CONSTRUCTION AND DESTRUCTION OF VOLCANIC KNOBS AT THE COCOS-NAZCA SPREADING SYSTEM NEAR 95-DEGREES-W

Characterization of volcanic knobs observed in Sea Beam bathymetry nea r the 95-degrees-W Galapagos propagator system on the Cocos-Nazca spre ading axis provides insight into volcanic and tectonic processes at pr opagators and mid-ocean ridges. Despite evidence suggesting a higher m agma supply rate at the propagator axis, crust accreted there contains fewer knobs than crust created at the failing or doomed spreading axe s. Fissure-fed flows rather than seamount construction are more import ant along the propagator. The process of transferring lithosphere from one plate to another as this ridge offset migrates through a region d estroys about half of the preexisting knobs. Data tentatively suggest that on-axis volcanic cones increase in size and contribution to crust al construction but decrease in abundance with decreasing spreading ra te, possibly reflecting the magma plumbing systems in differing therma l regimes.