LATE MIOCENE TO RECENT ARC-FOREARC RESPONSE TO PLATE TECTONICS SURROUNDING THE PANAMA TRIPLE JUNCTION, SOUTHERN CENTRAL AMERICA
Open Access
- Author:
- Morell, Kristin Diane
- Graduate Program:
- Geosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 01, 2011
- Committee Members:
- Donald F Isher, Dissertation Advisor/Co-Advisor
Donald Myron Fisher, Committee Chair/Co-Chair
Eric Kirby, Committee Member
Derek Elsworth, Committee Member
Peter Christopher Lafemina, Committee Member - Keywords:
- Panama Triple Junction
neotectonics - Abstract:
- This dissertation explores how the changing plate tectonics surrounding the Panama (CO-NZ-CA) Triple Junction along the southern Central American Convergent Margin has affected the evolution of the upper plate of this system since the Middle Miocene, with a focus on study areas in the arc, inner forearc and outer forearc regions inboard of the triple junction. New structural and geomorphic analyses on the Burica peninsula, an outer forearc peninsula located only ~100 km inboard the Panama Triple Junction, reveal that the peninsula is dominated primarily by contractional deformation along three listric thrust faults that root in the underlying plate boundary. The geometry and spatial distribution of these thrusts indicate that this deformation occurs primarily in response to the change in crustal thickness occurring as a result of eastern migration of the flank of the Cocos Ridge coeval with migration of the Panama Triple Junction at a rate of ~55 mm/yr to the southeast. Mapping and detailed elevation surveys reveal eight marine terraces on the peninsula with a distribution of inner edge elevations indicating that uplift is spatially uniform from north to south along-strike in this area. Age control provided by 14C, OSL and soil chronosequences indicate that the terraces within the easternmost portion of the peninsula range in age from Marine Isotope Stage (MIS)-3 to Holocene, a result that indicates that this portion of the peninsula is younger than ~60 ka. Time-averaged uplift rates calculated from marine terraces and other Quaternary marine deposits yield consistent 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 the 8 terraces preserved on the peninsula are produced co-seismically wherein the anomalously high uplift rates calculated from the youngest samples (< 1 ka) are not yet averaged over a complete seismic cycle. These observations, combined with 1) shortening estimates from balanced cross-sections indicating that minimum shortening decreases from northwest to southeast as well as 2) the observation of growth strata within the youngest marine units, are consistent with a space-for-time model for triple junction migration. New geomorphic and longitudinal profile analyses combined with revised plate reconstruction models provide a new perspective with which to view the evolution of the Central American volcanic arc. We identify a low-relief surface in the northeastern flanks of the Cordillera de Talamanca, the late Miocene volcanic arc of southern Costa Rica, which, combined with longitudinal profile analyses, suggests the existence of a transient landscape within this region. Rock uplift calculations based on channel reconstruction by extrapolation of the current low-relief surface estimate that the rock uplift associated with this transient is on the order of ~2 km since the inception of the transient. Our results from a synthesis of radiometric ages combined with newly revised plate reconstruction models suggest that arc cessation between both the Cordillera de Talamanca and the Cordillera Central of western Panama occurred coeval with the initiation of oblique subduction of the Nazca plate during the late Miocene. This revision to previous plate reconstruction models, which relies on revised magnetic plate anomalies associated with the extinction of the Sandra Rift in the east Panama basin, suggests the existence of a North Nazca microplate prior to ~8-9 Ma, as well as a 2-fold decrease in convergence rate at this time. These results suggest that initiation of shallow subduction of the Cocos Ridge at the Middle American Trench, which has long been associated with the volcanic extinction of the Cordillera de Talamanca, occurred at ~ 1.5-2 Ma: more than ~7 million years after the extinction of the Central American volcanic arc. We also use new geologic, stratigraphic and geomorphic data along with age constraints to characterize the Late Pleistocene to Holocene sequence of deposits associated with edifice failure and sector collapse of the active Volcán Barú (alt. 3374 m) in westernmost Panama. This new stratigraphic control provides new constraints on the timing of thrusting associated with termination of the Fila Costeña inner forearc thrust belt, which is migrating to the southeast coeval with the Panama Triple Junction. Radiocarbon dating of organic material, together with 40Ar/39Ar ages from clasts within the deposits, identify at least three debris avalanche events (DA1, DA2 and DA3). Preliminary volume estimates for the youngest deposit (DA3) range from a minimum of ~30 km3 to a maximum of ~60 km3. Radiocarbon analysis of wood and other organic material extracted from this debris avalanche (n=3) yield ages that range between 8, 625 +/- 75 YBP and 12, 845 +/- 55 YBP. The oldest deposit contains a soil profile that appears significantly more developed than younger deposits and yields ages > 44,000 YBP. 40Ar/39Ar dating of plagioclase feldspar crystals extracted from clasts within the DA1 deposit, however, yield dates as young as 231 +/- 32 ka, constraining the lower age boundary. We map and distinguish three lithofacies for the debris avalanche, which we establish on the basis of surface morphology, abundance of clasts, and matrix composition. Finally, we also present new results regarding the kinematics, timing and evolution of the Fila Costeña Thrust Belt for many of the thrusts that intersect the volcanic units characterized here. These results include new shortening amounts based on balanced cross-sections within thrusts that cut surficial lahar units, as well as the recognition of new thrust structures that place constraints on thrust timing within this region.