Altiplano-Puna Volcanic Complex

The Altiplano-Puna Volcanic Complex (APVC) is located in the central volcanic zone of South America. Over the last ~10 million years, a magmatic flare-up has manifested in an extensive ignimbrite plateau which covers around 70,000 square kilometers with over 15,000 cubic kilometers of silicic ignimbrites and lavas that have erupted from several large calderas and source structures.

To date, my work on the APVC has primarily focused on the thermal and chemical evolution of the magma system(s) the fed series of late-pleistocene lava domes, and which represent the most recent manifestation of volcanism from a waning APVC flare-up. Research on the five domes (Chao, Chillahuita, Tocopuri, Chanka, and Chascon Runtu-Jarita) involved a number of investigations and analytical approaches including petrography, thermobarometry, Ar/Ar eruption dating, and zircon geochronology via U-Th and U-Th.

The most impactful part of this research was published in Geology (Tierney et al. 2016) and involved the combination of zircon geochronology and thermochemical modeling to attempt to constrain the rates and volumes of magmatism and pluton formation during a distinct waning stage of the APVC. It was found that the magmatic system that fed the domes was likely active for about 500 ka prior to eruption and all of the domes experience very similar magmatic histories.

A finite-difference thermal- and mass-balance model for open-system magma evolution was developed that assessed the rates of magmatic recharge (i.e. magma flux) required to match observed zircon age spectra. A best fit rate of 1.1x10-3km3/yr results in at least 600km3 of “mushy” intrusions are expected to underpin each of the five domes by time of eruption.

Given the combined volume of 3000km3 for the plutonic volumes, this dwarfs the erupted volumes (~40km3). Moreover, an intrusive to extrusive ratio of 75:1 exceeds commonly cited estimates of 10:1 or even geophysically constrained ratios of 20-35:1 for the duration of the APVC flare-up. Essentially, the work reveals growth of a voluminous pluton in the upper crust during period of relative volcanic quiescence in the waning stages of a large ignimbrite flare-up. It also indicates that eruptive flux is not necessarily always a good proxy for intrusive flux at depth and that significant plutonic volumes can develop during the lulls and waning stages of flare-ups, and that the accumulation of a plutonic body with dimension equivalent to a supereruption does not necessarily culminate in such an event.

Figure 2 from Tierney et al (2016)

Figure 3 from Tierney et al (2016)

Supplemental Figure 8 from Tierney et al (2016)