Absolute Paleointensity Through Quantum Diamond Microscope Measurements

Absolute paleointensity reconstructions provide critical constraints on the dynamics and long-term evolution of the geodynamo. Yet, a high failure rate persists in paleointensity experiments due to limitations inherent to bulk measurement techniques. As a result, measurements are often compromised by mineralogical alteration, multidomain behavior, magnetic interactions, and the presence of non-ideal remanence carriers that cannot be spatially isolated or individually evaluated. We present a new approach to absolute paleointensity determination based on Quantum Diamond Microscopy (QDM), enabling direct observation of thermoremanent magnetization (TRM) acquisition and decay at the sub-millimeter scale. We apply this technique to natural basalt and archaeological ceramic samples subjected to controlled laboratory TRM inductions, providing an opportunity to investigate magnetic recording processes at the level of localized anomalies. Experimental tests of TRM acquisition demonstrate that the direction of the applied laboratory field can be recovered from the magnetic vectors obtained from several hundred individual anomalies. For bias fields exceeding 2μT, the recovered vectors closely match the bulk direction, with minimal angular misfits across the population of carriers. This result provides direct physical validation, at the grain scale, of fundamental paleomagnetic recording assumptions that are traditionally inferred from statistical behavior in bulk measurements. This directional fidelity establishes the physical basis for extending micro-scale observations to quantitative paleointensity analysis. Using QDM, we implemented a full Thellier-style zero-field/in-field (ZI) protocol, monitoring both the thermal decay of natural remanent magnetization (NRM) and the acquisition of partial TRM (pTRM) on an anomaly-by-anomaly basis. This allows the identification and isolation of ideal magnetic recorders while excluding poorly behaving carriers, and enables the construction of localized Arai diagrams with a level of selection and quality assessment unattainable in conventional bulk techniques. The ceramic sample shows highly consistent paleointensity estimates, highlighting the robustness of the method. In contrast, paleointensity estimates for the basalt sample show larger variability, reflecting the influence of non-ideal magnetic carriers and local mineralogical heterogeneity. However, when rigorous spatial quality criteria are applied, including high Arai diagram linearity and vectorial decay constraints, the resulting paleointensity estimates converge toward the laboratory field with substantially improved accuracy and reduced uncertainty compared to bulk magnetometer results. Our results demonstrate that absolute paleointensity can be reliably determined at the micro-scale through the controlled ensemble analysis of magnetic anomalies. This approach represents a significant methodological advance in paleomagnetism, opening new perspectives for high-precision paleointensity studies of magnetically heterogeneous, minute, or rare materials, including meteorites, archaeological artifacts, and single crystals.