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Kinematics and Transfer Mechanisms of Strain Accommodation at the Transition between the Northern and Central Walker Lane, Western Nevada
AuthorCarlson, Chad W.
AdvisorFaulds, James E.
Geological Sciences and Engineering
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The Walker Lane is a relatively young and developing tectonic intraplate boundary, where ~20% of the dextral motion between the Pacific and North American plates is accommodated. Paralleling the more discrete, well-developed, and through-going San Andreas fault system to the west, the Walker Lane consists of discontinuous structural domains characterized by systems of dextral, sinistral, and normal faults. These domains occupy a wide belt of deformation accommodating the northwestward translation of the Sierra Nevada microplate relative to the bulk of the Basin and Range province. The manner in which some these disparate faults systems accommodate and transfer dextral strain remain enigmatic and are relatively understudied. Also, it has been suggested that the Walker Lane will eventually mature and take over as the principal tectonic boundary between the Pacific and North American plates in the future. As such, the Walker Lane provides a natural laboratory to examine the early development of a major tectonic plate boundary.At the transition between the central and northern Walker Lane, all three characteristic types of Walker Lane structural domains reside, share boundaries, and have been documented to accommodate regional dextral shear. In the central Walker Lane (Walker Lake structural domain), northwest-striking dextral faults accommodate northwest translation of crustal blocks. Northwest of these dextral faults, east-northeast-striking sinistral faults and oroclinal flexure in the southern part of the northern Walker Lane (Carson structural domain) accommodate clockwise, vertical-axis rotation of sinistral fault-bounded blocks. A region of northerly-striking normal faults and asymmetric basins resides west of the central Walker Lane and south of the northern Walker Lane, where geodetic studies define northwest-directed dextral strain devoid of major strike-slip fault systems. Combined, these regions act in concert to accommodate dextral shear at the latitudes of the central-northern Walker Lane transition.The purpose of this dissertation was to elucidate kinematics and transfer mechanisms of regional dextral shear accommodation among and between disparate styles of deformation. To accomplish this, geologic mapping of key regions and paleomagnetic study of Tertiary volcanic rocks were completed. The results of this work are compiled and presented in three chapters outlined below.Chapter 1 presents detailed geologic mapping (1:24,000 scale) of major fault blocks in the northernmost Walker Lake domain of the central Walker Lane to test the apparent right-lateral separation across the inferred northernmost segment of the Benton Spring fault. Occupying a significant gap between previous studies of regional dextral shear completed in the northern and central Walker Lane, the results of mapping are used to: 1) determine the magnitude of dextral offset and slip rate accommodated on the northern Benton Spring fault; 2) identify mechanisms of fault termination and strain transfer accommodated on northeast-striking normal faults; 3) identify volcanic units useful for paleomagnetic study; and 4) support previously inferred northern continuations of central Walker Lane dextral fault systems, thereby better constraining the location of transition between the central and northern Walker Lane.Chapter 2 utilizes paleomagnetic data from late Oligocene ash-flow tuffs and Miocene lavas to determine the distribution and magnitudes of vertical-axis rotation at the central-northern Walker Lane transition. Results are used to: 1) test the hypothesis that geodetically-defined dextral strain among north-striking normal faults and asymmetric basins is accommodated by the clockwise vertical-axis rotation of fault blocks; 2) correlate magnitudes of vertical-axis rotation to styles of faulting and defined boundaries between structural domains; and 3) compare vertical-axis rotation magnitudes of Oligocene ash-flow tuffs to Miocene and Pliocene lavas to determine initiation and long-term rates of dextral shear accommodation in the southern part of the northern Walker Lane (Carson domain). Chapter 3 combines observations from previous studies and this investigation with new geologic mapping completed at the transition between dextral faults of the central Walker Lane and sinistral faults of the northern Walker Lane. Results are used to: 1) identify a relatively discrete transition between the central and northern Walker Lane; 2) infer a relatively focused zone of through-going dextral shear from the central to northern Walker Lane; and 3) develop a kinematic model accommodating the abrupt transition between the northwestward translating fault blocks of the central Walker Lane (Walker Lake domain) and sinistral faults, oroclinal flexure, and normal faults in the southern part of the northern Walker Lane (Carson domain).