Abstract
Tanna, one of the southernmost islands of the New Hebrides volcanic arc, is made of Late Pliocene to Recent island arc tholeiitic basalts and andesites, with SiO2 contents ranging from 45 to 57%. These lavas are highly porphyritic (30–50% in volume): phenocrysts of plagioclase are the most abundant, together with olivine and clinopyroxene. The groundmass contain plagioclase, augite, olivine, magnetite and glass; pigeonite, tridymite, sanidine and, rarely, biotite may also occur. The olivines and clinopyroxenes show an iron enrichment from the cores of phenocrysts to their rims and the groundmass crystals, but their compositional variations are not correlated with the Mg/Fe ratio of bulk host rocks, the most Fe-rich compositions being found in Mg-rich lavas. Plagioclase compositions range from An95 to An60 in the basalts and An60 to An50 in the andesites, but, within each group, they are not correlated with SiO2 or Na2O contents of host lavas. Consequently, the bulk major element compositions of Tanna volcanic rocks cannot be considered as primarily controlled by crystal separation from successive liquids. The oxyde-SiO2 variations diagrams, and the modal compositions and mineral chemistry show that crystal accumulation is the predominant mechanism accounting for bulk rock compositions. However, this does not exclude fractional crystallization: the variation of the calculated groundmass mineralogy strongly suggest the occurrence of crystal removal mainly clinopyroxene and magnetite.
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References
Carney, andMacfarlane, 1976,Volcanotectonic Events and Prepliocene Crustal Extension in the New Hebrides. In:Geodynamics in South West Pacific, p. 91–104, Technip Editions, Paris.
————— and —————, 1978,Geological Map Of Tanna, Aneityum, Futuna and Aniwa, 1:100,000. Geol. Surv. New Hebrides, Sheet 11.
————— and —————, 1979,Geology of Tanna, Aneytyum, Futuna and Aniwa. Reg. Rept. Surv. New Hebrides, 77 pp.
Clarke, D. B., 1970,Tertiary Basalts of Baffin Bay: Possible Primary Magma from the Mantle. Contr. Mineral. Petrol.,25, p. 203–224.
Coffrant, andGirod, M., 1981,Batch Fractionation Model: a Likely Process of Differentiation for the New Hebrides Basaltie Rocks. Bull. Volcanol. (submitted).
—————, —————, andRoca, J. L., 1978,Application de l’analyse en composantes principales à l’étude pétrologique des laves des Nouvelles Hébrides. Bull. Soc. Geol. France,20, p. 503–509.
Colley, andWarden, A. J., 1974,Petrology of the New Hebrides. Geol. Soc. Am. Bull.,85, p. 1635–1646.
Coulon, C., Maillet, andMaury, R. C., 1979,Contribution à l’étude du volcanisme de l’arc des Nouvelles Hebrides: Pétrologie de l’île d’Efaté. Bull. Soc. Geol. France,5, p. 619–629.
Cox, K. G. andBell, 1972,A Crystal Fractionation Model for the Basaltic Rocks of the New Georgia Group, British Solomon Islands. Contr. Mineral. Petrol.,24, p. 1–13.
Dubois, J., 1969,Contribution à l’étude structurale du Sud-Ouest Pacifique. Ann. Geophys.,25, p. 923–972.
————— andLouat, R., 1975,Fossés d’effondrement en arrière de l’arc des Nouvelles Hébrides. Mécanisme proposé. Rev. Geogr. Phys. Geol., Dyn., Paris,17, p. 73–94.
Dugas, F., Carney, J. N., Cassignol, C., Jezek, P. A. andMonzier, 1976,Dredged Rocks along a Cross-section in the Southern New Hebrides Island Arc and Their Bearing on the Age of the Arc. In:Geodynamics in on the Age of the Arc. In:Geodynamics in South-West Pacific, p. 105–116, Technip Editions, Paris.
Eggler, D. H., 1972,Water-saturated and Undersaturated Melting Relations in a Paricutin Andesite and an Estimate of Water Content in the Natural Magma. Contr. Mineral. Petrol.,34, p. 261–271.
Ewart, A., 1976,Mineralogy and Chemistry of Modern Orogenic Lavas: Some Statistics and Implications. Earth Planet. Sci. Letters,31, p. 417–432.
Girod, M., Maury, R. C. andBarsdell, M., 1979,Coexistence de basaltes sursaturés et sous-saturés en silice aux Nouvelles Hébrides: problème de leurs relations génétiques. C.R. Acad. Sci. Paris,288, p. 1355–1358.
Gorton, M. P., 1974,The Geochemistry and Geochronology of the New Hebrides. Ph. D. Thesis, Australian National University, Camberra (unpublished).
—————, 1977,The Geochemistry and Origin of Quaternary Volcanism in the New Hebrides. Geoch. Cosmoch. Acta,41, p. 1257–1270.
Green, T. H., 1972,Crystallization of Calcalkaline Andesite under Controlled Highpressure Hydrous Conditions. Contr. Mineral. Petrol.,24, p. 150–166.
Hamm, H. M. andVieten, K., 1971,Zur Berechnung der kristallchemischen formel und des Fe3+Gehaltes von Klinopyroxen aus Elektronenstrahl Mikroanalysen. N. Jb. Miner. Monath., p. 310–314.
Lacroix, A., 1939,Composition minéralogique et chimique des laves des volcans des îles de l’Océan Pacifique situées entre l’Equateur et le Tropique du Capricorne, le 175° de longitude ouest et de 165° de longitude est. Mem. Acad. Sci. Paris,63, 97 pp.
McBirney, A. R. andNoyes, R. M., 1980,Crystallization and Layering of the Skaergaard Intrusion. J. Petrol.,20, p. 487–554.
Marsh, B. D., 1976,Some Aleutian Andesites: Their Nature and Source. J. Geol.,84, p. 27–45.
Miyashiro, A., 1974,Volcanic Rock Series in Island Arcs and Active Continental Margins. Amer. J. Sci.,274, p. 321–355.
Nisbet, E. A. andPearce, J. A., 1977,Clinopyroxene Composition in Mafic Lavas from different Tectonic Settings. Contrib. Mineral. Petrol.,63, p. 149–160.
O’Hara, M. J., 1965,Primary Magmas and the Origin of Basalts. Scott. J. Geol,1, p. 19–40.
Pearce, J. A., 1976,Statistical Analysis of Major Element Patterns in Basalts. J. Petrol.,17, p. 15–43.
Pringle, G. J., Trembath, L. T. andPajari Jr, C. E., 1974,Crystallization History of a Zoned Plagioclase. Miner. Mag.,39, p. 867–877.
Roca, J. L., 1978,Contribution à l’étude pétrologique et structurale des Nouvelles Hébrides. Thesis, Montpellier University, France (unpublished).
Roeder, P. L. andEmslie, R. F., 1970,Olivineliquid Equilibrium. Contr. Mineral. Petrol.,29, p. 275–289.
Williams, C. E. F. andWarden, A. J., 1964,Table of Chemical Analyses. New Hebrides. Geol. Surv. Prog. Rept., 1959–1962.
Yoder, H. S. andTilley, C. E., 1962,Origin of Basaltic Magmas. An Experimental Study of Natural and Synthetic Rock System. J. Petrol.,3, p. 342–532.
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Coulon, C., Maury, R.C. Petrology of tholeiitic lavas from Tanna Island (New Hebrides): Importance of cumulative processes in Island arc magmatism. Bull Volcanol 44, 661–680 (1981). https://doi.org/10.1007/BF02597090
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DOI: https://doi.org/10.1007/BF02597090