Abstract

Isocon and Pearce element ratio diagrams are two means of recovering the nature and extent of material transfer processes from rock compositions. Both use the concept of a conserved property to relate changes in concentrations to extensive compositional variations. We demonstrate the fundamental commonality of the two methods and show the sole differences to be a scaling factor and the choice of graphical projection (i.e., diagram axes). We propose a modification of the isocon diagram that improves visualization of element behavior and is especially effective for dilute components that normally plot near the origin. The procedure involves transforming the mass concentration data to Pearce element ratios and then subtracting a reference rock composition from all other compositions. The former step establishes a proportionality with material transfer, and the latter step translates the data set such that the reference composition corresponds to the origin. The translated rock compositions explicitly show the material differences between each sample and the reference composition; positive values represent gains and negative values losses. Presentation of the translated ratios in a spider diagram-like figure enables straightforward visualization of geochemical variability. The algorithm proposed herein is amenable to all geochemical problems involving material transfer processes where at least one element is conserved. We demonstrate the approach by application to synthetic and real data sets.

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