TIME-ANIMATED GEOCHEMICAL VARIATION DIAGRAMS AS A TOOL FOR EXPLORING LARGE DATASETS

Animations of the large datasets available in geochemical databases such as NAVDAT can illuminate new spatial and temporal trends. Commonly, geochemical data are plotted for large areas over large time spans on a single diagram or on a few paneled time slices. Although large-scale patterns can be perceived through such portrayals, the details of subtle transitions or sudden changes are commonly missed. Animating geochemical variation diagrams and the locations of events side by side over small time intervals makes spatial and temporal trends in chemistry easier to interpret.

Geochemical data drawn from NAVDAT have been time-animated in a number of ways to reveal interesting trends in magmatism of the western U.S. One example, an animated K₂O-SiO₂ variation diagram for samples from eastern California and west-central Nevada, shows magma compositions changing from silicic and high-K to more mafic low- and intermediate-K over the interval 10-5 Ma, followed by a pulse of high-K mafic magmatism associated with the 3.5 Ma delamination(?) event. An animated total alkalis-silica volcanic classification diagram of rocks from the same area shows that they are distributed somewhat evenly across the range of rock types from 10-3 Ma, then separate into bimodal basaltic and rhyodacitic populations from 3 Ma to the present. In a third example, we evaluated the conclusion of Ormerod et al. (1988) that the Zr/Ba ratio in late Cenozoic basalts of the western Great Basin changes in concert with a transition in magmatism from basalts derived above a subduction zone to basalts derived from the convecting upper mantle following the south-to-north passage of the trailing edge of the subducting slab. Time-animation of a NAVDAT dataset incorporating six recent studies agrees with their south-to-north migration model.

Time-animation of geochemical variation makes interpretation of otherwise cumbersome datasets easier by putting them in a temporal context. User control over animations increases understanding of the dataset. The greater resolution of time-animations will become increasingly important in interpretation as the amount of information contained in databases such as NAVDAT grows.