IS THE RECENT VOLCANIC ACTIVITY IN NORTHERN PATAGONIAN ANDES DRIVEN BY NORTHWARDS SHIFTING OF FRACTURED OCEANIC CRUST?

Recent volcanic eruptions in the Northern Patagonian Andes show a striking northwards shift over time. Hudson Volcano (45.90º S) erupted in August 1991, Chaitén Volcano (42.83º S) in May 2008 and recently, Puyehue Volcano (40.59º S) in June 2011. In this section of the Pacific margin, the Nazca Plate is subducting beneath the South America Plate at a rate of 9 cm/year with an oblique component. This oblique East-Northeast component induces a dextral stress along the present volcanic arc activating the 1,000 km long strike-slip Liquiñe-Ofqui fault. The displaced western block of the Liquiñe-Ofqui fault drags the oceanic crust and may fracture it developing a coast parallel fracture system. The fractures favor the trapping of sea water in the downward-moving oceanic slab. Due to the oblique subduction, the fracture swarms reach critical depth at different times. Dehydration of the water enriched descending plate generates melts in overlying mantle and crust, causing the northwards shifting of eruptions in the different volcanoes. If this scheme is valid, we may expect eruptions at volcanic centers further north in the future.