  The occurrence of metavolcanic rocks within the Paleozoic basement of the
Alpi Apuane metamorphic complex has been known since long time. Among them,
some massive porphyritic tourmaline-bearing rocks cropping out in the southern
sector of the Alpi Apuane present some distinctive and peculiar features,
differing from the better known middle Ordovician metarhyolites of the
Porfiroidi e scisti porfirici Fm. The porphyritic tourmaline-bearing rocks
belong to the recently proposed Fornovolasco Metarhyolite Fm. They are granular
to porphyritic, with phenocrysts of quartz (often with magmatic embayment),
pseudomorphosed feldspars, and mica (both biotite and muscovite), in a
groundmass formed by quartz, white mica, albite, and Kfeldspar. Tourmaline
(schorl-dravite in composition) is an abundant accessory mineral, in some cases
forming cm-sized spots. The studied rocks plot into the rhyolite field of the
Total Alkali vs Silica classification diagram. They show a peraluminous nature,
having an Alumina Saturation Index ranging from 1.3 and 3.2. Their
trace-element signature is that typical of highly evolved orogenic magmas.
Laser ablationICPMS UPb datings on zircon suggest a Permian crystallization age
(weighted average ages of the four samples ranging from 292 and 271 Ma), thus
relating these rocks to a post-Variscan magmatism. This new dating represents
the very first evidence of a Permian magmatism in the pre-Triassic basement of
the Northern Apennines. The potential relationships between Permian felsic
magmatism and the ore genesis in the Alpi Apuane metamorphic complex are also
discussed.

Geophysics