Indirect Study of Subducted Oceanic Lithosphere at the Central American Margin

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The PIs plan mapping and sampling features on the Cocos and Nazca plates to provide a basis for inferring the properties of the subducted Cocos plate under Central America. The basic premise is that the Nazca plate south of Grijalva was formerly contiguous with Cocos plate under Nicaragua and parts of Costa Rica and that this fossil plate boundary could form an important structure in the down-going slab. Because a small fragment remains unsubducted, the investigators propose to not only study it, but also it's conjugate off Peru, where much more remains. At that locality, the structure can be mapped more thoroughly and the results extrapolated to the subducted slab beneath Costa Rica. Further, dredging will provide essential samples to measure the composition of the lithosphere that is beneath the Central American arc.