The age of magmatic and metamorphic events in the Mid-Atlantic Ridge: interpretation of K-Ar isotope dating data
S. A. Silantiev1, L. K. Levskiy2, M. M. Arakelyants3,
V. A. Lebedev3, A. Bugo4, and M. Kannat51GEOKHI RAS, Moscow, Russia 2Institute of geology and geochronology RAS, Sankt-Peterburg, Russia 3Institute of geology of deposits, petrography and mineralogy RAS, Moscow, Russia 4IFREMER, Brest, France 5Universite Pierre et Marie Curie (Paris 6), Paris, France
Abstract
[1] The object of this study was gneissose gabbro from the plutonic rocks composing the
opposite sides of the rift valley of the MAR segment located directly north of the 15o 20
fracture zone. The results of our K-Ar dating suggested the potential age asymmetry of the similar rocks
composing the opposite side of the MAR rift valley between the
15o and
16o of the north latitude.
The age value obtained for the gabbro sample collected from
the western side of the rift valley seems to reflect the time of the magmatic interaction of this gabbro
with the injections of tronghjemite melt and
apparently corresponds to the crystallization
stase of tronghjemite vein complex. On the other hand the age defined for the gabbro
sample collected from the eastern side of the
rift valley probably marking the time of its crystallization in the magma system, or the time
of its high-temperature crystallization during the metamorphism.
The proved age asymmetry of the opposite sides of the rift valley is believed to have been unassociated with any
differences in the metamorphic evolution of the gabbro, its samples showing the same degree of metamorphism.
The results of this study and the synthesis of all data available for the isotopic dating of the various MAR plutonic
rocks suggest the presence of two types of igneous rock complexes in the crest zone of the ridge, which do
not correspond to the modern igneous activity of the rift valley: (1) the rocks localized in the segments with
the Hess-type crust, associated with very low spreading rates and with the repeated melting under the
mantle-like conditions of the lenses and interlayers of cumulative rocks often of abnormal geochemistry;
(2) The rocks represented by the lithospheric relicts of the Gondwana supercontinent lithosphere,
characterized by the isotopic ages of hundreds of million
years.
Received 16 November 2000; published 5 January 2001.
Citation: Silantiev, S. A., L. K. Levskiy, M. M. Arakelyants, V. A. Lebedev, A. Bugo, and M. Kannat (2000), The age of magmatic and metamorphic events in the Mid-Atlantic Ridge: interpretation of K-Ar isotope dating data, Russ. J. Earth Sci., 2, No.3, 269-278, doi:10.2205/2000ES000044.
Copyright 2001 by the Russian Journal of Earth SciencesPowered by TeXWeb (Win32, v.2.0).