Archean felsic volcanic rocks in felsic rocks. Timing of felsic volcanism and tectonic constraints can be identified by radiometric dating and isotopic analysis. In Archean, underwater eruptions of felsic lava were common. Submarine eruption is evident by coarse volcanic breccia formed in situ, hyaloclastite or underwater pyroclastic deposits (clastic rock, composed of tephra only). Since felsic magma is viscous, volcanic eruptions that form dacite or rhyolite are explosive and violent. The Archean felsic eruption may be assigned to Vesuvius eruption type in the present day. Submarine rhyolitic flows were widespread in Archean but it is uncommon in the modern volcanic environment. Viscous felsic eruption
Geology of Nicaragua Geology of Nicaragua The geology of Nicaragua includes Paleozoic crystalline basement rocks, Mesozoic intrusive igneous rocks and sedimentary rocks spanning the Cretaceous to the Pleistocene. Volcanoes erupted in the Paleogeneand within the last 2.5 million years of the Quaternary, due to the subduction of the Cocos Plate, which drives melting and magma creation. Many of these volcanoes are in the Nicaraguan Depression paralleled by the northwest-trending Middle America Trench which marks the Caribbean-Cocos plate boundary. Almost all the rocks in Nicaragua originated as dominantly felsic continental crust, unlike other areas in the region which include stranded sections of mafic oceanic