Curie Point Depth Calculator
Estimate the depth at which crustal rock reaches the Curie temperature and loses ferromagnetism, from a simple linear geotherm.
🧲 What is Curie Point Depth?
Curie point depth is the depth within Earth's crust at which rock temperature reaches the Curie temperature of its dominant magnetic mineral, the temperature above which a material loses its permanent (ferromagnetic) magnetization and becomes paramagnetic. Below this depth, crustal rock can no longer contribute to the magnetic anomalies that geophysicists measure at or above the surface.
Geophysicists use Curie point depth estimates to map regional heat flow from aeromagnetic survey data, since the depth to the Curie isotherm tracks the same underlying thermal structure that direct borehole heat flow measurements describe. Geothermal energy exploration teams use Curie depth maps as an inexpensive first-pass screening tool, since shallower Curie depths often flag areas of elevated geothermal potential worth investigating with more expensive direct methods. Volcanologists use Curie depth changes over time and space to track the thermal evolution of magmatic systems. Academic researchers use global compilations of Curie point depth to study lithospheric thickness and thermal structure at continental scale.
A common point of confusion is assuming a single universal Curie temperature applies everywhere. In reality, the dominant magnetic mineral varies by rock type, magnetite (about 580 degC) dominates most continental crust, while titanomagnetite (around 320 degC, depending on composition) is common in oceanic basalt. Using the wrong mineral's Curie temperature can shift the computed depth substantially.
This calculator applies the standard simple linear-geotherm approximation used throughout magnetic-anomaly interpretation: given a Curie temperature, a surface temperature, and a geothermal gradient, it estimates how deep the crust must go before reaching that Curie temperature, and charts how that depth changes as the geothermal gradient varies.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — Typical Continental Crust (Magnetite)
Tcurie = 580 °C, Tsurface = 15 °C, G = 25 °C/km
Example 2 — Volcanic/Geothermal Area (Titanomagnetite)
Tcurie = 320 °C, Tsurface = 20 °C, G = 40 °C/km
Example 3 — Stable Craton, Low Gradient (Magnetite)
Tcurie = 580 °C, Tsurface = 10 °C, G = 18 °C/km
❓ Frequently Asked Questions
🔗 Related Calculators
What is Curie point depth?
Curie point depth is the depth in Earth's crust at which rock temperature reaches the Curie temperature of its dominant magnetic mineral, above which the rock loses its permanent (ferromagnetic) magnetization. Below this depth, crustal rock cannot contribute to measured magnetic anomalies.
What is the formula for Curie point depth?
Using a simple linear geotherm, Curie point depth is D_curie = (T_curie - T_surface) / G, where T_curie is the Curie temperature of the dominant magnetic mineral, T_surface is the surface temperature, and G is the geothermal gradient in degC/km. The result is in kilometers.
What Curie temperature should I use for magnetite?
Magnetite, the most common magnetic mineral in continental crust, has a Curie temperature of about 580 degC, the default value in this calculator. Use this unless you have specific evidence the dominant magnetic mineral in your area is something else.
How does titanomagnetite change the calculation?
Titanomagnetite, common in oceanic basalt, has a much lower Curie temperature, around 320 degC depending on its titanium content, versus 580 degC for magnetite. Using titanomagnetite's lower Curie temperature in the formula produces a shallower Curie point depth for the same geothermal gradient.
Why is Curie point depth shallower in volcanic and geothermal areas?
Volcanic and active geothermal areas have much steeper geothermal gradients than stable continental crust, so the Curie temperature is reached at a much shallower depth. This is exactly why the formula divides by the gradient, a larger G produces a smaller D_curie for the same Curie and surface temperatures.
How is Curie point depth used in geophysics?
Curie point depth maps, derived from the spectral analysis of magnetic survey data, are widely used as a proxy for regional heat flow and geothermal energy potential, since the depth where crustal rock demagnetizes tracks the same thermal structure that heat flow measurements describe directly.
How accurate is the linear-geotherm approximation used here?
It's a useful first-order estimate but a simplification. Real crustal temperature profiles curve with depth because of radiogenic heat production within the crust and depth-dependent thermal conductivity, so professional Curie depth studies often use more detailed thermal models than a single linear gradient.
What is the typical Curie point depth under continental crust?
Roughly 10 to 30 kilometers under stable continental crust with typical geothermal gradients of 20 to 30 degC/km, though this varies significantly with local tectonic setting. Under active volcanic or high-heat-flow geothermal areas, Curie point depth can be just a few kilometers.
Does surface temperature significantly affect Curie point depth?
Only modestly for most inputs, since surface temperature (typically 0 to 30 degC) is small compared to the Curie temperature (300 to 600+ degC). The geothermal gradient has a far larger effect on the result, since it's in the denominator of the formula.
What happens if the geothermal gradient is very low?
A very low geothermal gradient produces a very large Curie point depth, since less temperature rise happens per kilometer, so much more depth is needed to reach the Curie temperature. This calculator requires a gradient greater than zero, since a zero or negative gradient would never reach the Curie temperature at any depth.