An investigation of the possibility of cryptic layering and the implications of garnet coronas in the Jay Mountain layered metagabbro

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Authors
Anderson, George A., III.
Issue Date
1972-06
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Electronic thesis
Thesis
Language
ENG
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Geology
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Abstract
The coronas have resulted from a reaction between olivine and plagioclase. They consist of an olivine core concentrically surrounded by an intergrowth of orthopyroxene and clinopyroxene, a moat of clear plagioclase, a rim of garnet, then the primary plagioclase. Recent experimental evidence indicates the coronas are formed by a two-stage viii reaction. A) Olivine + Plagioclase Orthopyroxene + AI-rich Clinopyroxene + Spinel B) AI-rich Orthopyroxene + AI-rich Clinopyroxene + Spinel + Plagioclase ~ Pyrope-Almandine-Grossular / Garnet. Garnet is forming at the expense of plagioclase, and pyroxene is forming at the expense of olivine. This implies the transformation of one type of silicate structure into a different type of silicate structure. To enable such a situation to occur, minute amounts of intergranular water vapor probably aid in the breaking of chemical bonds, allowing structural rearrangement and ion migration along concentration gradients to complete the new mineral structures.
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June 1972
School of Science
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Rensselaer Polytechnic Institute, Troy, NY
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