A Study of Compositional Zoning in Garnets From the Ducktown Mining District, Tennessee: Implications for Mathematical Modelling of Garnet Growth

Garnets from the Ducktown mining district were examined for compositional zoning. Unzoned garnets are common in the sphalerite rich areas--the garnets are 50% spessartine--and in the calc-silicate nodules--the garnets show extreme sieve texture. Normal (convex manganese profile) zoning is prevalent among most of the remaining garnets, but clusters of garnets with inverted or reverse zoning have also been found. The most probable origin for these clusters is nucleation on preexisting fragments. The profiles are examined in relation to the surrounding minerals (all unzoned except plagioclase) and in relation to existing models of zoning formation. A new zoning model based on diffusion independence of growth is presented. The effects of slight variations in temperature and in composition are found to be extremely important and must be included. The presence of many variables and no single rate determining step more realistically models natural garnet growth and requires a numerical solution for the model.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Geology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Babb, Robert Frederick, II

• Geology

Language dc:language

eng

Identifier

(UMI)AAI8203395

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/68065