(Source: aqqindex, via mmmmilk)
The deformation in the Grand Canyon
These are the same two units I showed in the last post moving up the Grand Canyon, but the setting in this photo illustrates an important part of the story; the deformation.
These rocks record the building of what was once a mighty mountain range that has now been worn away. In this photo, the Zoroaster granite and the Vishnu Schist are seen in their typical state.
The schist was once sedimentary rock trapped in a continental collision. The granites intruded them, heating and recrystallizing them to metamorphic rocks. Meanwhile, far above these rocks, mountains were being built. The pressures of the mountain building process twisted and folded the hot rocks deep below.
Similar features are observed in the deepest parts of many mountain ranges when they are exhumed; twisted layers of granite and metasedimentary rocks. The directions of the folds vary somewhat but they generally record the direction that the rocks were moving, constraining the impact of an island arc with the continental mass to the North.
The ages of the deformation in these rocks vary from 1.70 to 1.68 billion years ago (a 20 million year pulse of mountain building!).
These rocks started at the Earth’s surface, were buried 20+ kilometers deep, and then within the next 100 million years brought back close enough to the surface to stop the metamorphic processes. A truly twisted path!
Image credit Penn State
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Calanque in La Ciotat, France. https://goo.gl/maps/tn4uz
isitabouttime said: Why isn't volcanic glass considered a mineral?
Volcanic glass is a mineraloid, but isn’t classified as a mineral because it lacks a crystalinw structure making it amorphous. It cools too quickly for the atoms to form a structure.
bmcintire said: what are minerals and what makes them a mineral
A mineral is a naturally occurring solid material that is not of organic composition. What makes them a mineral is just that.
Picture of the Haleakala Crater on Maui, Hawaii that I took on my trip
Humans will now be forever inscribed into the Earth’s geological history. Our everlasting signature? Plastic-infused stones. The newly identified stone, according to a report from The Geological Society of America, has been officially named plastiglomerate. It is formed when plastic trash melts and fuses together with natural materials such as basaltic lava fragments, sand, shells, wood and coral, resulting in a plastic-rock hybrid. Researchers say the new material is likely to last a very long time, possibly becoming a permanent marker in Earth’s geologic record. In the photo above: An example of clastic plastiglomerate found on Kamilo Beach. Clastic type is a combination of “basalt, coral, shells, and local woody debris” that are “cemented with grains of sand in a plastic matrix.” (via Plastiglomerate: The New And Horrible Way Humans Are Leaving Their Mark On The Planet)