Everyone had fun identifying various features of granite, including the minerals it is made of as well as xenoliths, autoliths and aplite dikes.2
Dwarfed by the immense size of the granite intrusion, it was amazing to realise that the quarry was once part of an enormous chamber deep under the earth and filled with molten granitic magma.
We discussed how geologists once thought granite needed millions of years to ascend through the crust, crystallize and cool. This was considered a fatal problem for a young earth and Flood geology. However, geological thinking now considers granite to have formed catastrophically (see Granite formation catastrophic in its suddenness and Granite grain size not a problem for rapid cooling of plutons).
It was during the first half of Noah’s Flood Flood that the magma intruded the surrounding sediments forming the magma chamber. This was around the time the sediments were uplifted and folded. In the second half of the Flood, kilometres of overlying rock was eroded away as the deep waters covering the Australian continent were receding into the oceans (see The Geological History of the Brisbane area, Australia).
Notes
- See John Duffy’s photos
- A xenolith is a fragment of rock foreign to the igneous mass in which it occurs, in this case to the granite. By way of contrast, an autolith is fragment of igneous rock enclosed in another igneous rock of later crystallization, each being derived from a common parent magma. Aplite is a fine-grained, light-colored granitic rock consisting primarily of orthoclase and quartz. It frequently crystallizes within cracks through the main igneous rock, forming characteristic dikes.