Turonian highly differentiated pyroclastic xenoliths and Cretaceous sedimentary record challenge mantle-plume view of Costa Rican forearc basement successions

Abstract

The Mesozoic basaltic basement of southern Central America is believed to consist of proxy sections of mantle-plume events leading to the Caribbean igneous province. A significant xenolith assemblage of radiolarite, tuffite, and Turonian (∼93 Ma) highly differentiated pyroclastic rock discovered in basalt of the Costa Rican forearc basement fundamentally challenge this long-held view, revealing bimodal Cretaceous island-arc activity and forearc basin development instead. The pyroclastic materials originally accumulated with monotonous radiolarite deposits in a deep-marine forearc basin slope environment to build part of the Mesozoic sedimentary cover of the evolving arc. Xenolith formation was related to widespread Turonian to Campanian intrusive basaltic activity on the Nicoya Peninsula that affected Albian-Turonian and Berriasian-Barremian radiolarite and pyroclastic deposits as well as Jurassic siliceous strata. Strong correlation with Cretaceous biotite- and hornblende-bearing pyroclastic beds reveals explosive calc-alkaline volcanic arc episodes alongside basaltic activity linked to marine forearc basin development. These materials provide decisive evidence of explosive calc-alkaline volcanic activity of the Cretaceous Costa Rican arc as well as the probable intraoceanic-arc nature of its basaltic forearc basement and a ∼90 Ma aged komatiite suite found at Tortugal. The resulting tectonic scenario shows the Caribbean Plate was separated in southern Central America from any potential Pacific or Galápagos hotspot sources by a subduction zone. This favours in-place origin of the Caribbean Plate and its igneous province between the Americas. The findings also reveal the unsuitability of basaltic forearc basement successions to deduce with certainty mantle-plume events and hotspot evolutions in adjoining oceanic domains.