QUANTIFICATION OF THE SPATIAL RELATIONSHIPS BETWEEN POPULATIONS OF FAULTS AND VOLCANOES: ASSESSING THE RELATIVE ROLES OF SOURCE GEOMETRY AND UPPER CRUSTAL STRUCTURE on THE DISTRIBUTION OF VENTS

The relationships between magmatism and faulting are well-defined at a plate tectonic scale (e.g. subduction-arcs). However, at the scale of regions/provinces and individual volcanic fields the relationships are less clear despite numerous studies that conclude close spatial and genetic relationships between individual and populations of faults and volcanoes. In this study we present a quantitative investigation of the spatial distribution of vents and faults within five volcanic fields from the Basin and Range, Colorado Plateau and eastern Snake River Plain (ESRP) Provinces, as well as the Japan and Central American arcs. These volcanic fields were chosen for their tectonic setting, the fact that they have been well-mapped, and have been cited as examples of volcanic fields where upper crustal faulting has played a fundamental role in the spatial distribution of vents. Additionally, tomographic data of upper crustal and mantle velocities are available for three of the volcanic fields. Density distribution maps of vent populations for individual volcanic fields are generated using a Gaussian kernel function. The results of this study illustrate that at the scale of individual volcanic fields (e.g. the ESRP) the distribution of volcanic vents are not clustered or spatially associated with faults within the field. Rather, for those fields where velocity data are available, the maximum density of vents and the associated optimal bandwidth matrix generally subparallel and coincide with regions of minimum velocities in the upper-most mantle inferred to be the most likely to produce melts. While most optimal bandwidth matrices also subparallel the trend of the fault traces at least one, the ESRP, departs dramatically from this relationship. These results suggest that the spatial distribution of vents fundamentally controlled by the source geometry and only subordinately affected by upper crustal structure.