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

Resumen

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 profi les 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 0.1 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 infl uencing 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.