Rocksberg Greenstone
This earthcache is designed to give you an understanding and appreciation of the large geological formation known as the Rocksberg Greenstone belt.
The amphibole and epidote-rich igneous rocks from the area between Dayboro and Mt. Mee were documented in 1906, but it wasn’t until 1928 that Alan Denmead first described the importance of greenstone. He coined the term “Rocksberg Greenstone”, naming it after the town where the stone is unusually well exposed, and this is now the widely accepted nomenclature for the formation.
The Rocksberg Greenstone belt extends from Petrie to Dayboro to Mt Mee, and is roughly 38km long and 8km across at its widest point, and is Late Devonian to Early Carboniferous in age (330-400 million years old). The regional strike of the metamorphic rocks averages 330°, and at its deepest point near Delaneys Creek is 2900 metres thick. It originated from a volcano located southwest of Maleny and formed as a series of olivine basaltic units which have since been regionally metamorphosed, and is known to comprise greenschist, glaucophane schist, amphibolite, actinolite schist and phyllite.
Basalt is an igneous rock that is formed from the rapid cooling of basaltic lava, and consists of fine-grained, hard rock and is commonly fractured into hexagonal columns through a process known as columnar jointing. Greenstone is quarried at two sites along Dayboro Road West of Petrie, and is used in concrete, asphalt aggregate and road base, thanks to its strength and durability. The outcrop you are visting is well documented as one of only three unique sites along the greenstone belt where large ellipsoidal and irregular rock formations are exposed and easily accessed. You will notice large slabs and boulders, as well as many caves and gullies.
This earthcache is best appreciated during daylight hours in dry conditions, when you can wander along the rock formations, climb the boulders, explore the caves and appreciate the beauty of the area. We strongly advise against climbing on the rocks when wet, as they are very slippery and can be dangerous, or at night due to large dropoffs. The answers can be safely obtained from the edge of the rocks without endangering yourself unnecessarily. If you choose to visit this earthcache during rain periods, stay well away from the rocks due to risk of flash flooding along Terror's Creek.
Answer the following questions, then submit via email:
1. Describe the colour texture and shape of the rocks you see here. Mention any evidence of erosion.
2. Directly across from you, looking Northwest is a large slab with several distinct steps, forming multiple tiers. How many tiers do you see?
3. Approximately how high is each tier?
4. What geological process do you think formed this distinctive appearance?
You may wish to take a photo of your experience (without revealing the answers) to add to your log (optional).It is expected that EACH TEAM wishing to log a find will SUBMIT THEIR OWN ANSWERS to the CO. Once your answers have been submitted, you are free to log your find. If there are problems with your answers you will be contacted. If you fail to submit answers, your log may be deleted.
For a detailed Rocksberg Greenstone geological research paper, download the PDF here, and for geotechnical data click here
Congrats to Slow Puncture Barbbowman and Fast Ed 59 on being FTF