A marine magnetotelluric survey in the New Ireland Basin, Papua New Guinea – First results from SO299 DYNAMET.

In easternmost Papua New Guinea, some of the most metal-enriched continental crust has formed, hosting some of the world’s largest copper and gold deposits that formed over the last 2-3 million years. The area is marked by a dynamic and complex geologic history at a convergent margin with arc-continent collision, subduction reversals producing a complex microplate mosaic, and continuous metasomatism of the mantle wedge. In 2023, the SO299 DYNAMET expedition set sail to target the New Ireland Basin with special focus on the South Lihir Volcanic Field and investigate the source of the youngest volcanic activity in this area. To detect potential ascending melts and aqueous fluids focusing in the suspected trans-lithospheric faults, our team deployed 16 ocean-bottom magnetotelluric stations (OBMT) with a bottom-time of up to 3 weeks in the New Ireland Basin south and west of Lihir Island. Given the assumed geological complexity, the stations were positioned in a 3D array with approximately 15 km spacing, including a dense cluster around the volcanic seamounts south of Lihir. After the deployment we found 12 stations recorded valid data which were segmented, filtered and robustly processed to electromagnetic impedances for periods between 60 and 20,000 s. Preliminary results based on analyzing the 1D Berdichevsky average response function, the 2D response functions and 1D inversions show anomalies for several stations close to Lihir island on an NW-SE pointing profile in approximately 20-30 kilometers depth. Dimensionality analysis points towards an at least 2D structured anomaly with a possible northern strike direction. However, the area's complex geometry and proximity to nearby islands introduce significant uncertainties and favors 3D inversion, which is currently work in progress.