Tourmaline B-isotopes as tracers of fluid sources in silicified Palaeoarchaean oceanic crust of the Mendon Formation, Barberton greenstone belt, South Africa

Pervasive silicification is a common phenomenon in Early Archaean volcano-sedimentary sequences, reflecting the interaction between Si-rich fluids and the Archaean oceanic crust. In the Palaeoarchaean Barberton greenstone belt, South Africa, the silicified zones locally contain abundant tourmaline....

Full description

Saved in:
Bibliographic Details
Published in:Chemical geology 2015-12, Vol.417, p.134-147
Main Authors: Farber, Katja, Dziggel, Annika, Trumbull, Robert B., Meyer, F. Michael, Wiedenbeck, Michael
Format: Article
Language:English
Subjects:
Barberton greenstone belt
Boron
Boron isotopes
Crusts
Fluid dynamics
Fluid flow
Fluids
Komatiites
Marine
Mendon Formation
SIMS
Tourmaline
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Pervasive silicification is a common phenomenon in Early Archaean volcano-sedimentary sequences, reflecting the interaction between Si-rich fluids and the Archaean oceanic crust. In the Palaeoarchaean Barberton greenstone belt, South Africa, the silicified zones locally contain abundant tourmaline. In order to constrain the source of fluids responsible for the alteration, six tourmaline-bearing samples from the 3.3Ga Mendon Formation were investigated by in-situ analyses of mineral chemistry and boron isotopes. The samples comprise a silicified, finely laminated sedimentary chert and five highly altered and silicified komatiites. Electron microprobe analysis (EMPA) indicates that tourmaline is mostly dravitic, with one sample between dravite and Mg-foitite. Tourmaline has a weakly-developed patchy colour- and chemical zonation, with variations in Al, Fe and Mg composition. Some samples show strong zoning in Cr-concentration with Cr enrichment in the core, and locally the high-Cr domains are at contacts with other Cr-rich phases such as magnesiochromite and chromian muscovite (“fuchsite”). Overall, the boron isotope composition (δ11B) ranges from −20.7 to +10.2‰. Two groups of tourmaline are distinguished based on the variation in δ11B ratios within single samples: 1) those with small (
ISSN:0009-2541
1872-6836
DOI:10.1016/j.chemgeo.2015.10.009