S U M M A R YThe Antarctic Peninsula (AP) consists of a long lived and uniquely well preserved magmatic arc system. The broad tectonic structure of the AP arc is well understood. However, magmatic processes occurring along the arc are only constrained by regional geophysical and relatively sparse geological data. Key questions remain about the timing, volume, and structural controls on magma emplacement. We present new high resolution aeromagnetic data across Adelaide Island, on the western margin of the AP revealing the complex structure of the AP arc/forearc boundary. Using digital enhancement, 2-D modelling and 3-D inversion we constrain the form of the magnetic sources at the arc/forearc boundary. Our interpretation of these magnetic data, guided by geological evidence and new zircon U-Pb dating, suggests significant Palaeogene to Neogene magmatism formed ∼25 per cent of the upper crust in this region (∼7500 km 3 ). Significant structural control on Neogene magma emplacement along the arc/forearc boundary is also revealed. We hypothesize that this Neogene magmatism reflects mantle return flow through a slab window generated by Late Palaeogene cessation of subduction south of Adelaide Island. This mantle process may have affected the final stages of arc magmatism along the AP margin.Key words: Magnetic anomalies: modelling and interpretation; Mantle processes; Volcanic arc processes; Continental margins: convergent; Crustal structure; Antarctica. I N T RO D U C T I O NThe magmatic arc along the Antarctic Peninsula (AP) once formed part of the tectonically active circum Pacific 'ring of fire'. Cessation of subduction due to Cenozoic ridge-trench collision along the AP has preserved an intact arc/forearc system (Larter & Barker 1991). The AP therefore provides a snapshot of arc processes during the final stages of subduction. The regional magmatic and tectonic evolution of the AP arc is inferred from reconnaissance aeromagnetic data, and geological observations of relatively sparse outcrops (Leat et al. 1995;Ferraccioli et al. 2006;Vaughan et al. 2012a critical questions remain about the volume of arc magmatism, migration of the arc through time, and the extent of structural control on the evolution of the arc magmatic system.One key area of the AP where many questions remain is along the arc/forearc boundary, where the latest phases of arc magmatism are thought to have occurred. Here we use recently acquired high resolution aeromagnetic data over Adelaide Island, on the western margin of the AP (Figs 1 and 2), to investigate the processes occurring along the arc/forearc boundary. High resolution aeromagnetic data has elsewhere been used to reveal tectonic structures in forearc regions (Ponce et al. 2003;Saltus et al. 2005), the geometry of arc magmatic intrusions (De Ritis et al. 2010), and tectonic and magmatic patterns in rift systems formed along the reactivated margins of older magmatic arc terranes (Ferraccioli et al. 2005). We apply digital enhancement, 2-D modelling and 3-D inversion to the new magnetic...