Morphological analysis and river inversion as a proxy to constraint upper crustal magmatic pluton emplacements: evidence from the Larderello-Travale Geothermal System, northern Apennines.

Geomorphological techniques are used worldwide to explore how the topography responds to surface, crustal and mantle processes. This is the case for the recent developed river dynamic model inversion, that promises to return time vs uplift rate histories required to achieve the modern fluvial configurations. In the framework of the ‘Migrate Project’, a multidisciplinary project combining geology, seismology and machine learning financially supported by the SNSF, we test a novel method of rivers inversion to constrain the surface vertical movements caused by the emplacement of middle-shallow crustal magmatic pluton. We selected, as case study, the Larderello-Travale Geothermal System (LTGS), in the northern Italian Apennines, where multiple magmatic bodies intruded since the late Pliocene causing a large-wavelength surface uplift of at least 600 meters. However, since none of the LTGS plutons reach the surface, their spatial distribution is only constrained by exploration wells or geophysical investigations. Our work aims to: (1) quantify the surface response to pluton emplacement and (2) identify intrusions not yet documented in the area.

We modelled 31 river basins draining the LTGS and surrounding regions. For all catchments, the available ages of plutons constrained by wells, spatially correlate with the local peaks of increasing uplift rates (> 0.2 mm/y). We document a diffuse regional uplift during middle/late Pliocene, likely a consequence of the first magmatic pluton emplacement, followed by a continuous uplift throughout Quaternary times. However, during this time interval, the uplift style changed to confined pulses, which we interpret as locally emplaced magmatic batches. In addition, uplift rates decreased systematically from 0.6 Ma to present, which suggests a potential reduction on the topographic response to magma emplacement, even if the thermal anomaly is still quite evident. This work confirms that plutons provide a topographic swell, and we suggest that our approach could be used to locate undocumented plutons, leading to new potential strategies for geothermal exploration.