HR: 14:55h
AN: T43D-06    [Abstracts]
TI: Melting Anomalies, Ridge-Crossing Seamounts, and Transform Faults
AU: * Beutel, E K
EM: beutele@cofc.edu
AF: College of Charleston, Dept. of Geology 66 George St. , Charleston, SC 29424 United States
AU: Anderson, D L
EM: dla@gps.caltech.edu
AF: Caltech, 1200 E. California Blvd., Pasadena, CA 91125 United States
AB: Some hotspot tracks appear to cross spreading-ridges. This has been used as evidence for relatively fixed deep-mantle plumes and therefore most previous studies have focused on ridge migration over a fixed thermal anomaly. However, we have developed several conceptual models that negate the need for a fixed thermal anomaly to explain this phenomenon and instead suggest two alternative transform related mechanisms. We hypothesize that a seamount chain crossing a ridge can be caused by a) ridge migration over fertile mantle blobs and/or b) the reorganization of a ridge with seamount production at a ridge-transform-intersection (RTI). Thus, the seamount chain appears to cross the ridge because production of seamounts is initially restricted to one plate ahead of the RTI and then switches to the other plate when the ridge reorganizes or the migrates. These models are based on the premise that, as crack tips, RTIs focus extensional stress and that when transform slip is inhibited, extensional stress at RTIs becomes large enough to result in decompressional melting and the formation of a seamount and/or ridge propagation. Because changes in transform strength are strongly tied to plate stress, motion changes, and ridge-reorganizations we suggest that seamount chains crossing ridges may be indicative of both the active role that transforms play in oceanic tectonics and changes in plate motions or ridge-reorganizations. Additionally, conventional wisdom suggests that we need to find an explanation for the production of seamounts, instead these models suggest that we need to find an explanation for why we wouldn't see seamounts when the mantle is at or near its melting point. As such, these models appear to offer a possible explanation for the large number of seamounts scattered throughout the Pacific and for the non-sequential age dates found in some of the seamount chains.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8150 Plate boundary--general (3040)
DE: 8164 Stresses--crust and lithosphere
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting