Garnet zoning in kyanite-bearing eclogite from Golfo Aranci: new data on the early prograde P-T evolution in NE Sardinia, Italy

Gabriele Cruciani

;Marcello Franceschelli;Massimo Scodina;Mariano Puxeddu

2019-01-01

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Abstract

Kyanite-bearing eclogites from the Migmatite Complex of Golfo Aranci area, NE Sardinia, have been investigated using microstructural analyses and thermodynamic modelling in order to define their early metamorphic evolution and P-T path. The eclogites underwent a clockwise P-T path recorded by the different composition of garnet core, mantle and rim. P-T pseudosection modelling allowed to estimate P-T conditions in the range T = 580-630 °C and P = 1.5-2.00 GPa for the formation of garnet core, between T = 620-690 °C and P = 2.0-2.3 GPa for garnet mantle and within T = 650-700 °C and P = 1.4-2.1 GPa for garnet rim. The first part of the P-T path is characterised by a prograde increase in P and T in the eclogite facies that occurred between the growth of the garnet core and mantle. After the peak pressure, recorded by the garnet mantle composition, the rocks underwent moderate temperature increase and significant pressure decrease until they reach the peak temperature near to the eclogite/upper granulite facies transition, recorded by the garnet rim composition. The P-T trajectory proposed for the early stage of the metamorphic evolution of the kyanite-bearing eclogites is similar to already existing observations from the Sardinian Low Medium Grade Metamorphic Complex, and introduce new constraints on their prograde eclogite facies evolution. The role of the new prograde path is then discussed in the light of the Variscan orogen.