Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Braga, R. Articles by Morten, L. Search for Related Content

An early metamorphic stage for the Variscan Ulten Zone gneiss (NE Italy): evidence from mineral inclusions in kyanite

R. Braga^1,*, H.-J. Massonne² and L. Morten^1,

¹ Dipartimento di Scienze della Terra e Geologico-Ambientali, Università di Bologna, Italy
² Institut für Mineralogie und Kristallchemie, Universität Stuttgart, Germany

^* E-mail: r.braga{at}unibo.it

The early P-T evolution of a garnet-kyanite gneiss from the Variscan Ulten Zone has been defined by detailed petrographic observations leading to the detection of chlorite-epidote- and staurolite-bearing assemblages enclosed in kyanite porphyroblasts. Calculations of P-T pseudosections in the system NaCaKFeMgAlSiHO allowed us to constrain the evolution of these relics to the earliest metamorphic stages. The overall path shows a P-T increase to a peak of 11–12 kbar and 600–650°C followed by decompressional heating to 720°C and 9–10 kbar and final cooling at 7 kbar, 550–600°C. This clockwise P-T path reflects crustal thickening and subsequent thermal decay related to the continental collision of the Variscan orogeny 330–340 Ma ago. Our study demonstrates that large kyanite porphyroblasts may preserve assemblages related to prograde metamorphic stages. As a result, the detection of mineral inclusions in kyanite can complement many similar studies on mineral suites hosted in garnet and zircon.

KEYWORDS: porphyroblast, inclusions, P-T path, garnet, kyanite, Variscan Ulten Zone, electron microprobe