Silicic calderas in arc settings: Characteristics, distribution, and tectonic controls

Abstract

Silicic calderas represent the surface expressions of large silicic magma bodies. Although development of sizable volumes of granite, sensu lato, is considered key in stabilizing continental crust, the factors that contribute to its origin are debated. Based on a comprehensive literature review, we analyze the characteristics, tectonic settings, and spatial distributions of 108 large (≥5 km diameter), Quaternary, silicic (>63 wt% SiO 2 ) calderas in arc settings. Generally, arcs associated with trench-normal convergence rates between 70 and 95 mm/yr are more likely to host silicic calderas, indicating that a larger flux of basalt favors formation of evolved magma, although New Zealand is a notable exception. The nature of the crust controls the types of calderas that develop; large and rhyolitic calderas tend to occur on old, thick, continental crust near preexisting structures and/or areas under local extension. In continental margins, silicic calderas are distributed more widely behind the volcanic front than are typical arc volcanoes. In addition, arcs with greater caldera densities tend to be young or have migrated, suggesting that the overlying crustal column can be depleted of a low–melting-temperature component over time. These results allow geologists studying batholiths to use silica content, size, and distribution of plutons to infer the tectonic properties of ancient arcs.