TETGAR_C: a novel three-dimensional (3D) provenance plot and calculation tool for detrital garnets

This paper presents a new interactive MATLAB-based visualization and calculation tool (TETGAR_C) for assessing the
provenance of detrital garnets in a four-component (tetrahedral) plot system (almandine–pyrope–grossular–spessartine).
Based on a freely-accessible database and additional electron-microprobe data, the chemistry of more than 2,600 garnet
samples was evaluated and used to create various subfields in the tetrahedron that correspond to calc-silicate rocks, felsic
igneous rocks (granites and pegmatites) as well as metasedimentary and metaigneous rocks of various metamorphic
grades. These subfields act as reference structures facilitating assignments of garnet chemistries to source lithologies.
An integrated function calculates whether a point is located in a subfield or not. Moreover, TETGAR_C determines
the distance to the closest subfield’s mean value. Compared with conventional ternary garnet discrimination diagrams,
this provenance tool enables a more accurate assessment of potential source rocks by reducing the overlap of specific
subfields and offering quantitative testing of garnet compositions. In particular, a much clearer distinction between
garnets from greenschist-facies rocks, amphibolite-facies rocks, blueschist-facies rocks and felsic igneous rocks is
achieved. Moreover, TETGAR_C enables a distinction between garnet grains with metaigneous and metasedimentary
provenance. In general, metaigneous garnet tends to have higher grossular content than metasedimentary garnet formed
under similar P–T conditions.