Timescale of a magmatic-hydrothermal system revealed by 40Ar-39Ar geochronology: the Mio-Pliocene Campiglia Marittima system (Tuscany, Italy)

Petrology and timing of magmatic-hydrothermal systems and the linkage between plutonic and volcanic domains are central topics in geosciences, because of broad implications for natural hazards and exploitation of natural resources. We investigated by the 40Ar39Ar method the timescale of a well-characterized natural example, the Mio-Pliocene Campiglia Marittima magmatic-hydrothermal system (Tuscany, Italy). 40Ar39Ar data from pristine and homogeneous trioctahedral micas and sanidine from the plutonic-hydrothermal-subvolcanic-volcanic sequence (from the Botro ai Marmi Granite to the San Vincenzo Rhyolite) record crystallization ages and define a temporal sequence lasting 973 +/- 43 ka, starting from 5.409 +/- 0.043 Ma. K-feldspar from mafic and felsic porphyries, unlike micas, are affected by submillimetre, micropore laden, alteration domains consisting of secondary K-feldspar and albite, and yielded staircase-shaped age spectra, compatible with a ternary mixing. Results document that the San Vincenzo Rhyolite consists of two diachronous batches, the first emplaced at 5.0024 +/- 0.0062 Ma, closely following emplacement of mafic porphyries, the second at 4.4359 +/- 0.0045 Ma. Bulk of hydrothermal deposits, consisting of skarns and associated Zn-Pb(-Ag) mineralization predating Fe-Cu ore, formed within the first similar to 400-ka lifetime of the whole sequence and was closely followed by the first eruption which should have run out most of the ore-forming potential of the system.

Automated summary

The petrology and timing of magmatic-hydrothermal systems and the connection between plutonic and volcanic domains have important implications for natural hazards and exploitation of natural resources. In this study, the 40Ar39Ar method was used to investigate the timescale of a well-characterized natural example in Tuscany, Italy. The results reveal a temporal sequence lasting approximately 973 +/- 43 ka, with the first emplacement occurring at 5.409 +/- 0.043 Ma. The study also shows that the hydrothermal deposits formed within the first 400 ka of the sequence, followed closely by the first eruption.