Abstract:
The processes of arc initiation at the margin of an oceanic plateau are remarkably well preserved along
the southern coastline of eastern Costa Rica and western Panama. We present new results of a combined
tectonostratigraphic and petrologic study with which protoarc initiation (75–73 Ma) at the margin of an
oceanic plateau (89–85 Ma) is documented. Dykes of protoarc igneous rocks within the plateau and occurrences
of protoarc igneous rocks are widely distributed. These types of field observations, geochemical
data, and paleontologic ages for Late Cretaceous to Eocene fore‐arc rocks of the Golfito Complex and
Azuero Marginal Complex (southern Costa Rica and western Panama) provide the first direct evidence that
a Coniacian–early Santonian oceanic plateau forms the arc basement. Stratigraphic and geochemical constraints
from Golfito and Azuero indicate subduction initiation in south Central America, associated with
geochemically distinctive suprasubduction igneous rocks, occurred in the late Campanian along the margin
of the newly defined Azuero Plateau. Overall, the Golfito Complex and Azuero Marginal Complex provide
a significant opportunity for exploration of petrologic mechanisms linking some oceanic plateaus to the
growth of continents. The Azuero Plateau may extend further toward the Colombian Basin and forms thickened
Caribbean crust. It served as a nucleus for accretion of additional oceanic plateaus, seamounts, and
oceanic islands of Pacific origins.
