T220 Developing Chronologies for Tectonic Geomorphic Studies

Tuesday, 2 November 2010
1:30 PM - 5:30 PM
Hall E

CONSTRAINING CENOZOIC UPLIFT/EXHUMATION OF THE PANAMA-CHOCO BLOCK BY APATITE AND ZIRCON LOW-TEMPERATURE THERMOCHRONOLOGY: INSIGHTS ON THE ONSET OF COLLISION AND THE MORPHOTECTONIC HISTORY OF THE REGION

Paper number: T220-4
Program: Technical Sessions
Time: 2:10 PM – 2:25 PM

Authors

Abstract

Analysis of low-temperature cooling patterns in mountainous settings of Panama and Western Colombia provide direct insight into critical morphotectonic processes, i.e., uplift-exhumation (U-E) that may be related to the collision of the Panama-Chocó Block (PCB) with northwestern South America. The PCB collision is one of the most significant geological events in the Americas during the Cenozoic with important tectonic, climatic, geographic, and biologic repercussions at the regional and global scales. Tectonically, the collision of the PCB has been regarded as the engine of the major phase of uplift and deformation in the Andes of Colombia in the Late Miocene-Pliocene. Although a cause-effect relationship between PCB collision and uplift of the Colombian Andes has been postulated, the chronology of the collision is still a matter of debate with ages ranging from ~ 27 to 4 Ma. During the last half-decade a significant amount of thermo-geochronological and stratigraphic data has been produced for the Central and Eastern Cordilleras of Colombia. This effort is now extended to include Western Colombia and Panama with the aim of using areas proximal to the colisional zone to unravel the timing of collision and the morphotectonic response of the PCB.

We present results of a low temperature thermochronology study (apatite and zircon (U-Th)/He and apatite fission-tracks) on ~40 samples collected along vertical profiles from Western Colombia and Panama. Significant UE phases (0.2-0.5 mm/yr) are found at ca. 47, 26, 14-11, and 5 Ma. Whereas the older Eocene event is probably a record of intra-oceanic tectonic stages in the PCB (seamount accretion or rebounding effects linked to crustal thickening by magmatic addition), the younger post-Oligocene events are consistent with Andean patterns and reflect the interaction with the South American margin and the final consolidation of the Isthmus. Special emphasis is given to the marked pulse of uplift and exhumation in the Colombian Andes and Panama at ~25 Ma. This event possesses synchronicity in the region and is related in space and time to a permanent shift in magmatic patterns in Panamanian arcs associated with extension during orocllinal development. We conclude that this strong pulse of uplift-exhumation marks the onset of collision of the PCB.