HR: 1340h
AN: T33B-1388    [Abstracts]
TI: The Interaction Between the Caribbean Plate and the Products of the Galapagos Hotspot in Southern Costa Rica: A Transition from Subduction Accretion to Erosion
AU: * Vannucchi, P
EM: paolav@geo.unifi.it
AF: University of Florence, Via La Pira, 4, Firenze, 50121 Italy
AU: Fisher, D M
EM: fisher@geosc.psu.edu
AF: Pennsylvania State University, Deike Blg., University Park, PA 16802 United States
AU: Gardner, T W
EM: tgardner@trinity.edu
AF: Trinity College, One Trinity Place, San Antonio, TX 78212 United States
AU: Bier, S
EM: sbier@geosc.psu.edu
AF: Pennsylvania State University, Deike Blg., University Park, PA 16802 United States
AB: The Costa Rica portion of the Middle America Trench (MAT) is characterised by active tectonic erosion, a process that causes the removal of material from the base of the upper plate as the plate boundary migrates upward. Offshore studies demonstrate accelerated subduction erosion starting at the Miocene-Pliocene boundary, as the result of subduction of thickened/Galapagos related crust, as presently represented by the Cocos Ridge. The subduction of the Cocos Ridge also caused the uplift of the outer forearc and its exposure in the Osa peninsula, which offers a window to explore the tectonic evolution of the area. The rocks outcropping on Osa Peninsula are of a Middle Eocene-Late Oligocene m‚lange dominated by basalt, chert and limestone. The igneous elements of the m‚lange and the coherent igneous rocks present inboard the m‚lange, still on the Osa peninsula, have a volcanic island chemical affinity, that together with the younger age, demonstrate they belong to an event different than the one which produced the Caribbean plate. The m‚lange and the coherent igneous rocks represent a tectonic rock assemblage accreted prior to the arrival of the Cocos Ridge, during subduction of seamounts. The accretion-dominated period of the MAT evolution ended at the Miocene Pliocene boundary, when continuously thickened crust produced at the Galapagos hotspot arrived at the trench. The thick crust caused uplift and severe tectonic erosion of the accretionary edifice allowing exhumation of the Osa M‚lange. The change for accretion to erosion caused the outer forearc to be offset along sub-vertical faults that define small (km-size) blocks that are going through differential vertical movements in response to the morphology of the subducting ridge. Subduction accretion and erosion are two processes that can alternate in time or coexist along the same margin, so that mass removal can develop on a previously growing margin and completely remove an accretionary prism.
DE: 9360 South America
DE: 8025 Mesoscopic fabrics
DE: 8045 Role of fluids
DE: 8105 Continental margins and sedimentary basins
DE: 8120 Dynamics of lithosphere and mantle--general
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting