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Kinematics of the west-central Walker Lane; spatially and temporally variable rotations evident in the late Miocene Stanislaus Group

Chad W. Carlson, Christopher J. Pluhar, Jonathan M. G. Glen and Michael J. Farner
Kinematics of the west-central Walker Lane; spatially and temporally variable rotations evident in the late Miocene Stanislaus Group
Geosphere (Boulder, CO) (December 2013) 9 (6): 1530-1551

Abstract

The Walker Lane currently accommodates approximately 20% of the dextral motion between the Pacific and North American plates. This accommodation occurs on regional-scale systems of strike-slip and normal faults located between the northwestward-translating Sierra Nevada microplate and the east-west-extending Basin and Range. At the western edge of the central Walker Lane (lat approximately 38 degrees -39 degrees N) is a region of crustal blocks bounded by asymmetric basins and normal faults, here defined as the west-central Walker Lane. Although this region is apparently devoid of major active strike-slip faults, the presence of Neogene clockwise vertical-axis tectonic block rotations indicates the accommodation of dextral shear. We measured vertical-axis rotation by comparing remanence directions of widespread members of the Eureka Valley Tuff of the Late Miocene Stanislaus Group within the west-central Walker Lane to the same units on the Sierra Nevada microplate. Results show that the study area is organized into discrete domains with heterogeneous regional distribution of clockwise vertical-axis rotation, ranging from approximately 10 degrees to 60 degrees , since ca. 9.5 Ma. The highest measured magnitudes of vertical-axis rotation ( approximately 50 degrees -60 degrees clockwise) are interpreted as a region of high deformation that includes the asymmetric Bridgeport Valley. Previous work underestimated vertical-axis rotation magnitudes in the region because published reference directions for two of the three members of the Eureka Valley Tuff (By-Day Member and Upper member) derive from the rotated region. We recalculate a reference direction for the By-Day Member of declination 353.2 degrees , inclination 43.7 degrees ; alpha (sub 95) = 10.8 degrees . This corroborates a reference direction for the By-Day Member from the Stanislaus Group type section, situated on the relatively stable Sierra Nevada microplate, providing a robust reference direction for paleomagnetic studies. We present a kinematic model in which dextral shear in the west-central Walker Lane is accommodated by approximately 30 degrees of clockwise rotation in the Sweetwater Mountains and Bodie Hills since the Late Miocene. This model incorporates rotation magnitudes, paleostress orientations, edge effects, and bounding faults of rotating tectonic blocks to reveal timing, patterns, and mechanisms of crustal deformation. The results and models presented here elucidate the complex and evolving nature of the west-central Walker Lane. The rotational history of dextral shear accommodation demonstrates that the west-central Walker Lane should be included as an important part of the Walker Lane transtensional zone. The results presented in this study not only improve understanding of deformation in the Walker Lane, but illuminate the potentially significant contribution of crustal block vertical-axis rotations in other transtensional regions of the world.


EISSN: 1553-040X
Serial Title: Geosphere (Boulder, CO)
Serial Volume: 9
Serial Issue: 6
Title: Kinematics of the west-central Walker Lane; spatially and temporally variable rotations evident in the late Miocene Stanislaus Group
Affiliation: California State University-Fresno, Department of Earth and Environmental Sciences, Fresno, CA, United States
Pages: 1530-1551
Published: 201312
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 92
Accession Number: 2014-004188
Categories: Structural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, geol. sketch map
N37°45'00" - N38°30'00", W119°45'00" - W118°30'00"
Secondary Affiliation: U. S. Geological Survey, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201404
Program Name: USGSOPNon-USGS publications with USGS authors
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