Terrestrial heat flow in Arizona

New heat flow data in Arizona suggest that the southern Basin and Range has recently undergone less extension than other areas of the Basin and Range province. Heat flow–heat production data imply that magmatism and hydrothermal circulation in the crust and upper mantle beneath southern Arizona and northwestern Mexico may be less extensive than along the Rio Grande rift. A heat flow transition between the Basin and Range and the Colorado Plateau occurs within a lateral distance of 60 km in central Arizona. Predicted steady state temperatures suggest that the M discontinuity may be nearly coincident with an isotherm along this transition. The new heat flow measurements from depths greater than 650 m suggest that the mean value for the Arizona Basin and Range is 1.94 ± 0.12 HFU, indicating as little as 0.3 to 0.4 HFU difference between the Colorado Plateau and the Arizona Basin and Range. This difference could be attributed primarily to widespread magmatic intrusion in the Basin and Range.