New 40Ar-39Ar geochronological data constrain the Timescale of the Mio‐Pliocene Campiglia Marittima magmatic‐hydrothermal system (Tuscany, Italy)
Petrology and timing of magmatic‐hydrothermal systems and the linkage between plutonic and volcanic domains are key topics in Earth sciences, because of broad implications for natural hazards (volcanic eruptions, gas emissions, earthquakes) and exploitation of natural resources (ore deposits and geothermal resources). This study reports the results of a detailed investigation, using the 40Ar–39Ar method supplemented by mineral-textural and chemical analysis at the microscale, on the timescale of a well‐characterized natural example, the Mio‐Pliocene Campiglia Marittima magmatic‐hydrothermal system (Tuscany, Italy). 40Ar–39Ar 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 (±2σ), starting from 5.409 ± 0.043 Ma (±2σ). 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 for the first time that the San Vincenzo Rhyolite consists of two diachronous batches, corresponding to the two groups already noted in the literature, the first emplaced at 5.0024 ± 0.0062 Ma (±2σ), closely following emplacement of mafic porphyries, the second at 4.4359 ± 0.0045 Ma (±2σ). Bulk of hydrothermal deposits, consisting of skarns and associated Zn–Pb(‐Ag) mineralization predating Fe–Cu ore, formed within the first ~ 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. Deuteric alteration of K-feldspar of the later felsic porphyries, continued until ~4.3 Ma.
Di Vincenzo G., Vezzoni S., Dini A., Rocchi S., 2022. Timescale of a magmatic‐hydrothermal system revealed by 40Ar–39Ar geochronology: the Mio‐Pliocene Campiglia Marittima system (Tuscany, Italy). Scientific Reports, https://www.nature.com/articles/s41598-022-10867-9.
For more information: Gianfranco Di Vincenzo (gianfranco.divincenzo(at)igg.cnr.it), Simone Vezzoni (simone.vezzoni(at)igg.cnr.it), CNR-IGG.