Relationships of cinder cones to stratovolcanoes in the Cascadia subduction zone

Basaltic magmatism may undergo magmatic differentiation and promote crustal melting that may produce more silicic volcanic centers like stratovolcanoes. Despite this fundamental tenet of igneous petrology, very few studies have quantified in detail the spatial distribution of mafic centers, like cinder cones, and larger silicic centers, like stratovolcanoes. Here, I explore these relations in the Cascades of the Pacific Northwest. Cinder cones distributed in the vicinity of central stratovolcanoes and shield volcanoes in the Cascades range are surface expressions of basaltic magma. I mapped all the volcanoes, including stratovolcanoes, shield volcanoes, cinder cones and domes, in the Cascadia volcanic arc based on 10 m resolution DEM. Histograms show the distribution pattern of cinder cones around stratovolcanoes and shield volcanoes, for which volumes are calculated. The distribution of all volcanoes with latitude is compared with geophysical data such as cumulative surface heat flow, seismic velocity models and crustal thicknesses. In the northern Cascades, only stratovolcanoes and a few cinder cones are distributed, while in the southern Cascades, all types of volcanoes exist and cinder cones are densely distributed around stratovolcanoes and shield volcanoes. There are four locations in Oregon and California where cinder cones show obvious alignment as a result of crustal extension. Crustal extension, the largest surface expressions of basaltic magma and the largest volumes of stratovolcanoes all occur in the southern part of the Cascades where the largest negative shear wave anomalies in the mantle occur as well. In relation to central volcanoes, cinder cones are mostly distributed in the range of 5 to 25km of the central volcano and tend to die out away from the central volcanoes. This distribution pattern supports recent models wherein basaltic magma drives stratovolcano volcanism but is prevented from erupting in the vicinity of the central volcano due to density filtering.