Metasomatic tourmaline in hybrid contact-bands between gneiss and peridotite in the Ulten zone of the Eastern Italian Alps

• Verfasst von: Marocchi, Marta [VerfasserIn]
• Verfasst von: Marschall, Horst R. [VerfasserIn]
• Verfasst von: Konzett, Jürgen [VerfasserIn]
• Verfasst von: Tropper, Peter [VerfasserIn]
• Verfasst von: Ludwig, Thomas [VerfasserIn]
• Verfasst von: Mair, Volkmar [VerfasserIn]
• Verfasst von: Bargossi, Giuseppe Maria [VerfasserIn]
• Titel: Metasomatic tourmaline in hybrid contact-bands between gneiss and peridotite in the Ulten zone of the Eastern Italian Alps
• Titelzusatz: chemistry and boron isotopic composition
• Verf.angabe: Marta Marocchi, Horst R. Marschall, Jürgen Konzett, Peter Tropper, Thomas Ludwig, Volkmar Mair, Giuseppe Maria Bargossi
• E-Jahr: 2011
• Jahr: February 01, 2011
• Umfang: 17 S.
• Fussnoten: Gesehen am 11.08.2022
• Titel Quelle: Enthalten in: The Canadian mineralogist
• Ort Quelle: Ottawa : Assoc., 1957
• Jahr Quelle: 2011
• Band/Heft Quelle: 49(2011), 1, Seite 245-261
• ISSN Quelle: 1499-1276
• DOI: doi:10.3749/canmin.49.1.245
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 181416782X

Abstract

Ultramafic rocks in the Ulten Zone (UZ) high-pressure mélange, in the Eastern Italian Alps, embedded in crustal gneisses, preserve a series of metasomatic hybrid bands generated by infiltration of aqueous fluids. These hybrid bands at the peridotite-gneiss contact comprise phlogopite and anthophyllite with accessory zircon, apatite and allanite. Here, we report the rare occurrence of centimeter-sized crystals of metasomatic tourmaline in two different UZ outcrops, at Mt. Hochwart and Malga Preghena. Tourmaline has a dravite-uvite-rich composition and shows optical and chemical zoning, with slightly variable Ti, Ca and Fe contents. Secondary-ion mass spectrometry (SIMS) analyses provide information on the intragrain B-isotopic zonation of the grains, which is correlated with optical and chemical zoning. The range in δ11B is from −7.4 to +0.3‰ for the Mt. Hochwart tourmaline, generally with an isotopically lighter core and heavier rim. The δ11B range for Malga Preghena tourmaline is from +1.2‰ in the core to −3.9‰ in the rim. Variable proportions of fluids derived from both the local crustal gneisses and a subducting slab control the B-isotope composition in the metasomatic tourmaline from the UZ. Fluid mixing in hybrid crustal-ultramafic bands can be monitored by metasomatic tourmaline, which may also have a significant impact on the B isotope budget of the subducted slab and the slab-mantle interface.