Abstract
Altered variolites described for the first time in the axial zone of the Mid-Atlantic Ridge are represented by rounded globules of andesite (icelandite) composition with light trachyandesite rim embedded in a picrobasaltic matrix. The globules were transferred with picrobasaltic melt and then floated to the surface of lava flow, while formation of leucocratic rims was presumably related to thermodiffusion (Soret effect) in a cooling heterogeneous melt. This heterogeneous melt was formed by penetration of ascending column of picrobasaltic magma in already existing small intracructsal magmatic chamber filled with residual icelanditetype andesite melt and involvement of the latter into a general upward movement. The rapid ascent of the melts in the oceanic spreading zones by means of turbulent flowing caused dispersion of the extragenous melt into small drops in a jet of picrobasaltic magma, without their interaction. Variolites were formed during cooling of such heterogeneous lava flow. No signs of liquid immiscibility were found in the studied variolites.
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References
A. A. Ariskin and G. S. Barmina, Simulation of Phase Equilibria during Crystallization of Basaltic Magmas (Nauka, Moscow, 2000) [in Russian].
G. M. Biggar, “Immiscibility in Tholeiites,” Mineral. Mag. 43(328), 543–544 (1979).
A. A. Borisov, “Experimental Investigation of K and Na Partitioning between Miscible Liquids,” Petrologiya 16(6), 593–605 (2008) [Petrology 16, 552–564 (2008)].
I. S. E. Carmichael, “The Petrology of Thingamuli, a Tertiary Volcano in Eastern Iceland,” J. Petrol. 5 (3), 435–460 (1964).
L. V. Danyshevsky, “The Effect of Small Amounts of H2O on Crystallization of Mid-Ocean Ridge and Back-Arc Basin Magmas,” J. Volcanol. Geotherm. Res. 110, 265–280 (2001).
A. D. Fowler, B. Berger, M. Shore, et al., “Supercooled Rocks: Development and Significance of Varioles, Spherolites, Dendrites and Spinifex in Archaean Volcanic Rocks, Abitibi Greenstone Belt, Canada,” Precambrian Res. 115, 311–328 (2002).
I. C. Freestone, “Immiscibility in Tholeiites,” Mineral. Mag. 43(328), 544–546 (1979).
E. J. Hanski, “Globular Ferropicritic Rocks at Pechenga, Kola Peninsula (Russia): Liquid Immiscibility Versus Alternation,” Lithos 29, 197–216 (1993).
F. Yu. Levinson-Lessing, Selected Works (Akad. Nauk SSSR, Moscow, 1949), Vol. 1 [in Russian].
A. R. Mc Birney, “Differentiation of the Skaergaard Intrusion,” Nature 253, 435–460 (1975).
A. R. Philpotts, “Comments on: Liquid Immiscibility and the Evolution of Basaltic Magma,” J. Petrol. 49(12), 2171–2175 (2008).
A. R. Philpotts, “Composition of Immiscible Liquids in Volcanic Rocks,” Contrib. Mineral. Petrol. 80, 201–218 (1982).
A. R. Philpotts, “Principles of igneous and metamorphic petrology,” (Cambridge, University Press, Prentice-Hall, 1990).
Yu. M. Pushcharovskii, S. G. Skolotnev, A. A. Peive, et al., Geology and Metallogeny of the Mid-Atlantic Ridge: 5–7°N (GEOS, Moscow, 2004) [in Russian].
E. Redder, “Silicate Liquid Immiscibility,” in The Evolution of Igneous Rocks: Fiftieth Anniversary Perspectives Ed. by H. S. Yoder (Princeton Univ. Press, Princeton, (Mir, Moscow, 1983), pp. 15–57 [in Russian].
E. Roedder, “Low Temperature Liquid Immiscibility in the System K2O-FeO-Al2O3-SiO2,” Am. Mineral. 36, 282–286 (1951).
E. Roedder and P. W. Weiblen, “Lunar Petrology of Silicate Melt Inclusion, Apollo 11 Rocks,” Geochim. Cosmochim. Acta. Suppl. 1. Proc. Apollo 11 Lunar Sci. Conf., 801–837 (1970).
E. Roedder and P. W. Weiblen, “Petrology of Silicate Melt Inclusion, Apollo 11 and Apollo 12, and Terrestrial Equivalents,” Geochim. Cosmochim. Acta. Suppl. 2, Proc. Second Lunar Sci. Conf. 507–528 (1971).
J.-G. Schilling, B. B. Hanan, B. McCully, and R. H. Kingsley, “Influence of the Sierra Leone Mantle Plume on the Equatorial MAR: a Nd-Sr-Pb Isotopic Study,” J. Geophys. Res. 99, 12005–12028 (1994).
U. Schreiber, D. Anders, and J. Koppen, “Mixing and Chemical Interdiffusion of Trachytic and Latitic Magma in a Subvolcanic Complex of the Tertiary Westerwald (Germany),” Lithos 46, 695–714 (1999).
E. V. Sharkov, K. N. Shatagin, I. S. Krasivskaya, et al., “Pillow Lavas of the Sierra Leone Test Site, Mid-Atlantic Ridge, 5–7°N: Sr-Nd Isotope Systematics, Geochemistry, and Petrology,” Petrologiya, No. 4, 356–375 (2008) [Petrology 16, 335–352 (2008)].
E. V. Sharkov, N. S. Bortnikov, O. A. Bogatikov, et al., “Third Layer of the Oceanic Crust in the Axial Part of the Mid-Atlantic Ridge (Sierra Leone MAR Segment, 6°N),” Petrologiya 13(6), 592–625 (2005) [Petrology 13, 540–570 (2005)].
V. A. Simonov, E. V. Sharkov, and S. V. Kovyazin, “Petrogenesis of the Fe-Ti Intrusive Complexes in the Sierra Leone Region, Central Atlantic,” Petrologiya 17(5), 521–538 (2009) [Petrology 17, 488–502 (2009)].
V. F. Smol’kin, Komatiitic and Picritic Magmatism of the Early Precambrian of the Baltic Shield (Nauka, St. Petersburg, 1992) [in Russian].
R. S. J. Sparks and L. Marshall, “Thermal and Mechanical Constraints on Mixing between Mafic and Silicic Magmas,” J. Volcanol. Geotherm. Res. 29, 99–124 (1986).
S. A. Svetov, Magmatic Systems of the Ocean-Continent Transition Zone in the Archean of the Eastern Fennoscandian Schield (Kar. Nauchn. Ts. RAN, Petrozavodsk, 2005) [in Russian].
S. A. Svetov, “Liquid Immiscible Differentiation in the Basaltic Systems by the Example of the Suisarian Variolites of the Yalguba Range,” in Geology and Mineral resources of Karelia, Ed. by A. I. Golubev (Kar. Nauchn. Ts. RAN, Petrozavodsk, 2008) [in Russian].
I. V. Veksler, A. M. Dorfman, A. A. Borisov, et al. “Liquid Immiscibility and the Evolution of Basaltic Magma,” J. Petrol. 48(11), 2187–2210 (2007).
D. Walker and S. E. DeLong, “Soret Separation of Mid-Ocean Ridge Basalt Magma,” Contrib. Mineral. Petrol. 79, 231–240 (1982).
E. B. Watson, “Basalt Contamination by Continental Crust: Some Experiments and Model,” Contrib. Mineral. Petrol. 80, 73–87 (1982).
A. N. Zavaritskii and V. S. Sobolev, Physicochemical Principles of Petrography of Igneous Rocks (Gosgeoltekhizdat, Moscow, 1961) [in Russian].
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Original Russian Text © I.S. Krassivskaya, E.V. Sharkov, N.S. Bortnikov, A.V. Chistyakov, N.V. Trubkin, T.I. Golovanova, 2010, published in Petrologiya, 2010, Vol. 18, No. 3, pp. 282–296.
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Krassivskaya, I.S., Sharkov, E.V., Bortnikov, N.S. et al. Variolitic lavas in the axial rift of the Mid-Atlantic Ridge and their origin (Sierra Leone area, 6°18′N). Petrology 18, 263–277 (2010). https://doi.org/10.1134/S0869591110030045
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DOI: https://doi.org/10.1134/S0869591110030045