Pressure-Temperature conditions

Pressure estimates have been performed using Si4+ content in phengitic micas (WmI and WmII) (Massonne and Schreyer 1987); temperature estimates have been done using Ti and AlVI contents in biotite (Schreurs 1985; Henry et al., 2005), garnet-biotite exchange (Thompson 1976; Holdaway and Lee 1977; Ferry and Spear 1978; Dasgupta et al. 1991; Perchuk 1991; Bhattacharaya et al. 1992), garnet-white mica (Green and Hellman, 1982; Hynes and Forest, 1988).

BtI microdomain

Temperatures of 700 to 730°C (Table 1) are estimated for highest Ti-rich biotite (BtI) using the calibration of Henry et al. (2005) with a standard deviation of 30°C. Such temperatures may be addressed to the pre-Alpine stage of this rock and likely to the igneous crystallization phase. At the rims of the BtI, GrtI is in contact with biotite with different compositions from BtI, Fe-Ti-rich, to BtII Ti-poor Mg-richer; the garnet-biotite calibrations applied on these pairs give three T intervals: 400-550°C, 550-620°C and 650-750°C in a range of P = 3-10kbar. The lower T interval corresponds to BtII with a more re-equilibrated composition. At the same rims WmII+GrtI also occurs and the application of garnet-phengite thermometer gives a T intervals 500°±50C in the pressure range 3-10kbar.

Pressure estimates using the Si4+ content in phengitic micas (WmII) give P = 10-12.5 kbar in the T range 450-600°C.

Pl microdomain

PlI microdomains are characterized by coarse rim of WmII + GrtI. Garnet-phengite calibrations applied on these pairs give T = 370±30°C in the pressure range of 3-10kbar. Si4+ content in WmII gives P = 10-12.5 kbar in the T range 450-650°C.

Summing up, a pre-Alpine stage is still recorded by the BtI composition that suggest T = 700-730°C, while no pressure estimates are available for this stage. The Alpine re-equilibration occurred at T between 450 and 550°C and minimum P at 10-12 kbar.