March/April Geological Society of America Bulletin media highlights

In order to erupt, magma must ascend through Earth’s crust. While several volcanoes and their eruptive rates have been studied in detail for the case of relatively thin crust, there is a lack of information for volcanic growth rates on extremely thick crust. Understanding how quickly volcanoes grow (and in this case, regrow following destruction by sector collapse) in this tectonic setting allows evaluation of the degree to which thick continental crust filters magmas passing through it. Through geologic mapping, volume estimation, and stratigraphy tied to age determinations using 40Ar/39Ar geochronology, Hora et al. describe in detail the evolution of Volcán Parinacota built on 70 km thick crust in northern Chile. Their data indicate that regrowth of this volcano following sector collapse happened rapidly over approximately the last 10,000 years, with eruption rates on par with other volcanoes on thin crust. The sixteen ages determined from lavas erupted during this period are among the youngest yet obtained using the 40Ar/39Ar method. While their data indicate that thick crust does not necessarily result in diminished eruption rates, certain magma types common in other arcs are very rare in the vicinity of Parinacota. This suggests that while evolved, water-rich magmas ascend relatively unhindered, dry basalts might be preferentially filtered.

Volcanic arc emplacement onto the southernmost Appalachian Laurentian shelf: Characteristics and constraints
James Tull, Florida State University, Department of Geological Sciences, Tallahassee, Florida 32306, USA; et al. Pages 261-274.

Keywords: Appalachians, volcanic arc, Talladega belt, Hillabee, Blue Ridge.