RSA Geotour 2015: Day 3 - 5

Lets continue!

Overview of the route along the Cape Fold Belt

Day 3

On this third day we continue through the Natal Sector of the NNMB as we depart PMB and travel across the Mzumbe Terrain. As we continue along the coast we’ll cross the Mellville Thrust Zone and enter the granulite-facies Margate Terrain. Here we encounter more granites and exotic varieties of the charnockite of the Oribi Gorge Suite. Charnockites are granitoids that contain orthopyroxene. In order to allow for the stabilisation of orthopyroxene, the bulk rock composition must have low water content and exist at high temperatures, i.e. in granulite facies space. One of the charnockite we’ll be visiting is the Port Edward Enderbite. This is a charnockite that consists of quartz, antiperthite, orthopyroxene and magnetite. The name Enderbite is derived from the type locality of this rock, in Enderby Land, Antarctica. For now, this is as close as we can get – however we should have some Antarctic alumni on our team, so remember to ask them about Enderby Land!

We will then continue south and exit the NNMB, for now, and enter the Karoo Supergroup once again. This time we now travel through the Adelaide Subgroup of the Beaufort Group. We will have a chance to look at this more carefully once we cross the historical Kei River. Soon after entering the Eastern Cape we’ll find our way to the overnight destination of East London. 

Day 4

By now I’m sure everybody’s heads will be spinning (like mine, for example, while typing all this geology); and this will thus be the ideal time to travel west and into the Cape Fold Belt (CFB). The rocks encompassed within the CFB were deposited ca. 485 – 300 Ma under continental shelf to beach marine environments. The Cape Supergroup comprises of three distinct lithostratigraphic groups. These include: The quartzite and shale of the Table Mountain Group; shale of the Bokkeveld and sandstone and shale of the Witteberg Group.

These rocks were later deformed to form the CFB. This was in response to compression associated with the formation of Gondwana. The CFB can be separated into three tectonic domains, including; the western and eastern limbs, separated by the Syntaxis situated north of Cape Town. Our journey will take us from East London to Port Elizabeth, across the CFB and along the Zuurberg Pass. Here we will be able to investigate the intricate structural features defining the Western Limb of the CFB. Perhaps we may also get the compasses out and get everybody to measure some strikes and dips!

After crossing the CFB we join the Garden Route and travel along the vast quartzite of the Peninsula Formation. For our engineering geology friends, we’ll stop and have a look at some of the incredible bridges build over the mammoth gorges. Our overnight stop on this day is Knysna.

Day 5

This is the final leg of this phase of the journey. Today we travel from Knysna to the Council for Geoscience regional office in Bellville. First, our journey continues out of this picturesque town and continues down the Garden Route toward George. Before this, we may have a quick stop at the famous Knysna Estuary and potentially some calc-silicate rocks associated with the Cape Granite Suite. Upon arriving in George, we’ll cut back across the CFB once again and head toward Oudtshoorn. In Oudtshoorn we’ll note a Cango Precambrian inlier of ca. 900 Ma rocks and one of the large E-W faults that define much of the CFB. These faults are often synonymous for the Enon Formation of red beds residing along the scarp. Also, these faults are renowned for controlling the development of numerous hot springs. Perhaps one day we’ll harness this heat and generate energy from it!

From Oudtshoorn we’ll take the R62 and see lots of cool stuff! Basically many, many more structural features, e.g. the Huis River Thrust Zone and Cogmanskloof. Eventually we’ll near the, now even more famous, Syntaxis and we’ll get to see how much more intensely the CFB features are around here. The remainder of this trip will take us through most of the Table Mountain Group, and eventually onto the Malmesbury shale. Sadly, these shale mark the approach of Bellville and the end of this first leg of our South African geological tour.

Our group Our group will now get to learn some remote sensing, GIS and participate in several lectures and short courses in Bellville. In addition, we’ll have a tour of the Cape Peninsula before starting the next leg of our geological tour. This next leg will take us from Cape Town, up the western Limb of the CFB and into the Namaqualand-sector of the NNMB. Stay tuned for that!