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The generation of small melt-fractions in truncated melt columns: constraints from magmas erupted above slab windows and implications for MORB genesis

Published online by Cambridge University Press:  05 July 2018

Malcolm J. Hole  and
Andy D. Saunders
Malcolm J. Hole
Affiliation:
Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen, AB9 2UE, UK
Andy D. Saunders
Affiliation:
Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH, UK
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Abstract

At a number of locations along the Pacific margin of the Americas and west Antarctica, small volumes of alkalic basalts were erupted following successive ridge crest-trench collisions. The basalts were generated as a result of upwelling of asthenosphere through windows in the subducted plate. There is no evidence for local high temperature mantle plumes or significant lithospheric extension associated with these basalts. For the best sampled area, the Antarctic Peninsula, mean values for fractionation-corrected iron content (FeO*) vary from 6.9 to 10.6 wt.%, and for Na2O (Na8.0) from 3.25 to 4.6 wt.%, implying generation of small melt-fractions at variable mean pressures. The results of rare earth element inversion modelling yield a melt generation interval of 100 to 52 km, with a maximum melt fraction of c. 7% generated from a MORB-like source at Tp 1300°C. Trace element and isotope systematics are also consistent with the generation of the basalts from a MORB-like source.

Mean pressures of melt generation increase with increasing distance from the original trench, but trace element and Na8.0 data suggest that there is no systematic variation in extent of melting with distance from the trench. The data are consistent with a model whereby a MORB melting column, initially intersecting the peridotite solidus at between 15 and 30 kbar, is truncated by a lithospheric cap which thickens from c. 15–20 km (≈ 5–8 kbar) up to a maximum of c. 50 km (≈ 15 kbar), such that the mean pressures of melting increase with increasing distance from the palaeo-trench. The MORB-like major element geochemistry of basalt samples closest to the ancestral trench are consistent with initial intersection of the peridotite solidus at low pressures (c. 15 kbar). For areas of thickest lithosphere, mean pressures of melt generation are higher, but extents of melting are lower than for a MORB melting column with a similar initial pressure of intersection of the peridotite solidus. All these basalts therefore potentially represent analogues for the small melt-fraction precursors to the generation of MOR tholeiites.

Thermal constraints suggest that these low volume, small melt-fractions, were generated with CO2 on the solidus, because mean pressures of melt generation are greater than the pressure of intersection of the Tp 1300°C mantle adiabat and the dry peridotite solidus. Potentially, all MORB may be generated initially with CO2 on the solidus, and if this is correct, it does not require thermal anomalies to generate large extents of melting at high mean pressures.

Keywords

MORBmelting columnsAntarctic PeninsulaREE inversionslab windows
Type
The 1995 Hallimond Lecture
Information
Mineralogical Magazine , Volume 60 , Issue 398 , February 1996 , pp. 173 - 189
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1996

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References

Barker, P.F. (1982) The Cenozoic subduction history of the Pacific margin of the Antarctic Peninsula: ridge crest-trench interactions. J. Geol. Soc. London, 139, 787–801.CrossRefGoogle Scholar
Beattie, P. (1993) Uranium-thorium disequilibria and partitioning on melting of garnet lherzolite. Nature, 363, 63–5.CrossRefGoogle Scholar
Bevier, M.L. (1983) Implications of chemical and isotopic composition for petrogenesis of Chilcotin Group Basalts, British Columbia. J. Petrol, 24, 207–26.CrossRefGoogle Scholar
Brodholt, J.P. and Batiza, R. (1989) Global systematics of unaveraged mid-ocean ridge basalt compositions: Comment on ‘Global correlations of ocean ridge basalt chemistry with axial depth and crustal thickness’ by E.M. Klein and C.H. Langmuir. J. Geophys. Res., 94, 4231–9.CrossRefGoogle Scholar
Chaffey, D.J., Cliff, R.A. and Wilson, B.M. (1989) Characterization of the St Helena magma source. In Magmatism in the ocean basins.(Saunders, A.D. and Norry, M.J., eds.. Spec. Pub. Geol. Soc. London, 42, 313–45.Google Scholar
Chauvel, C., Hofmann, A.W. and Vidal, P. (1992) HIMU-EM: the French Polynesian connection. Earth Planet. Sci. Lett., 110, 99–119.CrossRefGoogle Scholar
Davies, G.R., Norry, M.J., Gerlach, D.C. and Cliff, R.A. (1989) A combined chemical and Pb-Sr-Nd study of the Azores and Cape Verde hotspots: the geodynamic implications. In Magmatism in the ocean basins. (Saunders, A.D. and Norry, M.J., eds.. Spec. Pub. Geol. Soc. London, 42, 231–56.Google Scholar
Dickinson, W.R. and Snyder, W.S. (1979) Geometry of subducted slabs related to the San Andreas transform. J. Geology, 87, 609–27.CrossRefGoogle Scholar
Elliot, T.R., Hawkesworth, C.J. and Gronvold, K. (1991) Dynamic melting of the Iceland plume. Nature, 351, 201–6.CrossRefGoogle Scholar
Fitton, J.G. and Dunlop, H.M. (1985) The Cameroon line, West Africa, and its bearing on the origin of oceanic and continental alkali basalt. Earth Planet. L .72, 23–38.CrossRefGoogle Scholar
Forsythe, R.D. and Nelson, E.P. (1985) Geological manifstations of ridge collision: evidence from the Golfo de Penas-Taito Basin, Southern Chile. Tectonics, 4, 477–495.CrossRefGoogle Scholar
Gill, J.B. (1981) Orogenic andesites and plate tectonics. Berlin: Springer-Verlag.CrossRefGoogle Scholar
Hart, S.R. (1988) Heterogeneous mantle domains: signatures, genesis and mixing chronologies. Earth Planet. Sci. Lett., 90, 273–96.CrossRefGoogle Scholar
Hole, M.J. (1988) Post-subduction alkaline volcanism along the Antarctic Peninsula. J. Geol Soc. London, 145, 985–8.CrossRefGoogle Scholar
Hole, M.J. (1990) Geochemical evolution of Pliocene- Recent post-subduction alkalic basalts from Seal Nunataks, Antarctic Peninsula. J. Volcanoi Geotherm. Res., 40, 149–67.CrossRefGoogle Scholar
Hole, M.J. and Larter, R.D. (1993) Trench proximal volcanism following ridge crest -trench collision along the Antarctic Peninsula. Tectonics, 12, 897–910.CrossRefGoogle Scholar
Hole, M.J., Saunders, A.D., Marriner, G.F. and Tarney, J. (1984) Subduction of pelagic sediments: implications for the origin of Ce-anomalous basalts from the Mariana islands. J. Geol. Soc. London, 141, 453—72.CrossRefGoogle Scholar
Hole, M.J., Rogers, G., Saunders, A.D. and Storey, M. (1991) The relationship between alkalic volcanism and slab-window formation. Geology, 19, 657–60.2.3.CO;2>CrossRefGoogle Scholar
Hole, M.J., Kempton, P.D. and Millar, I.L. (1993) Trace element and isotope characteristics of small degree melts of the asthenosphere; evidence from the alkalic basalts of the Antarctic Peninsula. Chem. Geol., 109, 51–68.CrossRefGoogle Scholar
Hole, M.J., Saunders, A.D., Sykes, M.A. and Rogers, G. (1995) The relationship between alkalic magmatism, lithospheric extension and slab window formation along continental destructive plate margins. I. Volcanism associated with extension along consuming plate margins (Smellie, J.L., ed.) Spec. Pub. Geol. Soc. London, 81, 265—85.Google Scholar
Humler, E., Thirot, J-L. and Montagner, J-P. (1993) Global correlations of mid-ocean ridge basalt chemistry with seismic tomography images. Nature, 364, 225–7.CrossRefGoogle Scholar
Ito, E White, W. M. and Gopel, C. (1987) The O, Sr, Nd and Pb isotope geochemistry of MORB. Chem. Geol., 62, 157–76.CrossRefGoogle Scholar
Johnson, C.M. and O'Neil, J. R. (1984) Triple junction magmatism: a geochemical study of Neogene volcanic rocks in western California. Earth Planet. Sci. Lett., 71, 241–62.CrossRefGoogle Scholar
Klein, E.M. and Langmuir, C.H. (1987) Global correlations of ocean ridge basalt chemistry with axial depth and crustal thickness. J. Geophys. Res., 92, 8089–115.CrossRefGoogle Scholar
Klein, E.M. and Langmuir, C.H. (1989) Local versus global variations in mid-ocean ridge basalt composition: a reply. J. Geophys. Res., 94, 4241–52.CrossRefGoogle Scholar
Larter, R.D. and Barker, P.F. (1991) Effects of ridgecrest trench interaction on Antarctic-Phoenix spreading: forces on a young subducting plate. J. Geophys. Res., 96, 9583-607.Google Scholar
LeMasurier, W.E. and Thomson, J.W. (1990) Volcanoes of the Antarctic Plate and Southern Oceans. American Geophysical Union, Antarctic Research Series, 48, 147—256.Google Scholar
McKenzie, D.P. (1984) The generation and compaction of partially molten rock. J. Petrol, 25, 713–65.CrossRefGoogle Scholar
McKenzie, D.P. (1985a) The extraction of magma from the crust and mantle. Earth Planet. Sci. Lett., 74, 81–91.CrossRefGoogle Scholar
McKenzie, D.P. (1985/7) 230Th-23SU disequlibrium and the melting processes beneath ridge axes. Earth Planet. Sci. Lett., 72, 149–57.CrossRefGoogle Scholar
McKenzie, D.P. and Bickle, M.J. (1988) The volume and composition of melt generated by extension of the lithosphere. J. Petrol, 29, 625–79.CrossRefGoogle Scholar
McKenzie, D.P. and O'Nions, R.K. (1991) Partial melting distributions from inversion of Rare Earth Element concentrations. J. Petrol., 32, 1021–91.CrossRefGoogle Scholar
McKenzie, D.P. and O’Nions, R.K (1995) The source regions of ocean island basalts.. J. Petrol, 36, 133–59.CrossRefGoogle Scholar
Morgan, J.P., and Chen, Y.J. (1993) Dependence of ridge-axis morphology on magma supply and spreading rate. Nature, 364, 706–8.CrossRefGoogle Scholar
Olafsson, M. and Eggler, D.H. (1983) Phase relations of amphibole, amphibole-carbonate and phlogopite- carbonate peridotite: petrologic constraints on the asthenosphere. Earth. Planet. Sci. Lett., 64, 305–15.CrossRefGoogle Scholar
Oxburgh, E.R. (1980) Heat flow and magmagenesis. In Physics of Magmatic Processes (Hargraves, R.B., ed.) New Jersey: Princeton Univ. Press, 161—99.Google Scholar
Palacz, Z.A. and Saunders, A.D. (1986) Coupled trace element isotope enrichment in the Cook-Austral- Samoa islands, southwest Pacific. Earth. Planet. Sci. Lett., 79, 270–80.CrossRefGoogle Scholar
Pearce, J.A. (1983) Role of the sub-continental lithosphere in magma genesis at active continental margins. In Continental Basalts and Mantle Xenoliths. (Hawkesworth, C.J. and Norry, M.J., eds.) Nantwich, England: Shiva Publishing, pp. 230—49.Google Scholar
Ringe, M.J. (1991) Volcanism on Brabant Island, Antarctica. In The geological evolution of Antarctica (Thomson, M.R.A., Crame, J.A. and Thomson, J.W., eds.) Cambridge, England: Cambridge University Press, 515—9.Google Scholar
Rogers, G. and Saunders, A.D. (1989) Magnesian Andesites from Mexico, Chile and the Aleutian Islands: implications for magmatism associated with ridge-trench collisions. In Bonninites and related rocks (Crawford, A.J., ed.) London: Unwin-Hyman, 416–45.Google Scholar
Saunders, A.D., Rogers, G., Marriner, G.F., Terrell, D.J. and Verma, S.P. (1987) Geochemistry of Cenozoic volcanic rocks, Baja California, Mexico: implications for the petrogenesis of post-subduction magmas. J. Volcanol. Geotherm. Res., 32, 223–45.CrossRefGoogle Scholar
Saunders, A.D., Norry, M.J. and Tarney, J. (1988) Origin of MORB and chemically depleted mantle reservoirs: trace element constraints. J. Petrol. Special Lithosphere Issue, 414—45.Google Scholar
Smellie, J.L., Pankhurst, R.J., Hole, M.J.and Thomsom, J.W. (1988) Age, distribution and eruptive conditions of late Cenozoic alkaline volcanism in the Antarctic Peninsula in eastern Ellsworth Land: Review. British Antarctic Survey Bull., 80, 21–49.Google Scholar
Storey, M., Rogers, G., Saunders, A.D. and Terrell, D., (1989) San Quintm volcanic field, Baja California, Mexico: within-plate magmatism following ridge subduction. Terra Nova, 1, 195–202.CrossRefGoogle Scholar
S-S., Sun and McDonough, W.F. (1989) Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. I. Magmatism in the ocean basins (Saunders, A.D. and Norry, M.J., eds.) Spec. Pub. Geol. Soc. London, 42, 313–45.Google Scholar
Thompson, A.B. (1992) Water in the Earth's mantle. Nature, 358, 295–302.CrossRefGoogle Scholar
Thorkelson, D.J. and Taylor, R.P. (1989) Cordilleran slab windows. Geology, 17, 833–6.2.3.CO;2>CrossRefGoogle Scholar
Weaver, B.L. (1991) The origin of ocean island basalt end-member compositions: trace element and isotopic constraints. Earth Planet. Sci. Lett., 382—97.Google Scholar
Wendlandt, R.F. and Mysen, B.O. (1980) Melting phase relations of natural peridotite +CO2 as a function of melting at 15 and 30 kbar. Amer. Mineral., 65, 37–44.Google Scholar
White, R.S., McKenzie, D.P. and O'Nions, R.K. (1992) Oceanic crustal thickness from seismic measurements and rare earth element inversions. J. Geophys. 97, 683—716.CrossRefGoogle Scholar
Wood, D.A., Varet, J., Bougault, H., Corre, O., Joron, J-L., Trueil, M., Bizouard, H., Norry, M.J., Hawkesworth, C.J. and Roddick, J.C. (1978) Transition metal and trace element analyses of Leg 49 samples. Init. Rep. Deep Sea Drill. Proj., 49, 897–902.Google Scholar
Wyllie, P.J. (1982) Subduction products according to experimental predictions. Bull Geol. Soc. America, 93, 468–76.2.0.CO;2>CrossRefGoogle Scholar
Wyllie, P.J. (1987) Discussion on recent papers on carbonated peridotite, bearing on mantle metasomatism and magmatism. Earth Planet. Sci. Lett., 82, 391–7.CrossRefGoogle Scholar