Reconnaissance geophysics and geology of the Pinacate craters,Sonora, Mexico

The Pinacate volcanic field of northwest Sonora, Mexico contains eleven tuff-rimmed explosion craters as well as hundreds of cinder cones. A multiphase eruptive and collapse history for each of the craters is evidenced by: cinder cones exposed in cross-section in crater rims, rim-breaking cinder cones, major eccentric vents, erosion hiatuses between tuff deposition, and coalescing craters exhibiting differeng degrees of erosion. Basaltic intrusions occurred along ring fractures and in the center of at least one crater. Magnetic surveys indicate that explosion craters have tuffaceous feeder vents whereas cinder cones have basaltic, highly magnetic plugs. Computer models illustrate that magnetic terrain effects can contribute to anomalies observed associated with craters, and need to be considered where magnetic surveys include irregularities such as rims or peaks.