Portal de Periódicos da CAPES

Rare-Earth variations across ‘normal segments’ of the Reykjanes Ridge, 60°-53°N, Mid-Atlantic Ridge, 29°S, and East Pacific Rise, 2°-19°S, and evidence on the composition of the underlying low-velocity layer

1975; American Geophysical Union; Volume: 80; Issue: 11 Linguagem: Inglês

10.1029/jb080i011p01459

2156-2202

J.‐G. Schilling,

earthquake and tectonic studies

Journal of Geophysical Research (1896-1977)Volume 80, Issue 11 p. 1459-1473 Rare-Earth variations across 'normal segments' of the Reykjanes Ridge, 60°–53°N, Mid-Atlantic Ridge, 29°S, and East Pacific Rise, 2°–19°S, and evidence on the composition of the underlying low-velocity layer J.-G. Schilling, J.-G. SchillingSearch for more papers by this author J.-G. Schilling, J.-G. SchillingSearch for more papers by this author First published: 10 April 1975 https://doi.org/10.1029/JB080i011p01459Citations: 155AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat Abstract Supplement is available with entire article on microfiche. Order from American Geonhvsical Union, 1909 K Street, N.W., Washington, D.C. 20006. Document J75-002; $1.00. Payment must accompany order. Rare-earth (RE) abundance patterns in 26 basalts occurring across normal segments of the Reykjanes ridge, 60°–53°N; the mid-Atlantic ridge, 29°S (Deep-Sea Drilling Project leg 3); and the East Pacific rise, 2°–19°S, including the Nazca plate, are reported. Without exception, all the RE patterns were found to be characteristically light RE depleted, reflecting to a first-order approximation, a mantle source with uniquely defined RE content. Computer multiphase and eutectic, equilibrium-partial melting models show that the reconstituted RE pattern of the mantle underlying these regions must be more depleted in light RE than the basalts generated. This is so whether a lherzolite (spinel free or bearing), garnet peridotite, or plagioclase peridotite is considered for the primary mantle source. The source is thought to be the low velocity layer apparently depleted in light RE and other large ionic lithophile elements. A lherzolite phase assemblage is found to be preferable for the depleted low-velocity layer source under normal midocean ridge segments at a depth greater than 30–38 km. Above 30–38 km, equilibration of normal ridge basalts with a plagioclase peridotite cannot be ruled out. Rare-earth results across these three normal ridge segments further emphasize (1) the spatial and temporal RE uniformity of the depleted low-velocity layer source, (2) the widespread geographic coverage of this mantle source, (3) its RE composition contrast with mantle source regions, such as those beneath Iceland, the Azores, and the Afar, which have been assumed to represent rising plumes (or blobs), and finally (4) the passive nature of volcanism along normal ridge segments occurring in response to the spreading as a simple 'healing' process. Supporting Information Supporting Information. Filename Description jgr13358-sup-0001-TablesandAppendices.pdf278.2 KB Supporting info item Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. References Anderson, R. N., D. P. McKenzie, J. G. Sclater, Gravity, bathymetry and convection in the earth, Earth Planet. Sci. Lett., 18, 391–407, 1973. 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, 2, Basalts from the area of Confederation peak, Can. J. Earth Sci., 5, 1–21, 1968. Bass, M. N., Variable abyssal basalt populations and their relation to sea floor spreading rates, Earth Planet. Sci. Lett., 11, 18–22, 1971. Bass, M. N., Occurrence of transitional abyssal basalt, Lithos, 5, 57–67, 1972. Bonatti, E., Palagonite, hyaloclastites and alteration of volcanic glass in the ocean, Bull. Volcanol., 28, 1–15, 1965. Bonatti, E., Deep sea volcanism, Naturwissenschaften, 57, 379–384, 1970. Bonatti, E., D. E. Fisher, Oceanic basalts: Chemistry versus distance from oceanic ridges, Earth Planet. Sci. Lett., 11, 307–311, 1971. Campsie, J., J. C. Bailey, M. Rasmussen, F. Dittmer, Chemistry of tholeiites from the Reykjanes ridge and Charlie Gibbs fracture zone, Nature Phys. Sci., 244, 71–73, 1973. Coryell, C. D., J. W. Chase, J. W. Winchester, A procedure for geochemical interpretation of terrestrial rare-earth abundance patterns, J. Geophys. Res., 68, 559–566, 1963. Davis, B. T. C., J. F. Schairer, Melting relations in the join diopside-forsterite-pyrope at 40 kilobars and one atmosphere, Carnegie Inst. Washington Yearb., 64, 123–126, 1965. Dickson, G. O., W. C. Pitman, J. R. Heirtzler, Magnetic anomalies in the South Atlantic and ocean floor spreading, J. Geophys. Res., 73, 2087–2100, 1968. Dudas, M. J., R. A. Schmitt, M. E. Harward, Trace element partitioning between volcamc plagioclase and dacitic pyroclastic matrix, Earth Planet. Sci. Lett., 11, 440–446, 1971. Fisher, D. E., Fission track ages of deep sea glasses, Nature, 221, 549–550, 1969. Fisher, D. E., E. Bonatti, O. Joensuu, J. Funkhouser, Ages of Pacific deep-sea basalts, and spreading of the sea floor, Science, 160, 1106–1107, 1968. Forsyth, D. W., F. Press, Geophysical tests of petrological models of the spreading lithosphere, J. Geophys. Res., 76, 7963–7978, 1971. Francis, T. J. G., The seismicity of the Reykjanes ridge, Earth Planet. Sci. Lett., 18, 119–124, 1973. Frey, F. A., Rare earth abundances in a high temperature peridotite intrusion, Geochim. Cosmochim. Acta, 38, 1429–1447, 1969. Frey, F. A., L. A. Haskin, M. A. Haskin, Rare-earth abundances in some ultramafic rocks, J. Geophys. Res., 76, 2057–2070, 1971. Frey, F. A., W. B. Bryan, G. Thompson, S. Roy, Petrological and geochemical results for basalts from DSDP legs 2 and 3 (abstract), Eos Trans. AGU, 54, 1004–1006, 1973. Gast, P. W., Trace element fractionation and the origin of tholeiitic and alkaline magma types, Geochim. Cosmochim. Acta, 32, 1057–1086, 1968. Green, D. H., Composition of basaltic magmas as indicators of conditions of origin: Application to oceanic volcanism, Phil. Trans. Roy. Soc. London, Ser. A, 268, 707–725, 1971. Green, D. H., W. Hibberson, The instability of plagioclase in peridotite at high pressure, Lithos, 3, 209–221, 1970. Hart, S. R., K, Rb, Cs, Sr and Ba contents and Sr isotope ratios of ocean floor basalts, Phil. Trans. Roy. Soc. London, Ser. A, 268, 573–587, 1971. Hart, S. R., J.-G. Schilling, J. L. Powell, Basalts from Iceland and along the Reykjanes ridge: Sr isotope geochemistry, Nature Phys. Sci., 246, 104–107, 1973. Haskin, L. A., F. A. Frey, R. A. Schmitt, R. H. Smith, Meteoritic, solar and terrestrial rare-earth distributions, Physics and Chemistry of the Earth, 7 L. H. Ahrens, F. Press, S. K. Runcorn, H. C. Urey, 167–321, Pergamon, London, 1966. Hermance, J. F., L. R. Grillot, Constraints on temperatures beneath Iceland from magnetotelluric data, Phys. Earth Planet. Interiors, 8, 1–12, 1974. Herron, E. M., Sea-floor spreading and the Cenozoic history of the east-central Pacific, Geol. Soc. Amer. Bull., 83, 1671–1692, 1972. Herzberg, C. T., Stability fields of plagioclase- and spinel-lherzolite, Progress in Experimental Petrology, Publ. Ser. D, 2 C. M. B. Henderson, D. L. Hamilton, 145, Natural Environment Research Council, London, 1972. Kay, R., N. J. Hubbard, P. W. Gast, Chemical characteristics and origin of oceanic ridge volcanic rocks, J. Geophys. Res., 75, 1585–1613, 1970. Krause, D. C., J-G. Schilling, Dredged basalt from the Reykjanes ridge, North Atlantic, Nature, 224, 791–793, 1969. Maxwell, A. E., R. P. Von Herzen, K. J. Hsu, J. E. Andrews, T. Saito, S. F. Percival Jr., E. D. Milow, R. E. Boyce, Deep sea drilling in the South Atlantic, Science, 168, 1047–1059, 1970. McBirney, A. R., I. G. Gass, Relations of oceanic volcanic rocks to midoceanic rises and heat floor, Earth Planet. Sci. Lett., 2, 265–276, 1967. Montigny, R., H. Bougault, Y. Bottinga, C. J. Allegre, Trace element geochemistry and genesis of the Pindos ophiolite suite, Geochim. Cosmochim. Acta, 37, 2135–2147, 1973. Moore, J. G., Rate of palagonitization of submarine basalt adjacent to Hawaii, U.S. Geol. Surv. Prof. Pap., 550-D, 163–171, 1966. Morgan, W. J., Convection plumes in the lower mantle, Nature, 230, 42–43, 1971. Morgan, W. J., Deep mantle convection plumes and Plate motions, Amer. Ass. Petrol. Geol. Bull., 56, 203–213, 1972. O'Hara, M. J., Non-primary magmas and dubious mantle plume beneath Iceland, Nature, 243, 507–508, 1973. Philpotts, J. A., C. C. Schnetzler, Speculations on the genesis of alkaline and sub-alkaline basalts following exodus of the continental crust, Can. Mineral., 10, 375–379, 1970. Philpotts, J. A., C. C. Schnetzler, S. R. Hart, Submarine basalts: Some K, Rb, Sr, Sr, Ba, rare-earth, H2O, and CO2 data bearing on their alteration, modification by plagioclase, and possible source materials, Earth Planet. Sci. Lett., 7, 293–299, 1969. Philpotts, J. A., C. C. Schnetzler, H. H. Thomas, Petrogenetic implications of some new geochemical data on eclogitic and ultrabasic inclusions, Geochim. Cosmochim. Acta, 36, 1131–1166, 1972. Presnall, D. C., The geometrical analysis of partial fusion, Amer. J. Sci., 267, 1178–1194, 1969. Rea, D. K., J. Dymond, G. R. Heath, D. F. Heinrich, S. H. Johnson, D. M. Hussong, New estimates of rapid sea-floor spreading rates and the identification of young magnetic anomalies on the East Pacific rise, 6° and 11°S, Earth Planet. Sci. Lett., 19, 225–229, 1973. Ridley, W. I., N. D. Watkins, D. J. MacFarlane, The oceanic islands: Azores, Ocean Basins and Margins, 2 F. Stehli, A. E. M. Nairn, 443–481, Plenum, New York, 1973. Scheidegger, K. F., Temperatures and compositions of magmas ascending along midocean ridges, J. Geophys. Res., 78, 3340–3355, 1973. Schilling, J.-G., Red Sea floor origin: Rare-earth evidence, Science, 165, 1357–1370, 1969. Schilling, J.-G., Sea-floor evolution: Rare-earth evidence, Phil. Trans. Roy. Soc. London, Ser. A, 268, 663–706, 1971. Schilling, J.-G., Iceland mantle plume: Geochemical study of Reykjanes ridge, Nature, 242, 565–571, 1973a. Schilling, J.-G., Afar mantle plume: Rare earth evidence, Nature Phys. Sci., 242, 2–5, 1973b. Schilling, J.-G., Iceland mantle plume, Nature, 246, 141–143, 1973c. Schilling, J.-G., E. Bonatti, East Pacific ridge (2°S-19°S) versus Nazca intraplate volcanism: Rare earth evidence, Earth Planet. Sci. Lett., 1975. Schilling, J.-G., J. W. Winchester, Rare-earth fractionation and magmatic processes, Mantles of the Earth and Terrestrial Planets S. K. Runcorn, 267–283, Interscience, New York, 1967. Schilling, J.-G., J. W. Winchester, Rare earth contribution to the origin of Hawaiian lavas, Contrib. Mineral. Petrol., 23, 27–37, 1969. Schnetzler, C. C., J. A. Philpotts, Partition coefficients of rare-earth elements between igneous matrix material and rock-forming mineral phenocrysts, 2, Geochim. Cosmochim. Acta, 34, 331–340, 1970. Sclater, J. G., R. N. Anderson, M. L. Bell, Elevation of ridges and evolution of the central eastern Pacific, J. Geophys. Res., 76, 7888–7915, 1971. Shaw, D. M., Trace element fractionation during anatexis, Geochim. Cosmochim. Acta, 34, 237–243, 1970. Talwani, M., C. C. Windisch, M. G. Langseth Jr., Reykjanes ridge crest: A detailed geophysical study, J. Geophys. Res., 76, 473–517, 1971. Tatsumoto, M., Isotopic composition of lead in volcanic rocks from Hawaii, Iwo Jima, and Japan, J. Geophys. Res., 71, 1721–1733, 1966a. Tatsumoto, M., Genetic relations of oceanic basalts as indicated by lead isotopes, Science, 153, 1094–1101, 1966b. Vogt, P. R., Asthenosphere motion recorded by the ocean floor south of Iceland, Earth Planet. Sci. Lett., 13, 153–160, 1971. Vogt, P. R., O. E. Avery, Detailed magnetic surveys in the northeast Atlantic and Labrador Sea, J. Geophys. Res., 79, 363–389, 1974. Vogt, P. R., G. L. Johnson, A longitudinal seismic reflection profile of the Reykjanes ridge, 2, Implications for the mantle hot spot hypothesis, Earth Planet. Sci. Lett., 18, 49–58, 1973. Vogt, P. R., E. D. Schneider, G. L. Johnson, The crust and upper mantle beneath the sea, The Earth's Crust and Upper Mantle, Geophys. Monogr. Ser., 13 P. J. Hart, 556–617, AGU, Washington, D. C., 1969. Yoder Jr., H. S., C. E. Tilley, Origin of basaltic magmas: An experimental study of natural and synthetic rock systems, J. Petrol., 3, 342–532, 1962. Citing Literature Volume80, Issue11Solid Earth and Planets10 April 1975Pages 1459-1473 ReferencesRelatedInformation