EFFECTIVE ELASTIC THICKNESS OF THE LITHOSPHERE ALONG THE EASTER SEAMOUNT CHAIN

Bathymetry and gravity data collected during Legs 5, 6, and 7 of the 1 993 GLORIA Expedition and the recently released 2-min altimetry-derive d global gravity grid are used to determine the effective elastic thic kness of the lithosphere along the Easter Seamount Chain (ESC). Forwar d modeling, admittance, and coherence methods yield consistent results . With the exception of the eastern and western ends of the ESC the ef fective elastic thickness along the chain is similar to 1-4 km. The th in elastic thickness for the majority of the ESC seamounts is compatib le with a young seafloor age at the time of loading derived from new r adiometric ages of the seamounts along the chain and a magnetic isochr on age interpretation of the Nazca plate seafloor age. The elastic thi ckness southeast of the Nazca fracture zone is similar to 6 km, appare ntly because of the seafloor age discontinuity across the fracture zon e. The elastic thickness near the San Felix Island, at the eastern end of the ESC, is even greater (similar to 11 km), which is compatible w ith the estimated seafloor age at the time of loading. A slight increa se in the effective elastic thickness of the far western part of the E SC suggests dynamic compensation or less thermal weakening of lithosph ere above a plume channel versus directly above the plume center. Thes e findings combined with published geochemistry support a hotspot orig in for the ESC, complicated by large-scale plate boundary reorganizati ons and channeling of plume material to the East Pacific Rise.