Role of aqueous fluids during low pressure partial melting of pelites in the Adamello pluton contact aureole (Italy)
Articolo
Data di Pubblicazione:
2022
Citazione:
Role of aqueous fluids during low pressure partial melting of pelites in the Adamello pluton contact aureole (Italy) / L. Magnani, F. Farina, F. Pezzotta, A. Dini, M.J. Mayne, O. Bartoli. - In: LITHOS. - ISSN 0024-4937. - 430-431:(2022 Nov 15), pp. 106853.1-106853.19. [10.1016/j.lithos.2022.106853]
Abstract:
The contact aureole of the Adamello pluton (Italy) exhibits a rare combination of pelitic rocks anatexis around a shallow metaluminous pluton and formation of interconnected leucosomes, aplites and small lithium and cesium enriched pegmatitic bodies. Contact metamorphic mineral assemblages are described in the non-graphitic pelites and psammites hosting the pluton in the central sector of the Adamello Massif. Three metamorphic zones are identified on the field: I – Muscovite-Biotite, II – Andalusite-Sillimanite-K feldspar, III – Melt zone. In the melt zone, the presence or absence of high temperature Crd defines two types of migmatites, a Crd-bearing metatexite characterized by orbicular textures and a Crd-absent stromatic metatexite. Peak P-T metamorphic conditions in the Adamello pluton thermal aureole were calculated at 690–700 ◦C and 3 kbar on the basis of phase equilibria and geothermobarometry. Phase equilibria modelling reveals that Crd-bearing migmatites, which produced around 20 vol% melt fraction, were generated through internal fluids-buffered partial melting conditions while Crd-absent stromatic metatexites, which produced ca. 35 vol% melt fraction, originated through local fluid present partial melting. Different types of leucosomes were produced by these two partial melting conditions. In-situ leucosomes linked to Crd-bearing migmatites are compositionally similar to primary liquid predicted by phase equilibria modelling (calculated at peak P-T conditions). Leucosomes within the Crd-absent stromatic metatexites show residual mineral compositions extremely enriched in Kfs and Bt and are connected to extraction structures. Their whole rock composition does not represent a primary melt while being compatible with Kfs cumulate textures. The extracted melt from the stromatic metatexites was calculated to be compatible with the spatially related Li-rich pegmatites mean composition, which are hosted by the same geological formation. The studied area shows the small-scale variability in intraformational fluids participation during metamorphic relactions while demonstrating the hybrid nature of partial melting in anatectic terranes.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
contact aureole; metamorphism; aqueous fluids; partial melting; LCT pegmatites
Elenco autori:
L. Magnani, F. Farina, F. Pezzotta, A. Dini, M.J. Mayne, O. Bartoli
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