Structure of the Michoacán-Guanajuato Volcanic Field, Mexico

The distribution and the alignment of volcanoes and fault scarps provide new insights into the structural framework of the Michoacán-Guanajuato volcanic field. A total of 1894 volcanoes occur over an area of 34,500 km2. Contour maps of the density of volcanoes and average volcano height indicate a shift from polygenetic to monogenetic volcanism from north to south in the field. Volcano edifice height has a bimodal density distribution, which can be described by two populations with mean heights of 95 m and 510 m. Plotting the distribution of these two populations on separate contour maps reveals a N35E trend in monogenetic volcanoes and a N60W trend in polygenetic volcanoes. Fault scarps cut Tertiary volcanic rocks and older Quaternary volcanoes, but are overprinted by volcanoes and lava flows in the central part of the field. Fault scarps define two fault zones oriented N60E in the northeastern part of the area and N60W in the northwest part of the area. E-W trending faults are common and alignments of volcanoes often parallel these faults. Regional trends in volcano distribution appear to be related to plate convergence. The N60W trend of the polygenetic volcanoes is colinear to the western Trans-Mexican volcanic arc, parallel to the Middle America Trench, and parallel to a major fault zone, and represents an extinct volcanic arc. The N35E band of monogenetic volcanoes may reflect the segmentation of the subducted plate