Upper Cretaceous to Miocene tectonostratigraphy of the Azuero area (Panama) and the discontinuous accretion and subduction erosion along the Middle American margin

The Central American forearc allows insight into the long-term evolution of the Middle American margin and possible shifts between accretionary and erosive periods of subduction. We present a revised tectonostratigraphic subdivision of the Azuero area based on new field observations and biochronologic data, and a synthesis of previous age, geochemical and stratigraphic data. The basement of the area is composed of an autochtonous oceanic plateau, the early Central American arc and accreted seamounts, which are unconformably overlain by forearc sediments. The nature and spatial arrangement of basement units combined with patterns of uplift and subsidence recorded in overlapping sediments allow reconstruction of the local evolution of subduction tectonics between the Upper Cretaceous and Miocene. Comparison of this evolution with that formerly proposed for the south Costa Rican margin based on a similar approach (Buchs et al., 2009, 2010) provides an insight into temporal and along-strike changes of subduction tectonics along a ~ 500 km-long segment of the Middle American margin. We find that subduction erosion (or non-accretion), punctuated by seamount accretion, was the dominant process along the margin between the late Campanian and Middle Eocene. In the Middle Eocene, uplift of the Central American forearc, initiation of a volcanic front retreat in Panama and a pulse of seamount accretion between south Costa Rica and west Panama are likely to relate to a reorganization of plate tectonics in the Pacific. A contrasted evolution occurred in south Costa Rica and Panama afterwards, with continued subduction erosion in the Azuero area and net accretion of olistostromal and hemipelagic sediments in south Costa Rica at least until the Middle Miocene. Our results show that tectononstratigraphic observations in the forearc may represent a valuable complement to offshore drilling and geophysical studies to understand modern subduction tectonics along the Middle American margin.