Submarine volcanic activity and giant amygdale formation along the Panama island arc as a precursor to 6000-year-old agate exploitation on Pedro González Island

Abstract An extensive deposit of agate occurs in Pedro González Island the Gulf Panama. Previous archaeological research showed that was exploited between 6200 and 5600 cal BP to make stone tools found at oldest known Preceramic human settlement Pearl archipelago. We constrain here origin geological context through a geochemical study island. show it includes primary volcanic breccias, lavas, tuffaceous marine deposits with sedimentary conglomerates debris flow deposits, which we define as Formation. This formation records submarine subaerial activity along an island arc during Oligo-Miocene, confirming previous regional models favour progressive emergence isthmus early Miocene. The igneous rocks have extreme tholeiitic character is interpreted reflect magmatic cessation eastern Panama hosted andesitic lavas unusually large amygdales up 20–40 cm diameter, well small (0.1–1.0 cm) bimodal distribution, veins. size agates made them suitable for tool manufacture. Field evidence suggests resulted from subaqueous lava–sediment interaction, water released unconsolidated base lava flows rose coalesced, accumulated below chilled top, subsequent hydrothermal mineralization. These could therefore be regarded unusual result combined peperitic processes.