The role of compressional structures in the development of collapse calderas: Insights from analogue models

Caldera volcano systems in compressional tectonic settings exhibit complex deformation histories shaped by the interaction between magmatic and tectonic processes. This study presents a series of analogue experiments designed to investigate how tectonic shortening induced from regional compression, represented by a fold-and-thrust belt (FTB), interacts with caldera collapse structures. Two experimental scenarios were tested: (1) collapse followed by regional compression and (2) regional compression preceding collapse. Regional shortening after collapse yielded elliptical collapse structures with a thrust-parallel elongation of the caldera outline. The models further indicate that advancing thrusts can locally reactivate suitably orientated sections of collapse-related ring-faults at the thrust front. Conversely, collapse after regional shortening did not involve significant reactivation of pre-existing thrust faults, because their low dip angles render them sub-optimally orientated for reactivation. On the other hand, models show that a thrust-related thickening of the magma reservoir roof can inhibit ring-fault localisation and propagation and can potentially lead to a thrust-perpendicular elongation of the caldera outline. Comparisons with natural calderas in the Central Andes (e.g., Jorquera, Bellavista, Puquios and Diamante calderas) and in Japan (Akaigawa caldera) reveal similar aspect ratios and structural trends, supporting the wider relevance of the experimental findings for understanding interactions between caldera formation and regional tectonics.