Slip partitioning along a continuously curved fault: Quaternary geologic controls on Denali fault system slip partitioning, growth of the Alaska Range, and the tectonics of south-central Alaska

Abstract

Active transpressional fault systems are typically associated with the development of broad zones of deformation and topographic development; however, the complex geometries typically associated with these systems often make it difficult to isolate the important boundary conditions that control transpressional orogenic growth. The Denali fault system is widely recognized as transpressional due to the presence of the Denali fault, a major, active, right-lateral fault, and subparallel zones of thrust faults and fault-related folding along both the north and south flanks of the Alaska Range. Measured Quaternary and Holocene slip rates exist for the Denali fault system and portions of the adjacent thrust system, but the partitioning of fault slip between contractional and translational components of this transpressional system has not been previously studied in detail. Exploiting the relatively simple geometry of the Denali fault, we analyze the style and distribution of active faulting within the Alaska Range to define patterns of strain accommodation and determine how contractional and translational strain is partitioned across the Denali fault system. As the trace of the Denali fault curves by ~70° across central Alaska, the mean strike of the thrust system to the north remains subparallel to the Denali fault, while to the south, the few faults with known or suspected Quaternary offset are oblique to the Denali fault. This relationship suggests that as the Denali fault system accommodates local fault-parallel strike slip, it partitions the residual part of the regional NW-directed plate motion into NW-SE shortening south of the Denali fault and shortening perpendicular to the Denali fault to the north. The degree of slip partitioning is consistent with a balanced slip budget for the two primary faults that contribute displacement to the Denali fault system (the eastern Denali fault and Totschunda fault). The current obliquity of displacement south of the Denali fault is the result of the late Cenozoic development of the Totschunda fault, which provides a more direct connection for the transfer of strain from the Fairweather transform fault to the Denali fault system. The transmitted strain is partitioned into right-lateral slip on the Denali fault and into Denali fault-normal shortening that is accommodated by thrust faulting in the Alaska Range and distributed left-lateral slip faulting within interior Alaska to the north.

Tectonic drivers of the Wrangell block: Insights on fore‐arc sliver processes from 3‐D geodynamic models of Alaska

“…A purely northwest motion of the Wrangell block with variable slip along the Denali fault has also been proposed [ Mériaux et al , ]. However, new interpretations of geologic studies suggest that the Wrangell block has both northwest motion and CCW rotation [ Haeussler , ; Bemis et al , ; Waldien et al , ]. Thus, the 3‐D geodynamic models presented here provide a dynamic mechanism for that motion, that is, the driving force of the flat slab and its coupling to the base of the upper plate.…”

Shear Wave Splitting and Mantle Flow Beneath Alaska

“…The western portion is approximately subducting with the Pacific plate and is likely the cause of the flat‐slab subduction in the easternmost Alaska subduction zone (Christeson et al, ; Eberhart‐Phillips et al, ). To the east, the thicker portions of the Yakutat block are being accreted to coastal Alaska and several major right‐lateral strike‐slip faults accommodate the associated deformation (Bemis et al, ; Bemis & Wallace, ; Page et al, ) (Figure ). Volcanism in the Wrangell volcanic field is located north of the accreting portion of the Yakutat block (Figure ).…”

Pace and Process of Active Folding and Fluvial Incision Across the Kantishna Hills Anticline, Central Alaska

“…Black numbers are slip rates (m/kyr) from Haeussler et al (2017a) for the combined Totschunda Fault (TF) and eastern Denali Faults (eDF), and segments of the central Denali Fault (cDF). Queried 3‐m/kyr shortening rate from Bemis et al (). Seismic zones from Tape et al ().…”

“…Researchers attribute the westward decrease in slip rate to right transpression across thrust faults that splay southwest off the Denali Fault (Haeussler et al, ), and to partitioning of the north‐northwest component of southern Alaska block convergence across an array of thrust faults and folds situated north of, and parallel to, the Denali Fault (the northern Alaska Range thrust system; Bemis & Wallace, ; Haeussler, ; Mériaux et al, ; Bemis et al, , ; Haeussler, Matmon, et al, ). This deformation fits a kinematic model in which the southern Alaska block (a) rotates counterclockwise at rates equivalent to Denali Fault slip, (b) shortens internally across the right‐transpressive faults, (c) extrudes westward at a modest pace, and (d) translates north‐northwest and indents central Alaska at a rate commensurate with shortening across the northern Alaska Range thrust system (Haeussler, Matmon, et al, ).…”

“…This deformation fits a kinematic model in which the southern Alaska block (a) rotates counterclockwise at rates equivalent to Denali Fault slip, (b) shortens internally across the right‐transpressive faults, (c) extrudes westward at a modest pace, and (d) translates north‐northwest and indents central Alaska at a rate commensurate with shortening across the northern Alaska Range thrust system (Haeussler, Matmon, et al, ). Absent direct constraints, Late Pleistocene rates of southern and central Alaska deformation off the Denali Fault remain unquantified, leaving unclear the far‐field distribution of strain related to the Yakutat microplate collision (e.g., Bemis et al, ; Haeussler, Matmon, et al, ).…”