- Email: [email protected]
Neodymium isotopic composition of Quaternary island arc lavas from Indonesia
NOTE
Neodymium isotopic composition of Quaternary island arc lavas from Indonesia Department
of Terrestrial
DAVID J. WHITFORD.* WILLIAM M. WHITE?! Magnetism. Carnegie Institution of Washington, Washington,
DC 10015, U.S.A.
and PETER A. JEZEK$ Mineral Sciences.
Smithsonian
Institution,
(Received 4 No~semher 19X0; accepted
Washington.
in reriscdjbrm
DC 20560. U.S.A. 3 February
1981)
Abstract--‘43Nd/‘44 Nd ratios measured in Quaternary lavas from Java and the Banda arc of Indonesia range from 0.51242 to 0.51280 and exhibit an inverse correlation with “Sr/“Sr. Isotopically. the Indonesian samples resemble Andean rather than island arc lavas. The samples from Java plot either within, or adjacent to the mantle array. towards higher *‘Sr,‘“%r ratios. Samples from the Banda arc and the anomalous talc-alkaline volcano Papandajan are characterized by relatively low ‘43Nd/‘44Nd and high R7Sr/8hSr ratios. These characteristics are consistent with the interpretation that subducted terrigenous material was involved in the genesis of these lavas. Furthermore the Banda arc samples appear to lie on a mixing line between isotopic compositions characteristic of the mantle and upper continental crust. A high-K trachyte from the alkaline volcano Muriah. Java, has isotopic characteristics of the mantle (‘43Nd/‘44Nd = 0.51370. 87Sr/8hSr = 0.70424). which implies that the extreme enrichment in large-ion-lithophile elements in its source must have occurred only shortly before its formation. The inferred ‘43Nd/‘44Nd ratio of the unmodified mantle beneath Java and the Banda arc is lower than that observed in mid-ocean ridge basalt, which may have important implications for a better understanding of the eeochemical structure of the mantle
greater variability in their sources, and for the Peruvian lavas, possible assimilation of old continental NEODYMIUM isotopes have been used in several recent crust (DEPAOLO and WASSERBURG, 1977; HAWKESstudies of lavas from both island arcs and active conWORTH et al., 1979a). tinental margins in an attempt to resolve some of the Perhaps of greater importance is the relationship long-standing problems surrounding the origin of this between ‘43Nd/‘44Nd and *‘Sr,@Sr. Oceanic basalts, group of rocks (DEPAOLO and JOHNSON. 1979; with 87Sr/8hSr ratios ranging from 0.7025 to 0.7055, DEPAOLO and WASSERBURG, 1977; HAWKESWORTH exhibit a well-defined inverse correlation that is et ~1.. 1977, 1979a. b; HAWKESWORTHand VOLLMER, generally assumed to reflect the isotopic heterogeneity 1979). Important questions remain unanswered. These of the mantle (DEPAOLO and WASSERBURG, 1976; include the relative importance of the mantle and the RICHARD et al.. 1976; O’NIONS et ul., 1977). The Nd isotopic compositions of many andesitic rocks from crustal components of the subducted lithospheric slab as magmatic sources, and the role, if any, of subvolcanic arcs are displaced from this mantle array towards higher *‘Sr:*YSr ratios. This phenomenon ducted sedimentary material in island arc magmatism. has been interpreted as the result of interaction of Andesitic rocks from the island arcs of the Marianas, New Britain and the South Sandwich Islands oceanic crust with seawater (*‘Sr/*%r = 0.709) and are characterized by relatively high 143Nd/144Nd the subsequent incorporation of subducted crust into ratios (0.51294.5131). Andesites from the Andes are the parental magmas of the erupted lavas (DEPAOLO characterized by a much broader range of compoand WASSERBURG, 1977; HAWKESWORTH et ul.. 1977). sitions from 0.5130 (Ecuador) to 0.5120 (Peru) Arc-related high-K alkalic rocks have not been (DEPAOLO and WASSERBURG, 1977), which suggests a widely studied in terms of their Nd isotopic composition. The only investigation to date has been carried * CSIRO Division of Mineralogy. P.O. Box 136. North out on lavas from western Italy by HAWKESW~RTH Ryde. N.S.W. 2113. Australia. and VOLLMER (1979). Lavas from Roccamonfina are t Max-Planck-Institut fir Chemie. 6500 Mainr. West characterized by high 87Sr/86Sr ratios (0.7066-0.7097) Germany. and low ‘4JNd;144Nd ratios (0.5122~0.5125). HAWKES$ Stone and Webster Engineering Corp., Boston, MA 02107, U.S.A. WORTH and VOLLMER (1979) suggested that these INTRODUCTION
990
Notes
values reflect a mantle source that has been metasomatically enriched prior to partial melting. The source of the metasomatic fluid remains unclear, but could perhaps be derived from a subducted lithospheric slab. On the other hand, TAYLORet al. (1979) argued that the Sr and 0 isotopic compositions of lavas from Roccamonfina reflect an important contribution from crustal assimilation. It is the purpose of this study to further investigate island arc petrogenetic processes using the isotopic composition of Nd in a small number of selected Quaternary lavas from two arcs in Indonesia--the Sunda arc in Java and the Banda arc of Eastern Indonesia. QUATERNARY LAVAS FROM INDONESIA AND THEIR SETTING The Sunda arc in Java exhibits many features considered typical of island arcs (HAMILTON,1979). The Java Trench to the south is underlain by oceanic crust and attains depths greater than 7 km. North of the trench, the Java Ridge manifests an accretionary wedge that is separated from the volcanic arc by a relatively shallow, sediment-filled basin. Details of the tectonic setting of Java and its relationship to the abundant Quaternary volcanism have been described by WHITFORDet al. (1979). The Pleistocene and Recent lavas from the Sunda arc in Java are typical of rocks from a mature island arc. Those showing affinities with island arc tholeiites lie 10&150 km above the Benioff seismic zone whereas those with compositions ranging from calcalkaline to high-K talc-alkaline occur 150-250 km above the seismic zone. More distant from the trench. where the depth to the Benioff zone is approximately 400 km, high-K alkaline lavas have been erupted from the Pleistocene volcano, Muriah (Fig. 1). The Quaternary talc-alkaline and high-K calc-alkaline lavas range from basalts to dacites with basaltic andesites (52-57 wt% SiOZ) predominant. The alkaline lavas from Muriah are mostly strongly undersaturated, ranging from olivine-leucitites and basanites to trachytes. These rocks are geochemically distinct from the high-K talc-alkaline lavas (WHITFORD, 1975a, b). Chondrite-normalized rare earth element (REE) abundances for the lavas analysed from Java are plotted in Fig. 2 (WHITFORD,1975b: WHITFORDet (I[.. 1979). The talc-alkaline and high-K talc-alkaline lavas plot as a coherent group with La abundances ranging from 50-100 times chondritic and Yb ranging from 7-13 times chondritic. With increasing K content, the lavas exhibit a well-defined increase in the chondrite-normalized La/Yb ratio, (La/Yb),, from approximately 5-10. The distinction between these and the alkaline trachyte 72-940 [(La/Yb), > 1001 is clearly shown in Fig. 2. 87SriR”Sr ratios in the lavas from Java range from 0.704 to 0.706 with most rocks between 0.704 and 0.705 (WHITFORD.1975a). The few scattered ratios between 0.7052 and 0.7060 have been interpreted
as the result
of crustal
contamination.
either during ascent of the magma or, in the case of the volcano Papandajan, from subduction and subsequent melting of terrigenous sediments (WHITFORD, 1975a, b). By contrast, the geochemistry of the Recent favas from the Banda arc appears to reflect their unusual tectonic setting where subduction of continental material is apparently taking place beneath a volcanic arc that is underlain by Mesozoic oceanic crust. In terms of their major and trace element abundances these rocks are typical island arc lavas. As in Java, they range from tholeiitic to high-K talc-alkaline varieties although there does not appear to be a corresponding increase in the depth to the underlying seismic zone. Rather, there is a consistent spatial variation along the strike of the arc from tholeiites in the north to high-K talc-alkaline lavas in the south (WHITFORDand JEZEK, 1979). They are characterized by a range of unusually high “Sr/s’%r ratios up to 0.7095 (WHITFORDand JEZEK,1979). Furthermore the rocks show an enrichment in 6*sO (up to 9.2”,,,, relative to SMOW) that correlates with *‘Sr/‘%r, which is interpreted to be the result of subduction and subsequent melting of sialic material derived from the Australian continental margin (MAGARITZe/ ctl.. 1978: WHITFORDand JEZEK.1979). ANALYTICAL METHODS Neodymium was separated and isotopically analysed following methods adapted from those of EUGSTERet crl. (1970) and described by WHI~ORD et u/. (1978). ‘43Nd/144Nd ratios have been normalized to 1“6Nd/‘44Nd = 0.7219 (O’NIONS et al.. 1977). Measured 143Nd/‘44Nd ratios for the standard BCR-1 and the UCSD Nd standard are 0.51271 + 3 and 0.51197 + 2 respectively. To facilitate comparison with other workers’ r&&s, ‘k3Nd/‘44Nd ratios a;e reported relative to BCR-1 ‘43Nd/144Nd = 0.51265 te.e. DEPAOU) and WASSERBLJRG. 1976; ‘ONIONS et al., 167< HAWKESWORWut al., 19771 HAWKESWORTH and VOLLMER, 1979). REE were anaiysed by spark-source mass spectrography following methods described by TAYLOR(1971) and TAYLORand GORTON(1977) and references therein.
RESULTS 143Nd/144Nd ratios are listed in Table 1 together with “Sr/s%r ratios and the concentrations of SiOz: and K20. 143Nd/144Nd ratios range from 0.51280 to 0.51242 and exhibit no correlation with either K20 or SiO,. There is an overall poorly-defined inverse correlation between *‘Sr/*%r and 143Nd/144Nd (Fig. 3). The measured Nd ratios lie well within the range defined by lavas analysed from other island arcs and active continental margins, although high “Sr/‘%r ratios clearly distinguish the Banda arc Iavas. Isotopitally the Indonesian samples resemble Andean rather than island arc lavas. DISCUSSION Most of the lavas from the Sunda arc in Java plot within or close to the mantle array (Fig. 3). That some
100s
-
_ _ - ._
-
110
..
OE
CONTOUR
locations
BATHYMETRIC
Fig. 1. Sampling
3000 -
110-E
..-
in Indonesia.
1 m)
I.
Volcano
KALIMANTAN
_^
100 !d:L1!
IAN
0
:
100
I
200
DO
OE 300
L
400
500
.-
.
.
_
_
-
-~.
_
km
OCEAN
Prahu. Teun.
.--_
abbreviations: Sum Sundoro. TP-Tangkuban Muriah. Se-Serua. Da Damar. Te-
D
-.-
120°E
._.“_^
Mp--Merapi.
_- .,.,.
Pp -Papandajan.
130 OE
Un--l’ngaran.
AUSTRALIA
_. __ -_
130 OE
Mh
10 0s
8
992
Notes
500
200 ," z 100 -u 2 5 \
50
G .s
20
10 5
I
I
I
1
I
La Ce Pr Nd
1
Sm Eu
I
I
I
I
I
Gd Tb Dy Ha Er
I
I
Yb
Fig. 2. Chondrtte-normalized rare earth element abundances for lavas from Java. The alkaline hrgh-k trachyte 72-940 is clearly distinguished from the talc-alkaline and high-K talc-alkaline lavas. Data from WHITFORD(1975b) summarised by WHITFORD er al. (1979). the high 87Sr/shSr side of the array suggests that mantle-type isotopic compositions may have been modified by the addition of a high 87Sr/86Sr component. either altered oceanic crust, or perhaps subducted sediments. possibly derived from Australia. plot towards
The anomalous talc-alkaline sample 71-991 from Papandajan is characterized by a relatively high R7Sr/*6Sr ratio together with an anomalous enrichment in large-ion-lithophile (LIL) elements, particularly in relation to the depth to the underlying Benioff zone (WHITFORD, 1975a: WHITFORD and NIC‘HOILS.
Table 1. Nd and Sr Isotopic composition of Quaternary lavas from Indonesia
-.I^_._-~--
__~~____
Sample No.
Volrano~
Suite;
SiO
(wt
87 2 %)
K2°
(wt %)
!
Sr18%r3
Lomean
14iNd 144"$d : i :.‘l.mean
Sunda arc 71-1026 72-1142 72-1076 71-991 71-980 71-982 72-940
su J'T' !lp Pp Cn Gn Mtl
CA CA CA ACA HKCA HKCA A
50.7 56.2 52.9 58.8 56.8 48.1 ~4.4
1.08 2 24 1 63 1 32 2 64 1 61 a 0
0.70476~10 0.70476?18 0.70498i16 0.70565klO 0.704881t10 0.70472ilO 0.70424tlO
o.jlZ77'3 O.'i1277-3 0.51280-3 0.51256~*4 0.51263t5 0.>126813 0.5127oi2 0.51270+3
Banda arc T7 T8 CH23 CH29
Se sc: Ih Te
CA CA HKCA HKCA
55.9 59.4 57.0 58.4
0.96 1.17 2.52 2.07
0.7084217 0.70947?8 0.70651+6 0.70767?7
0.5125213 0.5124213 0.51259?3 0.51252?3
’ Volcanoes: Su Sundoro. TP- Tangkuban Prahu, MpMerapi, Pp Papandajan. Un--Ungaran, Mh--Muriah. Se- Serua, Da--Damar, Te-Teun. ’ Suites: CAB-talc-alkaline: ACA ~~~anomalous talc-alkaline: HKCA-high-K calc-alkaline: A alkaline (high-K). 3 Sr isotopic compositions and SiO, and K20 concentrations from WHITFORD(1975a) and WHITFORDand JEZEK(1979). s7Sr/s6Sr ratios have been normalized to %rlBSSr = 0.1194 and are reported relative to E&A Sr 87Sr~RhSr . = 0.70800 (Banda arc) and NB’S SRM 987 Sr “‘Sr?‘Sr = 0.71022 (Sunda arci.
993
Notes
L NEWflRllAlN
0 CALL -ALKALINE 0 HIGH -K CALL-ALKALINE A ALKALINE
5115k+e%e+20
O 0 5120L
1
I 0 705
I
I 875r
1
I
0 125
I 0.710
/%
Fig. 3. 143Ndi’J’Nd vs 87Sr?6Sr plot for Quaternary lavas from the Sunda and Banda arcs of Indonesia. ehld refers to the deviations in parts in lo4 between the measured ‘43Nd/1J4Nd ratios and that in a chondritic uniform reservoir (CHUR) (DEPAOLO and WASSERBURG. 1976). The anomalous talc-alkaline lava 71-991 from Papandajan is denoted A. Also plotted are fields defined by lavas from other island arcs. the active continental margin of South America. and Roccamonfina in Italy An additional lava from Grenada is denoted G. The mantle array is the field defined by oceanic basal&. The lavas from the Banda arc appear to lie on a mixing line between the mantle array and DEPAOLO and WASSERBUR(;‘S (1979) estimate of the isotopic composition of the average upper crust. Data sources: DEPAOLO and JOHNSON(1979). DEPAOLO and WASSERBURG(1977). HAWKESWORTH and VOLLMER (1979). HAU’KESWORTH et ul. (1977; 1979a.b). O’NIONS rt ul. (1977). RICHARDet ul. (1976).
1976).
The
volcano
is
located
over
Benioff
of only
IO&150
km in an area dominated
zone
by low-K tholeiitic volcanoes. High zo7Pb/Z04Pb ratios (up to 15.77 at 206Pb/Z04Pb 18.98) in lavas from Papandajan suggest the involvement of an old crustal component in their generation: the most likely source being from subducted sediments (WHITFORD. 1975b). Sample 71-991 plots close to the mantle array in Fig. 3 although it is clearly enriched in 87Sr/s6Sr. The relatively low 143Nd/144Nd ratio is compatible with the view that the source of this lava was contaminated with a crustal component characterized by radiogenic Sr and non-radiogenic Nd. The high-K trachyte 72-940 is from the alkaline volcano Muriah. It plots well within the mantle array (Fig. 3) which reinforces the argument that despite the enrichment in K and related elements, these rocks are mantle-derived and do not manifest crustal contamination. In addition, the 143Nd/144Nd and 87Sr/s6Sr ratios are close to those predicted for single-stage mantle evolution (e.g. O’NIONS et al., 1977) which sug-
depths
gests that the implied large-ion-lithophile element enrichment in the source regions of these lavas (WHITFORD, 1975a) must have occurred only shortly before their formation. Any long-term enrichment for periods greater than a few hundred million years would have resulted in lower 143Nd!‘44Nd ratios and substantially higher “Sr/‘“Sr ratios. The four lavas analysed from the Banda arc plot in a linear field from the mantle array towards the average upper crustal composition (DEPAOLO and WASSERBURG. 1979). The Banda arc array projects back towards the field defined by the samples from the Sunda arc, which may therefore model the uncontaminated end member in the mixing process. The estimated maximum proportion of sialic material involved is about 25-30”:. very close to that determined by MAGARITZ et ~1. (1978) on the basis of 618@87Sr/s6Sr relationships. Evidence from Sr, Nd. Pb and 0 isotopic studies lends very strong support to the hypothesis that at least some of the lavas from the Banda arc. notably
994
Notes
those from Serua (Fig. l), reflect mixing of mantlederived and sialic components (WHITFORD and JEZEK, 1980). The source of the sialic component, however, is not entirely clear. It can be argued that, because of the location of the arc on relatively young, thin oceanic crust, the most likely source of sialic material is terrigenous material subducted beneath the arc. However until the crustal structure immediately beneath the volanic arc is better known, the possibility of sialit contamination in an initial elastic wedge (KAY tit ul., 1978) cannot be ruled out (WHITFORDand JEZX
DEPAOLOD. J. and WASSERBUR~; G. J. (1976) Nd Isotopic variations and petrogenetic models. Grqhvs Rec. Lt,tr.
3. 249.-252. DEPAOLOD. J. and WASSERBURG G. J. (1977) 7’he sources of island arcs as indicated by Nd and Sr isotopic studies. Geophys. Res. Lett. 4, 465-468.
DEPAOLOD. J. and JOHNSONR. W. (1979) Magma genesis in the New Britain island arc: constraints from Nd and Sr isotopes and trace element patterns. Cnmrrih. ,ifinrrl~l. Petrol. 70. 367-379. DEPAOLOD. J. and WASSERBURG G. J. (I 979) Petrogenetic mixing models and Nd-Sr isotopic patterns &ochim Cosmochim.
Adu 43. 615627.
E~C;STER 0.. TEKAF.. BURNFTT D. S. and W-ZSSI.HUI.K(;G J. (1970) isotopic composition of gadolinium ,mtl neutron A further important result concerns the nature of capture effects in some meteorites. J. Gc,o(~/~! \ Re.5. 75. the mantle beneath Java and the Banda arc prior to 2753 -2768. HAMILTONW. (1979) Tectonics of the Indoncsldn regton. modification by the subducted slab. With the possible C’.S. Geol. Surr Prqf: Pup. 1078, 345 pp. exception of the anomalous talc-alkaline lava 71-991, HAWKESWORTH C. J., O’NIONS R. K.. PA!%&&1 R. J.. the volcanic rocks analysed from Java may have been HAMILTONP. J. and EVENSENN. M. (1977) A geochemiderived from a mantle source with similar cal study of island-arc and back-arc tholeiitey from the 143Nd/144Nd ratios, but lower “Sr/%r ratios to Scotia Sea. Earth Planet. .Sc,i. Lett. 36, 253- 262 C. J. and VOLI.MERR. (19791 C’rtiital conthose observed in the lavas (DEPAOLOand WASSER- HAWKESWORTH tamination versus enriched mantlc: ‘3”Nd,“JJNd and BURG, 1977; HAWKESWORTHet a[.. 1977). These 87Sr/8hSr evidence from the Itahan \olc;cnich i‘,mrril~ inferred 143Nd/‘44Nd ratios for the mantle beneath Mineral. Pefrol. 69, 151.. 165. Java are lower than those observed in mid-ocean HAWKESWORTH C. J., NORRYM. H.. KOIXX~h .I C’.. BAKER P. E.. FRANCIS P. W. and THORPE K. S (1979~1 ridge basalt (MORB) (generally > 0.5130; DEPAOLO 143Nd1144Nd, “Sr,i”%, and incompatible clement and WASSERBURG,1976; RICHARD et al., 1976; variations in talc-alkaline andesites and plateau lacas O’NIONS et al., 1977; CARL~~N et al., 1978) and clearly from South America. Etrrrl~ Ptlrrtrt. 51.1 I.l,rt. 42. distinguish Java from other island arcs with the poss45-57. ible exception of Grenada (Fig. 3). Even where there is HAWKESWORTH C. J., O’NIONS R. K. and AKCULUS R. J. (1979b) Nd and Sr isotope geochemistry of island arc clear evidence for the addition of a lo~-‘~~Nd/‘~~Nd volcanics. Grenada, Lesser Antilles. Earrll Planer. Sci sialic component such as the Banda arc lavas, 1980).
inferred mantle compositions are still characterized by relatively low 143Nd/‘44Nd ratios (Fig. 3). It is possible to construct ud hoc mixing models to derive the Indonesian lavas from a modified MORBsource mantle. On the other hand, from the limited data available, it is probably more plausible that the mantle beneath Java and the Banda arc is not of the MORB-source type, but is more enriched in LIL elements and radiogenic Sr and Pb. It is not clear whether this phenomenon simply reflects a long period of enrichment due to repeated melting of subducted oceanic crust and/or sediments, or whether the mantle beneath Indonesia is intrinsically more enriched, perhaps similar to the source of ocean island basalts. Both alternatives have important implications for an understanding of the geochemical structure of the mantle (cf. HOFMANNet al., 1978).
Lett. 45, 237~-248.
HOFMANN A. W., WHITEW. M. and WHI~ORD D. J. ( I978i Geochemical constraints on mantle models. Carnr~qic Inst. Washington Yearb. 71, 548-562. KAY R. W., SUN S.-S. and LEE-HI! C.-N. (1978) Pb and Sr
isotopes in volcanic rocks from the Aleutian Istands and Pribiloff Islands, Alaska. Geachim Cosmochim. .Ictli 42, 263-273.
MAGARITZM., WHITFORDD. J. and JAMESD. 1:. (19781 Oxygen isotopes and the origin of high-s’Sr’“‘%r andesites. Earth Planet. Sci. Lett. 40, 220-230.
O’NIONSR. K.. HAMILTONP. J. and EVENSENN. M. (1977) Variations in 143Ndi’44Nd and s’Sr/86Sr ratios in oceanic basalts. Earth Planet. Sci. Lett. 34, 13-E RICHARD P., SHIMIZU N. and ALL~GRE C. J. (19761 ‘43Nd/‘46Nd, a natural tracer: an application to oceanic basalts. Earth Planet. Sci. Left. 31, 269.-278. TAYLORH. P.. GIANNETTIB. and T~JRI B. (1979~ Oxygen isotope geochemistry of the potassic igneous rocks from the Roccamonfina volcano, Roman eomagmatic region. Italy. Abstr. Progr. Geol. Sot. Am. 11, 526-527. TAYLORS. R. (1971) Geochemical application of sparksource mass spectrography- II. Photoplate data praAcknowledgements-Samples were collected in cooperation cessing. Geochim. Cosmochim. Acta 35, 11X7- 1196. with the Indonesian Institute of Sciences and the GeologiTAYLORS. R. and GORTONM. P. (1977) Geochemical cal Research and Development Centre (I+. M. S. HARTONO. application of spark source mass spectrography-~~111. Director). The advice and assistance of the staff of these Element sensitivity precision and accuracy. Georhim. organizations are gratefully acknowledged. R. A. BINNS, Cosmochim. Actu 41. 1375- 1380. S.-S. SUN, M. VAA~JOKIand R. W. T. WILKINScritically WHITFORDD. J. (1975a) Strontium isotopic studies of the reviewed the manuscript. volcanic rocks of the Sunda arc. Indonesia, and their petrogenic implications. Geochim. Cosmochim. ,dcta 39, 1287-1302. REFERENCES WHITFORDD. J. (1975b) Geochemistry and petrology of volcanic rocks from the Sunda Arc, Indonesia. Unpublished Ph.D. Thesis, Australian National Univ. CARLSONR. W., MACD~UGALLJ. C. and LUGMAIRG. W. (1978) Differential Sm/Nd evolution in oceanic basal& WHITFORDD. J. and NICHOLLSI. A. (1976) Potassium variation in lavas across the Sunda arc in Java and Bali In Geophys. Res. Lett. 5, 229-232.
Notes Volcanism in Australusiu (ed. R. W. Johnson), pp. 63-75. Elsevier. WHITFORDD. J. and JEZEK P. A. (1979) Origin of lateCenozoic lavas from the Banda arc, Indonesia: trace element and Sr isotope evidence. Contrib. Mineral. Petrol. 68.141-150.
WHITFORDD. J. and JEZEKP. A. (1980) Isotopic constraints on the role of subducted sialic material in Indonesian
995
island arc magmatism. Geol. Sot. Am. Bull. (submitted). WHITFORDD. J., WHITEW. M., HOFMANNA. W. and JAMES D. E. (1978) Separation and isotopic analysis of neodymium. Carnegie Inst. Washington Yearh. 11, 620-623. WHITFORDD. J., NICHOLLSI. A. and TAYLORS. R. (1979) Spatial variations in the geochemistry of Quaternary lavas across the Sunda arc in Java and Bali. Conrrih. Mineral. Petrol. 70. 341-356.
Neodymium isotopic composition of Quaternary island arc lavas from Indonesia Department
of Terrestrial
DAVID J. WHITFORD.* WILLIAM M. WHITE?! Magnetism. Carnegie Institution of Washington, Washington,
DC 10015, U.S.A.
and PETER A. JEZEK$ Mineral Sciences.
Smithsonian
Institution,
(Received 4 No~semher 19X0; accepted
Washington.
in reriscdjbrm
DC 20560. U.S.A. 3 February
1981)
Abstract--‘43Nd/‘44 Nd ratios measured in Quaternary lavas from Java and the Banda arc of Indonesia range from 0.51242 to 0.51280 and exhibit an inverse correlation with “Sr/“Sr. Isotopically. the Indonesian samples resemble Andean rather than island arc lavas. The samples from Java plot either within, or adjacent to the mantle array. towards higher *‘Sr,‘“%r ratios. Samples from the Banda arc and the anomalous talc-alkaline volcano Papandajan are characterized by relatively low ‘43Nd/‘44Nd and high R7Sr/8hSr ratios. These characteristics are consistent with the interpretation that subducted terrigenous material was involved in the genesis of these lavas. Furthermore the Banda arc samples appear to lie on a mixing line between isotopic compositions characteristic of the mantle and upper continental crust. A high-K trachyte from the alkaline volcano Muriah. Java, has isotopic characteristics of the mantle (‘43Nd/‘44Nd = 0.51370. 87Sr/8hSr = 0.70424). which implies that the extreme enrichment in large-ion-lithophile elements in its source must have occurred only shortly before its formation. The inferred ‘43Nd/‘44Nd ratio of the unmodified mantle beneath Java and the Banda arc is lower than that observed in mid-ocean ridge basalt, which may have important implications for a better understanding of the eeochemical structure of the mantle
greater variability in their sources, and for the Peruvian lavas, possible assimilation of old continental NEODYMIUM isotopes have been used in several recent crust (DEPAOLO and WASSERBURG, 1977; HAWKESstudies of lavas from both island arcs and active conWORTH et al., 1979a). tinental margins in an attempt to resolve some of the Perhaps of greater importance is the relationship long-standing problems surrounding the origin of this between ‘43Nd/‘44Nd and *‘Sr,@Sr. Oceanic basalts, group of rocks (DEPAOLO and JOHNSON. 1979; with 87Sr/8hSr ratios ranging from 0.7025 to 0.7055, DEPAOLO and WASSERBURG, 1977; HAWKESWORTH exhibit a well-defined inverse correlation that is et ~1.. 1977, 1979a. b; HAWKESWORTHand VOLLMER, generally assumed to reflect the isotopic heterogeneity 1979). Important questions remain unanswered. These of the mantle (DEPAOLO and WASSERBURG, 1976; include the relative importance of the mantle and the RICHARD et al.. 1976; O’NIONS et ul., 1977). The Nd isotopic compositions of many andesitic rocks from crustal components of the subducted lithospheric slab as magmatic sources, and the role, if any, of subvolcanic arcs are displaced from this mantle array towards higher *‘Sr:*YSr ratios. This phenomenon ducted sedimentary material in island arc magmatism. has been interpreted as the result of interaction of Andesitic rocks from the island arcs of the Marianas, New Britain and the South Sandwich Islands oceanic crust with seawater (*‘Sr/*%r = 0.709) and are characterized by relatively high 143Nd/144Nd the subsequent incorporation of subducted crust into ratios (0.51294.5131). Andesites from the Andes are the parental magmas of the erupted lavas (DEPAOLO characterized by a much broader range of compoand WASSERBURG, 1977; HAWKESWORTH et ul.. 1977). sitions from 0.5130 (Ecuador) to 0.5120 (Peru) Arc-related high-K alkalic rocks have not been (DEPAOLO and WASSERBURG, 1977), which suggests a widely studied in terms of their Nd isotopic composition. The only investigation to date has been carried * CSIRO Division of Mineralogy. P.O. Box 136. North out on lavas from western Italy by HAWKESW~RTH Ryde. N.S.W. 2113. Australia. and VOLLMER (1979). Lavas from Roccamonfina are t Max-Planck-Institut fir Chemie. 6500 Mainr. West characterized by high 87Sr/86Sr ratios (0.7066-0.7097) Germany. and low ‘4JNd;144Nd ratios (0.5122~0.5125). HAWKES$ Stone and Webster Engineering Corp., Boston, MA 02107, U.S.A. WORTH and VOLLMER (1979) suggested that these INTRODUCTION
990
Notes
values reflect a mantle source that has been metasomatically enriched prior to partial melting. The source of the metasomatic fluid remains unclear, but could perhaps be derived from a subducted lithospheric slab. On the other hand, TAYLORet al. (1979) argued that the Sr and 0 isotopic compositions of lavas from Roccamonfina reflect an important contribution from crustal assimilation. It is the purpose of this study to further investigate island arc petrogenetic processes using the isotopic composition of Nd in a small number of selected Quaternary lavas from two arcs in Indonesia--the Sunda arc in Java and the Banda arc of Eastern Indonesia. QUATERNARY LAVAS FROM INDONESIA AND THEIR SETTING The Sunda arc in Java exhibits many features considered typical of island arcs (HAMILTON,1979). The Java Trench to the south is underlain by oceanic crust and attains depths greater than 7 km. North of the trench, the Java Ridge manifests an accretionary wedge that is separated from the volcanic arc by a relatively shallow, sediment-filled basin. Details of the tectonic setting of Java and its relationship to the abundant Quaternary volcanism have been described by WHITFORDet al. (1979). The Pleistocene and Recent lavas from the Sunda arc in Java are typical of rocks from a mature island arc. Those showing affinities with island arc tholeiites lie 10&150 km above the Benioff seismic zone whereas those with compositions ranging from calcalkaline to high-K talc-alkaline occur 150-250 km above the seismic zone. More distant from the trench. where the depth to the Benioff zone is approximately 400 km, high-K alkaline lavas have been erupted from the Pleistocene volcano, Muriah (Fig. 1). The Quaternary talc-alkaline and high-K calc-alkaline lavas range from basalts to dacites with basaltic andesites (52-57 wt% SiOZ) predominant. The alkaline lavas from Muriah are mostly strongly undersaturated, ranging from olivine-leucitites and basanites to trachytes. These rocks are geochemically distinct from the high-K talc-alkaline lavas (WHITFORD, 1975a, b). Chondrite-normalized rare earth element (REE) abundances for the lavas analysed from Java are plotted in Fig. 2 (WHITFORD,1975b: WHITFORDet (I[.. 1979). The talc-alkaline and high-K talc-alkaline lavas plot as a coherent group with La abundances ranging from 50-100 times chondritic and Yb ranging from 7-13 times chondritic. With increasing K content, the lavas exhibit a well-defined increase in the chondrite-normalized La/Yb ratio, (La/Yb),, from approximately 5-10. The distinction between these and the alkaline trachyte 72-940 [(La/Yb), > 1001 is clearly shown in Fig. 2. 87SriR”Sr ratios in the lavas from Java range from 0.704 to 0.706 with most rocks between 0.704 and 0.705 (WHITFORD.1975a). The few scattered ratios between 0.7052 and 0.7060 have been interpreted
as the result
of crustal
contamination.
either during ascent of the magma or, in the case of the volcano Papandajan, from subduction and subsequent melting of terrigenous sediments (WHITFORD, 1975a, b). By contrast, the geochemistry of the Recent favas from the Banda arc appears to reflect their unusual tectonic setting where subduction of continental material is apparently taking place beneath a volcanic arc that is underlain by Mesozoic oceanic crust. In terms of their major and trace element abundances these rocks are typical island arc lavas. As in Java, they range from tholeiitic to high-K talc-alkaline varieties although there does not appear to be a corresponding increase in the depth to the underlying seismic zone. Rather, there is a consistent spatial variation along the strike of the arc from tholeiites in the north to high-K talc-alkaline lavas in the south (WHITFORDand JEZEK, 1979). They are characterized by a range of unusually high “Sr/s’%r ratios up to 0.7095 (WHITFORDand JEZEK,1979). Furthermore the rocks show an enrichment in 6*sO (up to 9.2”,,,, relative to SMOW) that correlates with *‘Sr/‘%r, which is interpreted to be the result of subduction and subsequent melting of sialic material derived from the Australian continental margin (MAGARITZe/ ctl.. 1978: WHITFORDand JEZEK.1979). ANALYTICAL METHODS Neodymium was separated and isotopically analysed following methods adapted from those of EUGSTERet crl. (1970) and described by WHI~ORD et u/. (1978). ‘43Nd/144Nd ratios have been normalized to 1“6Nd/‘44Nd = 0.7219 (O’NIONS et al.. 1977). Measured 143Nd/‘44Nd ratios for the standard BCR-1 and the UCSD Nd standard are 0.51271 + 3 and 0.51197 + 2 respectively. To facilitate comparison with other workers’ r&&s, ‘k3Nd/‘44Nd ratios a;e reported relative to BCR-1 ‘43Nd/144Nd = 0.51265 te.e. DEPAOU) and WASSERBLJRG. 1976; ‘ONIONS et al., 167< HAWKESWORWut al., 19771 HAWKESWORTH and VOLLMER, 1979). REE were anaiysed by spark-source mass spectrography following methods described by TAYLOR(1971) and TAYLORand GORTON(1977) and references therein.
RESULTS 143Nd/144Nd ratios are listed in Table 1 together with “Sr/s%r ratios and the concentrations of SiOz: and K20. 143Nd/144Nd ratios range from 0.51280 to 0.51242 and exhibit no correlation with either K20 or SiO,. There is an overall poorly-defined inverse correlation between *‘Sr/*%r and 143Nd/144Nd (Fig. 3). The measured Nd ratios lie well within the range defined by lavas analysed from other island arcs and active continental margins, although high “Sr/‘%r ratios clearly distinguish the Banda arc Iavas. Isotopitally the Indonesian samples resemble Andean rather than island arc lavas. DISCUSSION Most of the lavas from the Sunda arc in Java plot within or close to the mantle array (Fig. 3). That some
100s
-
_ _ - ._
-
110
..
OE
CONTOUR
locations
BATHYMETRIC
Fig. 1. Sampling
3000 -
110-E
..-
in Indonesia.
1 m)
I.
Volcano
KALIMANTAN
_^
100 !d:L1!
IAN
0
:
100
I
200
DO
OE 300
L
400
500
.-
.
.
_
_
-
-~.
_
km
OCEAN
Prahu. Teun.
.--_
abbreviations: Sum Sundoro. TP-Tangkuban Muriah. Se-Serua. Da Damar. Te-
D
-.-
120°E
._.“_^
Mp--Merapi.
_- .,.,.
Pp -Papandajan.
130 OE
Un--l’ngaran.
AUSTRALIA
_. __ -_
130 OE
Mh
10 0s
8
992
Notes
500
200 ," z 100 -u 2 5 \
50
G .s
20
10 5
I
I
I
1
I
La Ce Pr Nd
1
Sm Eu
I
I
I
I
I
Gd Tb Dy Ha Er
I
I
Yb
Fig. 2. Chondrtte-normalized rare earth element abundances for lavas from Java. The alkaline hrgh-k trachyte 72-940 is clearly distinguished from the talc-alkaline and high-K talc-alkaline lavas. Data from WHITFORD(1975b) summarised by WHITFORD er al. (1979). the high 87Sr/shSr side of the array suggests that mantle-type isotopic compositions may have been modified by the addition of a high 87Sr/86Sr component. either altered oceanic crust, or perhaps subducted sediments. possibly derived from Australia. plot towards
The anomalous talc-alkaline sample 71-991 from Papandajan is characterized by a relatively high R7Sr/*6Sr ratio together with an anomalous enrichment in large-ion-lithophile (LIL) elements, particularly in relation to the depth to the underlying Benioff zone (WHITFORD, 1975a: WHITFORD and NIC‘HOILS.
Table 1. Nd and Sr Isotopic composition of Quaternary lavas from Indonesia
-.I^_._-~--
__~~____
Sample No.
Volrano~
Suite;
SiO
(wt
87 2 %)
K2°
(wt %)
!
Sr18%r3
Lomean
14iNd 144"$d : i :.‘l.mean
Sunda arc 71-1026 72-1142 72-1076 71-991 71-980 71-982 72-940
su J'T' !lp Pp Cn Gn Mtl
CA CA CA ACA HKCA HKCA A
50.7 56.2 52.9 58.8 56.8 48.1 ~4.4
1.08 2 24 1 63 1 32 2 64 1 61 a 0
0.70476~10 0.70476?18 0.70498i16 0.70565klO 0.704881t10 0.70472ilO 0.70424tlO
o.jlZ77'3 O.'i1277-3 0.51280-3 0.51256~*4 0.51263t5 0.>126813 0.5127oi2 0.51270+3
Banda arc T7 T8 CH23 CH29
Se sc: Ih Te
CA CA HKCA HKCA
55.9 59.4 57.0 58.4
0.96 1.17 2.52 2.07
0.7084217 0.70947?8 0.70651+6 0.70767?7
0.5125213 0.5124213 0.51259?3 0.51252?3
’ Volcanoes: Su Sundoro. TP- Tangkuban Prahu, MpMerapi, Pp Papandajan. Un--Ungaran, Mh--Muriah. Se- Serua, Da--Damar, Te-Teun. ’ Suites: CAB-talc-alkaline: ACA ~~~anomalous talc-alkaline: HKCA-high-K calc-alkaline: A alkaline (high-K). 3 Sr isotopic compositions and SiO, and K20 concentrations from WHITFORD(1975a) and WHITFORDand JEZEK(1979). s7Sr/s6Sr ratios have been normalized to %rlBSSr = 0.1194 and are reported relative to E&A Sr 87Sr~RhSr . = 0.70800 (Banda arc) and NB’S SRM 987 Sr “‘Sr?‘Sr = 0.71022 (Sunda arci.
993
Notes
L NEWflRllAlN
0 CALL -ALKALINE 0 HIGH -K CALL-ALKALINE A ALKALINE
5115k+e%e+20
O 0 5120L
1
I 0 705
I
I 875r
1
I
0 125
I 0.710
/%
Fig. 3. 143Ndi’J’Nd vs 87Sr?6Sr plot for Quaternary lavas from the Sunda and Banda arcs of Indonesia. ehld refers to the deviations in parts in lo4 between the measured ‘43Nd/1J4Nd ratios and that in a chondritic uniform reservoir (CHUR) (DEPAOLO and WASSERBURG. 1976). The anomalous talc-alkaline lava 71-991 from Papandajan is denoted A. Also plotted are fields defined by lavas from other island arcs. the active continental margin of South America. and Roccamonfina in Italy An additional lava from Grenada is denoted G. The mantle array is the field defined by oceanic basal&. The lavas from the Banda arc appear to lie on a mixing line between the mantle array and DEPAOLO and WASSERBUR(;‘S (1979) estimate of the isotopic composition of the average upper crust. Data sources: DEPAOLO and JOHNSON(1979). DEPAOLO and WASSERBURG(1977). HAWKESWORTH and VOLLMER (1979). HAU’KESWORTH et ul. (1977; 1979a.b). O’NIONS rt ul. (1977). RICHARDet ul. (1976).
1976).
The
volcano
is
located
over
Benioff
of only
IO&150
km in an area dominated
zone
by low-K tholeiitic volcanoes. High zo7Pb/Z04Pb ratios (up to 15.77 at 206Pb/Z04Pb 18.98) in lavas from Papandajan suggest the involvement of an old crustal component in their generation: the most likely source being from subducted sediments (WHITFORD. 1975b). Sample 71-991 plots close to the mantle array in Fig. 3 although it is clearly enriched in 87Sr/s6Sr. The relatively low 143Nd/144Nd ratio is compatible with the view that the source of this lava was contaminated with a crustal component characterized by radiogenic Sr and non-radiogenic Nd. The high-K trachyte 72-940 is from the alkaline volcano Muriah. It plots well within the mantle array (Fig. 3) which reinforces the argument that despite the enrichment in K and related elements, these rocks are mantle-derived and do not manifest crustal contamination. In addition, the 143Nd/144Nd and 87Sr/s6Sr ratios are close to those predicted for single-stage mantle evolution (e.g. O’NIONS et al., 1977) which sug-
depths
gests that the implied large-ion-lithophile element enrichment in the source regions of these lavas (WHITFORD, 1975a) must have occurred only shortly before their formation. Any long-term enrichment for periods greater than a few hundred million years would have resulted in lower 143Nd!‘44Nd ratios and substantially higher “Sr/‘“Sr ratios. The four lavas analysed from the Banda arc plot in a linear field from the mantle array towards the average upper crustal composition (DEPAOLO and WASSERBURG. 1979). The Banda arc array projects back towards the field defined by the samples from the Sunda arc, which may therefore model the uncontaminated end member in the mixing process. The estimated maximum proportion of sialic material involved is about 25-30”:. very close to that determined by MAGARITZ et ~1. (1978) on the basis of 618@87Sr/s6Sr relationships. Evidence from Sr, Nd. Pb and 0 isotopic studies lends very strong support to the hypothesis that at least some of the lavas from the Banda arc. notably
994
Notes
those from Serua (Fig. l), reflect mixing of mantlederived and sialic components (WHITFORD and JEZEK, 1980). The source of the sialic component, however, is not entirely clear. It can be argued that, because of the location of the arc on relatively young, thin oceanic crust, the most likely source of sialic material is terrigenous material subducted beneath the arc. However until the crustal structure immediately beneath the volanic arc is better known, the possibility of sialit contamination in an initial elastic wedge (KAY tit ul., 1978) cannot be ruled out (WHITFORDand JEZX
DEPAOLOD. J. and WASSERBUR~; G. J. (1976) Nd Isotopic variations and petrogenetic models. Grqhvs Rec. Lt,tr.
3. 249.-252. DEPAOLOD. J. and WASSERBURG G. J. (1977) 7’he sources of island arcs as indicated by Nd and Sr isotopic studies. Geophys. Res. Lett. 4, 465-468.
DEPAOLOD. J. and JOHNSONR. W. (1979) Magma genesis in the New Britain island arc: constraints from Nd and Sr isotopes and trace element patterns. Cnmrrih. ,ifinrrl~l. Petrol. 70. 367-379. DEPAOLOD. J. and WASSERBURG G. J. (I 979) Petrogenetic mixing models and Nd-Sr isotopic patterns &ochim Cosmochim.
Adu 43. 615627.
E~C;STER 0.. TEKAF.. BURNFTT D. S. and W-ZSSI.HUI.K(;G J. (1970) isotopic composition of gadolinium ,mtl neutron A further important result concerns the nature of capture effects in some meteorites. J. Gc,o(~/~! \ Re.5. 75. the mantle beneath Java and the Banda arc prior to 2753 -2768. HAMILTONW. (1979) Tectonics of the Indoncsldn regton. modification by the subducted slab. With the possible C’.S. Geol. Surr Prqf: Pup. 1078, 345 pp. exception of the anomalous talc-alkaline lava 71-991, HAWKESWORTH C. J., O’NIONS R. K.. PA!%&&1 R. J.. the volcanic rocks analysed from Java may have been HAMILTONP. J. and EVENSENN. M. (1977) A geochemiderived from a mantle source with similar cal study of island-arc and back-arc tholeiitey from the 143Nd/144Nd ratios, but lower “Sr/%r ratios to Scotia Sea. Earth Planet. .Sc,i. Lett. 36, 253- 262 C. J. and VOLI.MERR. (19791 C’rtiital conthose observed in the lavas (DEPAOLOand WASSER- HAWKESWORTH tamination versus enriched mantlc: ‘3”Nd,“JJNd and BURG, 1977; HAWKESWORTHet a[.. 1977). These 87Sr/8hSr evidence from the Itahan \olc;cnich i‘,mrril~ inferred 143Nd/‘44Nd ratios for the mantle beneath Mineral. Pefrol. 69, 151.. 165. Java are lower than those observed in mid-ocean HAWKESWORTH C. J., NORRYM. H.. KOIXX~h .I C’.. BAKER P. E.. FRANCIS P. W. and THORPE K. S (1979~1 ridge basalt (MORB) (generally > 0.5130; DEPAOLO 143Nd1144Nd, “Sr,i”%, and incompatible clement and WASSERBURG,1976; RICHARD et al., 1976; variations in talc-alkaline andesites and plateau lacas O’NIONS et al., 1977; CARL~~N et al., 1978) and clearly from South America. Etrrrl~ Ptlrrtrt. 51.1 I.l,rt. 42. distinguish Java from other island arcs with the poss45-57. ible exception of Grenada (Fig. 3). Even where there is HAWKESWORTH C. J., O’NIONS R. K. and AKCULUS R. J. (1979b) Nd and Sr isotope geochemistry of island arc clear evidence for the addition of a lo~-‘~~Nd/‘~~Nd volcanics. Grenada, Lesser Antilles. Earrll Planer. Sci sialic component such as the Banda arc lavas, 1980).
inferred mantle compositions are still characterized by relatively low 143Nd/‘44Nd ratios (Fig. 3). It is possible to construct ud hoc mixing models to derive the Indonesian lavas from a modified MORBsource mantle. On the other hand, from the limited data available, it is probably more plausible that the mantle beneath Java and the Banda arc is not of the MORB-source type, but is more enriched in LIL elements and radiogenic Sr and Pb. It is not clear whether this phenomenon simply reflects a long period of enrichment due to repeated melting of subducted oceanic crust and/or sediments, or whether the mantle beneath Indonesia is intrinsically more enriched, perhaps similar to the source of ocean island basalts. Both alternatives have important implications for an understanding of the geochemical structure of the mantle (cf. HOFMANNet al., 1978).
Lett. 45, 237~-248.
HOFMANN A. W., WHITEW. M. and WHI~ORD D. J. ( I978i Geochemical constraints on mantle models. Carnr~qic Inst. Washington Yearb. 71, 548-562. KAY R. W., SUN S.-S. and LEE-HI! C.-N. (1978) Pb and Sr
isotopes in volcanic rocks from the Aleutian Istands and Pribiloff Islands, Alaska. Geachim Cosmochim. .Ictli 42, 263-273.
MAGARITZM., WHITFORDD. J. and JAMESD. 1:. (19781 Oxygen isotopes and the origin of high-s’Sr’“‘%r andesites. Earth Planet. Sci. Lett. 40, 220-230.
O’NIONSR. K.. HAMILTONP. J. and EVENSENN. M. (1977) Variations in 143Ndi’44Nd and s’Sr/86Sr ratios in oceanic basalts. Earth Planet. Sci. Lett. 34, 13-E RICHARD P., SHIMIZU N. and ALL~GRE C. J. (19761 ‘43Nd/‘46Nd, a natural tracer: an application to oceanic basalts. Earth Planet. Sci. Left. 31, 269.-278. TAYLORH. P.. GIANNETTIB. and T~JRI B. (1979~ Oxygen isotope geochemistry of the potassic igneous rocks from the Roccamonfina volcano, Roman eomagmatic region. Italy. Abstr. Progr. Geol. Sot. Am. 11, 526-527. TAYLORS. R. (1971) Geochemical application of sparksource mass spectrography- II. Photoplate data praAcknowledgements-Samples were collected in cooperation cessing. Geochim. Cosmochim. Acta 35, 11X7- 1196. with the Indonesian Institute of Sciences and the GeologiTAYLORS. R. and GORTONM. P. (1977) Geochemical cal Research and Development Centre (I+. M. S. HARTONO. application of spark source mass spectrography-~~111. Director). The advice and assistance of the staff of these Element sensitivity precision and accuracy. Georhim. organizations are gratefully acknowledged. R. A. BINNS, Cosmochim. Actu 41. 1375- 1380. S.-S. SUN, M. VAA~JOKIand R. W. T. WILKINScritically WHITFORDD. J. (1975a) Strontium isotopic studies of the reviewed the manuscript. volcanic rocks of the Sunda arc. Indonesia, and their petrogenic implications. Geochim. Cosmochim. ,dcta 39, 1287-1302. REFERENCES WHITFORDD. J. (1975b) Geochemistry and petrology of volcanic rocks from the Sunda Arc, Indonesia. Unpublished Ph.D. Thesis, Australian National Univ. CARLSONR. W., MACD~UGALLJ. C. and LUGMAIRG. W. (1978) Differential Sm/Nd evolution in oceanic basal& WHITFORDD. J. and NICHOLLSI. A. (1976) Potassium variation in lavas across the Sunda arc in Java and Bali In Geophys. Res. Lett. 5, 229-232.
Notes Volcanism in Australusiu (ed. R. W. Johnson), pp. 63-75. Elsevier. WHITFORDD. J. and JEZEK P. A. (1979) Origin of lateCenozoic lavas from the Banda arc, Indonesia: trace element and Sr isotope evidence. Contrib. Mineral. Petrol. 68.141-150.
WHITFORDD. J. and JEZEKP. A. (1980) Isotopic constraints on the role of subducted sialic material in Indonesian
995
island arc magmatism. Geol. Sot. Am. Bull. (submitted). WHITFORDD. J., WHITEW. M., HOFMANNA. W. and JAMES D. E. (1978) Separation and isotopic analysis of neodymium. Carnegie Inst. Washington Yearh. 11, 620-623. WHITFORDD. J., NICHOLLSI. A. and TAYLORS. R. (1979) Spatial variations in the geochemistry of Quaternary lavas across the Sunda arc in Java and Bali. Conrrih. Mineral. Petrol. 70. 341-356.