A112-25

Geochemical and structural studies of the Lamont seamounts - Seamounts as indicators of mantle processes FORNARI, DANIELJ | PERFIT, MICHAELR | ALLAN, JAMESF | BATIZA, RODEY | HAYMON, RACHEL Earth and Planetary Science Letters. Vol. 89, no. 1, pp. 63-83. June 1988 The petrologic and geochemical characteristics of lavas from the Lamont seamounts (located just west of the East Pacific Rise, EPR) and their flanking cones were investigated using information obtained from dive traverses, deep-sea camera tows, and dredging, as well as results from Sea MARC 1 and Sea Beam sonar surveys. All of the lavas from the seamounts and cones analyzed are light REE-depleted tholeiitic basalts which have lower incompatible element ratios than lavas from the adjacent EPR. The seamount magmas appear to reflect near-primary melting events in the mantle, whereas EPR lavas are the product of shallow-level crystallization and mixing in crustal magma chambers. The data indicate that Lamont seamount or cone lavas were not derived from a subcrestal EPR magma chamber and that there is apparently no communication between the ridge crest and the Lamont seamount magmatic plumbing systems.