Evolution of the geometry of normal faults in the Oligocene volcanic field of the Mesa Central, Mexico

摘要

We document that the direction of fault traces and the long axis of volcanic domes show a similar distribution, which indicates that the normal faults controlled in some way the location of volcanic rocks. In this study we analyze the evolution of the faults from a geometric point of view, without considerations about the volcanic processes. Bed tilt was controlled by fault block rotation with continuous fault activity. Multi-peak profiles of bed tilt along the fault strike and evident corrugation of the fault traces in the study area should be partly due to segment linkage during fault evolution. Some normal faults are associated with mode I fracture mechanism, whereas some other faults are due to mode II fracture mechanism according to the calculated initial dips. The plot of maximum fault displacement (D) versus trace length (L) is very scattered. Faults with D/L ratios larger than 0.l and smaller than 0.1 can be distinguished; these two fault groups are produced by the effects of fault evolution and sampling. The principal factor influencing D/L ratios is the interaction and linkage among the faults. In addition, fault block rotation, fault initial mechanism, lithology of volcanic rocks, and denudation are other factors.