Cala dei Mugni (Mugni beach), Franco Promontory, Giglio Island, Isola del Giglio, Grosseto Province, Tuscany, Italyi

Regional Level Types
Cala dei Mugni (Mugni beach)	- not defined -
Franco Promontory	- not defined -
Giglio Island	Island
Isola del Giglio	Commune
Grosseto Province	Province
Tuscany	Region
Italy	Country

At Cala dei Mugni there is a spectacular outcrop that illustrates the succession of two main deformation and metamorphic episodes, which are characteristic of the early Apennine orogenic history. The first episode is related to the HP/LT stage, the second to the retrogressive stage with a final re-equilibration in the low-grade greenschist facies during eastward-directed shearing.

Verrucano rocks exposed at Cala dei Mugni consist of ferrocarpholite, phengite, chlorite, quartz, and minor ankerite. Late, static formation of green biotite is locally observed. Fibrous ferrocarpholite crystals are commonly observed on quartz-rich segregations lying parallel to the foliation planes.

Ferrocarpholite compositions range from XMg= 0.37 to 0.41. Ferrocarpholite phenoblasts are locally replaced by fine-grained aggregates of phyllosilicates (white mica + chlorite). Further alteration of carpholite produced kaolinite. The absence of chloritoid indicates that the exhumation path did not cross the chloritoid-producing carpholite breakdown reaction, and hence, the P-T gradient must have remained relatively cool. Replacement of ferrocarpholite by late kaolinite suggests cooling during decompression within the kaolinite + quartz stability field. Finally, the presence of static green biotite in some samples reflects a late influence by the nearby pluton and a short-lived temperature increase to about 400°C.

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References