6. Conclusions
New geochronological and thermochronological data constrain several
cooling phases in the Western Cordillera of Ecuador. AFT ages record
cooling associated with post-magmatic thermal relaxation of early and
middle Miocene intrusions. This suggests that the AFT thermochronometer
is not well suited to decipher the exhumation of the Miocene magmatic
arc in the northern Andes. Thermal modeling of our data constrains two
cooling phases: a post-magmatic cooling during early and middle Miocene
associated with thermal relaxation, a period of tectonic quiescence, and
a second phase driven by uplift and exhumation since
~6-5 Ma in the Western Cordillera. This latest Miocene
onset of exhumation correlates well with the onset of active shortening
and rock uplift, as well as coeval exhumation previously identified in
the Coastal Cordillera and the Eastern Cordillera of the northern Andes.
We propose that the onset of regional shortening and exhumation at
~6-5 Ma was triggered by the effects of initial
subduction of the Carnegie Ridge that caused stronger plate coupling.