Spatiotemporal patterns in glaciation and deformation across the Sierra Nevada---Walker lane transition

This study centers on Tertiary and Quaternary deformation across the transition from the central Sierra Nevada to Walker Lane belt. Rates and styles of deformation are derived from: (i) geologic and geomorphic mapping, (ii) detailed chronological studies of Quaternary glacial deposits using 10Be surface exposure dating techniques, (iii) differential GPS and total-station surveys of faulted landforms, and (iv) paleomagnetic sampling of Tertiary volcanic rocks. These data enable me to define mean deformation rates, and also, by utilizing markers of different ages, to test for changes in rates through time. Of special interest is my ability to document rates and timing of faulting, rotations at multiple timescales, which enable me to (1) assess the constancy of fault slip rates and (2) quantify rigid-body rotations.;Sites throughout the range indicate Last Glacial Maximum (LGM) retreat at 18.8 +/- 1.9 ka (2sigma) that suggests rather consistent changes in atmospheric variables, e.g., temperature and precipitation, throughout the range. The penultimate glacial retreat occurred at 144 +/- 14 ka (2sigma). At each site where multiple glacial deposits are deformed across range front faults, data permit that average rates are temporally constant: 0.3 +/- 0.1 mm yr-1 (mode and 95% CI) or 0.4 +0.3/-0.1 mm yr-1 over timescales of ∼20 ky and ∼150 ky. Where Tertiary and Quaternary deposits are differentially offset across the same fault, fault slip rates increase from 0.1-0.2 mm yr-1 to 0.3 +/- 0.1 mm yr-1 (95% confidence) from the Late Miocene to Quaternary. However, slip rates display high spatial variability over the last ∼20 ky, with ranges from 1.3 +0.6/-0.3 mm yr-1 to 0.3 +/- 0.1 mm yr-1 along strike. In the region where slip rates decrease along strike, paleomagnetic data from Upper Miocene volcanic rocks suggest clockwise vertical axis block rotations of 19-85°. Results from additional volcanic strata suggest clockwise rotations (R +/- DeltaR, 95% confidence limits) of 74 +/- 8°, 42 +/- 11°, and 14 +/- 9° since Middle Miocene (12-20 Ma), Late Miocene (8-9 Ma), and Pliocene (∼3 Ma) time, respectively.;Few previous studies have developed such a high-precision glacial record over such a broad spatial range (400 km N-S). This chronology can be readily applied to glacial deposits elsewhere in the Sierra Nevada for a broad range of climatic, geomorphic, and tectonic studies. Absolute ages for geomorphic markers facilitate the unique opportunity to investigate the spatial and temporal evolution of fault systems across an incipient plate boundary. High resolution slip rate histories across normal faults that span >100 ky are rare. My data are consistent with steady tectonic rates when integrated over multiple seismic cycles at timescales of ∼20 ky and ∼150 ky for individual faults and over three Tertiary timescales for rotating blocks.;Furthermore, my data permit that block rotation rates are steady within the resolution of my paleomagnetic analysis (<50%) over 1 My to 10 My timescales. The detection of such block rotations is notable, but even rarer is the opportunity to reconstruct the rotations through time. My results show that significant deformation can be accommodated by block rotation and folding, especially in zones of transpression or transtension. Identification of rotations and folding is required for constructing valid deformation models, e.g., block models used to interpret modern geodetic data. Constraints on the timing of transrotational deformation provide striking evidence for transmission of far-field stresses and dextral shear deep into the North American plate beginning in the Middle Miocene. The kinematic patterns of faults that facilitate block rotations underscore the potential importance of inherited crustal anisotropy. Regional spatial patterns in fault slip rates suggest focusing of extension on the Sierra Nevada frontal fault zone in the Mono Basin, and transfer of slip among multiple normal faults and block rotations to the north between the Sierra Nevada and central Walker Lane belt. Along-strike changes in deformation modes indicate that zones of transtension, transpression, transrotation, and partitioned extension with dextral shear can all occur within a compact area. (Abstract shortened by UMI.)...