Thermal structure insights from Curie Point Depth estimation in Java Island, Indonesia using the IRLS-de-fractal method

Java Island is formed above the subduction zone where the Eurasian and Indo-Australian plates interact, creating a volcanic arc rich in geothermal potential. Studying the shallow crustal thermal structure through Curie Point Depth (CPD) estimation is critical for understanding regional geodynamics, particularly the interplay between tectonism, volcanism, and geothermal distribution. CPD serves as a proxy for determining geothermal gradients and heat flow. We propose a novel Iteratively Reweighted Least Squares (IRLS)-de-fractal method for CPD estimation, which integrates two established schemes into a unified framework. This method applies fractal correction to the observed magnetic spectrum and uses robust inversion to reduce sensitivity to outliers. Magnetic anomaly data (WDMAM) were divided into 33 overlapping blocks (184 km × 184 km, 50% overlap) and processed using the Reduction to the Pole (RTP). The results show that CPD values range from 14.21 km to 23.41 km, the geothermal gradient from 23.69 to 39.03 °C/km, and the heat flow from 75.21 to 143.82 mW/m 2 . Shallow CPD values, associated with high geothermal gradients and elevated heat flow, are identified in the Quaternary volcanic belt of the mountain complex in the southern part of the West Zone and the East Zone. In the West Zone, thermal anomalies are controlled mainly by subduction slab geometry and fault-related heat transfer. In contrast, East Zone anomalies primarily reflect magmatic intrusions and intense volcanic activity. These findings confirm that Java’s regional thermal structure is mainly controlled by tectonism and lithospheric magmatic activity, directly indicating the presence of viable geothermal sources in these areas.