Reconnaissance isotopic investigations on rocks of an undeformed granite contact within the coesite-bearing unit of the Dora Maira Massif

Diffusion versus recrystallization processes in Rb–Sr geochronology: Isotopic relics in eclogite facies rocks, Western Gneiss Region, Norway

“…More recent studies of Sr isotope systematics in rock systems with solely diffusion-controlled isotope exchange reveal Sr redistribution patterns strikingly similar to the one observed here. Tilton et al (1997) have shown that in a metagranite form the Dora Maira, Western Alps, Sr signatures in feldspar were preserved through temperatures >700°C at UHP conditions, while biotite shows only partial rejuvenation and apatite exhibits large proportions of 'excess' radiogenic Sr. Similar observations were made in statically heated ultramafic rocks from the Bergen Arcs, Norway (Kühn et al, 2000).…”

Laser step–heating ⁴⁰Ar/³⁹Ar analyses of biotites from meta–granites in the UHP Brossasco–Isasca Unit of Dora–Maira Massif, Italy

“…In either case, the argon release could have been enhanced by the pervasive deformation occurred during exhumation. The two metagranite samples of this study (DM 1517 andDM 1540) have been collected from the narrow NW termination of the BIU, significantly closer to both the Pinerolo and the Rocca Solei Units in comparison with the metagranites studied by Tilton et al (1997) (see the cross sections of Fig. 1).…”

“…Solid circles show the location of the analyzed samples (DM1517 and DM1540), that are undeformed metagranites preserved within strongly deformed augen gneiss. The circles in the cross sections show the location of samples studied in this paper and of those studied by Tilton et al (1997).…”

“…Tilton et al (1997) carried out the 40 Ar/ 39 Ar analyses of the biotite separates from similar undeformed metagranites collected near Bastoneri, 7-9 km SE of the sites of the samples DM1540 and DM1517. Their age spectra are complicated, having the troughs between 900-971°C and the age variation from 70 to 215 Ma, younger than the granite protolith (late Permian).…”

“…The BIU has experienced the HP-UHP Alpine evolution (peak P-T conditions at 4.2 GPa, 730°C, e.g., Ferrando et al, 2009 and references therein). This suggests that the biotites in the metagranites should have been reset, as concerning the K-Ar system, during the Alpine evolution and could trap the EAW generated during exhumation of the BIU, arising the problem of explaining why the biotites from the metagranites analysed by Tilton et al (1997) are much younger than those from the metagranites (DM 1517 andDM 1540) in the northwestern part of the BIU. This difference may be due to the fact that the metagranites analysed by Tilton et al (1997) were far from the source of EAW in comparison with the studied metagranites (DM 1517 andDM 1540).…”