito
et
al.,
Chem.
Geo
l.
, ( 1987)
7:
Ander
son
et
al.,J.
Geo
l.
(
19
7 1
);
Muehlenbachs
&
Ku
shiro
Carnegie
Ins
t.
Washington
Yearb.,
(
19
74);
Kyser
et
al.
, CMP,
(1981)
8:
Clayton
et
al.
,
Pro
c.
Second
Lunar
Sci.
Conf.
, ( 1971)
9:
Woodhead
e t al.,
Natu
re.
(
19
93)
10
:
Matsuh
isa,
Y.
J.
Volcano!.
Geo
therm
. Res.,
( 1979
);
Mu
eh
lenbachs
&
Bye
rl
y,
CMP
,
( 1982)
; Sheppard
&
Harri
s, CMP
, (
19
85);
Wei
s
et al.,
EP
SL
(1987)
11
:
Kys
er
et al.,
CMP,
( 1982
);
Garcia
e t al. , JGR,
(1989);
Ga
rcia et
al.
, JGR
, (199
3)
12
:
Sigmarsson
et
al.,
C
MP
, ( 1992);
Hemond
et
a
l.
, JGR
, ( 1993)
13:
Far
ley
et
al.,
CMP
, (
1993
)
14 :
Hart
,
EPSL
(
19
88);
Weaver
, Geolo
gy
(1991)
36
I
I
20
10
(J)
Ql
0..
E
a:s
(/)
0
~
4
3
2
1
5
Xe
nol
ith
Olivine
(5.
19
±0.14)
i
M
attey
et
a
l.
, 1
994
K .H .
01
{thi
s s
tud
y)
S.C.
01
(this
st
udy)
Pitcairn
Island
Ol
i
vine
(5.21±0.08)
A
6
7
5
I
MORB
glass
(5.7
±0.2)
I
.I
Pi
tcairn
Seamount
glass
I
6
7
s:
18
u
O
SMOW
15
10
5
D
4
3
2
1
Fi
g ure
I :
Hi
s to
gra
m s
of
()l
80
va
lu es.
(a)
O
li
vine
from
mantl
e
xe
no liths;
(b
)
olivine
ph
en
oc
rysts
fro
m
Pi
tcairn
Isla nd
alka
li basa
lts
(t
hi
s s
tud y;
each
sam
pl e is coun
ted
only
once,
i.e.,
mul tip
le analy
ses
of
o
li
vines
from
a single
sa
mp
le have
been
ave
r
age
d ); (c)
basaltic
glas
ses
from
a
wor
ld
-wide
s
am
pling o f
MORB
s;
and
(d
) basaltic
-
to-e
vol ved glasses
from
the
Pitcai
rn
sea
mount
s
9.
5.5
$
t
0
f
Ci
~
()
0
5 .3
G
©
@
e
©~
18
5
.1
8
0
4.9
QI
@
'"
0
©
@
0
0
0
0
0
Coo
0
0
co
000
0
<D
0
0
~
Mauna
Loa
0
0
4.7
0
Mauna
Kea
6
7
18
.3
18.5
2
06
p~04
Pb
18.
1
cNd
Figu
re
2:
Valu
es
o f()
l 80 measured
in ol ivi
ne
from
lavas
fr
om
the
Ha waiian
Sc
ientifi
c Dr
illing
Project
c
ore
a
nd
rela
ted samp les,
pl
ott
ed vs.
whole
rock
radiogenic
i
so
tope ratios
(r
eport
ed by H
of
ma
nn
et a
l.
, Lassiter
et
a
l.
, and
Kurz er
al.,
JGR
in
r
ev
iew).
L
ow-8
I
80
Mauna
Kea
sa
mpl
es
have
3H
e/4
He and radioge
nic
isotope
ra
tios
c hara
ct
er
i
st
ic
o f a
mor
e
MORB-lik
e
so
ur
ce
th an the Hawaii
an plum
e.
37
c
(<
si
d1
SC
OJ
C<
ei
cc
O<
re
Sl
th
b€
cl
te
se
g<
cc
S
\:
ef
sl
oc
th
SU
PLUME
2
Convenors:
D.L.
Anderson
California
Institute
of
Technology,
Pasadena
S .
R.
Hart
Woods
Hole
Oceanographic
Institute,
Woods
Hole
A.
W.
Hofmann
Max-Planck-lnstitut
fiir
Chemie
,
Mainz
Organisation:
K .
Lehnert
Max-Planck-lnstitut
fiir
Chemie,
Mainz
Sponsors:
Max-Planck-Gesel
I
schaft
Alf
red-Wegene
r-Stift
u n
.g
MOnchen
Bonn
Extended
abstracts
in
this
publication
may
be
cited
as
follows
:
Author
, A.A.
, 1995,
Title
of
paper
,
in
Anderson
, D.
L.
,
Hart
,
S . R .,
and
Hofmann
, A.
W.,
convenors
,
Plume
2 , Terra
Nostra,
311995,
p .p.
xx-yy,
Alfred-Wegener-Stiftung
,
Bonn