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Whole-lithosphere shear during oblique rifting

Journal Article · · Geology
DOI:https://doi.org/10.1130/g49603.1· OSTI ID:1868294
 [1];  [1];  [2];  [1]
  1. New Mexico Institute of Mining and Technology, Socorro, NM (United States)
  2. New Mexico Institute of Mining and Technology, Socorro, NM (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
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Processes controlling the formation of continental whole-lithosphere shear zones are debated, but their existence requires that the lithosphere is mechanically coupled from base to top. We document the formation of a dextral, whole-lithosphere shear zone in the Death Valley region (DVR), southwest United States. Dextral deflections of depth gradients in the lithosphere-asthenosphere boundary and Moho are stacked vertically, defining a 20–50-km-wide, lower lithospheric shear zone with ~60 km of shear. These deflections underlie an upper-crustal fault zone that accrued ~60 km of dextral slip since ca. 8–7 Ma, when we infer that whole-lithosphere shear began. This dextral offset is less than net dextral offset on the upper-crustal fault zone (~90 km, ca. 13–0 Ma) and total upper-crustal extension (~250 km, ca. 16–0 Ma). We show that, before ca. 8–7 Ma, weak middle crust decoupled upper-crustal deformation from deformation in the lower crust and mantle lithosphere. Between 16 and 7 Ma, detachment slip thinned, uplifted, cooled, and thus strengthened the middle crust, which is exposed in metamorphic core complexes collocated with the whole-lithosphere shear zone. Midcrustal strengthening coupled the layered lithosphere vertically and therefore enabled whole-lithosphere dextral shear. Where thick crust exists (as in pre–16 Ma DVR), midcrustal strengthening is probably a necessary condition for whole-lithosphere shear.
Research Organization:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
National Science Foundation (NSF)
Grant/Contract Number:
89233218CNA000001
OSTI ID:
1868294
Report Number(s):
LA-UR-21-28189
Journal Information:
Geology, Journal Name: Geology Journal Issue: 4 Vol. 50; ISSN 0091-7613
Publisher:
Geological Society of AmericaCopyright Statement
Country of Publication:
United States
Language:
English

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