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Dynamic Development and Reactivation of a Newly
Discovered Frictional-Plastic Deformation System
Joseph L. Allen, Department of Physical Sciences, Concord University, Athens, WV
Understanding the origin and early geologic evolution of faults is
important to petroleum exploration and reservoir development because they
serve as zones of weakness in the crust that are preferentially reactivated
and rejuvenated through time. The reactivation of old zones of weakness
can subsequently serve as a path for the migration of fluids. Reactivation
can also influence the distribution, thickness, and 3-D shape of overlying
sedimentary strata that form petroleum traps.
The goal of this research is to define controls on the location, geometry, and dynamics of fault rupture in the middle part
of the Earth’s crust (approximately 10-12 km deep), and investigate how these geologic structures localized shallow
fault reactivation that affected sedimentary strata 1.4 billion years later. We have mapped the distribution of rocks
recording fault-related rupture in the middle crust (see photo above left of the geologically rare fault-related rock
“pseudotachylyte”). These fault-related rocks are the fossil record of ancient earthquakes in the middle crust. The fault
zone was found to be remarkable uniform in orientation when it formed in the middle crust (see figure below left), and
this uniform orientation controlled reactivation in the shallow crust (<10 km deep) 1.4 billion years later (see photo
below right showing northeast-oriented fold in younger sedimentary strata).