Abstract
Serpentinites occur in transverse fracture zones and adjacent areas in the Mid-Atlantic Ridge near 24° and 30° N. In two fracture zones, about 700 km distant from each other, serpentinites show practically the same trend and range of variation in chemical composition. Their CaO content ranges from 2.05 to 0.07% by weight. Serpentinites relatively high in CaO content contain pargasite, whereas those relatively low in CaO do not. Serpentinites relatively high in CaO are chemically similar to high-temperature peridotites which are widely believed to have been derived from the upper mantle. With a decrease in CaO, the Al2O3, TiO2, K2O and FeO contents and the Fe/Mg ratio tend to decrease, whereas the H2O+ content tends to increase. This compositional variation is probably due partly to heterogeneity of uper mantle peridotite from which the serpentinites were derived, and partly to chemical migration during serpentinization. The interior of the Mid-Atlantic Ridge may be mainly made up of serpentinites. Alternatively, the Mid-Atlantic Ridge Serpentinites may have been formed by serpentinization of peridotites that were intruded into fracture zones from a great depth.
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References
Bonatti, E.: Ultramafic rocks from the Mid-Atlantic Ridge. Nature 219, 363–364 (1968).
Bowen, N. L., and O. F. Tuttle: The system MgO-SiO2-H2O. Geol. Soc. Am. Bull. 60, 439–460 (1949).
Bowin, C. O., A. J. Nalwalk, and J. B. Hersey: Serpentinized peridotite from the north wall of the Puerto Rico Trench. Geol. Soc. Am. Bull. 77, 257–270 (1966).
Boyd, F. R.: Hydrothermal investigations of amphiboles. In: Researches in geochemistry (ed. P. H. Abelson), p. 377–396. New York: John Wiley 1959.
Chernysheva, V. I., and P. L. Bezrukov: Serpentinite from the crest of the Indo-Arabian Ridge. Dokl. Akad. Nauk S.S.S.R. 166, English adeition 207–210 (1966).
Dietz, R. S.: Ocean-basin evolution by sea-floor spreading. In: Continental drift (ed. S. K. Runcorn), p. 289–298. New York and London: Academic Press 1962.
Ewing, M.: Exploring the Mid-Atlantic Ridge. Nat. Geogr. Mag. 94, 275–294 (1948).
Green, D. H.: The petrogenesis of the high-temperature peridotite intrusion in the Lizard area, Cornwall. J. Petrol. 5, 134–188 (1964a).
—: The metamorphic aureole of the peridotite at the Lizard, Cornwall. J. Geol. 72, 543–563 (1964b).
—: High-temperature peridotite intrusions. In: Ultramafic and related rocks (ed. P. J. Wyllie), p. 212–222. New York: John Wiley 1967.
Harris, P. G., A. Reay, and I. G. White: Chemical composition of the upper mantle. J. Geophys. Res. 72, 6359–6369 (1967).
Hekinian, R.: Rocks from the mid-oceanic ridge in the Indian Ocean. Deep-Sea Res. 15, 195–213 (1968).
Hess, H. H.: The oceanic crust. J. Marine Res. 14, 423–439 (1955).
— History of ocean basins. In: Petrologic studies: Buddington Volume (ed. A. E. J. Engel, H. L. James, and B. F. Leonard), p. 599–620. Geol. Soc. of America 1962.
—: The oceanic crust, the upper mantle and the Mayaguez serpentinized peridotite. In: A study of serpentinite (ed. C. A. Burk). National Acad. Sci.-National Res. Coun., Washington, D. C., Publ. No. 1188, 1964, p. 169–175.
Johannes, W.: Experimental investigation of the reaction forsterite + H2O ⇌ serpentine + brucite. Contr. Mineral. and Petrol. 19, 309–315 (1968).
Kitahara, S., and G. C. Kennedy: The calculated equilibrium curves for some reactions in the system MgO-SiO2-H2O at pressures up to 30 kilobars. Am. J. Sci. 265, 211–217 (1967).
Melson, W. G., E. Jarosewich, V. T. Bowen, and G. Thompson: St. Peter and St. Paul Rocks: a high-temperature, mantle-derived intrusion. Science 155, 1532–1535 (1967).
Miyashiro, A., F. Shido, and M. Ewing: Petrologic models for the Mid-Atlantic Ridge. Deep-Sea Res., in press (1969).
Olsen, E.: Equilibrium calculations in the system Mg, Fe, Si, O, H and Ni. Am. J. Sci. 261, 943–956 (1963).
Page, N. J.: Serpentinization considered as a constant volume metasomatic process: a discussion. Am. Mineralogist 52, 545–549 (1967).
— and R. G. Coleman: Serpentine-mineral analyses and physical properties. U. S. Geol. Surv. Profess. Paper 575-B, B103-B107 (1967).
Shand, S. J.: Rocks of the Mid-Atlantic Ridge. J. Geol. 57, 89–92 (1949).
Tilley, C. E.: The dunite-mylonites of St. Paul's Rocks (Atlantic). Am. J. Sci. 245, 483–491 (1947).
—: A note on the dunite (peridotite) mylonites of St. Paul's Rocks (Atlantic). Geol. Mag. 103, 120–123 (1966).
Tolstoy, I., and M. Ewing: North Atlantic hydrography and the Mid-Atlantic Ridge. Geol. Soc. Am. Bull. 60, 1527–1540 (1949).
Whittaker, E. J. W., and J. Zussman: The characterization of serpentine minerals by X-ray diffraction. Mineral Mag. 31, 107–125 (1956).
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Lamont-Doherty Geological Observatory Contribution No. 1354.
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Miyashiro, A., Shido, F. & Ewing, M. Composition and origin of serpentinites from the Mid-Atlantic Ridge near 24° and 30° North Latitude. Contr. Mineral. and Petrol. 23, 117–127 (1969). https://doi.org/10.1007/BF00375173
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DOI: https://doi.org/10.1007/BF00375173