HR: 11:35h
AN: V31F-05    [PDF]
TI: Transform Control on Ridge Propagation and Hotspot Formation
AU: * Beutel, E K
EM: beutele@cofc.edu
AF: College of Charleston, 66 George St., Charleston, SC 29424
AB: Large extensional stresses at ridge-transform intersections provide a mechanism for both the propagation of mid-ocean ridge segments and the formation of hotspot seamounts at ridge-transform intersections (RTIs). I propose that extensional stress is increased at ridge-transform intersections when slip along transforms is impeded. Thus, the inability of transforms to slip may cause either ridge-propagation and/or the formation of hotspot seamounts at RTIs. Extensional stress at the ridge-transform intersection may result in decompression melting and a change in the physiographic and thermal gradient in the upper mantle. Under these conditions excess magma at or near the ridge would result in the formation of a hotspot seamount at the ridge-transform intersection rather than in the segment center. Conversely, ridge propation may occur when the magma supply is lower and the stress concentration is high enough. Because transform slip can be impeded by a number of factors ranging from hydrothermal alteration to plate motion changes, the coupling of ridge-propagations to transform slip does not decouple the propagation of ridges from changes in plate motion. Rather, in addition to providing an alternative means of propagation during plate motion changes, the coupling of ridge-propagation to transform slip provides a mechanism for ridge-propagation during steady-state plate motions. Thus, a simple lithospheric mechanism is proposed, under certain conditions, to be responsible for the propagation of mid-ocean ridge segments and the location of hotspot seamounts at RTIs. To test the viability of this proposal a three-dimensional finite element grid of a series of three ridges and 2 transforms was constructed. Slip along the transforms was impeded by changing the strength of the transform and by varying plate motions. Large extensional stresses were concentrated at ridge-transform intersections when slip along the transform was impeded. Changes in the stress of the mantle were also observed when slip along the transform was impeded. Large concentrations of extensional stress at transforms may result in either the propagation of the ridge or, when magma supply is high, the formation of a hotspot. Thus, a lithospheric element is suggested as a mechanism for ridge propagation and hotspot formation.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8150 Plate boundary--general (3040)
DE: 8164 Stresses--crust and lithosphere
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting