The temporal record of magmatism at Cerro Uturuncu, Bolivian Altiplano

Abstract

Twenty-six new 40 Ar/ 39 Ar plateau ages for 23 lavas and domes from the Uturuncu volcano in the Altiplano of SW Bolivia reveal a protracted eruptive history from 1050 + 5 to 250 + 5 ka. Eruptions have been exclusively effusive, producing some 50 km 3 of high-K dacites and silicic andesites. Bimodal mineral compositions, complex mineral textures, the presence of andesitic magmatic enclaves within dacites and linear chemical trends on binary element plots all indicate that magma mixing is an important petrogenetic process at Uturuncu. Post-458 ka, distinct high and low MgO-Cr magmas are resolved. These magmas erupt during similar times, suggesting that eruptions are tapping different parts of the magma system, albeit from the same vent system. Volcanic and petrological features are consistent with the existence of a vertically extensive magma mush column beneath Uturuncu, and calculated buoyancy forces are sufficient to drive effusive eruptions. Eruptive activity is episodic, with six eruptive periods separated by hiatuses of .50 kyr. Cumulative volume curves demonstrate that the majority of the edifice formed between 595 and 505 ka. The episodicity of eruptions is most likely to be related to fluctuations in the magma supply to the underlying Altiplano-Puno Magma Body.Supplementary material: Detailed 40 Ar/ 39 Ar data, and lava flow and dome areas, volumes and stratigraphic ages where absolute ages are lacking are available at www.geolsoc.org.uk/ SUP18815The tempo of crustal volcanism is a complex interplay of magma supply rate to the crust, magma storage within the crust, and the regional and local stress regime (Caricchi et al. 2014), as well as nonmagmatic factors, such as glaciations that affect crustal loading and magma generation (e.g. Maclennan et al. 2012). Unravelling the importance of these factors in a given magmatic province requires integration of geochronology, petrology, tectonics (e.g. Hawkesworth et al. 2004;Davidson et al. 2005) and climate. In the case of long-lived, potentially explosive silicic arc volcanoes, detailed geochronological studies are surprisingly scarce. Many investigations focus on the overall geochemical variation at a given volcano, but the temporal changes in chemistry, erupted volume or eruptive style are rarely quantified. Consequently, our understanding of the evolution of crustal arc magma systems over periods of thousands to hundreds of thousands of years is limited, and represents a significant impediment to modelling. Examples of continental stratovolcanoes with compositional and physical attributes such as mean output rate integrated with detailed, accurate geochronological data include Montserrat (Harford et al.

Thermomechanical modeling of the Altiplano-Puna deformation anomaly: Multiparameter insights into magma mush reorganization

“…4). While other deeper storage regions from which andesite has been sourced may exist beneath Uturuncu, our assumption is consistent with the available petrological, geochemical, and geophysical constraints (Michelfelder et al, 2014;Muir et al, 2015;Laumonier et al, 2017). The top of the column at z = -6 km marks the upper bound of the BDTZ, for which we set a temperature of T = 387 °C (660 K) (Priestley et al, 2008).…”

“…Gottsmann et al | Mush reorganization at Uturuncu GEOSPHERE | Volume 13 | Number 4 the heat source for crustal anatexis (Muir et al, 2015). These observations and interpretations are consistent with the hot zone concept of Annen et al (2006), whereby repeated incursions of hot mantle-derive magmas into the lower or mid-crust drive differentiation by a combination of crystallization and anatexis.…”

“…The piecemeal assembly and eruption of chemically distinct batches of dacite magma from a chemically heterogeneous magma system beneath Uturuncu dominated the eruptive history during its protracted activity from 1050 to 250 ka (Muir et al, 2015(Muir et al, , 2014a. Experiments determined the preeruptive dacite storage pressures at Uturuncu to be 100 ± 50 MPa (Muir et al, 2014b) at ~870 °C (1143 K).…”

The temporal evolution of chemical and physical properties of magmatic systems

“…This paper shows that the relative distance and thickness of metamorphic isograds depend not only on the total volume of magma injected, but also on the frequency at which single magma batches are injected. In another contribution, Muir et al (2015) combine radiometric dating with remote sensing to constrain extrusive magma fluxes from Uturuncu Volcano in the Bolivian Altiplano. Their data show that the periodicity of the eruptions and the volume released in each extrusive event are not constant.…”

Magma diversity reflects recharge regime and thermal structure of the crust

“…Understanding the variability and temporal evolution of erupted magma chemistry is critical to quantify magmatic and ore forming processes 1,2,3 , and to anticipate the potential future activity of volcanoes 4 . Detailed age-resolved geochemical records show that some volcanic centres erupt a wide variety of magma compositions, while others produce restricted chemical diversity throughout their lifetime 5,6,7,8,9,10,11,12 (Fig. 1).…”