Kinematics of Transrotational Tectonism in the California Transverse Ranges and Its Contribution to Cumulative Slip Along the San Andreas Transform Fault System

Abstract

The evaluation of total tectonic transport across a complex transform fault system of finite width requires taking into account tectonic rotations about vertical axes of crustal blocks within the transform zone. The Luyendyk hypothesis of transrotation, based on paleomagnetic evidence for tectonic rotations within the Transverse Ranges, offers the means to reconcile disparate estimates of San Andreas transform motion based on (1) summation of fault offsets on land, and (2) global analysis of seafloor magnetic anomalies. In recent years, expanded geodetic data and improved global plate circuits have largely resolved the discrepancy for current transform motion rate, but not the discrepancy for cumulative transform slip through time.A coherent kinematic model for transrotational deformation developed in this paper indicates that discrepancies between overall displacements inferred from offsets of geologic features and from worldwide correlation of sea-floor magnetic anomalies can be reconciled for at least the past 16-22 m.y. by allowing explicitly for transrotational effects. All summations of fault displacements within the San Andreas system that do not take the paleomagnetic evidence for transrotation into account are discounted as incomplete. The kinematic model is compatible with a range of dynamic models for transrotation, and does not permit a choice to be made among alternate geodynamic rationales.The kinematic model includes preferred "pinned" and alternate "decoupled" geometric variants, and describes the movements of (1) structural panels bounded by sinistral faults and rotating clockwise, and (2) irrotational sliding blocks bounded by dextral faults subparallel to the San Andreas trend. Geometric expressions are presented for cumulative slip on the rotating sinistral faults and the nonrotating dextral faults, as the sliding blocks move out of the way of the rotating panels, in terms of initial and final angles between the trends of the sinistral and dextral faults, and for the spacings of the faults. The net shear imparted parallel to the transform direction by panel rotation within the shear system can also be calculated. Analysis shows that transpressional and transtensional deformation is the general rule within domains of both rotating panels and sliding blocks associated with transrotation.The application of the kinematic model to tectonic analyses of key geologic provinces yields the following comparative results. (1) Net slip on the array of eastwest sinistral faults in the eastern Transverse Ranges, but not the observed distribution of slip on individual faults of the array, is predicted successfully by calculations.(2) Net slip across northwest-trending dextral faults of the Mojave block is compatible with the transrotational shear imparted by the eastern Transverse Ranges, provided allowance is made for partial transposition of the shear locus through the

Pore pressure sensitivities to dynamic strains: Observations in active tectonic regions

“…Even though strain rates on the SJF are of the order of the southern portion of the SAF , the SJF has at least an order of magnitude less cumulative displacement than the SAF [Dickinson, 1996] and is structurally complex [Zigone et al, 2014]. This implies that spatial variations in pore pressure response across the SJF are aggregate BARBOUR SEISMIC RESPONSE OF PORE PRESSURE MEASUREMENTS 5872 Figure 5.…”

Paleotectonics of a complex Miocene half graben formed above a detachment fault: The Diligencia basin, Orocopia Mountains, southern California

“…The uppermost Oligocene/ Lower Miocene Vasquez Formation is rotated 40°, whereas the Middle Miocene Mint Canyon Forma tion has not been rotated, thus bracketing the time of clockwise rotation as 18-16 Ma; ~55° of clockwise rotation occurred at this time, with later counterclockwise rotation of ~15°, resulting in a net clockwise rotation of 40° (Terres, 1984;Terres and Luyendyk, 1985;Luyendyk, 1991). The western Transverse Ranges have been rotated clockwise more than 90°, beginning around 18 Ma (Luyendyk, 1991;Nicholson et al, 1994;Dickinson, 1996;Ingersoll and Rumelhart, 1999;Ingersoll, 2008a). Figure 16C shows reversal of clockwise rotation of 40° for the Soledad area, and reversal of clockwise rotation of 90° for the western Transverse Ranges.…”

“…1 and 2). Clockwise vertical-axis rotation of ~41° affected several blocks of the eastern Transverse Ranges between 10 and 4.5 Ma, with the Diligencia basin being rotated ~110° and rotations of individual blocks of up to 180° near the Clemens Well fault (Carter et al, 1987;Richard, 1993;Dickinson, 1996;Law et al, 2001). The increase in magnitude of vertical-axis rotation of basalt within the Diligencia Formation from ~110° to 180° is best explained by having most of the regional rotation take place prior to local shortening by faulting and folding, which locally increased clockwise rotation (Terres, 1984;Law et al, 2001).…”

Acceleration and evolution of faults: An example from the Hunter Mountain–Panamint Valley fault zone, Eastern California

“…However, before this can be realized, we need to better understand the various sources for discrepancies between rates spanning different times. For large offset, mature fault zones such as the Carizzo segment of the San Andreas fault in central California, geodetic rates averaged over decadal time scales, and geologic rates over longer time scales, are usually very similar (Sieh and Jahns, 1984;Lisowski et al, 1991;Dickinson, 1996;Meade and Hager, 2005;Liu-Zeng et al, 2006;Schmalzle et al, 2006).…”