Volcanic and geodynamic evolution of the Bouvet triple junction: Evidence from basalt chemistry
A. A. Peyve, and S. G. Skolotnev
Geological Institute (GIN), Russian Academy of Sciences, Moscow, Russia
 This study focuses on mafic volcanic rocks from the
Bouvet triple junction, which fall into six geochemically distinct groups:
(1) N-MORB, the most widespread type, encountered throughout the
(2) Subalkaline volcanics, hawaiites and mugearites, strongly
enriched in lithophile elements and radiogenic isotopes and composing the
Bouvet volcanic rise, and compositionally similar basalts and basaltic
andesites from the Spiess Ridge, generated in a deeper, fertile mantle
(3) Relatively weakly enriched basalts, T-MORB, derived by the
mixing of Type 1 and 2 melts and exposed near the axes of the Mid-Atlantic,
Southwest Indian, and America-Antarctic ridges.
(4) Basalts with a degree of trace lithophile element enrichment
similar to the Spiess Ridge and Bouvet I. rocks, but higher in K, P, Ti, and
Cr. These occur within extensional structures: the rift valley of the
Southwest Indian Ridge, grabens of the East Dislocation Zone, and the
linear rise between the Spiess Ridge and Bouvet volcano. Their parental
melts presumably separated from a plume material that spread from the
main channels and underwent fluid-involving differentiation in the mantle.
(5) A volcanic suite ranging from basalt to rhyolite, characterized by
low concentrations of lithophile elements, particularly TiO2, and
occurring on the Shona Seamount and other compressional features within
the Antarctic and South American plates near the Bouvet triple junction.
Unlike Types 1 to 4, which display tholeiitic differentiation trends, this
suite is calc-alkaline. Its parental melts were presumably related to a plume
material as well but, subsequently, they underwent a profound
differentiation involving fluids and assimilated surrounding rocks in closed
magma chambers in the upper mantle. Alternatively, the Shona Smt. might
be a fragment of an ancient oceanic island arc.
(6) Enriched basalts, distinguished from the other enriched rock
types in having very high P and radiogenic isotope abundances and
composing a tectonic uplift near the junction of the three rifts.
It thus follows that the main factors responsible for the
compositional diversity of volcanic rocks in this region include (i) mantle
source heterogeneity, (ii) plume activity, (iii) an intricate geodynamic setup
at the triple junction giving rise to stresses in adjacent plate areas, and (iv)
the geological prehistory. The slow spreading rate and ensuing inefficient
mixing of the heterogeneous mantle material result in strong spatial
variations in basaltic compositions.
Citation: Peyve, A. A., and S. G. Skolotnev (2001), Volcanic and geodynamic evolution of the Bouvet triple junction: Evidence from basalt chemistry, Russ. J. Earth Sci., 3, No.1, 33-57, doi:10.2205/2001ES000052.