Relations between Subduction Parameters and Magmatism

Abstract

One of the main effects of plate tectonics is volcanism. When two lithospheric plates converge, one must be subducted, usually beneath the younger and less dense plate; this subduction leads to arc volcanoes observed behind the subduction front. This research seeks to test the correlation of various subduction parameters (ie. convergence rate, dip angle, etc.) against the frequency of volcanoes in an arc, or more generally, to find how variation in slab dynamics affects the presence and density of volcanoes at the surface. Previous work published in Jarrard (1986) focuses on the relationships between 26 subduction parameters for 39 modern subduction zones. This work focuses on taking those measured parameters along with other acquired data, and relating them to known volcanic activity. First tested was the reliability of the generally held belief that arc gap is determined by the angle of subduction. Using data from Jarrard (1986), along with data collected from Google Earth, the relation between was found to be good (𝑅2 = 0.77). However, the variability that is present in the data supports the work done previously in England (2003) suggesting that there is greater variation in partial melting depth for each arc than previously thought; 65-130 km. For 35 of the 39 volcanic arcs, volcano count and length of the subduction zone were obtained using Google Earth interactive maps, yielding essentially a volcano concentration for each arc. There is a great degree of variability observed in the volcano concentration, from zero Holocene (recently active) volcanoes observed in the Central Chile subduction zone, to 73 in the Kamchatka arc. As length of subduction increases, a greater number of volcanoes would be expected, however, this accounts for only 19% of the variability of the volcano frequency; there must be other contributing factors (figure 2). Strain class, convergence rate, and maximum earthquake moment were shown to be weakly correlated to the observed volcanism, while slab dip, age, and many other variables appear to have no effect on volcano concentration at the surface. Maximum earthquake moment was the largest contributing factor (R2=0.19), suggesting that no one factor can be attributed to observed volcanism, but likely many factors have an impact.