Comment on ‘New Constraints on the P–T Evolution of the Alpe Arami Garnet Peridotite Body (Central Alps, Switzerland)’ by Paquin & Altherr (2001)

Abstract

The ‘Alpe Arami controversy’ seems destined not to to is representative of the P–T recorded by the Alpe Arami end as more and more new analytical data become peridotite during Alpine subduction metamorphism dated at available. Recently, Paquin & Altherr (2001; hereafter 43 Ma (Gebauer et al., 1992; Becker, 1993; Gebauer, PA (3) a short-lived thermal event at T [ 1100°C, element zoning profiles in garnets and in various genprobably related to magmatic intrusion at 35 Ma (see erations of pyroxenes from the Alpe Arami peridotite Gebauer, 1996), caused complete re-equilibration of garbody. The results led the authors to conclude that the net Fe–Mg and Ni, but left pyroxene Ca, Cr, Al core peridotite experienced peak metamorphic conditions of contents virtually unaltered; (4) no unequivocal baro1180°C and 5·9 GPa. These values are in fairly good metric estimate can be given for this high-T stage on the basis of available data, although pressures not very agreement with the high P–T estimates of Brenker & dissimilar from those achieved at the peak of subduction Brey (1997), but are at variance with the more recent metamorphism are the most likely. estimates of Nimis & Trommsdorff (2001; hereafter NT Harley, 1984; perature estimates are not in conflict with each other and Krogh Ravna, 2000), Co and Ni partitioning between reflect two distinct stages of equilibration characterized by clinopyroxene (Cpx) and orthopyroxene (Opx) (Seitz et different thermal conditions; (2) the low-T stage coral., 1999), and Ni partitioning between Ol and Grt (Canil, 1999). When coupled with the Opx–Grt barometer of responds to N&T’s estimates of 840°C and 3·2 GPa and