Magnitude of crustal extension across the northern Basin and Range province: constraints from paleomagnetism

The magnitude of crustal extension across the northern Basin and Range province is a matter of longstanding controversy; estimates range from 10 to 3009~,. Recently published estimates of extension across the southern Basin and Range province (36°N) are in the range of 80-100%. Thus, the larger values suggested for the northern part of the province (40°N) seem to require substantial counterclockwise rotation of the Sierra Nevada during 'l-ertiary extension. Paleomagnetic data from the range, however, limit rotation to 4 + 10 ° at the 95~ confidence level. These limits. combined with estimates of extension near the Garlock fault, allow severe constraints to be placed on the magnitude of extension across more northerly parts of the province. We conclude that the maximum extension at 40°N is about 50%. and that values of 39 512q~ (188 + 43 km) are likely.