Day 1 (Wednesday, Sept. 6th)
Roger Hart and the Vredefort Impact Structure!
We had a wonderful buffet hotel breakfast to start the day early (6 AM), and we
were on the road by 7:15. 45 minutes of rush-hour traffic on the Jo'berg
freeways brought us to the University of the Witswatersrand, where we met
Roger Hart. We made only one wrong turn, saved by the Motorola radios guiding
the four Toyota Ventures in a line like baby ducks. Having 4 non-jetlagged
drivers made a BIG difference.
Zoom! Off South on the M-1 to the Vredefort, the world's largest and oldest
proven impact structure, formed in the early Proterozoic 2.0 billion years ago. Roger
showed his mettle, with an intellectually simulating journey. First, an
overview of the crater from the summit of a small hill, with many colorful
maps, many questions, and a visit to a small quarry with pseudotachylite
(shock-melted rock). Then to one of the best exposures of shatter cones along
the Vaal river, and some of the oldest and nicest beach cross-beds in the lower
Transvaal river. What a view of the complete Transvaal group, tilted 90+
degrees over on the side and exposed continuously. The impact appears to have
produced the world's only complete cross-section of the Earth's crust, perhaps
down through the Moho. Ostriches, baboons, pink flamingos, and large green
grasshoppers with red wings were sighted. Next to a contact metamorphic
aureole with minerals wild enough to whet the appetite of many a petrologist!
Lunch at last! Stopped at a small take-away store in the town of Parys (named
by the Hottentots after Paris, because of an island in the Vaal river which
reminded them of Notre Dame). A shop down the road had the best beef jerkey
(biltong) in the Orange Free State.
Then to a quarry in the granites near the base of the sedimentary package,
where building stones for the Jans Smit International airport in Jo'burg were
taken. Beautiful, 10-cm thick dikes of pseudotachylite had large pancakes of
granite boulders floating in them. Next, a charikite/granite 3.4 Gyr old which
have intensely shocked quartz grains with astounding stable and strong remnant
magnetizations. After this, we went a bit further and examined the remnants of
banded iron stones entrained in the Archean granites. Totally metamorphosed,
but clearly a recognizable BIF, even after the unimaginable blast from the
impact. Finally, a treck to the most beautiful place: ground Zero center of
the Vredefort impact basin. Although it has a gravity high, it had a thin
sheen of water over the floor of a lake, filled with pink flamingos. As the
sun was going lower in the West, we stopped over the mouth of a 300m hole,
where they had drilled into Hartzburgites, perhaps the relict of the Archean
Moho!
On the way back to our new hotel (in N. Pretoria), we were treated to
Alpha-Centauri and Scorpio upside down. Dinner was at the ‘Train' restaurant,
which specialized in exotic meat dishes. We had elephant, zebra, hippo,
giraffe, spring buck, crocodile, fried worms, an aquarium of fish, and a suite
of traditional South African and traditional desserts. We literally ate the
zoo! We were also joined by Prof. Lew Ashwal and his wife (who helped make
arrangements to the platinum mine), leading to a marvelous and lively diner for 20.
We crashed at the Formula 1 Inn in Petoria. Not recommended by anyone, but at
least someone else's car was stolen that night.
Written by JLK et al.
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