Pyrrhotite nano-inclusions in apatite from Les Guilleries lamprohyres (NE Iberian Peninsula)
Martínez, Marina (Universitat Autònoma de Barcelona. Departament de Geologia)
Corbella i Cordomí, Mercè (Universitat Autònoma de Barcelona. Departament de Geologia)

Date:	2023
Abstract:	Apatite is ubiquitous in most types of rocks but in trace amounts, and can form by a variety of processes. Apatite is of great interest because it is an important carrier of volatiles (F, Cl, and OH) and rare-earth elements (REEs), and can be used to reconstruct petrogenetic processes in different environments (e. g. , [1]). However, very few studies are dedicated to understanding apatite microstructures (e. g. , [2]). Here, we explore apatite in Les Guilleries lamprophyre dykes to gain insights into the parental melt and potential processes of re-mobilization of REEs. The studied dykes are calc-alkaline and represent upwelling of deep lithospheric mantle material (least modified magmas) that emplaced at the end of the Hercynian orogeny in a variety of igneous rocks [3]. The texture and composition of apatites were examined in two thin sections of the least altered dykes, numbered GUI-40 and GUI-41, using SEM/EDS, EPMA, and FIB-TEM. Our results show that apatites in GUI-40 are REE-depleted, mostly rounded, subhedral, and range from ~5 to ~35 μm in size. Their average X-site occupancy is F=78, Cl=2, and OH=20 (mol%). Apatites in GUI-41 are highly acicular (~3-10 μm wide and up to ~120 μm long), REE-enriched compared to GUI-40, and their average X-site occupancy is F=64, Cl=5, and OH=31 (mol%). TEM work on an apatite grain in GUI-40 reveals the presence of abundant nano-inclusions, ~10-60 nm in size, with euhedral, hexagonal shapes in the apatite core (Fig. 1). The nano-inclusions are (i) fully occupied by pyrrhotite, (ii) half occupied by pyrrhotite, or (iii) completely empty. The data suggest that apatites in GUI-40 are primary and their microstructure reflect immiscibility of liquids, interpreted as a characteristic inherited from the primary lamprophyre melt. The presence of Fe in the magma and/or the reducing conditions likely prevented S to form ellestadite domains within the apatite structure. This study also demonstrates that slight REE re-mobilization did occur during a secondary, hydrothermal event.
Grants:	Agencia Estatal de Investigación PID2019-109018RB-I00 Agència de Gestió d'Ajuts Universitaris i de Recerca 2022/SGR-00308
Rights:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan aquestes es distribueixin sota la mateixa llicència que regula l'obra original i es reconegui l'autoria de l'obra original.
Language:	Anglès
Document:	Pòster de congrés
Subject:	Apatite ; Nanoinclusions ; Pyrrhotite ; FIB-TEM ; Lamprophyres
Published in:	Goldschmidt Conference. Lyon, France, : 2023

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