|Title:||Preservation of primary mineral inclusions and secondary mineralization in igneous zircon: a case study in orthogneiss from the Blue Ridge, Virginia|
|Authors:||E. A. Bell|
|Publication:||Contrib. Mineral. Petrol., v. 171, p. 1‐15.|
A wide variety of minerals occur as inclusions in igneous zircon and can provide valuable evidence of source magma composition from originally magmatic zircons in metamorphic and clastic sedimentary rocks. However, it is not clear the extent to which zircons preserve the primary composition of their inclusions through a variety of geologic processes. This paper documents a case study of inclusion‐rich, originally igneous zircon from an orthogneiss in the Blue Ridge of southwest Virginia. Zircon inclusions isolated from cracks contain 4% clearly metamorphic phases (mainly in hosts with disturbed U–Pb systems) and otherwise retain distinct plagioclase chemistry, K‐feldspar/plagioclase pairs, and biotite with much wider‐ranging Mg/(Mg + Fe) than biotite in the rock matrix. A clearly secondary mineralization suite filling cracks in the zircons consists of quartz, biotite, albite, and epidote. Overall, these zircons preserve mineral inclusions distinct from their current host rock (except when exposed to external environments via cracks), demonstrating that non‐metamict zircons may preserve their primary inclusion assemblages through later amphibolite to lower granulite facies metamorphism.