LITHIUM ENRICHMENT IN ANATECTIC PEGMATITES: NEW INSIGHTS FROM THE THERMOMETAMORPHIC AUREOLE OF THE ADAMELLO BATHOLITH
type: CreativeWork
description: In the contact aureole of the collisional metaluminous Adamello pluton (Italy), pelites reached hornfels facies conditions locally undergoing partial melting, forming Crd-bearing and Crd-absent migmatities. This small-scale migmatitic field is spatially associated with barren and Lithium-Cesium-Tanatalum (LCT) pegmatitic dykes of granitic composition, suggesting a direct link between low-pressure partial melting and generation of Li-enriched felsic melts. Phase equilibria modelling reveals that the Crd-bearing metapelitic migmatites produced around 20 vol.% melt fraction through fluid-assisted melting reactions, while the Crd-absent stromatic metatexites produced ca. 35 vol.% of melt during fluid-rich partial melting. Peak P-T metamorphic conditions were calculated at 690-700°C and 300 MPa for both rock types. Because of the steep contact thermal gradient, the underlying and older conglomerates of the Verrucano Formation, of which the pelitic succession is part of, as well as rock of the Collio Formation experienced comparably lower temperature metamorphism. Their mica-poor mineral compositions prevented them from melting and influencing the local anatectic processes. Crd-bearig migmatites leucosomes are compositionally similar to anatectic melts obtained by phase equilibria modelling, connected to fluid-assisted melting and defined as unfractionated, while the leucosomes dominated by Kfs-Bt cumulus structures and extremely enriched in K2O, Sr and Ba are connected to fluid-rich melting and Crd-absent migmatites. Major and trace element modelling suggests that part of the melt formed in the latter case was extracted from the source and that the composition of this evolved anatectic magma is compatible with the chemical composition of the migmatites-hosted LCT pegmatites. Whole rock Sr-Nd isotopic data confirm that the Li-rich pegmatites of the Forcel Rosso area are indeed crustally derived, marking them as produced by direct anatexis of metapelites. They also show th…
abstract: In the contact aureole of the collisional metaluminous Adamello pluton (Italy), pelites reached hornfels facies conditions locally undergoing partial melting, forming Crd-bearing and Crd-absent migmatities. This small-scale migmatitic field is spatially associated with barren and Lithium-Cesium-Tanatalum (LCT) pegmatitic dykes of granitic composition, suggesting a direct link between low-pressure partial melting and generation of Li-enriched felsic melts. Phase equilibria modelling reveals that the Crd-bearing metapelitic migmatites produced around 20 vol.% melt fraction through fluid-assisted melting reactions, while the Crd-absent stromatic metatexites produced ca. 35 vol.% of melt during fluid-rich partial melting. Peak P-T metamorphic conditions were calculated at 690-700°C and 300 MPa for both rock types. Because of the steep contact thermal gradient, the underlying and older conglomerates of the Verrucano Formation, of which the pelitic succession is part of, as well as rock of the Collio Formation experienced comparably lower temperature metamorphism. Their mica-poor mineral compositions prevented them from melting and influencing the local anatectic processes. Crd-bearig migmatites leucosomes are compositionally similar to anatectic melts obtained by phase equilibria modelling, connected to fluid-assisted melting and defined as unfractionated, while the leucosomes dominated by Kfs-Bt cumulus structures and extremely enriched in K2O, Sr and Ba are connected to fluid-rich melting and Crd-absent migmatites. Major and trace element modelling suggests that part of the melt formed in the latter case was extracted from the source and that the composition of this evolved anatectic magma is compatible with the chemical composition of the migmatites-hosted LCT pegmatites. Whole rock Sr-Nd isotopic data confirm that the Li-rich pegmatites of the Forcel Rosso area are indeed crustally derived, marking them as produced by direct anatexis of metapelites. They also show th…
author: MAGNANI, LORENZO
language: eng
keywords: lithium, cesium, tantalum, pegmatite, anatectic, fluid, present, melting, phase equilibria, tourmaline, Settore GEO/08 - Geochimica e Vulcanologia
date published: 2023-04-17
date modified: 2026-07-27T20:19:03Z
provider: Università degli Studi di Milano
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Università degli Studi di Milano

PropertyValue
property ID: Handle
value: https://hdl.handle.net/2434/966036

PropertyValue
property ID: DOI
value: 10.13130/magnani-lorenzo_phd2023-04-17