THERMAL AND HALF THERMAL SPRINGS IN THE NORTHEASTERN US-RELATIONSHIP TO LOCAL TECTONICS AND THE NAA (NORTH APPALACHIAN ANOMALY)

Thermal springs can indicate high regional heat flow and deep penetration of water into the crust. Following Gilbert’s usage, we define a thermal spring as one with an anomaly of more than 15°F (8.3°C). We also define a “half-thermal” spring as one with an anomaly of half that amount (7.5°F, 4.2°C). We visited over 100 springs in New England, New Jersey and New York and measured their water temperature, elevation, location, and flow rate. We derived a temperature anomaly for each spring, as the water temperature minus the mean air temperature at the site, estimated using NOAA climate data and corrected for elevation. We visited the three previously studied thermal springs and described eight new half-thermal springs. All of the thermal springs and all but one of the half-thermal springs lie within the Northern Appalachian Anomaly (NAA), an area where seismic tomography has identified unusually hot asthenosphere. Our findings suggest that the hot asthenosphere is locally warming the crust. We more fully test this hypothesis by developing and analyzing a database of over 500 springs, 400 from historical sources. This more extensive data set contains 8 thermal springs and 40 half-thermal springs. Seven out of 8 thermal springs and 28 out of 40 half-thermal springs lie within the footprint of the NAA. The other 12 half-thermal springs mostly are located in western New York State. Many of the thermal and half-thermal springs are associated with thrust faults, carbonate rocks, or both. For instance, the two thermal springs in Williamstown, Massachusetts are on thrust faults with carbonate rich rock in the footwall and the more silicic meta-sediments of the Taconic Allochthon in the hanging wall. Overall, our data point to a model where specific fault configurations favor the escape of warmer fluids from depth.