P–T Modelling Constrains the Depth of Emplacement of the Porto Azzurro Pluton and Implies Minor Exhumation Caused by the Zuccale Fault (Island of Elba, Italy)

Understanding the pressure of emplacement of granitic intrusions is crucial to understanding the exhumation history of plutons and constraining the tectonic setting of magma emplacement. However, P–T and geochronological constraints from exhumed plutons are often characterized by large uncertainties, especially in shallow crustal settings with p < 2–3 kbar, where minimal changes in estimated pressure can drastically change the exhumation model. We show an example from a typical upper crustal intrusion, the Porto Azzurro Pluton on the Island of Elba (Italy). This pluton emplaced at ~6.5 Ma at less than 7–8-km depth and is believed to have been exhumed under a regional low-angle normal fault, known as the Zuccale Fault. Phase equilibrium modelling of garnet ± cordierite ± andalusite-bearing parageneses in hornfels shows that the metamorphic pressure registered by the contact aureole rocks is lower than previously thought, constraining the Porto Azzurro Pluton to ~3.8–4.6-km depth (p = 1.0–1.2 kbar). Our P–T data constrain, for the first time, the minimum and maximum metamorphic pressure of the Zuccale Fault footwall and hanging wall blocks. P estimates overlap in the footwall (p = 0.3–1.8 kbar) and hanging wall (p = 0.4–1.2 kbar) blocks of the Zuccale Fault. Moreover, both fault blocks show a similar thermal evolution, which indicates that the fault contributed little, if at all, to the exhumation of the intrusion.