Investigating the relationship between pluton growth and volcanism at an active intrusions in the central Andes

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How magma is emplaced and interacts with its surrounding rock is of central interest in the Earth Sciences. The intrusion of magma into the Earth's crust plays a major role in the dynamics and the evolution of continental crust. In many cases magmas are funnelled upwards and erupt at volcanoes that dot the Earth's surface, particularly in areas where tectonic plates collide. The Andes are part of such a collision zone where large magma bodies (batholiths) form, due to chemical evolution of intruding deeper magma as well as partial melting of surrounding rocks. A common style of volcanic activity in the Andes is the catastrophic eruption of many hundreds to thousands of cubic kilometres of magma in the form of ignimbrites (volcanic rock containing ash and pumice) which often results in the collapse of the magma chamber roof upon eruption, leaving behind more or less ring-shaped surface depressions with diameters of many kilometres. The project is motivated by results obtained from space-borne satellites indicating ground deformation and significant uplift at in the central Andes at Uturuncu volcano, Bolivia, where magma may be accumulating for 270 thousand years. It is suspected that this inflation is caused by the growth of a large magma body at depth. If this interpretation is correct then these anomalies provide an outstanding opportunity to answer questions such as how large magma bodies are assembled in the crust to form plutons, how they evolve, how they relate to volcanism in general and how they manifest at the Earth's surface, potentially before eruption. We aim to find answers to these questions via a coordinated, integrated approach across various disciplines of the Earth Sciences. Central to this ambitious project lies the amalgamation of geodesy, geophysics, geology, petrology and mathematical modelling to document pluton growth in real time. The implications of the proposed work include assessing the role of plutons in continental dynamics and the potential for large volcanic eruptions. We requests funds for the UK component of a collaborative UK-US project, which also involves partners from Spain, Chile and Bolivia. We propose an integrated investigation of the Uturuncu uplift to test the hypothesis that pluton growth is occurring, to document the dynamics of growth, and to explore the links between plutonism, volcanism and tectonics. The core of the study will be a geophysical experiment over a 4-year period to study the ground deformation, mass changes and seismicity, and to image the sub-surface structure beneath the volcano. The geophysical experiment will be complemented by geological and petrological investigations as well as mathematical modelling to set the geophysical experiment in the context with igneous processes and the long-term magmatic evolution. A key outcome of the research will be a new generation of mathematical models to inform on how large magma chambers grow and which geodetic or geophysical signals we might expect to record at the Earth's surface. We will quantify the nature of the sources responsible for ground inflation by separating the contributions of shallow migration of (hot) water and gases, and deep magma replenishment and ponding, to geophysical signals. We are also interested to find out where these reservoirs are located, how many there are and how they relate to the depth of magma chambers that have led to eruptions in the volcano's past. For the latter, lava morphology studies and petrology will give insights onto the conditions in these magma chambers. We aim at developing advanced models of magma systems embedded in continental crust incorporating complexities such as variable mechanical properties of the crust, plastic deformation of deeper crust as well as the influence of crystallization of gas-saturated magma and shallow hydrothermal systems on ground deformation.