The geology of Mt. Gravatt and other places in Brisbane to a degree reflect the geology of the entire State of Queensland. Brisbane back in the early Palaeozoic or late Precambrian times (about 500-1,000 million years ago) was an offshore part of eastern Australia. It was under water and part of a huge marine area, an area of sedimentation in which tens of thousands of feet of sediments were deposited.
The rocks that formed at this time have an interesting geological history and now are the backbone rocks of eastern Australia, having been converted from fine muddy and sandy sediments to the Metamorphic rocks which you can see around Mt Gravatt.
"Meta" denotes a change of condition and "morphē" means form. So Metamorphic rocks are rocks that have changed form.
A metamorphic rock is a result of a transformation of a pre-existing rock. To transform into a Metamorphic rock the original rock has been subjected to very high heat and pressure, which causes obvious physical changes. They can be formed by pressures deep inside the Earth, by tectonic processes such as continental collisions, or when they are heated up by an intrusion of hot molten rock called magma from the Earth's interior.
To find this cache, follow the instructions below and email your answers to the cache owner for review.
Instructions
- Go and stand at the lookout at the posted coords.
- Look down and you will see some Metamorphic rocks.
- Take a walk down to take a closer look at them.
Questions:
NOTE: To answer the questions look at two different large Metamorphic rocks (and ignore the lichen growth).
- What are the difference in colours between the rocks? What do you think would cause the different colours (keeping in mind how the rocks are formed)?
- You will notice that the rocks look to be made up of different layers. How thin is the thinest layer you can find and how thick is the thickest? What would make the layers different thicknesses (considering that this are of the world used to be under water)?