Abstract

Cordón Caulle in southern Chile has produced three dacitic to rhyolitic fissure eruptions over the past century (in 1921–1922, 1960 and 2011–2012), and thereby provides an ideal opportunity to examine the architecture of its underlying silicic system. While the 2011–2012 eruption has been extensively studied, comparatively little is known about the 1921–1922 and 1960 events. Major-element matrix glass analyses from the 1960 products (71.5 wt.% SiO2) are indistinguishable from the 2011–2012 data (72.2 wt.% SiO2), but the 1921–1922 analyses form a discrete, slightly less evolved sub-population (69.0 wt.% SiO2). We utilise rhyolite-MELTS geobarometry to estimate both the storage and extraction depths of all three magmas. For all three eruptions, magma was stored in the shallow crust, between 80–150 MPa (3.5–6.6 km). The 2011–2012 magma body spanned this whole depth range but the 1921–1922 and 1960 magma bodies were more confined in pressure, at 90–112 MPa (4.0–5.0 km) and 123–143 MPa (5.4–6.3 km) respectively. Melt extraction from a parental crystal-mush occurred in the range 70–200 MPa (3.1–9.0 km) for all three eruptions, suggesting contiguous melt segregation and storage in the shallow crust. Finally, we discuss whether the deeper magma storage in 1960 reflects the influence of a seismic trigger by events associated with the Mw9.5 Great Chilean earthquake.