abstract

Pn arrival times were measured along three north-south profiles in northern Nevada and southeastern Oregon. Apparent arrival velocities of 8.0, 8.2, and 8.4 km/sec were observed on the southern ends of the profiles and are explained by crustal thinning of up to 8 km along the profiles. This interpretation is supported by the shape of the Bouguer gravity anomaly and a prominent second arrival interpreted to be a Moho reflection observed from a local quarry blast along one of the lines. The Battle Mountain heat flow high as outlined by the 2.5 HFU contour of Sass et al. (1976) does not correlate well with the area of thin crust in north central Nevada. However, the southern boundary of the heat flow high corresponds to a decrease in crustal thickness on all profiles—the crust inside the heat flow high is 5 to 8 km thinner than the crust to the south. The crustal thickness of 21 to 23 km in the Battle Mountain-Winnemucca area is compared to estimated depths to the wet and the dry basaltic solidus and no partial melting of the lower crust is expected if it is dry, while partial melting is expected if it is wet. A prominent later phase at distances greater than 550 km is modeled by an increase in P velocity of 0.2 to 0.3 km/sec at a depth between 70 and 90 km. A low-velocity zone may exist in the mantle above this velocity increase but is not required by our data.

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