TY - JOUR
T1 - Distributed Neogene faulting across the western to central Arizona metamorphic core complex belt
T2 - Synextensional constriction and superposition of the Pacific-North America plate boundary on the southern Basin and Range
AU - Singleton, John S.
AU - Seymour, Nikki M.
AU - Reynolds, Stephen J.
AU - Vomocil, Terence
AU - Wong, Martin S.
N1 - Funding Information:
Partial funding for this project was provided by National Science Foundation Tectonics Program award 1557265 to J. Singleton and M. Wong and by Colorado State University startup funds to J. Singleton. We thank Evan Strickland, Mike Wyatt, and Jacqueline Benefield for assistance with some of the data collection. This manuscript was improved by reviews from Sue Beard, an anonymous reviewer, and Associate Editor Bob Miller. Discussion of oblique divergence in the Arizona core complex belt was inspired by insightful comments from Sue Beard.
Publisher Copyright:
© 2019 The Authors.
PY - 2019/8/1
Y1 - 2019/8/1
N2 - We present fault data from a belt of Miocene metamorphic core complexes in western and central Arizona (USA) to determine patterns of brittle strain during and after large-magnitude extension, and to evaluate the magnitude of postextensional dextral shear across the region. In the White Tank Mountains, coeval WNW- to NW-striking dextral, normal, and oblique dextral-normal faults accommodated constrictional strain with extension subparallel to the direction of ductile stretching during core complex development. Northwest-striking oblique dextral-normal faults locally accommodated similar strain in the Harquahala Mountains, whereas in the South Mountains, constriction was primarily partitioned on NE-dipping normal faults and conjugate NW- and north-striking strike-slip faults. We interpret brittle constrictional strain to have developed during the late stages of large-magnitude extension associated with core complex development and folding of detachment fault corrugations. The oblique orientation of the Arizona core complex belt with respect to the extension direction likely resulted in a minor component of dextral transtension, accounting for much of the constrictional strain. In addition, far-field stresses associated with the transtensional Pacific-North America plate boundary may have contributed to constriction, which characterizes most Neogene detachment fault systems in the southwest Cordillera. Following cessation of detachment fault slip across the Arizona core complex belt (ca. 14-12 Ma), distributed NW-striking dextral and oblique dextral-NE-side-up (reverse) faults modified the topographic envelope of corrugations to an orientation clockwise of the core complex extension direction. Based on our analysis of this misalignment, we interpret the postdetachment fault dextral shear strain to increase northwestward from 0.03 across the South Mountains (0.5-0.6 km total slip across 18 km) to > 0.03-0.07 across the Harquahala and Harcuvar Mountains (1.2-2.5 km of total slip across ~35 km) and ~0.2 across the Buckskin-Rawhide Mountains (7-8 km across 36 km). This along-strike variation in dextral shear is consistent with the regional pattern of distributed strain associated with the Pacific-North America plate boundary, as cumulative dextral offset in the lower Colorado River region increases toward the eastern Mojave Desert region to the northwest.
AB - We present fault data from a belt of Miocene metamorphic core complexes in western and central Arizona (USA) to determine patterns of brittle strain during and after large-magnitude extension, and to evaluate the magnitude of postextensional dextral shear across the region. In the White Tank Mountains, coeval WNW- to NW-striking dextral, normal, and oblique dextral-normal faults accommodated constrictional strain with extension subparallel to the direction of ductile stretching during core complex development. Northwest-striking oblique dextral-normal faults locally accommodated similar strain in the Harquahala Mountains, whereas in the South Mountains, constriction was primarily partitioned on NE-dipping normal faults and conjugate NW- and north-striking strike-slip faults. We interpret brittle constrictional strain to have developed during the late stages of large-magnitude extension associated with core complex development and folding of detachment fault corrugations. The oblique orientation of the Arizona core complex belt with respect to the extension direction likely resulted in a minor component of dextral transtension, accounting for much of the constrictional strain. In addition, far-field stresses associated with the transtensional Pacific-North America plate boundary may have contributed to constriction, which characterizes most Neogene detachment fault systems in the southwest Cordillera. Following cessation of detachment fault slip across the Arizona core complex belt (ca. 14-12 Ma), distributed NW-striking dextral and oblique dextral-NE-side-up (reverse) faults modified the topographic envelope of corrugations to an orientation clockwise of the core complex extension direction. Based on our analysis of this misalignment, we interpret the postdetachment fault dextral shear strain to increase northwestward from 0.03 across the South Mountains (0.5-0.6 km total slip across 18 km) to > 0.03-0.07 across the Harquahala and Harcuvar Mountains (1.2-2.5 km of total slip across ~35 km) and ~0.2 across the Buckskin-Rawhide Mountains (7-8 km across 36 km). This along-strike variation in dextral shear is consistent with the regional pattern of distributed strain associated with the Pacific-North America plate boundary, as cumulative dextral offset in the lower Colorado River region increases toward the eastern Mojave Desert region to the northwest.
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U2 - 10.1130/GES02036.1
DO - 10.1130/GES02036.1
M3 - Article
AN - SCOPUS:85070790798
SN - 1553-040X
VL - 15
SP - 1409
EP - 1435
JO - Geosphere
JF - Geosphere
IS - 4
ER -