Contraints on crustal composition beneath a metamorphic core complex

Results from 3-component wide-angle seismic data along the eastern flank of the ruby mountains, Nevada

P. Satarugsa, Roy A Johnson

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9 Citations (Scopus)

Abstract

Metamorphic core complexes expose rocks deformed at deep upper to middle crustal levels during extreme crustal extension. However, mechanisms of crustal extension and exhumation of core complexes remain to be fully understood. Detailed study of crustal velocity structure and inferences about the composition of the crust beneath core complexes (and nearby) provide useful constraints on core-complex evolution. P- and S-wave velocity structures determined from seismic experiments along the eastern flank of the Ruby Mountains metamorphic core complex, Nevada, show that the crust can be divided into three main layers corresponding to the upper, middle and lower crust. We interpreted crustal composition by integrating results of P-wave velocities (Vp). S-wave velocities (Vs), Poisson's ratios (σ), seismic anisotropy, and reflection character with published geologic maps of the area. Near-surface estimates of Vp, Vs, σ, and anisotropy of 1.90-4.8 km/s, 1.01-2.75 km/s, 0.25-0.33, and 0.6-2.5%, respectively, are consistent with surface exposures of unconsolidated to consolidated sedimentary rocks, limestone, dolomite, siltstone, sandstone, porous sandstone, conglomerate, and weathered granite. Results from analysis of reflection responses, Vp, Vs, σ, and anisotropy also indicate that: (1) upper crustal rocks most likely consist of metaquartzite, schist, granite gneiss, and granite-granodiorite with Vp of 5.80-6.25 km/s, Vs of 3.20-3.72 km/s, σ of 0.22-0.25, and anisotropy of 0.6-2.5%: (2) possible middle crustal rocks are paragranulite, felsic granulite, felsic amphibolite gneiss, granite-granodiorite, and mica-quartz schist with Vp of 6.35-6.45 km/s, Vs of 3.70-3.75 km/s, and σ of 0.24; and (3) lower crustal rocks most likely consist of granulite-rather than amphibolite-facies rocks with Vp of 6.60-6.80 km/s, Vs of 3.85-3.92 km/s, σ of 0.24-0.25, and anisotropy of <3%. Our principal conclusions are: (1) significant addition of gabbroic rocks (underplating) is unlikely in the lower crust; (2) lower crustal rocks were stretched into sub-horizontal geometries with aligned minerals during extension, creating seismic lamellae in the lower crust; (3) present-day seismic velocities of highly extended core complex crust and normally extended Basin and Range crust are similar; and (4) orientations of fast shear waves near the surface and in the upper crust are sub-parallel to the regional maximum horizontal compressive stress in the Nevada part of the Basin and Range province.

Original languageEnglish (US)
Pages (from-to)223-250
Number of pages28
JournalTectonophysics
Volume329
Issue number1-4
DOIs
StatePublished - 2000

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ruby
mountains
seismic data
crusts
mountain
rocks
rock
anisotropy
granite
lower crust
crust
wave velocity
S-wave
granulite
velocity structure
granodiorite
S waves
gneiss
schist
P-wave

Keywords

  • Crustal velocity structure
  • Metamorphic core complexes
  • Poisson's ratio
  • Ruby Mountains
  • Seismic anisottropy
  • Shear-wave splitting

ASJC Scopus subject areas

  • Earth-Surface Processes
  • Geophysics

Cite this

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title = "Contraints on crustal composition beneath a metamorphic core complex: Results from 3-component wide-angle seismic data along the eastern flank of the ruby mountains, Nevada",
abstract = "Metamorphic core complexes expose rocks deformed at deep upper to middle crustal levels during extreme crustal extension. However, mechanisms of crustal extension and exhumation of core complexes remain to be fully understood. Detailed study of crustal velocity structure and inferences about the composition of the crust beneath core complexes (and nearby) provide useful constraints on core-complex evolution. P- and S-wave velocity structures determined from seismic experiments along the eastern flank of the Ruby Mountains metamorphic core complex, Nevada, show that the crust can be divided into three main layers corresponding to the upper, middle and lower crust. We interpreted crustal composition by integrating results of P-wave velocities (Vp). S-wave velocities (Vs), Poisson's ratios (σ), seismic anisotropy, and reflection character with published geologic maps of the area. Near-surface estimates of Vp, Vs, σ, and anisotropy of 1.90-4.8 km/s, 1.01-2.75 km/s, 0.25-0.33, and 0.6-2.5{\%}, respectively, are consistent with surface exposures of unconsolidated to consolidated sedimentary rocks, limestone, dolomite, siltstone, sandstone, porous sandstone, conglomerate, and weathered granite. Results from analysis of reflection responses, Vp, Vs, σ, and anisotropy also indicate that: (1) upper crustal rocks most likely consist of metaquartzite, schist, granite gneiss, and granite-granodiorite with Vp of 5.80-6.25 km/s, Vs of 3.20-3.72 km/s, σ of 0.22-0.25, and anisotropy of 0.6-2.5{\%}: (2) possible middle crustal rocks are paragranulite, felsic granulite, felsic amphibolite gneiss, granite-granodiorite, and mica-quartz schist with Vp of 6.35-6.45 km/s, Vs of 3.70-3.75 km/s, and σ of 0.24; and (3) lower crustal rocks most likely consist of granulite-rather than amphibolite-facies rocks with Vp of 6.60-6.80 km/s, Vs of 3.85-3.92 km/s, σ of 0.24-0.25, and anisotropy of <3{\%}. Our principal conclusions are: (1) significant addition of gabbroic rocks (underplating) is unlikely in the lower crust; (2) lower crustal rocks were stretched into sub-horizontal geometries with aligned minerals during extension, creating seismic lamellae in the lower crust; (3) present-day seismic velocities of highly extended core complex crust and normally extended Basin and Range crust are similar; and (4) orientations of fast shear waves near the surface and in the upper crust are sub-parallel to the regional maximum horizontal compressive stress in the Nevada part of the Basin and Range province.",
keywords = "Crustal velocity structure, Metamorphic core complexes, Poisson's ratio, Ruby Mountains, Seismic anisottropy, Shear-wave splitting",
author = "P. Satarugsa and Johnson, {Roy A}",
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pages = "223--250",
journal = "Tectonophysics",
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TY - JOUR

T1 - Contraints on crustal composition beneath a metamorphic core complex

T2 - Results from 3-component wide-angle seismic data along the eastern flank of the ruby mountains, Nevada

AU - Satarugsa, P.

AU - Johnson, Roy A

PY - 2000

Y1 - 2000

N2 - Metamorphic core complexes expose rocks deformed at deep upper to middle crustal levels during extreme crustal extension. However, mechanisms of crustal extension and exhumation of core complexes remain to be fully understood. Detailed study of crustal velocity structure and inferences about the composition of the crust beneath core complexes (and nearby) provide useful constraints on core-complex evolution. P- and S-wave velocity structures determined from seismic experiments along the eastern flank of the Ruby Mountains metamorphic core complex, Nevada, show that the crust can be divided into three main layers corresponding to the upper, middle and lower crust. We interpreted crustal composition by integrating results of P-wave velocities (Vp). S-wave velocities (Vs), Poisson's ratios (σ), seismic anisotropy, and reflection character with published geologic maps of the area. Near-surface estimates of Vp, Vs, σ, and anisotropy of 1.90-4.8 km/s, 1.01-2.75 km/s, 0.25-0.33, and 0.6-2.5%, respectively, are consistent with surface exposures of unconsolidated to consolidated sedimentary rocks, limestone, dolomite, siltstone, sandstone, porous sandstone, conglomerate, and weathered granite. Results from analysis of reflection responses, Vp, Vs, σ, and anisotropy also indicate that: (1) upper crustal rocks most likely consist of metaquartzite, schist, granite gneiss, and granite-granodiorite with Vp of 5.80-6.25 km/s, Vs of 3.20-3.72 km/s, σ of 0.22-0.25, and anisotropy of 0.6-2.5%: (2) possible middle crustal rocks are paragranulite, felsic granulite, felsic amphibolite gneiss, granite-granodiorite, and mica-quartz schist with Vp of 6.35-6.45 km/s, Vs of 3.70-3.75 km/s, and σ of 0.24; and (3) lower crustal rocks most likely consist of granulite-rather than amphibolite-facies rocks with Vp of 6.60-6.80 km/s, Vs of 3.85-3.92 km/s, σ of 0.24-0.25, and anisotropy of <3%. Our principal conclusions are: (1) significant addition of gabbroic rocks (underplating) is unlikely in the lower crust; (2) lower crustal rocks were stretched into sub-horizontal geometries with aligned minerals during extension, creating seismic lamellae in the lower crust; (3) present-day seismic velocities of highly extended core complex crust and normally extended Basin and Range crust are similar; and (4) orientations of fast shear waves near the surface and in the upper crust are sub-parallel to the regional maximum horizontal compressive stress in the Nevada part of the Basin and Range province.

AB - Metamorphic core complexes expose rocks deformed at deep upper to middle crustal levels during extreme crustal extension. However, mechanisms of crustal extension and exhumation of core complexes remain to be fully understood. Detailed study of crustal velocity structure and inferences about the composition of the crust beneath core complexes (and nearby) provide useful constraints on core-complex evolution. P- and S-wave velocity structures determined from seismic experiments along the eastern flank of the Ruby Mountains metamorphic core complex, Nevada, show that the crust can be divided into three main layers corresponding to the upper, middle and lower crust. We interpreted crustal composition by integrating results of P-wave velocities (Vp). S-wave velocities (Vs), Poisson's ratios (σ), seismic anisotropy, and reflection character with published geologic maps of the area. Near-surface estimates of Vp, Vs, σ, and anisotropy of 1.90-4.8 km/s, 1.01-2.75 km/s, 0.25-0.33, and 0.6-2.5%, respectively, are consistent with surface exposures of unconsolidated to consolidated sedimentary rocks, limestone, dolomite, siltstone, sandstone, porous sandstone, conglomerate, and weathered granite. Results from analysis of reflection responses, Vp, Vs, σ, and anisotropy also indicate that: (1) upper crustal rocks most likely consist of metaquartzite, schist, granite gneiss, and granite-granodiorite with Vp of 5.80-6.25 km/s, Vs of 3.20-3.72 km/s, σ of 0.22-0.25, and anisotropy of 0.6-2.5%: (2) possible middle crustal rocks are paragranulite, felsic granulite, felsic amphibolite gneiss, granite-granodiorite, and mica-quartz schist with Vp of 6.35-6.45 km/s, Vs of 3.70-3.75 km/s, and σ of 0.24; and (3) lower crustal rocks most likely consist of granulite-rather than amphibolite-facies rocks with Vp of 6.60-6.80 km/s, Vs of 3.85-3.92 km/s, σ of 0.24-0.25, and anisotropy of <3%. Our principal conclusions are: (1) significant addition of gabbroic rocks (underplating) is unlikely in the lower crust; (2) lower crustal rocks were stretched into sub-horizontal geometries with aligned minerals during extension, creating seismic lamellae in the lower crust; (3) present-day seismic velocities of highly extended core complex crust and normally extended Basin and Range crust are similar; and (4) orientations of fast shear waves near the surface and in the upper crust are sub-parallel to the regional maximum horizontal compressive stress in the Nevada part of the Basin and Range province.

KW - Crustal velocity structure

KW - Metamorphic core complexes

KW - Poisson's ratio

KW - Ruby Mountains

KW - Seismic anisottropy

KW - Shear-wave splitting

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