Trace and minor elements in garnet and quartz: novel approaches to understanding crustal evolution

Ackerson, Michael R.
Thumbnail Image
Other Contributors
Watson, E. Bruce
Spear, Frank S.
Amidon, William H
Roecker, Steven W.
Schaller, Morgan F.
Issue Date
Terms of Use
This electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author.
Full Citation
PART I: Garnet is a common and important mineral in metamorphic systems yet the mechanisms by which it incorporates Ti— one of the major elements in the crust— are not well constrained. This study uses garnets synthesized at a range of temperatures and pressures to understand Ti solubility and the substitution mechanisms that govern its incorporation into garnet at eclogite and granulite facies conditions. Garnets from these experiments can incorporate up to several wt. % TiO2. Comparing Ti content with deficits in Al and Si in garnet indicate that Ti is incorporated by at least two substitution mechanisms (VITi4+ + VIM2+ ↔ 2VIAl3+, and VITi4+ + IVAl3+ ↔ VIAl3+ + IVSi4+). Increasing Ti solubility is correlated with increasing Ca and Fe/Mg ratios in garnet, clinopyroxene and melt. The complexity of the substitution mechanisms that account for Ti solubility in garnet make practical Ti in garnet thermobarometry infeasible. However, a model fit to Ti partitioning between garnet and the melt from which it crystallized could be used to predict melt compositions in high grade metamorphic systems. Additionally, the solubility and substitution mechanisms described here can help explain the presence of crystallographically-aligned rutile needles in high grade metamorphic systems.
August 2015
School of Science
Dept. of Earth and Environmental Sciences
Rensselaer Polytechnic Institute, Troy, NY
Rensselaer Theses and Dissertations Online Collection
Restricted to current Rensselaer faculty, staff and students. Access inquiries may be directed to the Rensselaer Libraries.