HR: 14:40h
AN: V12G-05    [PDF]
TI: Magmatic Consequences of Failed Rift Zones: Examples from the Eastern Pacific
AU: * Harpp, K S
EM: kharpp@mail.colgate.edu
AF: Colgate University, 13 Oak Drive, Hamilton, NY 13346 United States
AU: Wanless, V D
EM: vwanless@soest.hawaii.edu
AF: Colgate University, 13 Oak Drive, Hamilton, NY 13346 United States
AU: Otto, R H
EM: rotto@mail.colgatealumni.org
AF: Colgate University, 13 Oak Drive, Hamilton, NY 13346 United States
AU: Hoernle, K
EM: khoernle@geomar.de
AF: GEOMAR, 1-3 Wischhofstr., Kiel, 24148 Germany
AB: The aseismic Cocos Ridge, one of the most prominent bathymetric features in the eastern Pacific, records ~20 million years of interaction between the Galapagos hotspot and the Galapagos Spreading Center. Two major clusters of seamounts are located along the northern flanks of the ridge, one near the Costa Rican coast and the second around Cocos Island. The Costa Rica and Cocos Seamount Provinces (including Cocos Island) have produced alkalic lavas accompanied by enrichment in incompatible trace elements beyond any observed in the Galapagos Archipelago today or in samples from the crest of the Cocos Ridge. Cocos Island is known to be millions of years younger than the hotspot track on which it lies, and the other seamounts likely share this characteristic. Trace element data determined by ICP-MS from over 90 dredged samples from the ridge and seamounts suggest that the compositions of the lavas are strongly controlled by the history of rift jumping in the region. The lavas are the result of small degrees of melting of a Galapagos plume-like source, predominantly in the garnet stability field. In the case of both seamount fields, their eruption immediately follows the failure of a rift zone at each province's location. Thus we attribute the anomalously young alkalic lavas of the seamount provinces to post-abandonment volcanism following either a ridge jump or rift failure, and not to the direct activity of the Galapagos plume. The seamounts and Cocos Island are instead the result of passive upwelling caused by a major tectonic rearrangement, such that the seamounts are significantly younger than their supporting lithosphere or the hotspot trace. The failed rift tapped mantle that had previously incorporated Galapagos plume material when the lithosphere was produced at the plume-affected GSC. Fundamentally, the hotspot's variable interaction with the Galapagos Spreading Center, coupled with rift failures associated with tectonic rearrangements of the ridge itself may be the dominant factors in controlling regional magmatism and may be responsible for the formation of some enigmatic oceanic volcanoes such as Cocos Island.
DE: 1025 Composition of the mantle
DE: 3035 Midocean ridge processes
DE: 3670 Minor and trace element composition
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8164 Stresses--crust and lithosphere
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting