Firstly, I must apologise for the delayed update. For the last few days our group has been living on the banks of the Komati river deep within the southern Barberton mountains. This isolated region is definitely an ideal location for investigating the Barberton greenstone belt and discussing many important aspects of the early Earth, however is too deep for any mobile reception.
Anyway, I am happy to report that the team did have three (and today being the forth) excellent days exploring the Barberton greenstone belt and have clearly gained much from this experience.
The proper Barberton Mountainland welcome
Day one
The first day was spent along the Komati River with a section across the topmost units of the Onverwacht Group. The group had an opportunity of closely examining the contact relationships between the Mendon, Kromberg and Hooggenoeg Formations/Complexes. The contact between these units are clearly defined by the occurence of thick chert layers. The Buck Reef Chert, which separates the Kromberg and Hooggenoeg also has apparent algal biomats and early signs of life. During this time, we also began the complex debate regarding the dynamic functionality of the early Earth.
TL: Alteration of Hooggenoeg ultramafic rocks; TR: Plagioclase-varioles in Hooggenoeg pillow basalt; BL: The H6 conglomerate near the top of the Hooggenoeg Formation; BR: Magmatic breccia contact between the 3450 Ma Theespruit Pluton and the c. 3.5 Ga Sandspruit ultramafics
This debate was exasperated when the group came across the H6 within the Hooggenoeg, which includes sandstone and conglomerates. This apparent volcano-sedimentary sequence is surrounded by mafic and felsic interlayered volcanics and suggests the presence of kind of fluvial environment and potentially detrital input associated to tectonic-related mountain building processes.
The team examining highly altered ultramafic rocks in the Komati river
Sheep bridge across the Komati River, built in c. 1890
Pillow basalts in the Hooggenoeg Formation/Complex
Day two
During the second day, the group completed the Onverwacht Group, visiting the lowermost units. This included the Sand/Theespruit and Komati Formations. Of particular interest was the magmatic breccia contact between the c. 3510 Ma Theespruit Ultramafic rocks and the 3450 Ma Theespruit pluton. Here, the ultramafic rocks are also metamorphosed to upper amphibolite facies, quite a substantial PT increase from the overall greenschist grade. Having not completed a Thermocalc course, we briefly discussed the metamorphic implications of this and closely examined the occurence of garnet in the Theespruit ultramafic rocks.
Getting a close-up view of the Trondhjemite-ultramafic intrusive contact
We then entered the Tjakastad Schist Belt and looked at ductile deformational features, especially mineral lineations and rotated porphyroclasts within a felsic agglomerate unit on the outskirts of the belt.
The team completed the second day with a section of the Moodies Group, near the Sheba Hills. Here we also looked at some of the later deformational structures and discussed their implication on gold mineralisation. Some of the team even managed to find sulphide mineralisation within the Moodies rocks.
TL: Magmatic breccia contact between the Theespruit Pluton and the Sandspruit ultramafics; TR: Felsic Agglomerate within the Theespruit Formation; BL: Olivine spinifex texture in the Komati Formation; BR: Moodies formation conglomerate
The team doing a road section along the Moodies
"Dangerous" river crossing - reflective vest is important in these conditions
After this day Tlou said: "...OMG this was such an amazing experience, I don't even know what to say, I have no words. At the CGS I have attended so many field trips, but this was clearly the best, OMG. I feel like my geology is coming back. Personally I would recommend that every young scientist attend this field school. It is worth it and I feel so sad to be leaving this place..."
Day three
On the third day, our team was given an opportunity of doing a geological mapping traverse through the Tjakastad Schist Belt. With this we began our mapping programme proper and got the team up to scratch with mapping techniques and then allowed them the opportunity of collecting data. While this is a highly complex region to begin with, the team did a wonderful job, inspite of the needing to identify and handle the various talc-carbonate schists, felsic agglomerates, pillow basalts and mylonites.
Measuring foliation on chlorite-bearing mylonite
With this introductory section complete (in Barberton nogal) the team should find mapping in the later Richtersveld mapping project a breeze.
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| TL: Beginning of the Tjakastad traverse on chlorite-bearing mylonites; TR: Rotated porphyroclast within a felsic agglomerate; BL: Sedimentary layering within the Hooggenoeg Formation; BR: The Theespruit Trondhjemite |
We now start day four with a short film on the Barberton Greenstone Belt, a trip to visit the oldest of the TTG gneisses and finally an overview of the various geology with a trip across the Barberton Geotrail. Keep following us for the latest developments!
Climbing up an interlayered felsic unit
After this day Ma Connie said: "...I think this day really showed me that Barberton has lived up to it's expectations. At first I was so confused that I even saw the Bushveld Complex. But, overall it has been a thrilling experience, you know how it is: you read about these important rocks, but now to see it, OMG..."
Day four
Our film didn't quite go according to plan - turns out the Barberton greenstone belt film is 6 hours long. Instead, we decided to use this time with an overview along the Geotrail. The Geotrail provides excellent exposures across the entire greenstone belt.
It begins on the c. 3.2 Ga Kaap Valley Tonalite and cuts across units of the Moodies, Fig Tree and ending with pillows within the Onverwacht. This provided the group with a great round up of the past few days.
TL: Moodies tidal sandstone; TR: Biomats within the Moodies, showing early signs of life; BL: Black chert within the Fig Tree; BR: Accretionary lapilli within the Fig Tree
We then also continued to investigate the oldest of the TTG gneisses in the region, namely, the c. 3450 Ma Steynsdorp Pluton.
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