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.

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]

Role of aqueous fluids during low pressure partial melting of pelites in the Adamello pluton contact aureole (Italy)

L. Magnani
Primo
Writing – Original Draft Preparation
;
F. Farina
Secondo
Supervision
;
2022

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.
contact aureole; metamorphism; aqueous fluids; partial melting; LCT pegmatites
Settore GEO/07 - Petrologia e Petrografia
DECC18MGIUD_01 - Dipartimenti di Eccellenza 2018-2022 - Dipartimento di SCIENZE DELLA TERRA "ARDITO DESIO" - GIUDICI, MAURO - DECC - Bando Dipartimenti di Eccellenza - 2018
Article (author)
File in questo prodotto:
File Dimensione Formato  
1-s2.0-S0024493722002626-main.pdf

accesso riservato

Tipologia: Publisher's version/PDF
Dimensione 11.56 MB
Formato Adobe PDF
11.56 MB Adobe PDF   Visualizza/Apri   Richiedi una copia
Pubblicazioni consigliate

Caricamento pubblicazioni consigliate

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/939326
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 0
  • ???jsp.display-item.citation.isi??? 0
social impact