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This Article Full Text (PDF) All Versions of this Article: B26237.1v1 121/7-8/992    most recent Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Sak, P. B Articles by LaFemina, P. C Search for Related Content GeoRef GeoRef Citation

Rough crust subduction, forearc kinematics, and Quaternary uplift rates, Costa Rican segment of the Middle American Trench

¹ Department of Geology, Dickinson College, Carlisle, Pennsylvania 17013, USA
² Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA
³ Department of Geosciences, Trinity University, San Antonio, Texas 78212, USA
⁴ Department of Geological Sciences, Cal Poly Pomona University, Pomona, California 91768, USA
⁵ Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA

Orthogonal subduction of bathymetrically rough oceanic lithosphere along the northwestern flank of the Cocos Ridge imprints a distinctive style of deformation on the overriding Costa Rican forearc. We divide the Costa Rican forearc into three 100-160-km-long deformational domains based on the bathymetric roughness and thickness of the Cocos plate entering the Middle American Trench, the dip of the subducting plate, the variation in surface uplift rates of late Quaternary coastal deposits, and the orientations and types of faults deforming Paleogene and Neogene sedimentary rocks. In the 100-km-long Nicoya domain, coastal deposits show localized surface uplift and arcward tilting above the downdip projections of the fossil trace of the Cocos-Nazca-Panama (CO-NZ-PA) triple junction and the Fisher seamount and ridge. In the 120-km-long central Pacific forearc domain between the Nicoya Peninsula and Quepos, shallower (60°) subduction of seamounts and plateaus is accompanied by trench-perpendicular late Quaternary normal faults. Steeply dipping, northeast-striking, margin-perpendicular faults accommodate differential uplift associated with seamount subduction. Uplift and faulting differ between the segments of the forearc facing subducting seamounts and ridges. Inner forearc uplift along the seamount-dominated segment is greatest inboard of the largest furrows across the lower slope. Localized uplift and arcward tilting of coastal deposits is present adjacent to subducting seamounts. In contrast, inboard of the underthrusting aseismic Cocos Ridge, along the 160-km-long Fila Costeña domain between Quepos and the Burica Peninsula, mesoscale fault populations record active shortening related to the 100-km-long Fila Costeña fold-and-thrust belt. The observed patterns of faulting and permanent uplift are best explained by crustal thickening. The uplifted terraces provide a first-order estimate of permanent strain along the forearc in Costa Rica. The permanent strain recorded by uplift of these Quaternary surfaces exceeds the predicted rebound of stored elastic strain released during subduction-zone earthquakes.