Understanding the contractional history of Surprise Canyon, California through digital field mapping, 3D modeling, and U-Pb zircon geochronology
Detailed digital mapping of lower-middle Surprise Canyon has revealed a more complex structure than previously interpreted. Rock units derived from the metamorphosed equivalents of the Pahrump Group exposed in Surprise Canyon display juxtapositions inconsistent with stratigraphic variations suggested in previous studies. This study proposes a contractional history of the central Panamint Mountains defined by two kinematically distinct and geochronologically constrained deformation events. D1 is characterized by a shallow dipping, NNW striking L and LS tectonite fabric ubiquitously observed in all metasedimentary and basement units. F1 folds are mesoscopic in scale and isoclinal with an axial planar S1 foliation. A prominent mineral and stretching lineation is developed on S1, parallel to the shallow NNW trending F1 axes. Large scale D1 structures were not observed in the mapped area. Four samples were collected from Surprise Canyon for LA-ICP-MS zircon U-Pb dating. Problems with high U content, metamict zircon development, and inheritance complicate the U-Pb system but the data collectively suggest the main metamorphism occurred between a. 182 – 237 Ma. D2 is characterized by a steeply W-dipping, S2 crenulation cleavage that crosscuts S1 and is axial planar to F2 folds. D2 folding is macroscopic in scale and is defined by tight to open folds that refold the F1 folds about similar, NNW-trending, shallow-plunging axes. A family of leucogranite plutons in the area post-date D1 and pre-date D2. An attempt to date one of these, a small pluton interpreted as an offshoot of the Hall Canyon pluton in Surprise Canyon produced incoherent data but a leucogranite sample from Wildrose Canyon with this relative age yielded a. 89.7 +/- 2.2 Ma date, indicating D2 is no older than 89.7Ma. Three samples from Pleasant Canyon were also dated, corroborating previous work that indicated a Proterozoic age for the World Beater Complex augen gneiss, as well as a micaceous quartzite. The moderate to high finite strain recorded in the LS tectonite fabric of the D1 event is attributed to deformation within a ductile shear zone; however, further study is needed to the tectonic setting of this event. 3D modeling of the mapped area highlights D2 mesoscopic structure and unit thickness variability.
Cobb, Joshua Azael, "Understanding the contractional history of Surprise Canyon, California through digital field mapping, 3D modeling, and U-Pb zircon geochronology" (2014). ETD Collection for University of Texas, El Paso. AAI1600313.