Abstract– Planar deformation features (PDFs) in quartz, one of the most commonly used diagnostic indicators of shock metamorphism, are planes of amorphous material that follow crystallographic orientations, and can thus be distinguished from non‐shock‐induced fractures in quartz. The process of indexing data for PDFs from universal‐stage measurements has traditionally been performed using a manual graphical method, a time‐consuming process in which errors can easily be introduced. A mathematical method and computer algorithm, which we call the Automated Numerical Index Executor (ANIE) program for indexing PDFs, was produced, and is presented here. The ANIE program is more accurate and faster than the manual graphical determination of Miller–Bravais indices, as it allows control of the exact error used in the calculation and removal of human error from the process.

A small, meta-granitic clast with a crosscutting microcrystalline vein was found enclosed within the Vredefort Granophyre. Semi-quantitative chemical analyses of the granophyre, granitic clast, and the vein were obtained in situ, demonstrating affinity to granitic composition for the vein. Microstructural and geochemical evidence is consistent with the vein representing pseudotachylite derived from granite. Within the granitic clast, evidence of high-grade metamorphism with preferential melting of biotite was observed. Brittle, ductile and shock deformation microstructures were found in quartz grains in the granite ground mass, including mosaicism, undulatory extinction, non-planar and curviplanar fractures and planar deformation features (PDFs) with crystallographic orientations {1121} and {2241} Similar deformation features were observed in quartz clasts within the vein. Pods of in situ pseudotachylitic material have been documented in foliated granite around the vein. The vein suggests that a generation of pseudotachylite was evolved and already solidified when the granophyre dyke intruded. Therefore, a minimum age of pseudotachylite emplacement is suggested by the presence of the pseudotachylite vein within the granophyre.

The Saw Mill Complex (SMC) is a 1 275 m thick layered komatiitic sequence in the 3.3 Ga Weltevreden Formation, uppermost stratigraphic unit of the Onverwacht Group in the northern part of the Barberton Greenstone Belt, South Africa. A series of ultramafic complexes in the Weltevreden Formation have previously been interpreted as layered ultramafic intrusions, consisting of thick, layered ultramafic units of peridotite, pyroxenite, dunite, and gabbro. However, recent work on the Pioneer complex of the Weltevreden Formation has demonstrated an extrusive origin of komatiitic flows and tuffs. The Weltevreden Formation has not been studied in the detail of other Onverwacht Group units, but it is likely composed of a number of individual tectonically juxtaposed terrains brought in by thrust faulting during deposition of Fig Tree Group sediments and felsic volcanics in a magmatic arc setting post-dating the Onverwacht mafic and ultramafic units, which are currently regarded as products of plume-based eruptive centers. This study represents an ongoing effort to elucidate the structure, stratigraphy, and petrogenesis of the Weltevreden Formation. A new 1:1000 scale map and stratigraphic section of the SMC reinterpret the igneous complex as extrusive, with lithologic units interpreted as layered komatiitic flows and interbedded tuffs. Flows accumulated olivine, forming distinct layers from bottom to top of: The chemical variation of flows is almost entirely controlled by olivine accumulation, with dunitic komatiites representing up to 70% accumulated olivine and 30% trapped liquid, and peridotitic komatiites representing only 25% accumulated olivine, while spinifex-textured komatiites are representative of quenched liquid. Minor (up to 1%) chromite accumulation partly affects bulk chemistry, while orthopyroxene accumulation may have an effect on bulk chemistry of SMC pyroxentitic komatiites. Layered flows are up to 120 m thick and some display spinifex-textured chilled upper margins. The original liquid was near primitive mantle composition that likely represents a two-stage melting process. The SMC was rapidly emplaced and was not near a major sedimentary depositional system, as no sediment other than tuff was deposited. Flows preserved in the SMC dominantly formed as open flow pathways, allowing for large quantities of olivine to accumulate in the lower portions of flows. Some flows formed as closed systems, possibly as a result of deforming tuffs below the flows to form lava lakes. Large cm-sized lapilli, including those with aerodynamic shapes, suggest subaerial explosions and possibly near-vent environments (though littoral rootless vents can develop 100’s of km’s from actual volcanic vents). Pillow structures have not been observed in the SMC. Geochemically, the SMC is very similar to Weltevreden Formation komatiites recently studied in the Pioneer complex. They have Al₂O₃/TiO₂ near 30, Gd/Lu normalized values between 0.8 and 1.2, maximum liquid compositions of approximately 33% MgO, and olivines up to Fo₉₄. Oxygen fugacity of the mantle source is most likely to have change in log(fO₂) of 0.00 relative to nickel-nickel-oxide buffer. SMC komatiites likely erupted at temperatures in excess of 1615°C based on MELTS modeling, and represent some of the hottest volcanism experienced on the early Earth.