The Grampians Geology has been studied in detail over the past 15 plus years by using many new technologies allowing a more accurate picture of how it was formed. The area was mapped chemically and physically and using ‘total intensity and residual magnetic mapping’ a picture of the underground rock formations was created. The chemical mapping and physical mapping came up with the same pictures. Some of the detailed studies on small scale have been extrapolated to the large scale giving a picture of the Grampians and surrounding areas and even what was happening on the rest of the continent. Mapping the Geology of the Grampians even has broarder implications. The fact the Grampians formation can be read from the surface informs on the formation of mountains and landscapes all over the world.
About 450 million years ago older mountains were eroded and formed the layers of sand forming the Grampians sandstone. Movement under the earth’s crust caused many induction zones leading to tilting and uplifting, but these were not simple geological actions as explained in text books. They were more complex actions with collisions and blockages explaining how layers have ended up where they are today. After the layering of sand and folding and faulting, the Grampians ranges were intruded by hot molten rock (magma) which cooled and crystallised to form the granite dyke rocks in the Victoria Valley, and at Mafeking and Wartook. Careful measurement of the radioactive decay of certain elements in these granites tell geologists that they were intruded around 400 million years ago.
At the end of the presentation most of us drove to the Mt William car park where we car pooled and headed through the gate and up to the very top. Here we found a sheltered spot out of the wind and enjoyed our picnic lunch in the sun and with a magnificent view.
We looked at some formations in sandstone which were made by an underwater creature 410 million years ago, as it foraged for food on the bottom of the water body and passed the sand out behind it. Back at the Mt William car park we looked at a landslide which had occurred hundreds or thousands of years ago, landslides have occurred frequently and been a major contributor to the shaping of the Grampians. Next we drove along Silver Band rd and stopped to look at more road cuttings exposing mudstone as well as some of the more recent landslides which occurred in 2011. The landslides exposed many cliffs and on one of these we could see a fault line which probably formed millions of years ago but is typical of faults which occurred throughout the Grampians forming the mountain range. From here we all headed home in our different directions with our heads spinning at the incredible talk and sites we had just experienced.
Ross Cayley et al published a paper in Nature last year and it has some modelled videos of the complex movements in the induction zone and the effects of collisions and blocking. Worth a watch. http://www.nature.com/nature/journal/v508/n7495/full/nature13033.html#videos