Abstract
An investigation of glassy volcanics erupted within the last ten-million years along various segments of the mid-Atlantic Ridge and the East Pacific Rise has revealed major crustal compositional changes. The available data from the mid-Atlantic Ridge shows the existence of two petrological provinces: One, located between latitudes 33° and 53° N, is characterized by volcanics which have a tendency to be oversaturated ocean ridge basalts (OSORB) with respect to normative quartz; the second group of rocks, found between 25° S and 33° N, is generally composed of saturated ocean ridge basalts (SORB). In addition, the SORB volcanics have higher TiO2 (1.7±0.3%), higher Na2O (2.8±0.2%) and higher FeO*/MgO (1.36±0.2) values than do the OSORB types (with 1.1±0.2%, 2.2±0.2% and 1.22±0.2 for the TiO2, Na2O, and FeO*/MgO respectively), There is a correlation between the rate of crustal spreading and the compositional changes observed on the volcanics erupted along various segments of oceanic ridges. Slow-accreting plate boundaries having a total spreading rate of 2–3 cm/year are characterized by a low TiO2 content (1.1±0.2%), low FeO*/ MgO ratio (1.22±0.2) and a high an/an+ab ratio (0.62±0.05). Segments of fast-spreading ridges (total rate 11–13 cm/year) show a higher range of TiO2 (2.1±0.4%) and FeO*/MgO (1.6±0.4) and a lower range of the an/an + ab ratio (0.5±0.07). Ridge segments with a total spreading rate of 5–9 cm/year con sist of volcanics having intermediate values for the above parameters. Different degrees of partial melting of rising mantle material are suggested as a possible mechanism for explaining the compositional diversities encountered along oceanic ridge systems.
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References
Arcyana: Transform fault and rift valley from bathyscaphe and diving saucer. Science 190, 108–116 (1975)
Atwater, T.: Implications of plate tectonics for the Cenozoic tectonic evolution of western North America. Bull. Geol. Soc. Am. 81, 3513–3536 (1970)
Aumento, F.: Magmatic evolution on the mid-Atlantic Ridge. Earth Planet. Sci. Lett. 2, 225–230 (1967)
Aumento, F.: The mid-Atlantic Ridge near 45° N. Basalts from the area of Confederation. Peak. Can. J. Earth Sci. 5, 1–21 (1968)
Aumento, F.: Diorites from the mid-Atlantic Ridge at 45° N, Science 165, 1112 (1969)
Batiza, R., Rosendahl, B.R., Fisher, R.L.: Evolution of oceanic crust 31. Petrology and chemistry of basalts from the East-Pacific Rise and the Siqueiros transform fault. J. Geophys. Res. 81, 265 (1977)
Bence, A.E., Taylor, S.R.: Petrogenesis of mid-Atlantic Ridge basalts at DSDP Leg 37, holes 332A and 332B from major and trace elements geochemistry. Initial report, DSDP Leg 37. Washington, D.C.: US Government Printing Office p. 705–710, 1977
Bender, J.F., Hodge, F.N., Bence, A.E.: Petrogenesis of basalts from the project FAMOUS area: Experimental study from 0 to 15 kbars. Earth Planet. Sci. Lett. 41, 277–302 (1977)
Bougault, H., Hekinian, R.: Rift valley in the Atlantic Ocean near 36°50′N: petrology and geochemistry of basaltic rocks. Earth Planet. Sci. Lett. 24, 249 (1974)
Bougault, H., Treuil, M.: Mid-Atlantic-ridge: zero-age geochemical variations between Azores and 22° N (in preparation)
Bryan, W.B., Moore, J.G.: Compositional variations of young basalts in the mid-Atlantic ridge rift valley near lat. 36°49′N. Bull. Geol. Soc. Am. 88, 556 (1977)
Bryan, W.B., Thompson, G.: Basalts from DSDP Leg 37 and the Famous area: Compositional and petrogenetic comparisons. Can. J. Earth Sci. 14, 875 (1977)
Corliss, J.B.: Mid-ocean ridge basalts. Ph.D. thesis, Scripps Institute of Oceanography, La Jolla, California (1970)
Cyamex: First manned submersible dives on the East Pacific Rise, 21° N (Project RITA): General results. Marine, Geophys. Res., in press (1980)
Dickey, J.S., Jr., Frey, F.A., Hart, S.R., Watson, B.B., Thompson, G.: Geochemistry and petrology of dredged basalts from the Bouvet triple junction, South-Atlantic. Geochim. Cosmochim. Acta 41, 1105–1118 (1977)
Dimitriev, L., Aumento, F.: Geochemical characteristics and evolution of basalts from DSDP, site 332. Can. J. Earth Sci. 14, 899 (1976)
Engel, A.E.J., Engel, C.G.: Igneous rocks of the East Pacific Rise. Science 146, 477 (1964)
Engel, A.E.J., Engel, C.G.: Composition of basalts from the mid-Atlantic Ridge. Science 144, 1330–1333 (1964)
Engel, A.E.J., Engel, C.G., Havens, R.G.: Chemical characteristics of oceanic basalts and the upper mantle. Geol. Soc. Am. Bull. 76, 719 (1965)
Frey, F.A., Bryan, W.B., Thompson, G.: Atlantic ocean floor: Geochemistry and petrology of basalts from Legs 2 and 3 of the Deep Sea Drilling Project. J. Geophys. Res. 79, 5507 (1974)
Green, D.H., Ringwood, A.E.: Mineralogy of peridotitic compositions under upper mantle conditions. Phys. Earth Planet. Inter. 3, 359 (1970)
Hekinian, R., Moore, J.G., Bryan, W.B.: Volcanic rocks and processes of the mid-Atlantic Ridge rift valley near 36°49′N. Contrib. Mineral. Petrol. 58, 83–110 (1976)
Kudo, A.M., Weill, D.F.: An igneous plagioclase thermometer. Contrib. Mineral. Petrol. 25, 52 (1969)
Kushiro, I.: The system diopside — forsterite — enstatite. Carnegie Inst. Washington Yearb. 101–108 (1963)
Melson, W.G., Byerly, G.R., Nelen, J.A., O'Hearn, T., Wright, T.L., Vallier, T.: A catalog of the major element chemistry of abyssal volcanic glasses. Smithson. Contrib. Earth. Sci 19, 31 (1977)
Melson, W.G., O'Hearn, T.: Basaltic glass erupted along the mid-Atlantic-ridge between 0–37° N: relationship between composition and latitude. In: Deep drilling results in the Atlantic Ocean: ocean crust (M. Talwani, C.G. Harrison, D.E. Hayes, eds.). Am. Geophys. Union, p. 249–261 (1979)
Minster, J.B., Jordan, T.H., Molnar, P., Haines, E.: Numerical modelling of instantaneous plate tectonics. Geophys. J. R. Astr. Sci. 36, 541–576 (1974)
Miyashiro, A., Shido, F., Ewing, M.: Diversity and origin of abyssal tholeiite from the mid-Atlantic Ridge near 24° and 30° N latitude. Contrib. Mineral. Petrol. 23, 38 (1969)
Miyashiro, A., Shido, F., Ewing, M.: Crystallization and differentation in abyssal tholeiites and gabbros from mid-oceanic ridges. Earth. Planet. Sci. Lett. 7, 361–365 (1970)
Moore, J.G., Schilling, J.G.: Vesicles, water and sulfur in Reykjanes ridge basalts. Contrib. Mineral. Petrol. 41, 105–118 (1973)
Moore, J.G., Normark, W.R., Hess, G.R., Meyer, C.E.: Petrology of basalt from the East-Pacific Rise near 21° north latitude. J. Res. US Geol. Survey 5–6, 753 (1977)
Morel, J.M.: Evolution magmatique le long des dorsales médio-Atlantique et Est-Pacifique. Thèse 108, Université de Bretagne Occidentale et Centre Océanologique de Bretagne. Brest, France (1979)
Muir, I.D., Tilley, C.E.: Basalts from the northern part of the mid-Atlantic ridge. J. Petrol. 7, 193–201 (1966)
Natland, J.H., Melson, W.G.: Composition of basaltic glasses from the East-Pacific Rise and Siqueiros fracture zone, near 9° N. DSDP 54 (in press 1980)
Nicholls, G.D.: Basalts from the deep ocean floor. Mineral. Mag. 34(1965)
Pitman, W.C., Larson, R.L., Herron, E.M.: The age of the ocean basins. Geol. Soc. Am. Charts (1974)
Reay, A., Harris, P.G.: The partial fusion of peridotite. Bull. Volcanol. 27, 115–127 (1964)
Rhodes, J.M., Dungan, M.A., Blanchard, D.P. Long, P.E.: Magma mixing at mid-ocean ridges: Evidence from basalts drilled near 22° N on the mid-Atlantique Ridge. Tectonophysics 55, 35–61 (1979)
Roeder, P.L., Emslie, R.F.: Olivine-liquid equilibrium. Contrib. Mineral. Petrol 29, 275–289 (1970)
Scheidegger, K.F.: Temperatures and compositions of magmas ascending along mid-ocean ridges. J. Geophys. Res. 78, 3340 (1973)
Schilling, J.G.: Iceland mantle plume: Geochemical evidence along Reykjanes ridge. Nature 242, 565 (1973)
Schrader, E.L., Furbish, W.J.: Mineralogy and geochemistry of ore minerals from basalt related to spreading centers of the Eastern Pacific with speculations on ore forming processes. DSDP 54 (in press 1980)
Shibata, T.: Phenocryst-bulk rock composition relations of abyssal tholeiites and their petrogenetic significance. Geochim. Cosmochim. Acta 40, 1407 (1976)
Shibata, T., Fox, P.J.: Fractionation of abyssal tholeiites: Samples from the oceanographer fracture zone (35° N, 35° W). Earth. Planet. Sci. Lett. 27, 62 (1975)
Shido, F., Miyashiro, A.: Compositional difference between abyssal tholeiites from north and south of the Azores on the mid-Atlantic Ridge. Nature (Lond.) Phys. Sci. 245, 59–60 (1973)
Sigurdsson, H., Schilling, J.G.: Spinels in mid-Atlantic Ridge basalts: Chemistry and occurrence. Earth Planet. Sci. Lett. 29, 7 (1976)
Walker, D., Shibata, T., Delong, S.E.: Fractionation and mixing in oceanographer fracture zone basalts (in press 1980)
White, W.N., Schilling, J.G.: The nature and origin of geochemical variation in mid-Atlantic Ridge basalts from the central North Atlantic. Geochim. Cosmochim. Acta 42, 1501–1516 (1978)
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Contribution n∘ 677 du Département de Géophysique, Géologie, Géochimie Marines du C.O.B.
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Morel, J.M., Hekinian, R. Compositional variations of volcanics along segments of recent spreading ridges. Contr. Mineral. and Petrol. 72, 425–436 (1980). https://doi.org/10.1007/BF00371349
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DOI: https://doi.org/10.1007/BF00371349