Clastic and carbonate metasediments, preserved in narrow synclines, have been correlated over an area of 2000 kmz. These strata, the Flinton Group, lie unconformably on metamorphosed volcanic, clastic, and carbonate rocks, and on large granitic intrusions. The group, which comprises six formations, has undergone at least two major folding episodes and one main regional metamorphism of varying grade. The only post-Flinton intrusions are pegmatites at high grade and one tectonically emplaced ultramafic slice.Depositional environment ranged from fluvial to moderate-depth marine. Rapid facies changes, coupled with persistence of some units along strike and close relationships between facies and underlying lithology, point to local sources and local tectonic control of deposition basins. At the onset of sedimentation, a deeply weathered source terrain yielded mature basal redbeds, which were succeeded by less mature clastics as block faulting caused increase of reliefbetween sources and basins. These facies passed offshore into finer, more reduced sediments. Deposition took place between 1050 and 1080 (+25) Ma ago, after arc volcanism, plutonism, uplift, and erosion, and before major regional metamorphism. All these events can be grouped within the Grenvillian orogenic cycle, spanning at least the interval 1300-1000 Ma and including, in eastern Ontario, the pre-Flinton Elzevirian Orogeny and post-Flinton Ottawan Orogeny.On a mis en correlation les metasediments clastiques et carbonates preserves dans des synclinaux etrois sur une region de 2000 kmz. Ces strates, le groupe de Flinton, reposent en discordance sur des roches volcaniques, clastiques et carbonatees metamorphisees et sur de vastes intrusions granitiques. Le groupe, qui comprend six formations, a subi au moins deux episodes importants de plissement et une phase principale de metamorphisme regional d'intensite variable. Les seules intrusions post-Flinton sont des pegmatites de haut niveau et une ecaille ultramafique mise en place tectoniquement.Le milieu de sedimentation variait de fluvial a marin de profondeur moyenne. Les changements rapides de facies, associes a la persistance de certaines unites selon la direction des strates et les relations etroites entre les facies et la lithologie sous-jacente, indiquent que la source des sediments etait locale et que le contr6le tectonique des bassins de sedimentation etait aussi local. Lorsque la sedimentation s'est amorcee, une region source profondement alteree a fourni les lits rouges matures a la base, immediatement suivis par des roches clastiques moins matures qui s'expliquent par une augmentation du relief entre les sources et les bassins comme resultat d'une tectonique cassante. Ces facies passaient au large en sediments plus fins, plus reduits. La sedimentation s'est produite entre 1050 et 1080 (f 25) Ma, apres les phases de volcanisme d'arc, de plutonisme, de soulevement et d'erosion et avant le metamorphisme regional de grande envergure. Tous ces evenements peuvent se regrouper dans le cycle orogenique de...

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Twelve Group II and fourteen Group I kimberlite diatremes in central South Africa were examined for upper crustal xenoliths in order to estimate the extent of various lithological units of the Karoo Supergroup in the main Karoo basin at times of kimberlite eruption, the Cretaceous erosional history of the area, and the approximate vertical extent of the kimberlite diatremes prior to erosion. Sandstone and amygdaloidal basaltic lava xenoliths from the Karoo Supergroup were specifically selected as their modal mineralogies and geochemical compositions respectively can be attributed to specific stratigraphic positions within the Karoo Supergroup. Results indicated that, at the time of Group II kimberlite eruption (~120 Ma), basaltic lavas of the Drakensberg Group covered the entire area, but by the time of Group I kimberlite eruption (~85 Ma), they were restricted to the south-eastern half of the study area. At the latter time, an escarpment is proposed to have existed at the basalt outcrop limit, some 180 km west of its current position. Sandstones of the Stormberg Group had a restricted original distribution in the north and east of the study area, whereas sandstones from all other Karoo groups occurred throughout the entire area. In the Kimberley area, approximately 500 m of erosion is estimated to have occurred from 120 to 85 Ma and 850 meters from 85 Ma to the present day at average rates of approximately 15 m/Ma and 10 m/Ma respectively. Both Group I and II kimberlite diatremes had vertical extents of approximately 1350 m at eruption. An inland scarp-retreat model is proposed for the Cretaceous erosion cycle in central South Africa.

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