28 October 2016

Friday fold: “the eye of Sauron” at Sibubule

Posted by Callan

Here’s a scene from the pre-IGC field trip I participated in, a week-long examination of the Barberton Greenstone Belt:

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Look at the mountain over to the right. It’s “looking” back at you!

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This is Sibubule, 1765m in elevation, as viewed from the R40 in Barberton Mountain Land, not far from the border with Swaziland.

It shows a more or less recumbent fold, like a taco lying on its side. The perspective of the photo is looking ~south at the ~eastern face of the mountain.

Here it is in Google Maps view:

Our field trip leader, Christoph Heubeck, furnished me with this information:

The mountain is incompletely mapped (that is, we only walked up to the base of the northern cliff and lateral equivalents) but there is a hinge at  25°57’9.10″S  31° 5’46.14″E well visible on Google Earth (best when viewed towards the south), and we have been there. I think the other hinge of the “eye” is at  25°57’35.84″S  31° 5’23.85″E but we have never climbed up there, either. Mapping the mountain would be beautiful and not difficult – alas, so little time…

The fold axial plane is moderately south-dipping. The big south-dipping slope of Sibubule appears [to be] a dip slope in overturned cherts of the uppermost Onverwacht (Mendon Formation).

These cherts bound a thick package of banded iron formation (BIF) of the Mapepe Formation (lower Fig Tree Group) in the middle. As a result, Chrisoph says,

“It’s a blood-shot eye!”

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