Texture development and PT time path of psammitic schist from the Hercynian chain of NW Sardinia (Italy)
Franceschelli, Marcello; Pannuti, Fortunata; Puxeddu, Mariano
European Journal of Mineralogy Volume 2 Number 3 (1990), p. 385 - 398
published: Jun 21, 1990
manuscript accepted: Jan 23, 1990
manuscript received: Apr 18, 1989
ArtNo. ESP147050203003, Price: 29.00 €
Abstract Mineral chemistry and petrography of psammitic schist of north-western Sardinia (Nurra) have been wed to determine the textural and PT evolution of these rocks during the Hercynian orogeny. Four deformation phases of variable intensity D1, D2, D3, D4 may be identified. The early phases are easier to recognize in south Nurra, whereas the later phases predominate in north Nurra. The chronologic relationships between mineral assemblages, textural features and mineral chemistry defined a loop-shaped clockwise PT time path, with attainment of peak temperature (garnet zone, north Nurra, T = 480°C at P = 6 kbar) in the early stages of uplift and exhumation. Mineral assemblages and textures are diachronous between south and north Nurra. The different texture histories of the two parts of Nurra, considered as a whole, are related to three superposed stages: crustal thickening, prograde metamorphism, uplift and exhumation. In south Nurra the textures record the development of S1 schistosity referable to the stage of continental thickening. In north Nurra the textures developed during the last two stages, just after the appearance of Si schistosity up to the development of S3 schistosity.