HR: 08:45h
AN: T11D-04 INVITED    [Abstracts]
TI: Geochemical Constraints on the pre-Cenozoic Subduction History of two Margins of the Chortis Block (Northern Central America)
AU: * Geldmacher, J
EM: geldmacher@iodp.tamu.edu
AF: IODP, Texas A&M University, 1000 Discovery Drive, College StationTX, 77845, United States
AU: Martens, U
EM: umartens@stanford.edu
AF: Geological and Environmental Sciences, Stanford University, 450 Serra Mall, Building 320, Stanford, CA 94305, United States
AU: Hoernle, K
EM: khoernle@ifm-geomar.de
AF: Leibniz-Institut fuer Meereswissenschaften, IFM-GEOMAR, Wischhofstrasse 1-3, Kiel, D- 24148, Germany
AU: Hauff, F
EM: fhauff@ifm-geomar.de
AF: Leibniz-Institut fuer Meereswissenschaften, IFM-GEOMAR, Wischhofstrasse 1-3, Kiel, D- 24148, Germany
AU: Bogaard, P
EM: pbogaard@ifm-geomar.de
AF: Leibniz-Institut fuer Meereswissenschaften, IFM-GEOMAR, Wischhofstrasse 1-3, Kiel, D- 24148, Germany
AU: Kluegel, A
EM: akluegel@uni-bremen.de
AF: Fachbereich Geowissenschaften, Universitaet Bremen, Postfach 330440, Bremen, 28334, Germany
AB: The igneous forearc basement along the Pacific coast of northern Central America (between southern Mexico and Costa Rica) comprises a highly tectonized accretionary assemblage of igneous and ultramafic rocks. Volcanic and gabbroic rocks with primitive arc geochemical signatures formed between ~100 and ~180 Ma and are interpreted to have originated by arc magmatism resulting from subduction of the Pacific/Farallon plate. Additionally, the forearc contains geochemically enriched ocean island basalt (OIB)-like units that are interpreted as accreted seamounts and islands of a 100 to ~220 Ma old hotspot track, which most likely originated from a long-extinct hotspot located in the Pacific. Based on their combined Pb, Nd, Hf isotopic compositions an affiliation of these isotopically strongly enriched rocks with the Caribbean Large Igneous Province or the Galápagos hotspot appears unlikely. Rocks of similar age and geochemistry are exposed in the Santa Elena Peninsula of Costa Rica, suggesting that the same type of forearc basement is accreted to the continental Chortis block all the way from southern Mexico to Costa Rica. In contrast, gabbroic rocks of the Motagua suture zone in central Guatemala (El Tambor accretionary complex) show depleted MORB signatures and have igneous ages of ~130Ma. These MOR Gabbros were accreted on the current northern margin of the Chortis block during subduction of proto-Caribbean crust. In contrast, geochemistry of gabbros and diorites of the Sierra de Santa Cruz (SSC) indicate medium to high K-series arc affinity and their Ar/Ar ages range from ~75 to 130 Ma. The SSC is interpreted as the western extension of the early Cuban arc that collided with the Maya block in the latest Cretaceous. Arc-derived volcanic clasts were subsequently shed into the Paleocene Sepur Formation of the Maya block. No evidence of accretion of OIB-like material was found in the Motagua suture or the SSC so far. These new data suggest that proto-Caribbean crust, possibly generated during the opening of the Gulf of Mexico, was formed without the involvement of a mantle plume.
DE: 1040 Radiogenic isotope geochemistry
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8104 Continental margins: convergent
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 8185 Volcanic arcs
SC: Tectonophysics [T]
MN: 2007 Fall Meeting