A new stratigraphy for the Tertiary volcanic rocks of the Nicaraguan Highland
Three major volcanic events have occurred in Nicaragua since middle Tertiary time. First, the Oligocene was dominated by rhyolite shield volcanism, producing the Highland ignimbrite. Second, creation of northeast- and later northwest-striking dilatational fracture zones allowed the extrusion of basaltic to andesitic magmas along the Pacific coast, constructing the northwest-oriented Coyol volcanic arc. This Miocene arc can be followed all along the Pacific coast of the Chortis block. Third, a Pliocene-Pleistocene southwestward shift of arc volcanism created the modern volcanic arc. This volcanic history is supported by a new stratigraphy based on volcanic centers and related facies. The old cyclic, layer-cake stratigraphy of the Coyol Group has been abandoned.