I expect that there will be many discussions about what kind of plate movement created this formation. Scientific Reports. What kind of plate movement made this formation the author asked? Instead of the normal slow plate movement over millions of years maybe it was very rapid caused by an immense sized asteroid or Large comet strike?
While deep burial is the usual choice, lateral compression leading to metamorphism should be considered. It could indicate a larger event. Email address is optional. Large intrusions, such as granite batholiths, may have metamorphic aureoles covering a significant area. Where the country rocks are pelitic in composition i. Hornfels may have a spotted appearance due to the growth of minerals such as cordierite and andalusite. In rocks of different compositions other minerals will form.
For example olivine may form in an impure limestone. The metamorphic grade of an aureole zone is quantified by which minerals occur within that zone. Shale closest to an intrusion may be altered to hornfels and contain minerals such as sillimanite or cordierite. Further from the intrusion, the same shale may seem reasonably unaltered apart from the development of some crystals of andalusite. Contact metamorphism and associated minerals for different types of country rock.
Aluminium-rich shale will form indicator minerals such as cordierite and sillimanite. Impure limestone may host indicator minerals such as olivine. Where there are significant volumes of fluid present, skarns may form. Image: Wolf All rocks are composed of minerals, and each mineral is only stable over a particular range of temperatures and pressures.
Outwith that range it will tend to break down or combine with a neighbouring mineral to form a new mineral. The process of metamorphism is associated with the formation of particular metamorphic minerals. Some silicate minerals are so diagnostic of metamorphism that their presence indicates that the rock is metamorphic.
These mineral are known as index minerals and include andalusite, kyanite, staurolite and sillimanite. Some other minerals, such as garnet, muscovite, feldspar, quartz and micas, are also present in metamorphic rocks, but these may also be found in igneous and sedimentary rocks.
The concept of metamorphic zones can be illustrated by considering what happens to mudrock as it becomes subjected to increasing levels of metamorphism. Microdiamonds in metamorphic rocks are important minerals because they form in continental collision zones and show that the crust has penetrated deeper than km below the surface.
This is the second area in the world, after the Italian Alps, that shows microdiamonds can form in metamorphic rock through subduction of oceanic plates. In recent years, microdiamonds have received a great deal of attention because they have been discovered in metamorphic rocks around the world and it has become clear that they are formed in collisions between continents. It was thought that Japan would not produce such microdiamonds because it is not a continental collision zone, but an oceanic plate subduction zone.
However, the first microdiamonds from metamorphic rocks in Japan were found in the Nishisonogi metamorphic rock formation in the west coast of Nagasaki Prefecture. The area where the microdiamonds were discovered is an approximately million-year-old Cretaceous metamorphic rock formation.
On the west coast of Saikai City in Nagasaki Prefecture, blocks of pelitic and basic schist are scattered amongst serpentinite that was created from mantle material. You cannot download interactives. Igneous rocks are one of three main types of rocks along with sedimentary and metamorphic , and they include both intrusive and extrusive rocks. Sedimentary rocks are one of three main types of rocks, along with igneous and metamorphic. Join our community of educators and receive the latest information on National Geographic's resources for you and your students.
Skip to content. Image Metamorphic Rock Isua Metamorphic rock, estimated to be as old as 3. Photograph by James L. Twitter Facebook Pinterest Google Classroom.
Encyclopedic Entry Vocabulary. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.
Media If a media asset is downloadable, a download button appears in the corner of the media viewer. Text Text on this page is printable and can be used according to our Terms of Service. Interactives Any interactives on this page can only be played while you are visiting our website. Related Resources.
0コメント