CRUSTAL VELOCITY STRUCTURE BENEATH THE EASTERN FLANK OF THE RUBY MOUNTAINS METAMORPHIC CORE COMPLEX - RESULTS FROM NORMAL-INCIDENCE TO WIDE-ANGLE SEISMIC DATA

P-wave velocity structure along the eastern side of the Ruby Mountains metamorphic core complex, determined using 2-D ray-inversion modeling , shows that: (1) the crust can be divided into three layers correspon ding to the upper, middle, and lower crust; (2) from east of Ruby Dome to the northern end of the seismic profile, velocities of the upper c rust range from 6.12 (+/-0.1) to 6.20 (+/-0.1) km/s and near-surface v elocities range from 1.90 (+/-0.1) to 4.80 (+/-0.1) km/s, From this po int to the southern end of the profile, upper crustal velocities range from 5.80 (+/-0.1) to 6.25 (+/-0.1) km/s and near-surface velocities range from 3.01 (+/-0.1) to 4.80 (+/-0.1) km/s; (3) middle crustal vel ocities range from 6.35 (+/-0.15) to 6.45 (+/-0.15) km/s; (4) lower cr ustal velocities range from 6.60 (+/-0.15) to 6.80 (+/-0.15) km/s; and (5) depths to the Moho vary irregularly between 30.5 and 33.5 km. Fro m interpretation of these results, we conclude that: (1) the transitio n in metamorphic grade from deep upper crustal rocks south of Harrison Pass to middle crustal rocks north of Harrison Pass does not correlat e with an increase in seismic velocity; near-surface basement seismic velocities increase in the central part of the range (near Ruby Dome) well north of the major metamorphic transition; (2) depths to the Moho do not reflect local surface relief; isostatic balance is achieved pr edominantly in the crust rather than by formation of a local crustal r oot; and (3) the crust has been modified during extension by intracrus tal processes rather than by large-scale magmatic underplating. (C) 19 98 Elsevier Science B.V. All rights reserved.