A 25 to 30 km wide magnetic anomaly within the >2.79 Ga granite-greenstone rocks of the northwestern Kaapvaal Craton is
spatially associated with megabreccia outcrops near the village of Setlagole in the North West Province, South Africa. The breccia
comprises angular to rounded ciasts of TTG gneisses, granites and granodiorites, with les.ser amounts of amphilxjlite, calc-silicate
rock and banded iron-formation as well as unusual dark grey to black, irregular, centimetre- to decimetre-sized clasts that show
evidence of fluidal behaviour and plastic deformation during incorporation into the breccia. The largest cla.sts reach up to several
metres in size. Evidence of fluvial transport is found in rare thin sandy to gritty layers that show crude bedding and upward-fining
with layers dipping gently to the northeast. The breccia matrix is highly variable but is dominated by angular mineral clasls (mainly
quartz and feldspar, with subsidiary biotite, amphibole and epidote) with interstitial chlorite. The clasts show variable amounts of
alteration (saussuritization, sericitization, chloritization of biotite and amphibole). The dark clasts contain angular quartz and
feldspar and small biotite fragments in a cryptocrystalline chlorite-dominant matrix. Textures indicate a lower greenschist faciès
metamorphic overprint. The absence of lava, dolomite or quartzite cla.sts suggests that the breccia formed prior to the deposition
of the Neoarchaean Ventersdorp and Eoproterozoic Transvaal Supergroups, whereas the metamorphic grade indicates that it
postdates the ca. 2.79 Ga amphibolite-facies metamorphic peak in the region. This suggests a late Mesoarchaean or early
Neoarchaean (ca. 2.79 to 2.71 Ga) age for the breccia. A similar age is inferred for the magnetic anomaly based on postulated crosscutting
dyke ages. Despite a comprehensive search, unequivocal shock-diagnostic microdeformation features have not yet Ixïen
found in either the breccia or the highly-weathered granitic gneiss outcrops in the central parts of the anomaly. The unusual
plastically-deformed dark clasts may represent chloritized mud clasts or impact melt clasts. Geochemical data on these clasts and
other components of the megabreccia provide no conclusive support for a meteoritic origin, but the unparalleled comptjsition of
the clasts and their high trace element abundances of Ni, Cr, V, Zn and Co relative to rocks of the Kraaipan granite-greenstone
basement, sugge.sts an unusual origin for this matrix material. Given the distinctive nature of the breccia and its proximity to a
large circular magnetic anomaly, it is postulated that the megabreccia could represent a mass or debris flow in a marine .setting
triggered by an impact tsunami or resurge. Subsequent faulting may have led to the preferential preservation of these deposits.
This interpretation of the Setlagole megabreccia and geophysical anomaly is evaluated in terms of other possible modes of origin
and it is concluded that a meteoritic source best fits the available data
