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Metasomatic events recorded in ultramafic xenoliths from the Hyblean area (Southeastern Sicily, Italy)

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Abstract

Three types of ultramafic xenoliths from the Hyblean area (Sicily) show prime evidence for mantle metasomatism, namely: 1) Spinel-facies depleted harzburgite veined by phlogopite-bearing clinopyroxenite; 2) Amphibole-bearing harzburgite; and 3) Al-spinel websterite. (2) and (3) exhibit glassy pockets having respectively mugearitic and basanitic compositions, but a little amount of glass with low Ca and very low alkalis in (2). Glasses generally show trace element distributions consistent with the partial melting of pargasite-dominated mineral assemblages. Abundant Ca-Mg-carbonate globules immersed in these glassy pockets testify to immiscibility between silicate and carbonatite melts. Silicate melts and hydrous-silicate supercritical fluids, which underwent phase separation during fluxing throughout the semi-brittle lithospheric mantle, may account for such metasomatizing processes. The nature and abundance of some fluid-mobile elements in glasses and hydrous minerals (especially the Ca-poor glass, with B = 59 ppm, Li = 27 ppm, Ba = 700 ppm and phlogopite, with Ba = 8,465 ppm, Sr = 260 ppm, F = 5,700 ppm) suggest that some hydrous fluids may derive from hydrothermally altered oceanic crust. Conversely, metasomatizing silicate melts probably have a deep-seated origin. These results confirm previous suggestions on the key role of mantle metasomatism in the origin of some alkaline Hyblean magmas.

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Acknowledgements

The Authors are grateful to Daniel Harlov for his invaluable suggestions and editing of the text as well as to Massimo Coltorti and Alessandra Montanini for their constructive comments that highly contributed to improve the early-submitted version of the manuscript. This work was financially supported by grants to R. Cristofolini and V. Scribano from the University of Catania (Ricerche di Ateneo, esercizio 2005–06).

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Scribano, V., Viccaro, M., Cristofolini, R. et al. Metasomatic events recorded in ultramafic xenoliths from the Hyblean area (Southeastern Sicily, Italy). Miner Petrol 95, 235–250 (2009). https://doi.org/10.1007/s00710-008-0031-4

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