Ridge-crossing seamount chains: A nonthermal approach

Abstract

Ridge-crossing seamount chains; a non-thermal approachIn this paper we examine whether it is viable to form an age-progressive ridge crossing seamount chain using a non-plume mechanism. Non-thermal melt sources considered include fertile mantle blobs and sub-solidus mantle while lithospheric stresses generated at the ridge and at ridge-transform intersections are tapped to bring the mantle to the surface. Finite element models, analog models, and an analysis of the Tristan de Cunha chain all show that ridge-crossing seamount chains may be created using these mechanisms. Essentially, as a ridge migrates or reorganizes excess magmatism may appear to switch sides of the ridge as areas of extensional stress at the ridge-transform intersection migrate with the ridge.. INTRODUCTIONHypotheses for ridge-crossing seamount chains have focused on the interaction of mantle plumes with migrating ridge segments (DePaolo & Manga, 2003;Sleep 2002b).These hypotheses call for a stationary plume of hot mantle material that rises to the base of the lithosphere and creates a chain of age-progressive seamounts in the middle of the plate. As a migrating ridge approaches the plume, buoyant mantle material rises along the base of the lithosphere like a helium balloon along a cathedral ceiling to the ridge and age progressive chains of seamounts are created on both sides of the ridge from a single hotspot source. Eventually the ridge moves away from the plume and seamount production switches across the ridge to the other plate, ceases to generate seamounts on 2 the ridge, and continues to generate seamounts on the new plate only (e.g., DePaolo & Manga, 2003;Sleep 2002b;Ribe et al., 1996;Kincaid et al., 1996;Small, 1995). This scenario results in the formation of an asymmetrical V-shaped array of seamounts such as the Tristan de Cunha chain in the South Atlantic (Figure 1).Because current non-thermal models of seamount formation are unable to explain this geometry, (e.g. propagating cracks are presumed to be unable to cross ridges, and asthenospheric heterogeneities are presumed to be moving rapidly), ridge-crossing seamount chains have been cited as evidence for plumes of material that remain relatively stationary in comparison to the plates. However, if the mantle is lithologically heterogeneous and contains areas with different melting points on a scale from km to 100's of km and/or if ridge-transform intersections are involved, then non-thermal ridgecrossing seamount chains are not only viable, but also likely. In this paper we propose a mechanism for the development of ridge-crossing seamount chains that does not invoke deep mantle plumes yet still accounts for the four primary elements necessary for a viable hypothesis for the origin of seamount chains ranging in size from 2 or 3 seamounts to seamount chains spanning a 100 Ma. The primary elements included in this mechanism are; a source of melt, a means of bringing melt to the surface, an asymmetrical ridgecrossing seamount chain, and an explanation for the age progressive nature o...

The “plate” model for the genesis of melting anomalies

“…The formation of a LIP followed by continuation of volcanism to form a time-progressive volcanic chain is a rare exception rather than a rule (e.g., Anderson, 2005b;Beutel and Anderson, this volume). No trace of such associations exist, for example, for the Siberian Traps, the Ontong Java Plateau, Afar, Hawaii, Samoa or Louisville.…”