Over 100 Myr of growth history of a passive diapir, analyzed through its tectonostratigraphic reconstruction (Maestu, northern Spain)

Abstract The passive growth history of the Maestu salt diapir spanned > 100 Myr. This was constrained using an integrated structural and tectonostratigraphic analysis of the diapir and its sedimentary country rocks, built on detailed surface mapping and reinterpretation of legacy seismic-reflection profiles. After > 40 Myr of Triassic evaporite deposition and a ca. 80 Myr interval of tectonic quiescence, a precursory fault nucleated. Then synsedimentary fault activity persisted for 21 Myr, followed by 10 Myr required for the formation of a nascent salt stem. Subsequent diapir growth lasted > 60 Myr, fed by salt withdrawn from the adjacent minibasin at decreasing rates. Part of the diapir’s growth history (between 48 and 30 Ma ago) overlapped the Alpine orogeny, during which the diapir and its country rocks were translated several km along a major thrust. Notwithstanding, the primary internal structure remained intact. Over the last 15 Myr (middle Miocene to Present), the diapir has undergone little change. Beyond documenting the tempo of passive diapirism and long-term strain rates, this study clarifies basement-cover decoupling during Cretaceous sedimentation and Cenozoic orogeny in northern Spain. Graphical Abstract