Structural characterization and K–Ar illite dating of reactivated, complex and heterogeneous fault zones: lessons from the Zuccale Fault, Northern Apennines
We studied the Zuccale Fault (ZF) on Elba, part
of the Northern Apennines, to unravel the complex deformation
history that is responsible for the remarkable architectural
complexity of the fault. The ZF is characterized
by a patchwork of at least six distinct, now tightly juxtaposed
brittle structural facies (BSF), i.e. volumes of deformed
rock characterized by a given fault rock type, texture,
colour, composition, and age of formation. ZF fault
rocks vary from massive cataclasite to foliated ultracataclasite,
from clay-rich gouge to highly sheared talc phyllonite.
Understanding the current spatial juxtaposition of these BSFs
requires tight constraints on their age of formation during the
ZF lifespan to integrate current fault geometries and characteristics
over the time dimension of faulting. We present
new K–Ar gouge dates obtained from three samples from
two different BSFs. Two top-to-the-east foliated gouge and
talc phyllonite samples document faulting in the Aquitanian
(ca. 22 Ma), constraining east-vergent shearing along the ZF
already in the earliest Miocene. A third sample constrains
later faulting along the exclusively brittle, flat-lying principal
slip surface t