Tasks:
1. How might the presence of xenoliths in granite indicate the age of the surrounding rock? What can these inclusions tell us about the time gap between the formation of the xenolith and the granite?
2. How do you think the xenoliths ended up in the granite? What does their presence suggest about the movement and flow of the magma before the granite solidified?
3. What can the type and composition of the xenoliths tell us about the geological processes happening in the Earth's crust or mantle at the time the granite was forming?
4. Please take a picture of yourself or an object on site to prove your visit and post it with your log.
Log this cache as “Found it” and send me the answers to the questions to “silka03.earthcache@gmail.com”, my profile e-mail or via Geocaching Message Center. Not in your log!
You may then log immediately. I will contact you if something is wrong.
If there are no answers after 14 days I have to delete your log.
Have fun!
Xenoliths are rock fragments that were captured by magma during a volcanic eruption, offering valuable insights into the Earth's geological past. This EarthCache leads you to a site where xenoliths are found in granite. Granite forms from the slow cooling of magma deep beneath the Earth's surface, and xenoliths become trapped as the magma rises.
What are Xenoliths?
The term "xenolith" comes from the Greek words "xenos" (foreign) and "lithos" (stone), meaning "foreign stone." Xenoliths are rock pieces that are not part of the magma itself but originate from deeper layers within the Earth. During a volcanic eruption, magma can carry these rock fragments from the mantle or crust upwards before it cools and solidifies at the surface.
These fragments are often quite different in composition from the surrounding volcanic rock and may include much older material. This provides geologists with a rare opportunity to study deeper layers of the Earth without the need for deep drilling.
How Xenoliths Form:
- Magma rises: Magma from the Earth's mantle ascends through weak zones in the crust.
- Xenoliths are trapped: As the magma moves upward, it carries pieces of rock from deeper layers with it.
- Solidification: When the magma reaches the surface and cools, these foreign rocks become trapped as xenoliths within the solidified volcanic rock.
Xenoliths in Granite:
Granite, an igneous rock, consists mainly of quartz, feldspar, and mica. Xenoliths found in granite may be fragments of much older rocks like basalt or shale. These inclusions typically stand out because of their texture, color, or structure, which contrasts with the surrounding granite. Unlike granite, they are often darker and coarser-grained, making them easily noticeable.
https://de.wikipedia.org/wiki/Xenolith
https://www.mineralienatlas.de/lexikon/index.php/Xenolith?lang=de