Christine Siddoway

Authors: Christine Siddoway and Elisa Fitz Díaz. With contributions from Steven A.F. Smith, R.E. Holdsworth, and Hannah Karlsson
Title: FIELD TRIP: Contractional linkage zones and curved faults, Garden of the Gods (Colorado Springs, CO), with illite geochronology exposé
Abstract: FIELD TRIP GUIDE: Contractional linkage zones and curved faults, Garden of the Gods, with illite geochronology exposé

This trip examines the structural geology and fault geochronology of Garden of the Gods, Colorado. An enclave of 'red rock' terrain that is noted for the sculptural forms upon steeply dipping sandstones (against the backdrop of Pikes Peak), this site of structural complexity lies at the south end of the Rampart Range fault (RRF) in the southern Colorado Front Range. It features Laramide backthrusts, bedding plane faults, and curved fault linkages within subvertical Mesozoic strata in the footwall of the RRF. Special subjects deserving of attention on this SGTF field trip are deformation band arrays and younger-upon-older, top-to-the-west reverse faults—that well may defy all comprehension!
The timing of RRF deformation and formation of the Colorado Front Range have long been understood only in general terms, with reference to biostratigraphic controls within Laramide orogenic sedimentary rocks, that derive from the Laramide Front Range. Using 40Ar/39Ar illite age analysis of shear-generated illite, we are working to determine the precise timing of fault movement in the Garden of the Gods and surrounding region provide evidence for the time of formation of the Front Range monocline, to be compared against stratigraphic-biostratigraphic records from the Denver Basin. The field trip will complement an illite geochronology workshop being presented by Elisa Fitz Díaz on 19 June. If time allows, and there is participant interest, we will make a final stop to examine fault-bounded, massive sandstone- and granite-hosted clastic dikes that are associated with the Ute Pass fault. These are newly demonstrated to be Neoproterozoic in age. There will be four hikes of short to moderate length, that entail off-trail walking and, in one instance, steep, rough terrain.
Field Trip Guide: Front Range monocline and Structure of Garden of the Gods, CO, with illite geochronology (Acrobat (PDF) 8.7MB Jun14 14)