Quartz Cementation Modeling to Elucidate the Timing of Deformation along the Pine Mountain Overthrust, Eastern Kentucky

In sandstones of the middle Pennsylvanian Lee and Breathitt formations along the Pine Mountain Overthrust, the proportion of inter- and intra-granular authigenic quartz differs markedly between samples of contrasting deformational state. Accurate assessment of quartz cement volumes in deformed (cataclasized) and undeformed sandstones was facilitated by the use of cathodoluminescence imaging. Relatively undeformed sandstones contain a dominant early generation of intergranular quartz (red luminescing) whereas fault gouge rocks contain both the early, pre-deformational, generation of intergranular cement and also later, more abundant intragranular quartz (blue luminescing) precipitated within the crushed grains. Quartz cementation modeling (Touchstone®) indicates that emplacement of the pre-deformation intergranular cements within the gouges was complete by 263 to 278 Ma, roughly corresponding with published estimates of the timing of movement on the overthrust.

Intragranular fracture surfaces generated during fault movement provided nucleation substrates favorable for the emplacement of substantial amounts of intragranular quartz (up to 11 volume percent in the Lee Formation). The diagenetic histories of different samples of Breathitt and Lee sandstones diverged markedly as a consequence of their deformation history and the cementation history of these rocks constitutes a chemical record that is relevant to deciphering the timing of deformation.