Back to Search
Start Over
A rare garnet-tourmaline-sillimanite-biotite-ilmenite-quartz assemblage from the granulite-facies region of south-central Massachusetts.
- Source :
-
American Mineralogist . Nov2006, Vol. 91 Issue 11/12, p1730-1730. 1p. - Publication Year :
- 2006
-
Abstract
- A rare lithology consisting of garnet-tourmaline-sillimanite-biotite-ilmenite-quartz has been found within the granulite-facies region of south-central Massachusetts. The homogeneous, Ti-rich oxy-dravitic tourmaline, XMg = Mg/(Mg + Fe) = 0.72-0.77, falls into the alkali group, and is similar in composition to lower grade tourmaline found in corresponding metapelitic rocks in Maine. Charge-balancing calculations and binary diagrams suggest that, like biotite in the region, tourmaline has undergone deprotonation by means of the exchange vectors AlOR-1 (OH)-1 and TiO2R-1 (OH)-2, where R represents Fe + Mg. The restriction of a concordant tourmaline-rich horizon in otherwise tourmaline-free rocks of this granulite-facies region suggests that either: (1) B, released during prograde fluid-absent dehydration reactions of muscovite and biotite, was locally available in a fluid phase or melt for later crystallization near the peak of granulite-facies metamorphism along pathways that provided a conduit for fluid migration; or (2) that this is simply a B-rich compositional horizon (tourmalinite) that survived anatexis and granulite-facies metamorphism and that records the incipient conditions of tourmaline breakdown and subsequent recrystallization near or post-peak metamorphism. [ABSTRACT FROM AUTHOR]
- Subjects :
- *GARNET
*PETROLOGY
*TOURMALINE
*BIOTITE
Subjects
Details
- Language :
- English
- ISSN :
- 0003004X
- Volume :
- 91
- Issue :
- 11/12
- Database :
- Academic Search Index
- Journal :
- American Mineralogist
- Publication Type :
- Academic Journal
- Accession number :
- 23186981
- Full Text :
- https://doi.org/10.2138/am.2006.2231