Paper No. 3
Presentation Time: 2:00 PM
QUATERNARY DEFORMATION AND UPLIFT INBOARD OF THE PANAMA TRIPLE JUNCTION, BURICA PENINSULA, CENTRAL AMERICA
MORELL, Kristin, School of Earth and Ocean Sciences, University of Victoria, 3800 Finnerty Road, Victoria, BC 16802, Canada, FISHER, Donald, Department of Geosciences, The Pennsylvania State University, University Park, PA 16802 and GARDNER, Thomas, Department of Geosciences, Trinity University, One Trinity Place, San Antonio, TX 78212, kmorell@uvic.ca
New structural and geomorphic analyses on the Burica peninsula, an outer forearc peninsula inboard the Panama Triple Junction, indicate records of both recent coseismic uplift, as well as longer-term Quaternary uplift and active thrusting. The Panama Triple Junction (Cocos-Nazca-Panama microplate) represents the point that abruptly separates the thick and rapidly subducting Cocos plate to the northwest from the thin and obliquely-subducting Nazca plate to the southeast along the Central American convergent margin. Short-term deformation on the Burica Peninsula is recorded most strikingly by as many as 8 laterally extensive marine terraces that occur along the coastal margins of the peninsula. Age control for terraces provided by
14C, OSL, and soil choronosequences indicate that the terraces likely range in age from MIS-3 to latest Holocene. Time-averaged uplift rates calculated from these terraces and other Quaternary shelfal deposits yield uplift rates that range between 2.1 +/- 0.1 to 7.7+/- 0.5 mm/yr for samples older than 1 ka and between 6.9 +/- 1.0 to 19.3 +/- 8.0 mm/yr for samples younger than 1 ka. We interpret this temporal distribution in uplift rates to suggest that terraces on the Burica Peninsula are produced coeval with seismic events such that the anomalously high uplift rates calculated from the youngest samples (< 1 ka) are not yet averaged over a complete seismic cycle.
Recent field observations suggest that the uplift recorded by these deposits is produced by longer-term deformation which is occurring primarily along three deeply-rooted listric thrust faults that deform via trishear. The geometry and spatial distribution of thrusts suggest that upper plate deformation occurs primarily in response to the large change in bathymetry occurring at the triple junction that marks the eastern edge of the thicker, Cocos plate. Two area-balanced cross-sections across the peninsula reveal that total margin-perpendicular shortening decreases from northwest (14 km) to southeast (12.5 km); a result that is consistent with a space-for-time model in which deformation propagates coeval with migration of the Panama Triple Junction at a rate of ~55 mm/yr.
