Exploring fault propagation and the role of inherited structures during caldera collapse through laboratory experiments

Caldera collapse received large attention during the last decades and was widely studied using various approaches, spanning from field-geology to numerical and analogue modelling. Analogue models allow to reproduce caldera collapse deformation, providing information otherwise difficult to obtain during such an extremely transient geological process. A wide range of analogue studies is available in literature, nonetheless, some aspects are still barely known, particularly the propagation of caldera faults and the role of inherited structures during caldera collapse. We have thus addressed the above research questions through analogue models. Our models show how calderas may experience asymmetry due to the lateral propagation of caldera-related faults. Furthermore, inherited discontinuities may affect caldera collapse by inducing rectilinear caldera faults that generate non-circular ring faults. Finally, sub-vertical discontinuities may be able, in specific conditions, to inhibit the formation of standard caldera structures that have been commonly observed in previous experimental series (i.e., early inward-dipping reverse faults followed by peripheral normal ring faults). Our models were then compared with four natural examples (the Acoculco and Los Humeros caldera complexes in Mexico, the Tuscolo-Artemisio caldera in the Colli Albani volcanic district, Italy and the Glencoe Caldera in Scotland), suggesting a relevant control exerted by inherited faults during caldera collapse. On the basis of the modelling results, we propose an evolutionary model that can be generalized and likely applied to many other caldera settings worldwide.