A NEWLY DISCOVERED FAULT ZONE NEAR BOONE, NORTH CAROLINA AND CENOZOIC TOPOGRAPHIC REJUVENATION OF THE SOUTHERN APPALACHIAN MOUNTAINS

During a recent bedrock mapping project near Boone, North Carolina, we discovered a brittle fault zone at the northern edge of the Grandfather Mountain window along what was previously mapped as the Linville Falls thrust fault. The minor faults associated with this zone typically have steep dips and strike WNW. There are normal (north-dipping) and reverse (south-dipping) faults and both show south-side-up motion. We are calling this the Boone fault, and it may have accommodated Cenozoic doming and blocky uplift of the southern Appalachians. To test the idea that the Boone fault is a late, post-orogenic structure in an ancient orogen, we performed a paleostress inversion of 187 minor faults. The inversion yields a stress tensor consistent with NNE-SSW extension, which does not fit Paleozoic SE-NW shortening or Mesozoic E-W rifting, but most likely represents Cenozoic NNE-SSW extension associated with doming and blocky uplift of the southern Appalachians.

We analyzed the longitudinal profiles of dozens of streams draining into the fault zone and found numerous knickpoints that are hundreds of meters above the valley floor. In addition to these disequilibrium profiles, some of the streams contain evidence of drainage capture consistent with recent uplift. We interpret the stream disequilibrium as a result of relatively recent motion on the Boone fault. These disequilibrium profiles are similar to those estimated to be Miocene in age by Gallen et al. (2013). Based on the stream geometry, abundance of knickpoints, and the existence of perched floodplains in the headwaters, the knickpoints near Boone are likely associated with Miocene uplift as well. The young faults and disequilibrium landscape suggest the Grandfather Mountain window is not entirely framed by a Paleozoic fault, but rather is bounded in part by a Miocene fault zone. Our data are consistent with a landscape responding to recent uplift, not one that has been steadily eroding since the Paleozoic.