Estimating the Curie Point Depth (CPD) Isotherm in Alberta Using Aeromagnetic Data

The Alberta Geological Survey (AGS) contracted Multiphysics Imaging Technology, 4th Resource Corp., and GEOSEIS Inc. to estimate the Curie point depth (CPD) isotherm across Alberta using aeromagnetic data. The CPD represents the depth at which crustal rocks reach approximately 580°C, the temperature at which ferromagnetic minerals lose their magnetization. Mapping this thermal boundary provides a regional proxy for crustal heat distribution, geothermal gradients, and mantle-derived heat flow, supporting geothermal resource evaluation and tectonic studies.

Residual magnetic intensity (RMI) grids were compiled from high-resolution airborne magnetic surveys acquired by the AGS (2021–2024), and supplemented with lower-resolution datasets from the Geological Survey of Canada and the U.S. Geological Survey. The RMI grid was subdivided into 660 overlapping 160 by 160 km windows, spaced at 40 by 40 km intervals between centroids. Of these, 417 windows fall within Alberta, providing dense spatial sampling for spectral analysis. Fast Fourier transform (FFT) power-spectrum analysis was applied to each window, and CPD was estimated using both centroid and fractal spectral methods. The results were interpolated to produce a continuous provincial grid.

The CPD estimates range from approximately 8 to 30 km, with a mean depth of 23 ±4 km. Shallow CPD values occur beneath the Rocky Mountain fold-and-thrust belt, whereas deeper values characterize the Rae and Hearne cratons. Intermediate depths are observed along the Snowbird tectonic zone. From these CPD results, geothermal gradients (average of 26 ±5°C/km) and heat-flow values (48 to 149 mW/m²) were derived, indicating elevated thermal conditions in southwestern Alberta. These estimates are consistent with borehole-based measurements and global heat-flow compilations, though they exclude radiogenic heat contributions from granitic rocks.

A complementary three-dimensional (3D) inversion of Bouguer gravity data was conducted to estimate Mohorovičić discontinuity (Moho) depths, which range from 35 to 46 km. A moderate negative correlation (r ≈ –0.70) between CPD and Moho depth suggests that thicker crustal regions may retain heat due to low thermal conductivity, resulting in shallower thermal isotherms above a deeper lithosphere.

This work was completed under the Mineral Grant provided by the Government of Alberta dated June 22, 2021.