TAS - Total Alkalis vs. Silica Variation Diagram for Volcanic Rocks. The TAS Diagram for volcanic rocks is used to classify igneous rocks using whole rock chemical data as adopted by the International Union of Geological Sciences (IUGS). The variation diagram scatter plot of weight percent Na2O + K2O vs. weight percent SiO2 is divided into regions based on the whole rock chemistry of rocks with petrographically-defined names (see the QAPF diagram). The TAS diagram enables classification of glassy and other volcanic rocks without petrographic data.
This page will scale and plot geochemical data from pre-selected datasets or from a dataset that you upload. Following the IUGS instructions (LeMaitre and others, 2005) the whole rock chemistry is normalized to 100% without volatiles before plotting. Preselected datasets are available from:
PetDB (Compiled and Maintained by EarthChem at Lamont-Doherty)
GEOROC (Compiled by the Max Planck Institute for Chemistry in Mainz)
PETROS Igneous Rock Database (Compiled by Felix Mutschler at Washington State University)
Ueki, Hino, and Kuwatani (2018) (Data compiled from PetDB and GEOROC)
Miscellaneous Example Data Sets. Compiled from a variety of sources.
Use the x-axis and y-axis pulldown lists to choose the plotting variables. Use the Maj+ and REE+ buttons to change between two variable selection lists. Major elements are in units of weight percent oxides (wt%=grams per hundred grams). Trace elements are in parts per million (ppm=grams per microgram). FeO(T) is total Fe recalculated as FeO.
To view other DataSets choose a DataSet Source of preformatted DataSets by selecting from the pull down list. Then choose from among the preselected DataSets from the pull down list. You can upload your own data from a comma separated value file (.csv) if the first row of the file has the oxide and element labels, and subsequet rows have sample data.
Your uploaded file will not be passed to the other diagram or map pages, but can be uploaded again on those pages.
If you want to see the contents of a selected DataSet, for more information or to see the format, click on the "View DataSet CSV File" button.
