Yosemite Granites

20 Aug 2018

This comes from www.sciencedaily.com/releases/2018/06/180627160430.htm ... Yosemite granite tells a different story about Earth's geological history, is the blurb. What do they mean? Granites in Yosemite National Park contain minerals that crystalised at a much lower temperature than previously thought possible. Apparently, this upends our understanding of how granites form - which seems very important (but is it?). Granites are igneous rocks - mainly quartz and feldspar. They are the link between igneous processes within the Earth and volcanic rocks that solidified at the surface. Granites are the product of processes by which our planet separated into layers and one key to the formation of continental crust. Minerals in granites record the planet's history - from 4.4 billion years ago. Until now the prevailing opinion was that the minerals in granites crystalise in molten rock as it cools at something like 600 and 700 degrees Celsius. Below these temperatures granites are presumed to be completely crystalised. Laboratory analysis was used to define the temperature of the crystals in Yosemite granite and it was demonstrated that crystalisation occurred at 474 and 561 Celsius - well below the mainstream consensus.

At https://phys.org/print453455414.html ... ancient changes along the Hudson River offer a glimpse to how the ice sheets grew. The Late Glacial Maximum covered much of Canada and NE states in the US (25,000 years ago). How quickly did it reach its ultimate size? This intrigued some geologists as the Hudson river has change course many times over the last million years. The last time was around 30,000 years ago and this has now been geologically mapped and charted. As the ic e sheet grew it depressed the crust due to the weight of ice involved - but the region around the edge of the ice sheet bulged upwards (causing rivers to change their route to the sea as they require a gradient). This is known as the peripheral bulge - and mapping it out is quite a clever idea. As it is lifted up, and tilted, the river is forced to change direction. It has no other choice. The drawback here is the study involved a lot of modelling - but in spite of this the findings were that the ice sheet grew rapidly (rather than a prolonged slower process). In other words, the findings do not contradict the idea of a catastrophist origin of the ice sheet.