Mantle substrate evolution of the Mid-Atlantic Ridge 14-16oN and 33o40' N:
time and matter limitations of accretion processes of the oceanic lithosphere from the data
of Sm-Nd research of isotope system
S. A. Silantiev1, S. F. Karpenko1, and B. V. Bel'yatskiy21GEOKHI RAS, Moscow, Russia 2Institute of geology and geochronology RAS, Sankt-Peterburg, Russia
Abstract
[1] The objects of this study were the ultrabasic rocks the samples of which were collected
from two areas of the crustal zone of the Mid-Atlantic Ridge (MAR): (1) 13-17o N (near the intersection
of the ridge axis with the 15o 20
fracture zone); and (2) 33o 40
N
(the western intersection of the MAR crest with the Heis fracture zone). 24 samples of peridotite and of
the plutonic and volcanic rocks associated with it were used to measure their Sm/Nd,
143Nd/144Nd, and
147Sm/144Nd ratios, which allowed to test the time
and genetic relationships between the evolution of the mantle material under the ridge crest and the
products of its magmatic activity. The results of this work proved the ubiquitous discrepancy between
the melting degree values of the extremely depleted mantle peridotites in the MAR area between 14o N and 16o N,
obtained using petrologic and geochemical methods. This discrepancy suggests the large-scale interaction
between the mantle material and magmatic melts and fluids, enriched in the incompatible elements or
fluids. The results obtained suggest that the repeated melting of the mantle under the axial MAR zone is the
universal characteristic of magmatism in low-velocity spreading centers. The results of this study also
proved the crestal MAR zone in the Central Atlantic region show distinct indications of the isotope-geochemical
segmentation of the mantle. It is suggested that the geochemically anomalous MAR mantle
peridotite in the zone of the MAR intersection with the 15o 20
fracture zone can be interpreted as the
fragments of the mantle substrate, foreign for the Atlantic mantle north of the
equator.
Received 16 November 2000; published 5 January 2001.
Citation: Silantiev, S. A., S. F. Karpenko, and B. V. Bel'yatskiy (2000), Mantle substrate evolution of the Mid-Atlantic Ridge 14-16o N and 33o40' N: time and matter limitations of accretion processes of the oceanic lithosphere from the data of Sm-Nd research of isotope system, Russ. J. Earth Sci., 2, No.3, 227-242, doi:10.2205/2000ES000042.
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