Montánchez Batholith EarthCache

         There’re three main types of rocks; sedimentary, metamorphic and igneous. Igneous rocks get its name from the Latin word “ignis” witch means fire. So, igneous rocks are formed by the solidifications of the cooled magma. During this process, these rocks can be formed with crystallization or without it, and below the surface as intrusive or plutonic rocks or on the surface as extrusive or volcanic rocks.
         Typically, the magma that origin igneous rocks, can be caused by an increase of temperature, pressure decrease or a change on its composition. Also this magma can be derived from melting of crust of the earth or its mantle.
         As describe, we can easily understand that almost all the upper part of our planet crust Is made of igneous rocks but, in fact, only a small part or it is visible, the rest is hidden under a thin layer of metamorphic and sedimentary rocks.

         As formed from magma, igneous rocks minerals and its chemistry give us important information about the composition of the mantle, its temperature, pressure and other pre-existing rock that melted. We can get their absolute ages from various forms of radiometric dating and thus can be compared to adjacent geological strata, allowing a time sequence of events. We can also do tectonic reconstitutions because, as prior described, its features are usually a characteristic of a specific tectonic environment.

         As we saw, if these rocks are formed on the surface, are volcanic, in the other hand, if formed from magma that cools and solidifies within the earth are plutonic or intrusive.
         Surrounded by pre-existing rock, called country rock, the magma cools slowly, and as a result these rocks are coarse grained.
         Like Montánchez mountain, most the central core of the mountains consist of intrusive igneous rocks, usually granite where when exposed by erosion, these cores, called batholiths, may occupy huge areas of the Earth's surface – a Batholith

         At the given coordinates, you will be at the top of the Montánchez Batholith, one of the most important granite outcrops of Cáceres region, Spain.
         The granite of Montánchez (Cáceres, Spain) is located to the S.E. of the Albalá granite and is separated from it by a strongly tectonized zone, a large fault belt. According to the mica content, three perografic faces have been distinguished in the Montánchez granite. Faces I is made up of medium to coarse grained, two mica granites richer in muscovite, which occupy the northern half of the granite and have been extremely deformed. Faces II consisting of coarse to very coarse grained, sometimes porphyrblastic, two-mica granites, richer in biotite, has not been deformed, or very little. Faces III is made of aplitic muscovite granites which are poor in biotite and rich in tourmaline. The Montánchez granite frequently contains tonalitic xenolith, sometimes quite large. (A xenolith is part of the walls of the magmatic chamber included in the magma during the intrusion. Is a rock fragment within an intrusive igneous body that is unrelated to the igneous body itself. Xenoliths, which represent pieces of older rock
         incorporated into the magma while it was still fluid, may be located near their original positions of detachment or may have settled deep into the intrusion, if their density is greater.)
         Regarding the geochemistry of the Montánchez granite, the major and some trace elements have been analyzed on 22 samples belonging to the three different faces and the tonalitic xenoliths.

To log this Earthcache as a find, you have to answer correctly this questions and send them to the owners before you log it. Please DON'T use the message center. We prefer e-mail.

• At the given coordinates you will be at the top of one huge rock. How do you classify it. Why?
• If Montánchez Batholith was solidified below the surface, what happed here for us to see it?
• Do you think that Montánchez Batholith is Plutonic or Volcanic. Why?
• Post one picture of you at the top of Montánchez Batholith and, if you can, another one of this batholith from distance.