Decades of study on volcanic arcs have provided insight into the overarching processes that control magmatism, and how these processes manifest at individual volcanoes.
The approach utilizes our basic understanding of the physical processes involved in volcanic arc formation to find intensive variables, such as specific heat and density, which can be used to quantitatively link and compare large-scale datasets from different disciplines.
We also incorporate statistical techniques to minimize the effects of nonrepresentative geochemical sampling.
We believe that the potential causes of volcanic diversity in arcs can be framed as two end-member hypotheses (Fig. In the first, the observed variations in arc volcanism are produced solely by differences in crustal processes and properties, with constant mantle flux along strike.
Alternatively, variations in volcanic fluxes and compositions are primarily the result of differences in the underlying mantle flux (controlled in turn by variations in the downgoing slab and/or mantle wedge), with processes within the arc crust playing only a secondary role.
The result is that geochemical and petrological datasets are hard to reconcile and compare with the regional and integrative datasets produced by many geophysical studies, and this leads to qualitative, rather than quantitative comparisons.
Finally, understanding of the larger-scale controls on volcanism and magmatism is also limited by the common approach of focusing on only one part of the subduction system (e.g., upper crust or mantle wedge), with very limited consideration of the feedbacks and interactions that occur across the entire arc system.
This is exemplified by the summary cartoon figures that classically accompany papers from the relevant scientific communities (including those we have written ourselves), with “disembodied volcanoes” missing the lower half of the magmatic system in the volcanology literature, or oversized “emoji volcanoes” that only allude to a shallower magmatic system in mantle-oriented petrologic studies (Fig. Representative figures from different communities studying volcanoes.
Left, archetypical mantle-focused subduction cartoon with an “emoji volcano” that only alludes to a shallower magmatic system.
However, there are other important aspects of arc volcanism that are quite poorly explained by existing models.
One notable example is the dramatic diversity evident in volcanic activity within the same volcanic arc.