Earth and Planetary Science Letters, 59 (1982) 101 - 118
101
Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
[31
Ti-V plots and the petrogenesis of modern and ophiolitic lavas
John W. Shervais *
Department of Geological Sciences, University of California, Santa Barbara, CA 93106 (U.S.A.)
Received September 1, 1981
Revised version received February 8, 1982
Plots of Ti vs. V for many modern volcanic rock associations are diagnostic of tectonic setting and can be used to
determine possible tectonic settings of ophiolites as well. The basis of this plot is the variation in the crystal/liquid
partition coefficients for vanadium, which range with increasing oxygen fugacity from > 1 to << 1. Since the partition
coefficients for Ti are almost always << 1, the depletion of V relative to Ti is a function of the fo2 of the m a g m a and its
source, the degree of partial melting, and subsequent fractional crystallization. Volcanic rocks from modern island arcs
have T i / V ratios of ~ 2 0 , except for calc-alkaline volcanics which show the effects of magnetite fractionation. MORB
and continental flood basalts have T i / V ratios of about 20-50 and alkaline rocks have T i / V generally >50. Back-arc
basin basalts may have either arc-like or MORB-like T i / V ratios, and sample suites from single back-arc basins may
have T i / V ratios ranging from 10 to 50. This range in T i / V ratios in samples from a restricted geographical area may be
diagnostic of the back-arc setting. The T i / V plot is applied here to published data on ophiolites from a variety of
postulated settings and in general supports the conclusions of previous investigators. Ophiolites from the western
Mediterranean (Corsica, northern Apennines) and the "lower" Karmoy volcanics have T i / V trends similar to MORB;
the "upper" Karmo'y volcanics have alkaline T i / V ratios. Lavas and tonalites in the Papuan ultramafic belt, the
high-Mg andesites of Cape Vogel, and the upper pillow lavas at Troodos all have T i / V ratios < 20, consistent with
formation in an island arc setting. More specific evaluation of the tectonic setting of these and other ophiolites requires
application of detailed geologic and petrologic data as well as geochemistry. The T i / V discrimination diagram, however,
is a potentially powerful adjunct to these techniques.
1. Introduction
Ophiolites are commonly considered to represent fragments of oceanic crust formed at spreading ridges, and emplaced tectonically in orogenic
zones. Since only the uppermost parts of in situ
oceanic crust are exposed or sampled by drilling,
most models of ocean crust formation draw heavily
on comparisons with ophiolite complexes. It has
become clear, however, that ophiolites may form
in a variety of tectonic settings, e.g., back-arc
basins, island arcs, ocean islands and intra-arc
rifts, as well as at mid-ocean ridges. Each of these
* Present address: Department of Geology, University of
California, Davis, CA 95616, U.S.A.
settings will have profound significance in reconstructing the geologic history of the region in
which the ophiolite is found, and also severely
constrains the extent to which models of ocean
crust formation may be based on specific ophiolite
complexes.
Because ophiolites are commonly in tectonic
contact with adjacent terranes, and because lowtemperature alteration and metamorphism are
ubiquitous in ophiolite complexes, structural relationships and major element geochemistry are not
definitive of origin in most cases. Trace elements
that are relatively immobile during metamorphism
have been used successfully as discriminants of
ophiolite petrogenesis [1,2] and that approach will
be explored further in this paper. Data presented
0012-821 X / 8 2 / 0 0 0 0 - 0 0 0 0 / $ 0 2 . 7 5 ©1982 Elsevier Scientific Publishing Company
102
here show that plots of Ti vs. V from many
modern volcanic rock associations are diagnostic
of tectonic setting and may by used to discriminate among possible tectonic settings of
ophiolite volcanic rocks as well. This is because the
crystal/liquid partition coefficients for V vary from
> 1 to << 1 with increasing oxygen fugacity, making it a sensitive indicator of fo2 conditions. The
depletion of V relative to the incompatible element
Ti is a measure of this variation and thus the
relative fo2 of the magma and its source. Recent
data show that the volatile content (and thus fo,)
of magmas erupted in oceanic settings increases in
the order: MORB < ocean islands < back-arc
basins<island arcs [3-5]. However, as we shall
see, the actual T i / V relationships are somewhat
complex, for reasons explored below.
Titanium and vanadium are present in basaltic
and intermediate rocks in abundances that greatly
exceed their detection limit in routine XRF analysis [6], making accurate determination reasonably
easy. The problem of Ti-K~ interference on V-K,~
may be dealt with using interference standards, as
discussed by Nisbet et ai. [6].
value in evaluating older, ophiolite-related
volcanics. Elements having small ionic radii and
low radius/charge ratios are called "high-field
strength" (HFS) cations; they tend to be strongly
incompatible, having very small bulk partition
coefficients in most situations and are considered
immobile during low-temperature alteration [9].
Elements whose cations are in this group include
Zr, Hf, Ti, P, Nb and Ta; however, only Zr, Ti and
P occur in basaltic rocks in concentration high
enough to be determined accurately by XRF analysis. Many of the transition metals (Ni, Co, Sc, Ti,
V, Cr) are also immobile during alteration and
metamorphism, but with the important exceptions
of Ti (a HFS cation) and V, they are compatible
elements which are moderately to strongly partitioned into refractory residual phases during partial melting and into early-liquidus mafic phases
during crystallization. The geochemical behavior
of Ti, which occurs terrestrially in only one valence state, is relatively well known and is a commonly used discriminator (e.g. [2]). The remainder
of this discussion will focus on the geochemical
behavior of vanadium under differing conditions.
2.2 Vanadium
2. Trace element behavior
2.1 Theory
The use of immobile trace elements as discriminants of ophiolite petrogenesis was pioneered by
Pearce and Cann [1,2,7,8] and has since been
applied by many others. Trace element discriminant diagrams have been largely empirical until
recently when papers by Saunders et al. [9], Pearce
and Norry [10], and Pearce [8] have attempted to
place them on a firmer theoretical basis. Saunders
et al. [9] have proposed a division of magmatophilic elements into two groups (excluding
REE) based on the ionic character of the elements.
Elements with large ionic radii, low charges and
high radius/charge ratios are called "low-field
strength" (LFS) cations. These cations, which are
equivalent to the " L I L " cation group of Schilling
[11], have been shown to be mobile during lowtemperature alteration (e.g. [ 12,13]). This mobility
renders the "LFS" (LIL) group of questionable
Vanadium like chromium, differs from the other
trace transition metals (Ni, Co, Sc, Ti), in having
three common valence states under terrestrial conditions that exhibit strongly contrasting geochemical behavior. Table 1 compares the ionic charge,
radius, and radius/charge ratio of vanadium to
the incompatible HFS element titanium, and to
the compatible transition metals, chromium,
scandium, nickel and cobalt. Also shown for comparison are aluminum and the mafic major elements magnesium and iron. All of these elements
have ionic radii in the range 0.6-0.8 A. The mafic
major elements and the compatible trace transition
metals have similar charges ( + 2 , +3) and relatively large radius/charge ratios (1>0.21). These
similarities account for the strongly compatible
character of these trace elements in the presence of
refractory or fractionating mafic minerals, where
they occur in octahedrally coordinated sites. In
contrast, titanium, with its high charge and small
radius/charge ratio, is a HFS cation [9] which has
103
TABLE 1
Ionic characteristics of v a n a d i u m , titanium and related species in octahedral coordination, listed in o r d e r increasing r a d i u s / ' c h a r g e
ratio [61]
V 5~
V 4+
Ti 4~
A13~
C r 3+
V 3+
Fe 3-
Sc 3~
Ni 2+
Mg 2+
Co 2'
Fe 2 '
Ionic radius (A)
0.62
0.67
0.69
0.61
0.70
0.72
0.73
0.83
0.77
0.80
0.83
0.86
Radius/charge
0.12
0.17
0.17
0.20
0.23
0.24
0.24
0.28
0.39
0.40
0.42
0.43
very small crystal/liquid partition coefficients for
most minerals, with the important exception of
magnetite solid solutions [14-17]. Reduced
vanadium (V 3+) has ionic characteristics similar
to the compatible trace transition metals and commonly substitutes for other trivalent cations in
spinel and pyroxene. The more oxidized species
(V 4+, V 5+) are HFS cations with high charges
and low radius/ charge ratios (~<0.17), similar to
titanium (Table 1).
Experimental determinations of the crystal/melt
partitioning of vanadium by Lindstrom [18] has
shown the D~1/1 for pyroxenes (both high and low
calcium) and magnetite vary by over two orders of
magnitude as a function of oxygen fugacity. At
low oxygen fugacities (Fe-Wti buffer, fo~ = 10 ~
to 10 12 at about 1200°C) V 3+ is the dominant
species and partition coefficients are much greater
than one; at high oxygen fugacities (fo, = 10 4.5)
V5 ÷ is the dominant species and partition coefficients are much less than one (Table 2). Varying
proportions of V 3+ , V 4+ and V 5+ are expected to
exist under intermediate ,/o2 conditions. Table2
summarizes the experimentally determined partition coefficients of Lindstrom [18] and some empirically derived partition coefficients from literature.
TABLE 2
C r y s t a l / l i q u i d partition coefficients
Augite
Low-Ca pyroxene
Olivine
Plagioclase
Magnetite
Hornblende
Titanium
1.0 ( 1 1 0 0 ° C ) ~
0.6 b
0.5 (1220°C) "
0.2-0.8 e
0.3 b
0.14--0.5 e
0.024
<0.05 ~
9 16 e
4.3 6.8 f
(l 1 1 2 - 1 1 3 4 ° C ) a
Vanadium
5
( l o g f o 2 = -- 12) a
2.5 c
1
(log fo2 = -- 10) ~
0.5 c
0.05
(log fo2 = --6) a
0.025 c
~' L i n d s t r o m [18].
b For same T as augite, using D ~ px/cpx - - 0 . 6 [18].
d
e
t
g
For same f o 2 as augite, using O~ xp/cpx = 0 . 5 [14].
Ewart et al. [14]: basalt to andesite.
L e e m a n et al. [16,17]: ferrobasalt to ferrolatite.
Luhr and C a r m i c h a e l [26].
Assumed,
0.03
(1112-1134°C;
Q F M buffer) a
--0.0 g
0.11(Iogfo >-4.2) a
23
(logfo =-10)"
67
(Io_gf % =
13) ~'
23-190 d
5-100 e
6.3-13 f
104
2.3 Partial melting and fractional crystallization
350
The experiments of Lindstrom [18] confirm the
predictions from ionic characteristics that vanadium is a sensitive indicator of oxygen fugacity
conditions during both partial melting and fractional crystallization. Fig. 1 shows partial melting
curves based on a fixed bulk partition coefficient
for titanium, and on bulk partition coefficients for
vanadium which vary as a function of oxygen
fugacity. The bulk partition coefficient for titanium
(DT~=0.15) was calculated from the data in
Table 2 and assumed refractory mantle mineralogies ranging from spinel lherzolite to harzburgite
(see Appendix A for a more detailed discussion of
the parameters and methods used in the construction of Fig. 1). The bu]k partition coefficient for
vanadium, /~v, for the same refractory mineralogies varies from ~ 0.15 (fo: ~ 10-7) to about 1.15
(fo:-~ 10-12) which spans the range of naturallyoccurring oxygen fugacities in most magmatic systems from the reducing conditions prevalent in the
source of MORB to the more oxidizing conditions
found in many convergent margin settings
[3,4,19,20,25]. Curves are drawn for D v = 0 . 1 5 ,
0.45, 0.75, 1.0 and 1.15. The curves have been
calculated from the Berthelot-Nernst equilibrium
melting equation assuming the bulk earth Ti and V
abundances of Ganapathy and Anders [21]. These
abundances are slightly higher than chondritic but
have about the same T i / V ratio (bulk earth T i / V
= 10; chondritic T i / V = 8.4-10 [22]) and are convenient for illustration. Also shown are trend lines
of constant initial T i / V for 20% and 30% partial
melts. It is readily apparent (Fig. 1) that the T i / V
ratios of "primary" mantle melts increase with (a)
decreasing fraction of melt produced and (b) increasing/ffv. Primary melts produced by 20-30%
partial melting under relatively reducing conditions like MORB (fo~ = 10-It to 10 12; /~v ~>0.6 )
will have initial T i / V ratios of about 20-50. Similar melts produced under more oxidizing conditions (such as the mantle wedge overlying a devolatizing, subducting oceanic slab) should have
/ffv ~<0.5 and initial T i / V ratios of around 10-20.
Subsequent silicate fractionation in the latter case
(high fo~) will parallel or sub-parallel the constant
T i / V trend lines as long as D--vi and /)v remain
Ti/V=IO
/
Ti/V=I 5
t
A~C
T i / V = 17.5
,
3OO
/.~i/ /~]lv=
20//TI/V
= 25
25O
i
/
t
V
ppm
,
' ,'
2OO
50
j
1"
/
t
/
. .~5
/
,;o
,T,,v:35
/ 10 /
z.z 3__0--/
/,
Ti/M= 4 8
,
150
.~ EO
I00
50
O,,o.,
¢~
'
H /
Earth . . ~
504.0 39
29
i
s
/
.,
/
."
10 ,/[~V= r5
/-
19
5V=l.0
/
./
Mt-%
~ ~ ~ ~
~ Mt-D
~
Ti ppm/1000
Fig. 1. T i / V plot showing partial melting and fractional crystallization trends. Melting curves (solid) are based on "bulk
earth" Ti and V abundances (solid star; [2]), bulk equilibrium
melting, /~Ti=0.15 and /fly=0.15, 0.45, 0.75, 1.0, and 1.15.
Bulk partition coefficients are chosen to span the range of
values calculated assuming spinel lherzolite and harzburgite
refractory mineralogy and fo2--10 -7 to 10 12, using the
crystal/liquid partition coefficients from Table 2 (see Appendix A for a detailed discussion of these calculations). Numbers
adjacent to the partial melting curves equal % of melt. Initial
T i / V ratios and their trends (dashed lines) for 20% and 30%
melts are shown for three of the curves; also shown is the trend
for T i / V = 100. Open star= C3 meteorite Ti and V abundances
[22]. Fractionation under high fo2 conditions parallels or subparallels the constant T i / V ratio trends. Fractionation under
lower fo2 conditions shown by the heavy solid line for the
assemblage olivine-+plagioclase and for olivine-gabbro; underlined numbers represent % crystallization. Mt-C (six-point
star)= 10% magnetite fractionation calculated assuming initial
Ti=4600 ppm, V=302 ppm (Ti/V = 15) and O~iit ---9, D ~ t = 17
[16,17]. Mt-D (heavy arrows)=magnetite fractionation trend
deduced from the trend of calc-alkaline series andesites and
dacites. H = 10% hornblende fractionation assuming initial Ti =
4600 ppm, V=302 ppm, and oh~ =4.9, Ohvb =8.8 [26].
105
similar and less than one. This will be true of most
fractionating assemblages under oxidizing conditions until the onset of magnetite or hornblende
fractionation, which will strongly deplete both Ti
and V [16,17,23,24-26].
The effects of magnetite fractionation are shown
in Fig. 1, as calculated from magnetite/liquid partition coefficients (10% magnetite removal) and as
deduced from the trend of calc-alkaline andesites
and dacites. These paths are virtually identical and
support the origin of these dacites by 10-15%
magnetite fractionation. Hornblende/liquid partition coefficients are about half those of magnetite,
with Dhvb / l ~ 1.5--2.5*DThih/l [26]. This means that
hornblende and magnetite will have the same relative effect on Ti and V concentrations, but that
approximately twice as much hornblende as magnetite must separate (Fig. 1). Recent studies of arc
volcanism have shown that hornblende is in general a late crystalling phase, and is less important
than magnetite in creating calc-alkaline trends (e.g.
[25]). In any case, samples subject to either or both
magnetite/hornblende fractionation will have
negative trends on plots of Ti (or V) vs. SiO 2, Zr,
or F e O * / M g O [23]; these samples will have
anomalously high T i / V ratios and should not be
used to discriminate tectonic setting on Ti-V plots.
In case of low-fo 2 conditions (MORB-type magmas) fractionation dominated by olivine and
plagioclase will follow the constant initial T i / V
trend lines because of their small crystal/liquid
partition coefficients for Ti and V under any conditions. Clinopyroxene or spinel fractionation will
cause curved fractionation trends that cross the
constant T i / V ratio lines at low angles. Fig. 1
shows a hypothetical fractionation path of the
assemblages ol, ol + pig, ol + pig + cpx (the crystallization sequence of most MORB) starting from
a 30% partial melt with an initial T i / V ratio of 20.
It should be noted that because /7 v is always
I>/)'ri, fractionation cannot drive magmas to lower
T i / V ratios than those inherited from the parental
melt. This means that even if high fo~ conditions
arise at some stage during the evolution of a
mid-ocean ridge magma system (e.g., near a fracture zone), silicate fractionation will evolve magmas that have T i / V ratios the same as or greater
than primary MORB.
An important implication of the chondritic or
near chondritic trends in the T i / V ratios of island
arc tholeiites is that their low Ti (and by analogy
other HFS cation) abundances cannot be due to
retention of Ti-rich minor phases (e.g., ilmenite,
rutile) in the refractory residue unless that phase
also retains V in chondritic proportion to Ti, or
unless V is retained by other refractory phases in
just the right modal proportions to maintain
chondritic T i / V ratios. Neither of these possibilities seems likely. The low HFS cation contents of
arc tholeiites are thus more probably due to greater
degrees of partial melting, followed by extensive
closed system fractional crystallization (e.g. [10]).
Similar arguments may also apply to calc-alkaline
magmas.
2.4. Stability of Ti and V during alteration and
metamorphism
Since the use of trace element plots to investigate ophiolite petrogenesis involves the application
of criteria based on more-or-less fresh samples to
ancient rocks which may have undergone several
episodes of alteration and metamorphism, it is
necessary to evaluate briefly the effect of these
processes on Ti-V distributions. These processes
include low-temperature sea floor weathering
("halmyrosis"), greenschist facies hydrothermal alteration and, possibly, subsequent regional metamorphism. The effect of seawater/basalt interaction at low and high temperatures has been studied
both experimentally (e.g. [27,28, and references
therein]) and on natural samples from dredge hauls
and DSDP cores (e.g. [28,29]). These studies have
shown that Ti and V are stable over a wide range
of temperatures and water/rock ratios, even in
samples which have been converted entirely to
chlorite+ quartz [28]. Absolute concentrations
may decrease due to dilution by hydration or by
the precipitation of anhydrite or calcite, and may
increase by passive accumulation as more mobil
elements are leached (e.g., Si, Ca). The largest
changes are observed during palagonitization of
glassy pillow rims, where Ti and V abundances
may drop by as much as 50% compared to fresh
cores [29]. Alteration of the crystalline interiors of
massive flows and pillows may either increase or
106
decrease Ti and V by 20% or more [29]. In most
cases, Ti and V show coherent behavior during
alteration, so that the T i / V ratio remains about
the same in the altered rock as in the fresh rock.
The data plotted in Fig. 2 (next section) include
many altered samples, although relatively fresh
rocks dominate. The altered samples plot in the
same tectonic setting, suggesting that seawater alteration effects on Ti and V are negligible.
Ophiolites may also undergo regional metamorphism at intermediate to high grades either during
or after emplacement. Recent studies of trace element mobility during amphibolite and granulite
facies metamorphism suggest that Ti and V are
relatively immobile under these conditions [30,31].
In summary, Ti and V appear to be stable over a
wide range of temperatures during both seafloor
and regional metamorphism. The glassy rims of
pillows are most susceptible to changes in T i / V
during alteration. However, this problem can be
overcome by judicious sampling in the field.
3. Ti/V plots of modern volcanic rocks
There are four basic tectonic settings in which
thick sections of basaltic rocks may accumulate:
ocean basins, island arcs, back-arc basins and continental interiors. Each of these settings may be
further subdivided on a geochemical or geological
basis (e.g., ridge basalts vs. oceanic islands). Alkalic rocks may occur in any of these settings. Fig.
2 A - D presents the Ti and V abundances of samples from a number of specific localities or regions
representative of these settings and their subdivisions. These data have been compiled from the
sources listed in Appendix B.
3.1 M O R B
MORB are confined almost entirely to T i / V
ratios between 20 and 50 regardless of whether
they are "normal" or "enriched" in LREE and
LIL (e.g. [32]; Fig. 2A). This is consistent with the
model presented in the preceding section: 20-30%
partial melting of a source with chondritic T i / V =
10, and with the difference ~[/~Ti - - / ) v ] = --0.6 to
--1.0 (Fig. 1). The crystallization sequence ob-
served in MORB (ol -+ sp, ol + plg, ol + plg + cpx)
is also consistent with the hypothetical fractionation path depicted in Fig. 1 for MORB: increasing
Ti and V along the ratio inherited from the primary
melt by olivine-+plagioclase fractionation, followed by a curved trajectory across the constant
ratio lines during olivine-gabbro fractionation.
There is a tendency for "enriched" MORB to have
higher absolute abundances of both Ti and V than
"normal" MORB, but both types span the same
range in T i / V ratios. There is also a pronounced
tendency toward regional variation: basalts from
the Pacific and Indian Oceans extend to higher Ti
and V abundances than those from the Atlantic
ocean, and are seldom as depleted (Fig. 2A). The
MORB field is overlapped in part by the field of
back-arc basin basalts; this will be discussed further below.
3.2 Flood basalts
Tholeiitic flood basalts of the Columbia River
plateau are similar to MORB, being derived by
large degrees of partial melting (20-30%) under
conditons of low volatile fugacities [33]. The Columbia River basalts have the same range in T i / V
ratios as MORB, but tend to have higher absolute
abundances (Fig. 2D). The contrasts in flow morphology and associated sediments between continental flood basalts and MORB makes it unlikely that these settings will be confused, despite
their similarity in T i / V ratios.
3. 3 Alkali basalts
Tholeiitic and alkalic basalts from both continents and oceans plot in distinct fields with a
minimum of overlap, separated by a T i / V ratio of
about 50 (Fig. 2A, B; [34,35]). Since both tholeiitic
and alkalic basalts form relatively deep in the
mantle under low fo2 conditions, the difference
6[/~Ti--Ov] should be about the same in both
cases. The consistent difference in T i / V ratios
between tholeiitic and alkalic basalts may reflect
either (a) primary differences in the T i / V ratios of
their respective sources, (b) retention of contrasting refractory assemblages during partial melting
of their sources, (c) derivation of alkali basalts
107
600
-
0
0
ATLANTIC
OCEAN
0
JURASSIC
ATLANTIC
fi;
.*
INDIAN
OCEAN
(47)
(14)
(23)
I’.‘\
PACIFIC
OCEAN
: 0:
\/
PACIFIC
SEAMOUNTS
*
RED SEA AXIS
(47)
(20)
(4)
MORB
500
-
400
-
300
-
v
wm
0
2
4
6
8
Ti ppm/
IO
12
14
16
I8
1000
Fig. 2. Ti/V plots of modern volcanic rocks. showing fields for specific regions and trend lines of constant TI/V ratios= IO. 20. 50
and 100 for reference. Data sources are listed in Appendix B. A. MORB: Atlantic Ocean ( )I ~61); Pacific Occ~n (PI ~47); Indian
Ocean (II = 23) and the Red Sea axis basalta (II =4). Fields drawn by cyc to include the mqority of samples for each given region.
from smaller amounts of partial melting, or (d)
formation
of alkalic magmas by partial melting
under high CO, activities, which will reduce the
activities
of both oxygen and water. It is not
possible to distinguish
between these possibilities
with Ti/V
data, and all may be operative
in
varying degrees (e.g. [ 11,281).
Alkali basalts in ocean basins may occur at
spreading centers, but are most common off-axis
as oceanic islands and seamounts.
Off-axis sills
which intrude
sediment
in the Shikoku
Basin
(DSDP Leg 38, Hole 444; [36]) are either tholeiitic
108
B A C K - A R C BASIN BASALTS ( n = 6 6 )
•
Lau Basin (22)
West Mariana Basin (8)
• Shikoku Basin (Basement) (26)
• Shikoku Basin (Sills) (10)
600
10
20
OCEAN ISLAND & ALKALIC BASALTS ( 7 7 )
Hawaii
[] Tholeiites (30)
O Alkalic Basalts (33)
500
East Pacific Rise
/
400
V
ppm
300
/
•
/"
•
200
•~
/
..
,, •
••
'/"
"..-° ° ~ : ° ° \
;~ oo \
;2 "...- ~,,~°~..-°°o-~oooo
i,
•I
Transitional (4)
Alkalic Basalts (10)
~-7".~."
•/I
,o
o o~
o.11---
...;/ ~'o
Oo
~
\
ol
/
7 t
,vv
~ S ~
I00
B
0
2
4
6
8
I0
12
14
16
18
20
22
24
Ti ppm/lO00
Fig. 2 (continued). B. Alkali basalts (n =43) and transitional tholeiites (n =34) from ocean islands and off-axis volcanic rocks are
shown by open symbols; back-arc basin basalts (n =66) from the western Pacific are shown by closed symbols.
( T i / V = 30-50) or transitional to alkaline ( T i / V
= 35-70). Transitional basalts from small
seamounts near the East Pacific Rise [37] have
T i / V ratios of 40-50, while Hawaiian tholeiites
[38] range from 42 to 60 and Hawaiian alkali
basalts [39] range from 50 to 110 (Fig. 2B). This
suggests that seamounts which form off-axis may
begin as tholeiitic basalts similar to "enriched"
M O R B and evolve toward more alkalic T i / V ratios
and compositions [40].
3.4 Island arc lavas
Volcanic rocks from island arc-related settings
may be divided into at least three suites [41]:
109
ARC THOLEIITES
600
•
NEW H E B R I D E S
Picrite-Ankaramite Suite
N--160
10,
20
~'
Tholeiites <57% SiO 2
Tholeiites
>57%SIO 2
SO. S A N D W I C H
•
< 56% SiO 2
>56% SiO2
MARIANAS SEAMOUNTS
500
•
<60% SiO2
O
>60% SiO 2
MARIANAS FORE-ARC
'~
'~
Basalts
Boninites
TONGA
V
400
• Whole Rock "~ <60% SiO
It'! Matrix
17 > 60% SiO 2
J
ppm
50
300
200
100
Z~
IOO
C
0
2
4
6
8
I0
12
14
16
18
Ti p p m l I 0 0 0
Fig. 2(continued). C. Island arc tholeiite series: basic rocks not affected by magnetite fractionation shown in solid symbols (n = 105);
intermediate rocks which have been affected by magnetite fractionation shown by open symbols (n = 30); boninites from the Mariana
fore-arc (n --6) shown by open five-point stars; ankaramites from the New Hebrides (n = 19) shown by solid six-point stars.
island arc tholeiite (Fig. 2C), calc-alkaline (Fig.
2D) and shoshonite (Fig. 2D). Recent work in
many intra-oceanics arcs has shown that all gradations exist between tholeiitic and calc-alkaline
suites [25]. These terms will be retained here, how-
ever, because they are representative of the gross
geochemical variations possible within arc terrains
and because they exhibit contrasting behavior with
respect to Ti and V. The arc tholeiite and calc-alkaline series are each represented by both basic
110
600
COLUMBIA RIVER
FLOOD BASALTS (22)
CALC-ALKALINE SUITE
SHOSHONITES
,o/
,o/
500
e.
O
/
O
O
4OO
/'0
V
C
o o/
ppm
/
300
200
'
0
/
IOO
°
-/ /
[ /
° /
.[3o~
i/
~A
-7A
a
J
CALC-ALKALINE SUITE
SiO2
<58% >58%
St. Kitts (18)
•
o
Lau Ridge (15)
•
A
New Britain ( 1 2 ) .
[]
Bagana (33)
,~ e~
100
~
-
7.,,7D~ O/
2
Fiji (8)
4
6
8
I0
12
-
"~
14
16
o
18
Ti p p m / 1 0 0 0
Fig. 2 (continued). D. Calc-alkaline series volcanic rocks: solid and plus symbols have SiO2 <58% (n =55); open symbols have
SiO2/>58% (n =22). Shoshonite series (n =8) shown by solid stars. Columbia River tholeiitic flood basalts (n -24) shown by circled
stars. Note the effects of magnetite fractionation in the calc-alkaline series rocks, causing trends toward increasing Ti/V with
increasing fractionation regardless of silica content. Magnetite fractionation can be detected by the use of supplementary plots, as
described in the text.
( S I O 2 < 5 8 - 6 0 % ) and m o r e fractionated interm e d i a t e rocks (SiO 2 > 58-60%). Shoshonites are
all relatively basic. Other, less c o m m o n rock suites
which m ay occur in an island arc setting are the
b o n i n i t e suite [42,43] and the p i c r i t e - a n k a r a m i t e
association [44,45].
Arc tholeiite series. A r c tholeiites with silica < 60%
plot almost exclusively on or near chondritic trends
an d have T i / V ratios ~< 20 (Fig. 2C). Th er e is
m i n o r overlap with M O R B ratios ( 2 0 - 2 7 ) when V
is less than 350 p p m ; however, suites of related
samples with a range of Ti and V a b u n d a n c e s will
111
display the distinctive "chondritic" trend that
clearly distinguishes arc tholeiites from MORB.
The more evolved rocks of the arc tholeiite suite
(SiO 2 > 58-60%) show the effects of titanomagnetite fractionation: sudden drastic reduction in Ti
and V abundances and increasing T i / V ratios.
The effects of magnetite fractionation are discussed in more detail below,
Calc-alkaline series. In contrast to the arc tholeiite
series, calc-alkaline series eruptives have negative
slopes on plots of Ti (or V) vs. Zr, F e O * / M g O , or
SiO 2 regardless of their silica content, which implies magnetite fractionation throughout their
evolution [23]. As a result, calc-alkaline volcanic
rocks define trends on Ti-V diagrams (Fig. 2D)
that are parallel to magnetite fractionation paths
(Fig. 1) calculated from empirically-derived magnetite/liquid partition coefficients [16,17]. The V
abundances of both tholeiitic and calc-alkaline
dacites are consistent with 1 0 - 1 5 % magnetite
fractionation from basalts containing 300-350 ppm
V (i.e., the same as the most V-rich calc-alkaline
basalts shown in Fig. 2D). Magnetite fractionation
causes T i / V ratios to increase, so that calc-alkaline rocks have Ti//V~> 15 (Fig. 2D). The influence of magnetite control can be easily
ascertained by the use of supplementary plots of
Ti and V against an independent fractionation
index such as Zr, F e O , / M g O or SiO 2 [23]. Rock
suites with negative slopes throughout their evolution are calc-alkaline with obvious island arc affinities and the T i / V plot is not applicable or needed.
Rock suites with positive slopes at low Zr (or
SiO 2) and negative slopes at high Zr (or SiO 2) are
tholeiitic, and samples from the positive slope may
be plotted on the T i / V diagram to distinguish the
nature of their original tectonic setting.
(Fig. 3). This coupled with the very low T i / V
ratios ( ~ 1/2 chondritic) in samples with the lowest
K 2 0 / N a 2 0 ratios, suggests that Ti and K 20 were
selectively added to a source region that had been
previously melted to create the low T i / V ratios, or
that a previously unmelted phase rich in TiO 2 and
K 2 0 (e.g., Ti-phlogopite) began to participate during progressive melting. Models similar to the latter
have been proposed by Jakeg and White [41].
Shoshonites are clearly distinguished from intraoceanic and continental alkali basalts by their
arc-like T i / V ratios.
Boninites. Boninites are petrographically and geo-
chemically distinctive rocks which have been found
only in the fore-arc region of modern oceanic arcs
[42,43]. They have low Ti//V ratios of about 10 or
less, but with lower Ti and V abundances than
most arc tholeiites (Ti ~< 2500 ppm; V ~< 200 ppm).
2O
Ti
v
I0
0
Shoshonites. Shoshonitic basalts from Fiji [46] have
T i / V ratios and abundaces similar to arc tholeiires, although T i / V may be as low as 4.5 (Fig.
2D). Vanadium generally decreases with increasing
silica, but Ti varies irregularly so that the effect of
magnetite fractionation is unclear. There is, however, a rough positive correlation between in creasing T i / V and K 2 0 / N a 2 0 in the Fiji shoshonites
1
.4
I
.6
I
I
.8
I
I
1.0
I
I
1.2
K20/Na20
Fig. 3. T i / V vs. K20/Na20 for the Fiji shoshonites [46]. The
positive correlation between these ratios (and the lack of correlation between TiO 2 and SiO2) implies either (a) that TiO 2 and
K 20 were selectively added to the source region or (b) that a
phase rich in TiO 2 and K 2 0 (like Ti-phlogopite) began to
participate during progressive partial melting.
112
This is consistent with their proposed origin by
hydrous melting of a source previously depleted by
arc tholeiite formation [42,43]. Meijer [43] has
described more fractionated rocks from the
Marianas which appear to be derived from a
boninite parent. These "boninite series" rocks
would be expected to have Ti and V abundances
somewhat higher than true boninites, but still depleted relative to equivalent arc tholeiites.
Ankaramites. The picrite-ankaramite association
has been documented in several island arcs, most
notably at New Georgia in the Solomons arc [44],
and throughout the New Hebrides arc (e.g. [45]).
These olivine and clinopyroxene-rich lavas are
sub-alkaline to mildly alkaline and appear to be
related to extensional tectonics within the
Solomons and New Hebrides arcs. Ankaramites
from the New Hebrides arc have T i / V ratios
ranging from 7 to 27, but most are between 10 and
20 (Fig. 2C). Ankaramites have the same range in
Ti and V concentrations, and the same "chondritic"
trend on the Ti-V plot, as the island arc tholeiites
with which they are commonly associated.
3.5 Back-arc basins
Basaltic rocks from back-arc basins [9, 47] define a field on the T i / V plot that overlaps both
MORB and island arc volcanic rocks, although
MORB-like abundances are most common (Fig.
2B). This tendency to show overlapping or transitional geochemical characteristics has been noted
by many investigators for other geochemical data
(e.g. [9,47]). It appears that the conditions of melting and fractionation vary between the two extremes of oxygen fugacity in a back-arc basin
setting. However, back-arc basin basalts tend to
show less enrichment in Ti and V than is seen in
either MORB or island arc basalts. This may be
related to slow, diffuse spreading centers in backarc basins, which lack well-developed magma
chambers [47].
cient to define the tectonic setting of any given
volcanic rock in most cases. More important are
the trends defined by suites of related samples that
exhibit a range of Ti and V abundances. The T i / V
plot is also poorly constrained (a) after the onset
of magnetite (-+ hornblende) fractionation, and (b)
for volcanic rocks of the calc-alkaline suite. The
first difficulty may be circumvented by first plotting either/or both Ti, V against an independent
fractionation index, e.g., Zr, F e O * / M g O or SiO2,
and omitting those data points that indicate magnetite control. This will also reveal whether the
rocks are calc-alkaline or tholeiitic [23]. The difficulties with calc-alkaline rocks are not serious,
since calc-alkaline series volcanic rocks in the geologic record are seldom mistaken for ophiolites,
and they are easily distinguished by their negative
slopes on Ti vs. Zr or SiO 2 plots. Shoshonites are
more problematical, but are generally spacially
associated with calc-alkaline rocks, and have arcrelated T i / V and Zr abundances (e.g. [46]). Island
arc tholeiites, boninites and ankaramites, however,
may form "ophiolite" assemblages. The T i / V plot
promises to be useful in distinguishing these from
MORB ophiolites and ocean islands. Distinguishing back-arc basin related ophiolites will require
careful study of local and regional geology as well
as geochemistry.
4. Application of Ti/V plots to ophiolite voicanics
3.6. Summary
In testing the applicability of a new discriminant diagram to older ophiolite terrains, it is desirable to apply it first to familiar, well-studied
examples whose tectonic settings are reasonably
well-constrained by previous geochemical and geologic investigations. Unfortunately, vanadium is
not commonly determined (or reported) for many
of these (e.g., Samail, Bay of Islands). Published
examples for which vanadium analyses are available include: Corsica [48]; the northern Apennines
[49]; Troodos [50] (ranges and means only reported by [48]); the K a r m ~ Complex in Norway
[51]; and Papua-New Guinea [52,53]. These data
are presented in Fig. 4.
It is clear from the foregoing discussion and
from Fig. 2 that T i / V ratios alone are not suffi-
Western Mediterranean. The ophiolites of Corsica
and the northern Apennines have volcanic rocks
113
500
vv
10 /
/30
$
400
300
V
II
OTL
/ I
it;". . . . . . . . .
-,
ppm
I
200
! l /
• •
<
I
/"
•
i
IOO
/
0
2
TROODOS OPHIOLITE
Means Ranges
(~
~
TU: Upper Volcanics
•
~ 2 qJ TL: Lower L. . . .
4
6
8
I0
12
14
16
18
WESTERN MEDETERRANEAN
• N. Apennines
• Corsica
KARMOY COMPLEX
[] Ophiolite Volcanies
A Off-AxisVolcanics
PAPUA
v PUB Volcanics
O PUB Tonalites
• Cape Vogel HMA
20
22
24
26
Ti p p m / 1 0 0 0
Fig. 4. Ti-V plots of ophiolites. Ophiolite volcanic rocks from Corsica [48], the northern Apennines [49] and the Karme~y Complex in
Norway [51] have Ti/V ratios between about 30 and 55, except for rare alkaline basalts in the western Mediterranean. The strong
linear trends in these suites imply fractionation dominated by olivine + plagioclasc (see Fig. I). These ratios and trends arc consistent
with their origin as MORB (see text). Alkaline basahs which are intercalated with sediments that overlie the Karme~y ophiolitc have
r i / v > 50, consistent with their proposed origin as an oceanic island [51]. V analyses for Troodos are unpublished [50], but the means
and ranges reported by Beccaluva et al. [48] are shown here: T L - Troodos lower pillow lavas: T U - Troodos upper pillow lavas: large
circles respective means. The Troodos upper pillow lavas and the lavas and tonalites of the Papuan uhramafic belt [52] and the
high-Mg andesites of Cape Vogel [53J, all have T i / V < 20, which implies their formation near a convergent plate boundary (e.g., within
an island arc, or in a small back-arc basin). Ranges reported for the Troodos lower pillow lavas [50] are too large for definite
interpretation, but the low mean (-- 1 I) implies origin in a setting similar to the Troodos upper lavas.
w i t h T i / V r a t i o s b e t w e e n 30 a n d 50, w i t h r a r e
examples of alkaline basalt with Ti/V
>50
( F i g . 4). T h e s e T i / V r a t i o s a n d t r e n d s a r e c o n s i s t e n t w i t h a n o r i g i n as M O R B , a n i n t e r p r e t a t i o n
s u p p o r t e d b y t h e p r i m a r y i n v e s t i g a t o r s [8,48,49,
54,55]. P e a r c e [8] h a s a l s o n o t e d t h e t e n d e n c y
t o w a r d a l k a l i n i t y in t h e s e r o c k s w h i c h h e a t t r i -
b u t e s to t h e i r o r i g i n in s m a l l o c e a n b a s i n s a l o n g a
rifted continental margin.
Troodos. T r o o d o s , i n t h e e a s t e r n M e d i t e r r a n e a n ,
has been a controversial subject since Miyashiro
[55] first s u g g e s t e d t h a t it w a s r e l a t e d t o i s l a n d a r c
v o l c a n i s m . S u b s e q u e n t d a t a a p p e a r to s u p p o r t his
114
contention (e.g. [7,8,42,56]), especially in regard to
the " U p p e r Pillow Lavas". The mean and ranges
of Ti and V from the " U p p e r " and "Lower"
volcanic sequences are shown in Fig. 4 [48,49]. The
means for both lava groups plot on the chondritic
trend of Ti//V ~ 10, however, the ranges for the
lower volcanic sequence are too large to draw any
definite conclusions. The ranges of Ti and V from
the upper pillow lavas are restricted to ratios close
to 10, suggesting that these rocks at least were
formed in a high volatile environment such as an
island arc or intra-arc basin. This conclusion is
consistent with Pearce [7,8], Cameron et al. [42],
and Dick et al. [56], but at odds with older interpretations [57,58].
KarrraCy. The Caledonian Karmery Complex in
Norway consists of two greenstone units: a lower
unit of ophiolitic lavas (Visne Group) and an
upper unit of alkaline basalts (Vikingstad Greenstone), which is intercalated with 700 m of hemipelagic sediments [51]. The Visne and Vikingstad
units have been interpreted by Sturt et al. [51] to
represent ocean crust and oceanic island rocks,
respectively. This conclusion is supported by their
Ti and V abundances, which show MORB and
alkaline characteristics, respectively (Fig. 4). Note
the distinct linearity sub-parallel to constant T i / V
ratios exhibited by the K a r n ~ y lava suites, and by
the western Mediterranean ophiolite lavas, which
suggest that fractionation of these lavas was
dominated by olivine and plagioclase.
Papua-New Guinea. The high-magnesium andesites
(HMA) of Cape Vogel are similar to both komatiites and boninites in their low abundances of
incompatible elements and high abundances of
MgO, Cr and Ni [53]. These rocks have very low
absolute abundances of Ti ( < 2600 ppm) and V
(~< 211 ppm) and low to very low T i / V ratios,
ranging from 4.3 to 16.7 (9.3 average) [53]. These
rations and abundance levels are consistent with
their origin by relatively large percentages of fusion of a previously depleted source, as suggested
by Jenner [53] for the Cape Vogel rocks, and by
others for boninites from Bonin-Marianas arc
[42,43]. This refractory source was enriched in
L R E E shortly before the second melting event
[53]. Jenner [53] claims that this component has an
oceanic island or continental affinity, and is not
similar to that found in island arcs. We have seen,
however, that alkalic rocks and transitional tholeiites from both ocean basins and continents have
high T i / V ratios (/> 35 about). Arc-related alkalic
rocks (shoshonites) have low T i / V ratios similar to
arc tholeiites. This suggests that the Cape Vogel
high Mg-andesites are related to some phase of
island arc volcanism, and that by inference the
L R E E component added may have been derived
from a subduction related source.
The Papuan ultramafic belt (PUB) comprises a
full ophiolite sequence which has been intruded by
Eocene tonalities [52]. The tonalities have T i / V
ratios of 10-20 and very low abundances ( T i <
2000 ppm; V < 150 ppm), consistent with their
proposed origin as early island arc magmas related
to the H M A of Cape Vogel [52]. Ophiolite basalts
of the PUB have T i / V ratios of 15-18 and V
abundances of 450-500 ppm. There is no overlap
between MORB and arc tholeiites at these abundance levels, and the island arc affinities of these
basalts are clearly demonstrated. Jaques and
Chappell [52] inferred that the PUB volcanics were
most similar to MORB, but noted many dissimilarities from MORB as well, such as low Ti, Zr
and H R E E at high F e O * / M g O , and the presence
of cumulate orthopyroxene in the plutonic section.
Geophysical evidence suggests that the PUB
formed in a marginal basin [59,60]. If so, it must
have been a small basin close to the subduction
zone since the T i / V ratios imply hydrous melting
of the mantle source. The high V abundances and
the presence of cumulate orthopyroxene are more
suggestive of arc tholeiite magmas than of most
"back-arc" basin basalts.
5. Conclusions
The data presented here show that plots of Ti
vs. V clearly distinguish arc related tholeiites,
MORB and alkali basalts. The T i / V ratio of individual samples is not as diagnostic as the trends
defined by suites of related samples that exhibit a
range in Ti and V abundances. The theoretical
basis of this plot can be modelled assuming a
115
c h o n d r i t i c m a n t l e (for Ti and V), r e a s o n a b l e refractory mineral assemblages, a n d bulk p a r t i t i o n
coefficients for V which vary as a function of
oxygen fugacity. The results of this m o d e l l i n g are
consistent with w h a t is k n o w n a b o u t the physical
c o n d i t i o n s u n d e r which each m a g m a series is gene r a t e d a n d with e x p e r i m e n t a l d e t e r m i n a t i o n s of
c r y s t a l / l i q u i d p a r t i t i o n coefficients for v a n a d i u m
a n d titanium. C a l c - a l k a l i n e m a g m a s m a y be genera t e d under c o n d i t i o n s similar to arc tholeiites, but
they are d o m i n a t e d b y m a g n e t i t e f r a c t i o n a t i o n
t h r o u g h o u t their evolution causing variable T i / V
ratios which overlap M O R B a n d alkali basalt ratios
at low a b u n d a n c e levels. This makes it necessary
to use s u p p l e m e n t a r y plots of V a n d / o r Ti vs. Zr,
F e O * / M g O o r S i O 2 in o r d e r to distinguish the
calc-alkaline series (which is definitely arc-related),
a n d to e l i m i n a t e tholeiite samples which are
d o m i n a t e d by m a g n e t i t e fractionation. Shoshonites
have T i / V ratios similar to arc tholeiites, which
serves to distinguish them from o t h e r basalts. Although V vs. SiO 2 plots i m p l y m a g n e t i t e control,
the source of shoshonites a p p e a r s to have been
enriched in Ti, so that Ti vs. SiO 2 plots are inconclusive. The only criteria b y which " b a c k - a r c "
basin basalts m a y be recognized on this plot are
v a r i a b l e T i / V ratios in a suite of samples from a
single g e o g r a p h i c area, a n d p o s s i b l y by a lack of
e n r i c h m e n t in either Ti or V, relative to the other
m a g m a series.
The use of V as a d i s c r i m i n a n t offers advantages over plots b a s e d on less a b u n d a n t elem e n t s (e.g., Ta, La, N b , Ce, etc.) because it is
easily a n a l y z e d b y routine X R F techniques (e.g.
[6]), having c o n c e n t r a t i o n s in basaltic rocks ( 5 0 600 p p m ) which greatly exceed the detection limit
(~3
ppm). A p p l i c a t i o n of this technique to
o p h i o l i t e volcanic rocks yields i n t e r p r e t a t i o n s
which are consistent with conclusions based on
o t h e r geochemical techniques a n d on recent petrologic and structural investigations.
The p r o b l e m s associated with transitional
tectonic settings such as b a c k - a r c basins or incipient ocean islands, however, require the a p p l i c a t i o n
of careful geologic, petrologic a n d structural investigations in a d d i t i o n to various geochemical metho d s to elucidate the origin of ophiolites f o r m e d in
these settings.
Acknowledgements
This w o r k is an o u t g r o w t h of research on the
trace element characteristics of C o r d i l l e r a n ophiolites begun when the a u t h o r was a N A T O postd o c t o r a l fellow at the Swiss F e d e r a l Polytechnic
Institute ( E T H ) in Ztirich u n d e r the s p o n s o r s h i p
of Prof. V. T r o m m s d o r f f . I wish to thank V.
Dietrich ( E T H - Z t i r i c h ) for my i n t r o d u c t i o n to trace
element analysis and s t i m u l a t i n g discussions on
o p h i o l i t e origins; and D.L. K i m b r o u g h (University
of C a l i f o r n i a at S a n t a Barbara) for discussion and
critical review of an earlier version of the
manuscript. C.A. H o p s o n , D.J. L i n d s t r o m a n d two
o t h e r reviewers c o n t r i b u t e d valuable c o m m e n t s
which i m p r o v e d the manuscript.
Appendix A
The bulk partition coefficients ( 4 ) for Ti and V used to
construct Fig. 1 were calculated from the relationship:
D, = a , D 7 / ' + f l , Di~/' + 3 , D , a/' + . . . + t~.,D,* '
where a=weight proportion of phase a, such that a + fl + 8
+ ... + ~ = 1.0, and D, '~/I =partition coefficient for element i
between phase a and the liquid. Two refractory mineralogies
were assumed: spinel lherzolite (65% ol, 20% opx, 12% cpx, 3%
Cr-spinel) and spinel harzburgite (70% ol, 24% opx, 3% cpx, 3%
Cr-spinel). These should span the range in the refractory source
regions of arcs and MORB, but probably not that of alkali
basalts. Spinel/liquid partition coefficients for Ti (-- 1.2) and V
(26.5) were estimated from an unpublished spinel-whole rock
pair (an arc-related ankaramite, corrected for phenocryst content). Other partition coefficients are from Lindstrom [18];
most of these values are summarized in Table 2. /gTi was
calculated from the high-temperature values in Table 2: lherzolite Dvi 20.17; harzburgite /~yi ~0.14; an "average"~0.15 is
assumed since residual harzburgite is more likely for moderate
to large degrees of melting. Dv was calculated from the data
below for both spinel lherzolite and spinel harzburgite at three
nominal oxygen fugacities, and are also listed below:
log[oD~, ~
D~'.P~/I
D~P ~/I
D ~
D v (harzburgite)
/5v (lherzolite)
8
10
12
0.03
0.05
0.10
6.50
0.23
0.24
0.03
0.50
I.(X)
6.50
0.37
0.44
0.04
2.5(1
5.(X1
6.5(1
0.97
1.32
/~v D-rl (----0.151is assumed to be the limiting case for high
fo: conditions. Due to uncertainties in (a) the experimental
116
data, (b) the estimated spinel/liquid partition coefficients, (c)
the assumed refractory assemblages, and (d) the actual values
of fo2 during partial melting in the upper mantle, these calculated values were used as guidelines in constructing Fig. 1,
rather than exact values. The D-v values used to construct Fig. 1
( D v =0.15, 0.45, 0.75, 1.0, 1.15) were chosen to span the range
of calculated values but with the melting curves sufficiently
spaced to be viewed clearly. Melting curves were calculated
from the batch melting equation:
-C] : C , / '[ D i +
(I-- ~)F]
where C] = concentration of element i in the liquid; C,' = initial
concentration of i in the source; Di =bulk partition coefficient
for i in the refractory residue, and F = % partial melt. Strictly
speaking, this equation applies to modal melting and thus
represents a grossly oversimplified model. However, in view of
the other uncertainties involved, the use of more complex
models is unwarranted and for a first approximation, unnecessary. Fractionation paths are based on Rayleigh fractionation:
CiI : COl(O, - I)
where C] = concentration of element i in the liquid, C,° = the
initial concentration of i in the magma, and f = fraction of melt
remaining.
Appendix B
Ash, R.P., Carney, J.N. and MacFarlane, A., 1980. Geology of
the northern Banks islands. Reg. Rep. Geol. Surv. New
Hebrides, 52 pp.
Baker, P.E., 1968. Petrology of Mt. Misery Volcano, St. Kitts,
West Indies. Lithos, I : 124-150.
Baker, P.E., 1978 The South Sandwich Islands, III. Petrology of
the volcanic rocks. Br. Antart. Surv., Sci. Rep., 93: 1-26.
Bryan, W.B., Frey, F.A. and Thompson, G., 1977 Oldest
Atlantic seafloor. Contrib. Mineral. Petrol., 64: 223-242.
Carney, J.N. and MacFarlane, A., 1979. Geology of Tanna,
Aneityum, Futuna and Aniwa. Reg. Rep. Geol. Surv. New
Hebrides, 71 pp.
Clague, D.A. and Beeson, M.H., 1980. Trace element geochemistry of the East Molokai volcanic series, Hawaii. Am. J.
Sci., 280-A: 820-844.
Coleman, R.G., Fleck, R.J., Hedge, C.E. and Ghent, E.D.,
1977. The volcanic rocks of southwestern Saudi Arabia and
the opening of the Red Sea. In: Red Sea Research 19701975. Mineral Resour. Bull. 22: DI-D30.
Colley, H. and Ash, R.P., 1971. The Geology of Erromango.
Reg. Rep. Geol. Surv. New Hebrides, 111 pp.
Dietrich, V.J., Emmerman, R., Oberhanski, R. and Puchelt, H.,
1978. Geochemistry of basaltic and gabbroic rocks from the
West Mariana basin and the Mariana Trench. Earth Planet.
Sci. Lett., 39: 127-144.
Dixon, T.H. and Stern, R.J., 1982. Volcanic seamounts in the
southern Marianas island arc. Geol. Soc. Am. Bull. (in
press).
Engel, A.E.J., Engel, C.G. and Havens, R.G., 1965. Chemical
characteristics of oceanic basalts and the upper mantle.
Geol. Soc. Am. Bull., 76: 719-734.
Ewart, A., Bryan, W.G. and Gill, J.B., 1973. Mineralogy and
geochemistry of the younger volcanic islands of Tonga,
S.W. Pacific. J. Petrol., 14: 429-465.
Fleet, A.J., Henderson, P. and Kempe, D.R.C., 1976. Rare
earth element and related chemistry of some drilled southern Indian Ocean basalts and volcanogenic sediments. J.
Geophys. Res., 81: 4257-4268.
Frey, F.A., Bryan, W.B. and Thompson, G., 1974. Atlantic
Ocean floor: geochemistry and petrology of basalts from
Legs 2 and 3 of the Deep Sea Drilling Project. J. Geophys.
Res., 79: 5507-5527.
Gill, J.B., 1970. Geochemistry of Viti Leva, Fiji, and its evolution as an island arc. Contrib. Mineral. Petrol., 27: 179-203.
Gorton, M.P., 1977. The geochemistry and origin of Quaternary
volcanism in the New Hebrides. Geochim. Cosmochim.
Acta, 41: 1257-1270.
Hawkins, J.W., 1976. Petrology and geochemistry of basaltic
rocks of the Lau Basin. Earth Planet. Sci. Lett., 28: 283-297.
Hubbard, N., 1967. Some trace elements in Hawaiian lavas. Ph.
D. Thesis, University of Hawaii, 123 pp.
Johnson, J.R., 1979. Transitional basalts and tholeiites from the
East Pacific Rise, 9°N. J. Geophys. Res., 84: 1635-1651.
Kempe, D.R.C., 1974. The petrology of the basalts, Leg 26. In:
Initial Reports DSDP, 26: 465-503.
Kempe, D.R.C., 1976. Petrological studies on DSDP Leg 34
basalts: Nazca plate, eastern Pacific Ocean. In: Initial Reports DSDP, 34: 189-213.
Langmuir, C.H., Bender, J.F., Bence, A.E., Hanson, G.N. and
Taylor, S.R., 1977. Petrogenesis of basalts from the FAMOUS area: Mid-Atlantic Ridge. Earth Planet. Sci. Lett.,
36: 133-156.
Leeman, W.P., Budahn, J.R., Gerlach, D.C., Smith, D.R. and
Powell, B.N., 1980. Origin of Hawaiian tholeiites: trace
element constraints. Am. J. Sci., 280-A: 794-819.
Lowder, G.G. and Carmichael, I.S.E., 1970. The volcanoes and
caldera of Talasea, New Britain: geology and petrology.
Geol. Soc. Am. Bull., 81: 17-38.
MacDonald, G.A. and Katsura, T., 1964. Chemical composition of Hawaiian lavas. J. Petrol., 5: 82-133.
McDougall, I., 1976. Geochemistry and origin of basalt of the
Columbia River Group, Oregon and Washington. Geol.
Soc. Am. Bull., 87: 777-792.
Muir, I.D. and Tilley, C.E., 1964. Basalts from the northern
part of the rift zone of the Mid-Atlantic Ridge. J. Petrol., 5:
409-434.
Nisterenko, G.V., 1980. Petrochemistry and geochemistry of
basalts in the Shikoku Basin and Daito Basin, Philippine
Sea. In: Initial Reports DSDP, 58: 791-804.
Sun, S.S. and Nesbitt, R.W., 1978. Geochemical regularities
and genetic significance of ophiolitic basahs. Geology, 6:
689-693.
Sun, S.S., Nesbitt, R.W. and Sharaskin, A.Y., 1979. Geochemical characteristics of mid-ocean ridge basalts. Earth Planet,
Sci. Lett., 44: 119-138.
117
Thompson, G., Bryan, W.B., Frey, F.A., Dickey, J.S. and Suen,
C.J., 1976. Petrology and chemistry of basalts from DSDP
Leg 34, Nazca plate. In: Initial Reports DSDP, 34: 215-226.
Wood, D.A., Tarney, J., Varet, J., Saunders, A.D., Bougault,
H., Joron, J.L., Trenil, M. and Cann, J.R., 1979. Geochemistry of basalts drilled in the North Atlantic by IPOD Leg
49: implications for mantle heterogeneity. Earth Planet. Sci.
Lett., 42: 77-97.
References
1 J.A. Pearce and J.R. Cann, Ophiolite origin investigated by
discriminant analysis using Ti, Zr and Y, Earth Planet Sci.
Lett. 12 (1971) 339-349.
2 J.A. Pearce and J.R. Cann, Tectonic setting of basic volcanic
rocks determined using trace element analyses, Earth Planet.
Sci. Lett. 19 (1973) 290-300.
3 J.B. Gill, Composition and age of Lau Basin and Ridge
volcanic rocks: implications for evolution of an interarc
basin and remnant arc, Geol. Soc. Am. Bull. 87 (1976)
1384-1395.
4 M.O. Garcia, D.W. Muenow and C.D. Byers, Volatiles in
spreading center lavas: mid-ocean ridges vs. back-arc basins.
Abstr., Am. Geophys. Union, C h a p m a n Conf. on Oceanic
Lithosphere ( 1981 ).
5 P. Fryer, J.M. Sinton and J.A. Philpotts, Basalts from active
back-arc basins, a comparison with MORB, Abstr., Am.
Geophys. Union, C h a p m a n Conf. on Oceanic Lithosphere
(1981).
6 E.G. Nisbet, V.J. Dietrich and A. Esenwein, Routine trace
element determination in silicate minerals and rocks by
X-ray fluorescence, Fortschr. Mineral. 57 (1979) 264-279.
7 J.A. Pearce, Basalt geochemist~ used to investigate past
tectonic environments on Cyprus, Tectonophysics 25 (1975)
41-67.
8 J.A. Pearce, Geochemical evidence for the genesis and
eruptive setting of lavas from Tethyan Ophiolites, Proc. Int.
Ophiolite Symp., Cyprus (1979) 261 272.
9 A.D. Saunders, J. Tarney, N.G. Marsh and D.A. Wood,
Ophiolites as ocean crust or marginal basin crust: a geochemical approach, Proc. Int. Ophiolite Symp., Cyprus
(1979) 193-204.
10 J.A. Pearce and M.G. N o r ~ , Petrogenetic implications of
Ti, Zr, Y, and Nb variations in volcanic rocks. Contrib.
Mineral. Pctrol. 69 (1979) 33-47.
I 1 J.G. Schilling, Iceland mantle plume: geochemical evidence
along the Reykjanes Ridge, Nature 242 (1973) 565 571.
12 D.A. Wood, I.L. Gibson and R.N. Thompson, Elemental
mobility during zeolite facies metamorphism of Tertiary
basalts of eastern Iceland, Contrib. Mineral. Petrol. 55
11976) 24t-254.
13 J.N. Ludden and G. Thompson, An evaluation of the
behaviour of the rare-earth elements during weathering of
sea-floor basalt, Earth Planet. Sci. Lett. 43 (1970) 85-92.
14 A. Ewart, W.B. Bryan and J.B. Gill, Mineralogy and geo-
chemistry of the younger volcanic islands of Tonga, S.W.
Pacific, J. Petrol 14 (1973) 429-465.
15 J.J. Dudas, M.E. Harward and R.A. Schmitt, Identification
of dacitic tephra by activation analysis of their primary
mineral phenocrysts, Quaternary Res. 3 (1973) 307-315.
16 W.B. Leeman, M.S. Ma, A.V. Murali and R.A. Schmitt,
Empirical estimation of magnetite/liquid distribution coefficients for some transition elements, Contrib. Mineral.
Petrol. 65 (1978) 269-272.
17 W.B. Leeman, M.S. Ma, A.V. Murali and R.A. Schmitt, A
correction, Contrib. Mineral. Petrol. 66 (1978) 429.
18 D.J. Lindstrom, Experimental study of the partitioning of
the transition metals between clinopyroxene and coexisting
silicate liquids, Ph.D. Dissertation, University of Oregon
(1976) 188 pp. (unpublished).
19 R.F. Fudali, Oxygen fugacities of basaltic and andesitic
magmas, Geochim. Cosmochim. Acta 29 (1965) 1063-1075.
20 I.S.E. Carmichael, The mineralogy of Thingmuli, a Tertiary'
volcano in eastern Iceland, Am. J. Sci. 276 (1967) 309-329.
21 R. Ganapathy and E. Anders, Bulk compositions of the
moon and earth, estimated from meteorites, Proc. Fifth
Lunar Sci. Conf., Suppl. 5, Geochim. Cosmochim. Acta 2
(1974) 1181-1206
22 B. Mason, Handbook of Elemental Abundances in
Meteorites (Gordon and Breach, New York, (N.Y. 1971)
555 pp.
23 A. Miyashiro and F. Shido, Tholeiitic and calc-alkalic series
in relation to the behaviors of titanium, vanadium, chromium and nickel, Am. J. Sci. 275 (1975) 265-277.
24 S.R. Taylor, M. Kaye, A.J.R. White, A.R. Duncan and A.
Ewart, Genetic significance of Co, Cr, Ni, Sc and V content
of andesites, Geochim. Cosmochim. Acta 33 (1969) 275-286.
25 J.B. Gill, Orogenic Andesites and Plate Tectonics
(Springer-Verlag, Berlin, 1981 ) 390 pp.
26 J.F. Luhr and I.S.E. Carmichael. The Cotina volcanic complex, Mexico, Contrib. Mineral. Petrol. 71 (1980) 343-372.
27 M.J. Mottl, H.D. Holland and R.F. Corr, Chemical exchange during hydrothermal alteration of basalt by seawater,
II. Experimental results for Fe, Mn, and sulfur species,
Geochim. Cosmochim. Acta 43 (t979) 869-884.
28 M.J. Mottl, Metabasalts, axial hot springs and the structure
of hydrothermal systems at mid-ocean ridges, Geol. Soc.
Am. Bull. (in review).
29 G. Thompson, A geochemical study of the low-temperature
interaction of sea-water and oceanic igneous rocks. Trans.
Am. Geophys. Union 54 (1973) 1015 1019.
3(1 C. Nicollet and D.R. Andrianbololona, Distribution of
transition elements in crustal metabasic igneous rocks,
Chem. Geol. 28 (1980) 79-90.
31 B.L. Weaver and J. Tarney, Chemical changes during dyke
metamorphism in high-grade basement terrains, Nature 289
( 1981 ) 47-49.
32 W.B. Bryan, G. Thompson, F.A. Frey and J.S. Dickey,
Inferred geologic settings and differentiation in basalts from
the Deep Sea Drilling Project, J. Geophys. Res. 81 (1976)
4285 -4304.
118
33 I. McDougall, Geochemistry and origin of basalt of the
Columbia River Group, Oregon and Washington, Geol.
Soc. Am. Bull. 87 (1976) 777-792.
34 S.Y. Wass, Geochemistry and origin of xenolith-bearing
and related alkali basaltic rocks from the southern highlands, New South Wales, Australia, Am. J. Sci. 280-A
(1980) 639-666.
35 C.H. Langmuir, J.F. Bender, A.E. Bence, G.N. Hanson and
S.R. Taylor, Petrogenesis of basalts from the FAMOUS
area: Mid-Atlantic Ridge, Earth Planet. Sci. Lett. 36 (1977)
133-156.
36 G.V. Nisterenko, Petrochemistry and geochemistry of
basalts in the Shikoku Basin and Daito Basin, Philippine
Sea, in: Initial Reports DSDP 58 (1980) 791-804.
37 J.R. Johnson, Transitional basalts and tholeiites from the
East Pacific Rise, 9°N, J. Geophys. Res. 84 (1979) 16351651.
38 W.P. Leeman, J.R. Budahn, D.C. Gerlach, D.R. Smith and
B.N. Powell, Origin of Hawaiian tholeiites: trace element
constraints Am. J. Sci. 280-A (1980) 794-819.
39 D.A. Clague and M.H. Beeson, Trace element geochemistry
of the East Molokai volcanic series, Hawaii, Am. J. Sci.
280-A (1980) 820-844.
40 R. Batiza, Age, volume, compositional and spatial relations
of small isolated oceanic central volcanoes, Mar. Geol. 24
(1977) 169-183.
41 P. Jake~ and A.J.R. White, Major and trace element abundances in volcanic rocks of orogenic areas, Geol. Soc. Am.
Bull. 83 (1972) 29-40.
42 W.E. Cameron, E.G. Nisbet and V.J. Dietrich, Petrographic
dissimilarities between ophiolitic and ocean floor basalts,
Proc. Int. Ophiolite Syrup., Cyprus (1979) 182-192.
43 A. Meijer, Primitive arc volcanism and a boninite series:
examples from the western Pacific island arcs, in: The
Tectonic Evolution of Southeast Asian Seas and Islands,
Hayer, ed., Am. Geophys. Union, Geophys. Monogr. (1980).
44 R.L. Stanton and J.D. Bell, Volcanic and associated rocks
of the New Georgia Group, British Solomon Islands Protectorate, Overseas Geol. Mineral. Resour. l0 (1969) 113145.
45 A.J. Warden, Evolution of Aoloa caldera volcano, New
Hebrides, Bull. Volcanol. 34 (1970) 107-140.
46 J.B. Gill, Geochemistry of Viti Leva, Fiji, and its evolution
as an island arc, Contrib. Mineral. Petrol. 27 (1970) 179-203.
47 J.W. Hawkins, Petrology of back-arc basins and island arcs:
48
49
50
51
52
53
54
55
56
57
58
59
60
61
their possible role in the origin of ophiolites, Proc. Int.
Ophiolite Syrup., Cyprus (1979) 244-254.
L. Beccaluva, D. Ohnenstetter, M. Ohnenstetter and G.
Venturelli, The trace element geochemistry of Corsican
ophiolites, Contrib. Mineral. Petrol. 64 (1977) I 1-3 I.
G. Ferrara, F. Innocenti, C.A. Ricci and G. Serri, Oceanfloor affinity of basalts from North Apennine ophiolites:
geochemical evidence, Chem. Geol. 17 (1976) 101-111.
A. Desmet, Contribution a l'6tude de la Croflte Oceanique
Mesozoique de Medeterann6e Orientale: les pillows lavas
due Troodos (Chypre), Thbse de Specialit+, Universit6 du
Nancy.
B.A. Sturt, A. Thon and H. Fumes, The geology and
preliminary geochemistry of the Karm~y ophiolite, Norway,
Proc. Int. Ophiolite Symp., Cyprus (1979) 538-554.
A.L. Jaques and B.W. Chappell, Petrology and trace element geochemistry of the Papuan ultramafic belt, Contrib.
Mineral. Petrol. 75 (1981) 55-70.
G.A. Jenner, Geochemistry of high-Mg andesites from Cape
Vogel, Papua-New Guinea, Chem. Geol. 33 ( 1981 ) 307-332.
G. Venturelli, R.S. Thorpe and P.J. Potts, Rare-earth and
trace element characteristics of ophiolitic metabasalts from
the Alpine-Apennine belt, Earth Planet. Sci. Lett. 53 (1981)
109-123.
A. Miyashiro, The Troodos ophiolite complex was probably
formed in an island arc, Earth Planet. Sci. Lett. 19 (1973)
218-244.
H.J.B. Dick, R.L. Fisher and T. Bullen, Mineralogy and
composition of abyssal versus alpine-type peridotites (in
press).
I.G. Gass and J.D. Smewing, Intrusion, extrusion and metamorphism at constructive margins: evidence from the
Troodos Massif, Cyprus, Nature (London) 242 (1973) 26-29.
J.D. Smewing, K.O. Simonian and I.G. Gass, Metabasalts
from the Troodos Massif: genetic implication deduced from
petrography and trace element geochemistry, Contrib.
Mineral. Petrol. 51 (1975)49-61.
D.E. Karig, Remnant arcs, Geol. Soc. Am. Bull. 83 (1972)
1057-1068.
D.M. Finlayson, B.J. Drummond, C.D. Collins and J.B.
Connelly, Crustal structures in the region of the Papuan
ultramafic belt, Phys. Earth Planet. Int. 14 (1977) 13-29.
E.J.W. Whittaker and R. Muntas, Ionic radii for use in
geochemistry, Geochim. Cosmochim. Acta 34 (1970) 945956.