Terrestrial heat flow determinations in the north central United States

Twenty-six new heat flow determinations in the north central United States range from 0.90 to 2.2 HFU (μcal/cm2sec). Two distinct provinces are characterized on the basis of both heat flow and physiography, although all the stations are located in the stable continental interior. The Interior Lowlands are characterized by a regional mean value of 1.4 HFU, whereas the regional value for the northern Great Plains is about 2.0 HFU. Local variations of heat flow in the Interior Lowlands are attributed to differences in basement rock type and the attendant contrasts in radiogenic heat production and thermal conductivity, Because basement lithologies and crustal thicknesses are quite similar in the Interior Lowlands and the northern Great Plains, most regional deviations in heat flow must be attributed to temperature differences in the upper mantle. The lower heat flow values (≤1.5 HFU) are associated with negative seismic travel time anomalies, whereas the high values (≥1.8 HFU) are related to positive station residuals. Lower Pn velocities are also associated with high heat flux in the northern Great Plains. These correlations support the conclusion that difference in regional heat flux can be attributed to differences in the temperature structure in the upper mantle.