But even the rock-mutts still fall into three basic types, classified by how they formed within the rock cycle: sedimentary, like this super sandstone, igneous , like this beautiful basalt, and metamorphic, like this nice, well, gneiss!All three of these rock types were involved in the formation of Los Cuernos.
Many different factors can cause rocks to bop back and forth in the rock cycle, changing identities over time. Igneous rock can become sedimentary, then metamorphic, then back to igneous or sedimentary again.Rocks go through more phases than me in middle school.
Look at those fuzzy little guys! The igneous rock at Los Cuernos is intrusive. That means it formed from magma that rose up and cooled very slowly, inside other rocks below Earth’s surface.
These are the three main chunks of strata in the Grand Canyon: the Vishnu Basement Rocks, the Grand Canyon Supergroup, and the Layered Paleozoic Rocks. A beautiful array of igneous , metamorphic, and sedimentary. Lookin’ good, ol’ GC!
We can assume the Vishnu Basement Rocks are older than any rocks above them, based on the principle of superposition. And the chunk of igneous rock must be younger than the metamorphic rock it intruded into, because of the principle of cross-cutting relation. Above the basement rocks, the Grand Canyon Supergroup tilts at an angle.
Remember that thick, light stripe on Los Cuernos? We can thank igneous rock for that! Around 12.5 million years ago, three pulses of magma pumped out of Earth’s depths and slid in between the sedimentary rock layers that now make up much of the mountain.
It intruded, if you will. But some igneous rocks, like the basalt and this pumice here, form in a way that’s extrusive. They’re created when magma exits up to the earth’s surface, becoming lava, where it cools and hardens into rock.
So if sedimentary rock layers don’t rest roughly horizontally, we can assume something— like shifting tectonic plates— knocked them into a wonky shape after the sediment solidified into stone. The same goes for layers of igneous rock. Sometimes, one layer of rock just barges into another at an angle.
Like, how is our planet a real place!? Let’s turn it over to… igneous rock: by far the most common rock type on Earth’s surface. What’s that, Dwayne? Sure, I guess classic rock is pretty common too.
Just go with me. A nonconformity is a surface where erosion wears down a layer of igneous or metamorphic rock, before new sediments are eventually deposited on top. You can see that here: The rocks at the bottom are the Grand Canyon's metamorphic basement that formed about 1.75 billion years ago.
What? No blink-182 is not classic rock! I’m not going through this again with you! Sorry about that. Anyway, igneous rock forms when molten rock cools down and crystallizes into a solid. Geologists give molten rock different names depending on where it’s hanging out: “magma” is when it’s underground, and “lava” Is when it’s above ground.
Around 12.5 million years ago, three pulses of magma pumped out of Earth’s depths and slid in between the sedimentary rock layers that now make up much of the mountain. As the magma cooled over time, it formed a special type of igneous formation called a laccolith. It’s giving… Belted Galloway cattle.
called the Grand Canyon Supergroup. Free band name. And at the very bottom of the canyon, the metamorphic and igneous Vishnu Basement layer — better free band name— tells us what Earth’s crust was like over 1.3 billion years ago, as volcanic island chains smashed into what was then the edge of our continent.
Just look at Dwayne! His journey started underground millions of years ago, when magma collected in a bleb under Earth's surface, slowly cooling to form our igneous buddy. Over many years, tectonic shifts pushed the land—and Dwayne—upward.