Orlando Quintela: Linking silicic magma reservoir growth to upper crustal deformation: Insights from the Slaufrudalur pluton, Iceland

Abstract

Silicic magma reservoirs are constructed by the successive emplacement of smaller magma pulses typically at timescales of tens of thousands of years. The construction of magma reservoirs in the upper Earth’s crust triggers volcanic eruptions at surface level. As the underlying reservoirs grow in volume, the probability of volcanic eruptions also increases. The study of silicic magma reservoirs is viewed, in this framework, as a proxy to assessing active volcanism.

On a deeper level, the mechanisms and rates of magma pulse emplacement have severe implications in the structure of the magma reservoir, for example, internal layering and mingling zones. Single magma pulses deform internally by processes that include thermal expansion and contraction, which also influences the magmatic fluid transport within and around the growing reservoir. However, space for magma accumulation and ponding has to be created in the upper crust, which typically involves roof uplift and floor subsidence. Depending on the interplay between pulsed magma emplacement and larger-scale reservoir growth, a structural aureole develops and accommodates deformation around the reservoir. The deformation that affects the surrounding host rocks is directly linked to the mechanisms of magma emplacement.

Here, we focus on the incremental growth of silicic magma reservoirs. We approach the Slaufrudalur pluton (Southeast Iceland), an exposed solidified reservoir, to investigate internal deformation, heat and fluid transport, and host rock deformation. We employ magnetic fabric analysis to decrypt the dynamics of magma reservoir growth, and we do structural analysis of the host basaltic rocks. The first research paper reveals the effects of heat and fluid transport on the magnetic fabric relations, and it proposes interaction and hydrothermal alteration of magma pulses. The second paper identifies and links the architectural elements of the structural aureole to a Riedel shear system with implications for the regional geology of Southeast Iceland. Lastly, the third paper identifies internal deformation structures, and it proposes a model of concurrent magma pulse emplacement and deformation.