Fault Slip Transfer in the Eastern California Shear Zone–Walker Lane Belt

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The Eastern California Shear Zone and Walker Lane Belt define a broad zone of active deformation that straddles the boundary between dominantly east-west exten- sion in the Basin and Range province and dominantly NW-dextral shear directed along the Pacific–North American plate boundary to the west (Fig. 1). The interaction between extension and transcurrent shear has resulted in a complex array of NW-striking dextral faults, NW-striking and NE-striking normal faults, and ENE-striking sinistral faults that accommodate intraplate strain east of the Sierra Nevada and into western Nevada (Figs. 1 and 2).

Plate circuit calculations suggest that motion of the Pacifi c plate relative to the North American plate changed from W to NW at ca. 7–8 Ma (Atwater and Stock, 1998). This observation is in good agreement with regional geologic constraints, which indicate that motion of the Sierra Nevada block relative to stable North America also changed from W to NW at ca. 8–10 Ma (Wernicke and Snow, 1998; Snow and Wernicke, 2000). A recent tectonic reconstruction of southwestern North America shows that a portion of plate boundary dextral shear jumped into the continent at 10–12 Ma (McQuarrie and Wernicke, 2005). On the basis of geologic studies, the rate of dextral shear within the Eastern California Shear Zone–Walker Lane Belt north of the Gar- lock fault has been ~15 mm/yr since ca. 7–8 Ma (Wernicke and Snow, 1998), account- ing for ~30% of the relative plate motion (Atwater and Stock, 1998). Today, geodetic data indicate that dextral shear, at a rate of ~10–13 mm/yr, still dominates within the Eastern California Shear Zone–Walker Lane Belt, accounting for 20%–25% of the total relative plate motion (Gan et al., 2000; McClusky et al., 2001; Oldow et al., 2001; Miller et al., 2001; Bennett et al., 2003).

In the northern Eastern California Shear Zone, dextral shear is accommodated to the east of the Sierra Nevada along three major, subparallel strike-slip fault zones, the Death Valley–Furnace Creek, Fish Lake Valley, and White Mountains–Owens Valley fault zones (Figs. 2 and 3). At the northern end of the Eastern California Shear Zone, NW-striking strike-slip faults abruptly swing eastward into an array of NE-striking normal and ENE-striking sinistral faults in the southern portion of the Walker Lane Belt known as the Mina deflection (Figs. 2 and 3). These curvilinear faults often form a “z”-shaped extensional relay zone that transfers residual plate motion eastward from the Death Valley–Furnace Creek, Fish Lake Valley, and White Mountains–Owens Valley fault zones into the Central Nevada Seismic Belt and Walker Lane Belt (e.g., Oldow, 1992; Oldow et al., 2001; Wesnousky, 2005). Within the Eastern California Shear Zone to the south, similar extensional relay zones, such as the Deep Springs and Towne Pass faults, transfer dextral slip from one strike-slip fault system to another (e.g., Lee et al., 2001).

During the past 10–15 years, a number of geologists and geodesists have been investigating the distribution of fault slip in space and time across the Eastern Cali- fornia Shear Zone and Walker Lane Belt to document the kinematics of strain release and strain accumulation and thereby provide insight into the geodynamic evolution of the region.

This field trip guide will focus on the kinematics of faulting across an extensional relay zone from the northern Eastern California Shear Zone into the southern Walk- er Lane Belt. We will review evidence for active dextral slip along the NW-striking White Mountains fault zone, normal slip along the NE-striking Queen Valley fault, and sinistral slip along the ENE-striking Coaldale fault, and the kinematics of fault slip transfer from one fault system to another (Fig. 3).


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© 2006 Geological Society of America.