Silicic Fe-Ti-oxide series of slow-spreading ridges: petrology, geochemistry, and genesis with reference to the Sierra Leone segment of the Mid-Atlantic Ridge axial zone at 6^o

Abstract

[1]  Silicic Fe-Ti-oxide magmatic series was first recognized in the Sierra Leone axial segment of the MAR near 6^o N. The series consists of intrusive rocks (harzburgites, lherzolites, bronzitites, norites, gabbronorites, hornblende Fe-Ti-oxide gabbronorites and gabbronorite-diorites, quartz diorites, and trondhjemites) and their subvolcanic (ilmenite-hornblende dolerites) and, possibly, volcanic analogues (ilmenite-bearing basalts). The deficit of most incompatible elements in the rocks of the series suggests that the parental melts were derived from a source that had already been melted. Correspondingly, these melts could not be MORB derivatives. The origin of the series is thought to be related to the melting of the hydrated oceanic lithosphere during the emplacement of an asthenospheric plume (protuberance on the surface of a large asthenospheric lens beneath MAR). The genesis of different melts was supposedly controlled by the ascent of a chamber of hot mantle magmas thought this lithosphere in compliance with the zone melting mechanism. The melt acquired fluid components from the heated rocks at the peripheries of the plume and became enriched in Fe, Ti, Pb, Cu, Zn, and other components mobile in fluids.

Received 15 December 2004; revised 10 February 2005; accepted 1 March 2005; published 14 August 2005.

Keywords: Slow-spreading ridges, Ultramafic cumulates, Fe-Ti-oxides.

Index Terms: 1032 Geochemistry: Mid-oceanic ridge processes; 1037 Geochemistry: Magma genesis and partial melting; 1065 Geochemistry: Major and trace element geochemistry; 3619 Mineralogy and Petrology: Magma genesis and partial melting.

Citation: Sharkov, E. V., N. S. Bortnikov, T. F. Zinger, and A. V. Chistyakov (2005), Silicic Fe-Ti-oxide series of slow-spreading ridges: petrology, geochemistry, and genesis with reference to the Sierra Leone segment of the Mid-Atlantic Ridge axial zone at 6° N, Russ. J. Earth Sci., 7, ES4001, doi:10.2205/2005ES000181.