Abstract
Integration of petrographic and geochemical data on each island in the Banks Group, northern Vanuatu (New Hebrides) has revealed a decrease in K2O (and related incompatible elements) across the islands, away from the New Hebrides trench. The correlation with depth to the Benioff zone is therefore the reverse of that typically found in island arcs. REE evidence and source modelling indicates that this variation represents a progressive depletion in LREE/HREE in the upper mantle, laterally away from the trench and a progressive increase in partial melting of the source, in the same direction. These variations in chemistry are attributed to an earlier west-dipping Miocene subduction system, and the variation in degree of partial melting to the location of the islands with respect to the active back-arc basin. An enrichment of the upper mantle in the Miocene is ascribed to the ascent of hydrous fluids enriched in incompatible elements, from the west-dipping Benioff zone, and subsequent reaction with the overlying upper mantle. The model thus envisages approximately contemporaneous development of the Central Chain volcanoes and the backarc basin in the late Pliocene, with partial melting of hydrous, laterally zoned upper mantle resulting from the convective thermal regime associated with the rifting apart of the back-arc basin. The role of the present subduction regime in magma generation is considered to be very limited.
Similar content being viewed by others
References
Arculus RJ, Johnson RW (1978) Criticism of generalised models for the magmatic evolution of arc-trench systems. Earth Planet Sci Lett 39:118–126
Barsdell M (1976) The Ilava volcanic complex of eastern Cumberland peninsula. New Hebs Geol Surv Occ Rep 10/76:24 pp
Barsdell M (1980) Petrological variation in the Banks Islands New Hebrides. Unpubl PhD Thesis University of Auckland
Carney JN, Macfarlane A (1978) Lower to middle Miocene sediments on Maewo, New Hebrides, and their relevance to the development of the outer Melanesian arc system. Bull Aust Soc Explor Geophys 9:123–130
Carney JN, Macfarlane A (1979) Geology of Tanna, Aneityum, Futuna and Aniwa. New Hebs Geol Surv Reg Rep 71 pp
Cawthorn RG (1977) Petrological aspects of the correlation between potash content of orogenic magmas and earthquake depth. Mineral Mag 41:173–182
Chung W-Y, Kanamori H (1978) A mechanical model for plate deformation associated with aseismic ridge subduction in the New Hebrides Arc. Tectonophysics 50:29–40
Coleman PJ (1970) Geology of the Solomon and New Hebrides islands as part of the Melanesian re-entrant. Pacific Sci 24:289–314
Colley C (1969) Progress report on the geology of Erromango. Ann Rep New Hebs Geol Surv for year 1967, pp 16–20
Colley H, Ash RP (1971) The geology of Erromango. New Hebs Geol Surv Reg Rep, 112 pp
Colley H, Warden AJ (1974) Petrology of the New Hebrides. Geol Soc Am Bull 85:1635–1646
Dickinson WR (1968) Circum-Pacific andesite types. J Geophys Res 73:2261–2269
Dickinson WR (1970) Relations of andesites, granites and derivative sandstones to arc-trench tectonics. Revs Geophys Space Physics 8:813–860
Dickinson WR, Hatherton T (1967) Andesitic volcanism and seismicity around the Pacific. Science 157:801–803
Dubois J, Dugas F, Lapouille A, Louat R (1978) The troughs at the rear of New Hebrides island arc: possible mechanisms of formation. Can J Earth Sci 15:351–360
Dugas F, Dubois J, Lapouille A, Louat R, Ravenne C (1977) Structural characteristics and tectonics of an active island arc: the New Hebrides. Proc Intern Sympos Geodyn in the South West Pacific, Ed Technip, Paris, pp 79–90
Falvey DA (1975) Arc reversals and a tectonic model for the North Fiji Basin. Bull Aust Soc Explor Geophys 6:47–49
Fyfe WS, McBirney AR (1975) Subduction and the structure of andesite volcanic belts. Am J Sci 275:285–297
Gill JB (1981) Orogenic andesites. Springer Verlag
Gorton MP (1974) Geochemistry and geochronology of the New Hebrides. Unpub PhD thesis, Australian National University Canberra
Gorton MP (1977) The geochemistry and origin of Quaternary volcanism in the New Hebrides. Geochim Cosmochim Acta 41:1257–1270
Green DH (1973) Experimental melting studies on a model upper mantle composition at high pressures under water-saturated and water-undersaturated conditions. Earth Planet Sci Lett 19:37–53
Jakěs P, Gill J (1970) Rare earth elements and the island arc tholeiitic series. Earth Planet Sci Lett 9:17–28
Jakěs P, White AJR (1972) Major and trace element abundances in volcanic rocks of orogenic areas. Geol Soc Am Bull 83:29–40
Johnson RW (1976) Potassium variation across the New Britain volcanic arc. Earth Planet Sci Lett 31:184–191
Johnson RW, MacKenzie DE, Smith IEM (1978a) Volcanic rock associations at convergent plate boundaries: reappraisal of the concept using case histories from Papua New Guinea. Geol Soc Am Bull 89:96–106
Johnson RW, MacKenzie DE, Smith IEM (1978b) Delayed partial melting of subduction-modified mantle in Papua New Guinea Tectonophysics 46:197–216
Malahoff A (1970) Gravity and magnetic studies of the New Hebrides island arc. New Hebs Geol Surv Reg Rep 67 pp
Mallick DIJ (1973) Some petrological and structural variations in the New Hebrides. In: PJ Coleman (ed) The Western Pacific: Island arcs, marginal seas, geochemistry. University of Western Australia. Press, Nedlands, pp 183–211
Mallick DIJ, Ash RP (1975) Geology of the Southern Banks Islands. New Hebs Geol Surv Reg Rep, 33 pp
Miyashiro A (1974) Volcanic rocks series in island arcs and active continental margins. Am J Sci 274:321–355
Nielson DR, Stoiber RE (1973) Relationship of potassium content in andesitic lavas and depth to the seismic zone. J Geophys Res 78:6887–6892
Norrish K, Chappell BW (1977) X-ray fluorescence spectrography. In: J Zussman (ed) Physical methods of determinative mineralogy. Academic Press London, England, pp 201–272
Oxburgh ER, Turcotte DL (1970) Thermal structure of island arcs. Geol Soc Am Bull 81:1665–1688
Pascal G, Isacks BL, Barazangi M, Dubois J (1978) Precise relocations of earthquakes and seismotectonics of the New Hebrides island arc. J Geophys Res 83:4957–4973
Pearce JA (1976) Statistical analysis of major element patterns in basalts. J Petrol 17:15–43
Ravenne C, Pascal G, Dubois J, Dugas F, Montadert L (1977) Model of a young intra-oceanic arc: the New Hebrides island arc. Proc Intern Sympos Geodyn in the South West Pacific, Technip, Paris, pp 63–78
Contribution à l'étude pétrologique et structurale des Nouvelles-Hébrides. Unpubl PhD Thesis, Université des Sciences et Techniques du Languedoc, Montpellier, 147 pp
Saunders AD, Weaver SD, Tarney J (1980) The pattern of Antarctic Peninsula Plutonism. In: C Craddock (ed) Antarctic geoscience Madison, Univ Wisconsin (in press)
Shaw DM (1970) Trace element fractionation during anatexis. Geochim Cosmochim Acta 34:237–243
Sleep NH (1973) Induced flow beneath island arcs and intra-arc spreading. Trans Am Geophys Union (EOS) 54:467 pp
Sleep NH, Toksoz MN (1971) Evolution of marginal basins. Nature 33:548–550
Smith IEM, Taylor SR, Johnson RW (1979) REE-fractionated trachytes and dacites from Papua New Guinea and their relationship to andesite petrogenesis. Contrib Mineral Petrol 69:227–233
Taylor SR, Gorton MP (1977) Geochemical application of spark source mass spectrography —III. Element sensitivity precision and accuracy. Geochim Cosmochim Acta 41:1375–1380
Toksoz MN, Bird P (1977) Formation and evolution of marginal basins and continental plateaux. In: M Talwani, WC Pitman III (eds) Island arcs, deep sea trenches and back-arc basins. Am Geophys Union, Washington DC, pp 379–393
Warden AJ (1967) The geology of the central islands. New Hebs Geol Surv Rep 5:108 pp
Weaver SD, Saunders AD, Pankhurst RJ, Tarney J (1979) A geochemical study of magmatism associated with the initial stages of back-arc spreading. Contrib Mineral Petrol 68:151–169
Whitford DJ, Nicholls IA (1976) Potassium variation in lavas across the Sunda arc in Java and Bali. In: RW Johnson (ed) Volcanism in Australasia. Elsevier, Amsterdam, pp 63–76
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Barsdell, M., Smith, I.E.M. & Spörli, K.B. The origin of reversed geochemical zoning in the northern New Hebrides volcanic arc. Contr. Mineral. and Petrol. 81, 148–155 (1982). https://doi.org/10.1007/BF00372051
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00372051