A volcanic production rate for the Mariana island arc

Despite the importance of volcanic production rates along subducting plate boundaries, few reliable values are available. A well-constrained rate has here been determined for the past 5 m.y. in the Mariana island arc. The calculation covers the period during the opening of the Mariana Trough (an active back-arc basin) in which the volcanic centers are located and most volcanic products are contained. About half the extruded volcanic rocks occur in central cones, with the other half in a large volcanicclastic apron. After correction of volumes for porosity and for changes in mineral densities, the average extrusion rate of 12.4 km³/km/m.y. was calculated. The local rate varies along the arc roughly as does the subduction rate. Before quantification of that correlation can be made, however, apparent temporal fluctuations of volcanism on a global scale, which do not appear to be correlated with subduction rates, must be examined and explained.