SHEARCALC—a computer program for the calculation of volume change and mass transfer in a ductile shear zone

Abstract

SHEARCALC was created to automate mass balance calculations in an alteration zone. The program can be most successfully applied to ductile shear zones, where an undeformed wall rock is transformed into a fine-grained mylonite via several protomylonitic stages. The program was written in Visual Basic 6.0 and offers numerous features typical for Windows™ applications to increase the user friendliness. SHEARCALC consists of an input part for entering sample names, specific weights and chemical data of the investigated rocks as well as for selecting immobile elements and scaling factors for an appropriate display of the data in the isocon diagram. In the calculation part, the slope of the isocon and related volume changes between two specific stages of alteration are computed. Additionally, gains and losses of the main elements during deformation are expressed by respective mass transfer equations. As a special feature, SHEARCALC contains an extensive diagram section, where the user can select between three chart types. Besides the classical isocon diagram, mass changes of elements are also displayed in specific two- or three-dimensional bar charts. Element behaviour along a transsect through the shear zone is documented by two- or three-dimensional profile graphs. SHEARCALC is a stand-alone application adapted to modern Windows™ operating systems and therefore differs from many available programs in the geoscience which only run in DOS mode.