Reflection Profiles from the Snake Range Metamorphic Core Complex: A Window into the Mid-Crust
- Muawia Barazangi and
- Larry Brown
Published Online: 15 MAR 2013
Copyright 1986 by the American Geophysical Union.
Reflection Seismology: The Continental Crust
How to Cite
McCarthy, J. (1986) Reflection Profiles from the Snake Range Metamorphic Core Complex: A Window into the Mid-Crust, in Reflection Seismology: The Continental Crust (eds M. Barazangi and L. Brown), American Geophysical Union, Washington, D. C.. doi: 10.1029/GD014p0281
- Published Online: 15 MAR 2013
- Published Print: 1 JAN 1986
Print ISBN: 9780875905143
Online ISBN: 9781118670118
- Seismic reflection method—Congresses
The northern Snake Range (NSR) metamorphic core complex in eastern Nevada is characterized by a detached and distended cover of Paleozoic strata overlying ductilely-strained and metamorphosed Precambrian sediments and Mesozoic and Tertiary(?) plutons. A gently-dipping to subhorizontal zone of detachment (the northern Snake Range decollement (NSRD)) separates these rheologically contrasting units. This decollement is best developed on the eastern flank of the range where lower plate ductile strain is greatest. Seismic profiles from the Consortium for Continental Reflection Profiling (COCORP) and Sohio Petroleum Company have traced this shallowly-dipping (5–10° ) reflecting horizon over 10 km to the east beneath the Confusion Range, where it dies out at a two-way travel time of 3.0 seconds. Along the western flank of the range, however, a 128-fold sign bit seismic line shot across Spring Valley between the Snake and Schell Creek Ranges was unable to image the westward continuation of the NSRD for any appreciable distance. The absence of ductile deformation exposed in the Schell Creek Range and the correlation of the NSRD with a purely brittle fault in this region suggest that the westward-disappearance ef the NSRD as a major reflecting horizon is due to a decrease in ductile strain to the west, away from the Snake Range. Although a westward transition of the rheological character of the NSRD from completely ductile deformation on the east flank of the NSR to completely brittle deformation on the west flank is compatible with a low-angle zone of simple shear rooted to the east into the lower crust or upper mantle, a major shear zone with displacements on the order of 60–100 km should be laterally more extensive and resolvable at greater crustal depths than those imaged on the seismic reflection profiles.
A highly-reflective middle and lower crust has also been imaged on COCORP and Sohio Petroleum seismic reflection profiles beneath the NSR. These strong, laminated reflections which extend from 4.0 seconds twoway travel time to the Moho are believed to represent a compositionally-layered and structurally-deformed fabric imposed on the middle and lower crust during Tertiary extension. If true, this implies that extension in the NSR has not been localized along the NSRD, but has been distributed throughout the entire crust down to the Moho.