TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

1.5 Crystal Stratigraphy - Microanalysis of Crystal Populations
Advances in microsampling and technology have made it possible to chemically
and in some cases isotopically dissect igneous rocks, mineral by mineral (e.g.,
[22]). Detailed rim-to-rim isotopic, major, and trace element studies (i.e., crystal
stratigraphy) have commonly documented phenocryst-host rock disequilibrium
(e.g., [39, 40, 134, 135, 143]). Crystal stratigraphy studies have also provided
insights into the microenvironments surrounding crystals as they grow or where
growth has been disrupted (e.g., [59, 60]). Processes affecting magmatic crystal
growth are revealed on a crystal-by-crystal basis using this method, however its
power requires a statistically relevant number of crystals be analyzed. Analysis
of too few crystals provides only a limited, local-scale history of the rock. As
an example of this potential limitation, consider a basaltic magma body that
has experienced numerous magma mixing events consisting of liquid ± crystal
exchange. Lavas produced from the system will carry crystals from some or all
of the mixing events (e.g., [59, 139]). Like whole-rock analysis, documenting the
histories of too few crystals from the basalt will not adequately characterize all
of the processes (in this case mixing events) responsible for the final texture and
composition of the rock. This potential limitation is minimized via integration of
CSDs and crystal stratigraphy studies, whereby CSDs are used to identify crystal
populations with related nucleation and growth histories that then become targets
for microanalysis.
1.5.1 Plagioclase as a Target for Microanalysis of Basaltic Igneous Rocks
In this study plagioclase feldspar is a frequent target for major and trace el-
ement microanalysis. As noted by Bindeman et al. [8], plagioclase is ideal for
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