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

Abstract

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.

WinGrt, a Windows program for garnet supergroup minerals

“…Grew et al (2013) proposed an IMA-approved nomenclature scheme for garnet supergroup minerals based on the dominant-valency rule and prepared an Excel spreadsheet to perform calculation, cation allocation, and classification of 32 approved species with group determination. Knierzinger et al (2019) presented a new interactive MATLAB-based calculation and visualization tool, called TETGAR_C, to assess better spatial and quantitative differentiation trends of detrital garnet minerals including almandine-pyropegrossular-spessartine end-members in the tetrahedral plot system for provenance studies.…”

Clay mineralogy of Miocene mudstones from the Lower Austrian Molasse Basin

“…The clay mineralogy and provenance of these fine-grained sediments in the basin subcrop have so far been largely unknown (Wimmer-Frey et al, 2013). Recent publications have mainly investigated the sands and sandstones regarding their lithostratigraphy, sedimentology and chemostratigraphy and log correlation (Palzer-Khomenko et al, 2018a, b), and examined the provenance of the sediments using heavy mineral analysis and mineral chemistry (Knierzinger et al, 2018(Knierzinger et al, , 2019.…”