Structural Evolution of the Maynard Lake Fault Within the Left-Lateral Pahranagat Shear Zone, Nevada, USA

摘要

The Pahranagat shear zone (PSZ) contains three ENE-striking left-lateral strike-slip faults: The Arrowhead Mine fault (AMF), Buckhorn fault (BF), and Maynard Lake fault (MLF) from north to south. This shear zone lies along the boundary between the northern and central Basin and Range physiographic sub-provinces (NBR-CBR). In addition, this zone is positioned SW of a regional strike-slip zone, the Caliente-Enterprise zone (CEZ), and surrounded by extensional domains with differences in timing and magnitude of extension. Hence, understanding the development of the PSZ, particularly the MLF, is essential to better understanding tectonic evolution of the boundary zone between the northern and central Basin and Range including the formation of strike-slip zones, geometry of structures, timing of deformation, and kinematic history.The knowledge of structural development of the western MLF, which has the largest offset of all faults within the PSZ, is needed to increase the understanding of the development of a major strike-slip zones within the NBR-CBR boundary. Key aspects in the development include the timing of deformation, heterogeneous deformation along strike-slip zones such as strike-slip duplex formation, and possibility of strain transfer locally between faults and regionally between extensional domains. The western extent of the MLF, geometry of the MLF, and occurrence of reverse faults within the MLF zone were unclear prior to this study. In this study, a new 1:12000 scale map of the western MLF and northwestern part of the Sheep Range provides data on the formation of strike-slip zones, timing of deformation, kinematic history, and geometry of structures.I used a well-documented regional stress field measurement for the area, as well as my own observations of fault strike orientation, map cross-cutting relationships, the attitude of beds and compaction foliations from ash-flow tuffs, and contractional features such as folds, to analyze the kinematic compatibility and timing of deformation for the PSZ including the MLF zone. The data and analysis show that the MLF is a sinistral strike-slip fault that transfers strain between two extended regions separated by a less extended region south of the MLF. This transfer zone, the PSZ and MLF, represents the SW continuation of the larger strike-slip zone, CEZ, in the vicinity of the NBR-CBR boundary. In addition, at least three stages of deformation were documented for the MLF zone; (1) Pliocene to Quaternary (2) middle-Miocene to Pliocene (3) early-middle Miocene.Supplemental Files include: 1. Geologic map of the western Maynard Lake fault 2. Geologic cross-sections of the western Maynard Lake fault