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| Titel |
Tracing fluid-induced metasomatism across a blueschist-facies shear zone (Sesia-Lanzo zone, Western Alps) using boron isotopes |
| VerfasserIn |
Ralf Halama, Matthias Konrad-Schmolke, Horst Marschall, Michael Wiedenbeck |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250082198
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| Zusammenfassung |
| Boron (B) is a useful tracer for slab-mantle-arc fluid transport and recycling processes in
subduction zones due to its high mobility in hydrous fluids and its significant isotope
fractionation by fluid-rock interaction. Although B isotope geochemistry provides
key evidence for slab to arc transfer by aqueous fluids, B isotope data on natural
high-pressure metamorphic rocks are still scarce and the effects and extent of fluid-rock
interaction remain poorly studied. Secondary ion mass spectrometry (SIMS) analyses
generally confirm that slab dehydration significantly lowers δ11B of subducted
oceanic crust and sediments, but the lack of a systematic relationship with peak
metamorphic conditions suggests additional processes have affected the exhumed
rocks.
Here, we evaluate the effects of deformation and fluid flux on the B isotopic composition
of phengitic mica along a structural profile with strain- and recrystallization gradient across a
major crustal shear zone that separates two tectonometamorphic units in the Sesia-Lanzo
Zone (SLZ), Western Alps. Weakly deformed, eclogite-facies samples contain phengites that
show significant major element compositional differences between pristine cores and
overprinted rims. Samples from the blueschist-facies shear zone contain fine-grained,
mylonitic phengite with a major element composition similar to the rims. Lithium (Li) and B
concentrations show a slight decrease in the overprinted rims (38-50 ppm Li, 30-33 ppm B)
compared to the cores (55-69 ppm Li, 44-48 ppm B), and a significant drop to |
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