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 ( V p), S-wave velocities ( V s), Poisson's ratios ( σ), seismic anisotropy, and reflection character with published geologic maps of the area. Near-surface estimates of V p, V s, 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, V p, V s, σ, and anisotropy also indicate that: (1) upper crustal rocks most likely consist of metaquartzite, schist, granite gneiss, and granite–granodiorite with V p of 5.80–6.25 km/s, V s 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 V p of 6.35–6.45 km/s, V s 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 V p of 6.60–6.80 km/s, V s 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.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.