Micaschist from Santa Lucia del Mela zone, (Peloritani Mountains), were studied by integrating information obtained from petrographic analysis, image assisted analysis on mineral phases compositions using X-Ray maps and thermodynamic modeling. These rocks are characterized by the presence of atoll garnets, and preserve a continuous array of textures from pristine garnets, to atoll textures, to completely substituted garnets. These textures are linked to the metamorphic evolution of the rocks, consisting of three main stages of metamorphic recrystallization and related deformation are recognized. The sequence of mineral parageneses recognised to successive deformation events is as follow: D1 is characterised by the assemblage wm1 + chl1 + bt1 + pl1 + grt1 (Inner Core) + qtz + ilm + ap; D2 by grt2 (a and b Relic Outer Core and Relic Rim) + wm2 + chl2+ bt2 + pl2 + qtz + ilm + ap + hem; D3 (associated to garnet core transformation) by grt3 (New Rim) + bt3 + pl3 + wm3 + qtz + chl3 + ilm. On the basis of textural observations and mineral parageneses, the atoll formation is related to the substitution of garnet cores during the D3 stage, with the consumption of garnet cores (grt1) and production of new garnet rim grt3 with wm, bi, qtz and pl. The recognition of the different stages of garnet growth and associated parageneses has been obtained using image analysis coupled with compositional maps, performed with a dedicated software (Ortolano et al., in press). Following the textural and minerochemical analyses, PT conditions associated to the three recrystallization phases have been determined from pseudosections. In order to determine the equilibrium volumes during the different stages of the metamorphic evolution, bulk compositions were determined by XRF and by modal determinations assisted by image analysis. Results indicate that in the Mela rocks is recorded a prograde evolution to amphibolite facies conditions in garnet cores, followed by decompression associated to the heating to lower amphibolite facies, and finally by a temperature increase, probably associated to the intrusion of late Variscan granitoids that are widespread in this unit.
|Titolo:||Sequential atoll-shaped garnets formation from the Aspromonte Peloritani unit (northeastern Sicily-Italy): Petrogenetic and Geothermobarometric implications|
|Data di pubblicazione:||2014|
|Appare nelle tipologie:||1.5 Abstract in rivista|