Metasomatic tourmaline in hybrid contact-bands between gneiss and peridotite in the Ulten zone of the Eastern Italian Alps: chemistry and boron isotopic composition
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 anthophyll...
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| Main Authors: | , , , , , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
February 01, 2011
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| In: |
The Canadian mineralogist
Year: 2011, Volume: 49, Issue: 1, Pages: 245-261 |
| ISSN: | 1499-1276 |
| DOI: | 10.3749/canmin.49.1.245 |
| Online Access: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.3749/canmin.49.1.245 Verlag, lizenzpflichtig, Volltext: https://pubs.geoscienceworld.org/canmin/article-abstract/49/1/245/127317/Metasomatic-tourmaline-in-hybrid-contact-bands?redirectedFrom=fulltext 
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| Author Notes: | Marta Marocchi, Horst R. Marschall, Jürgen Konzett, Peter Tropper, Thomas Ludwig, Volkmar Mair, Giuseppe Maria Bargossi |
| Summary: | 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. |
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| Item Description: | Gesehen am 11.08.2022 |
| Physical Description: | Online Resource |
| ISSN: | 1499-1276 |
| DOI: | 10.3749/canmin.49.1.245 |