This Earthcache will allow the geocacher to investigate the metamorphic rocks of the Western Gneiss Terrane at the picturesque Bells Rapids Park, where the Swan River crosses the Darling Escarpment. The Earthcache will help interpreting a complex geological sequence of very old rocks.
Ancient foundations
At Bells Rapids and the quarries on the Darling Plateau there is a complex geological history of the ancient Yilgarn Craton, a very old block of rock which extends from here and past Kalgoorlie.
Granite and gneiss outcrops at the Darling Range are the 'roots' of this mountain chain originally formed many kilometres below the Earth's surface. Under intense heat and pressure in the collision zone, the granite became 'plastic' and mineral crystals gathered into tell tale bands as it was transformed to gneiss.
These large volumes of granite (light coloured), greenstone (dark coloured) and gneiss (light coloured and banded) were uplifted and then eroded and deeply and intensely weathered over millions of years. The rocks are now visible here.
Now it’s time to inspect and interpret the rocks at ground zero. The questions will allow you to accurately name the rock.
1. Describe the colour of the rock. Would you consider it to be light coloured or dark coloured?
2. From this what rock could it be? (Note: it could be one of three rocks - granite, gneiss or greenstone)
3. Look at the texture of the rock outcrop. Does it have lines or is banded? If so, describe what you see.
4. Based on this answer to 1. and 3. above what rock are we looking at? (Note: it could be one of three rocks - granite, gneiss or greenstone)
5. Finally, a task is to take a photo of you or your GPS at GZ showing the view.
You may log your find, but your answers need to be sent within 10 days otherwise your log will be deleted.