direction sliding over the smaller plates as well as the huge oceanic Pacific

Direction sliding over the smaller plates as well as

This preview shows page 2 - 4 out of 16 pages.

direction, sliding over the smaller plates as well as the huge oceanicPacific Plate(which is moving in a northwest direction) in other locations such as theSan Andreas Faultin central and southern California. Age of oceanic crustal rocksAll three rock types in the earth’s crust—igneous, sedimentary, and metamorphic—can also be recycled back to their original molten magma form. This process occurs when oceanic crust is pushed back into the mantle at subduction zones. As old oceanic crust is subducted and melted into magma, new oceanic crust in the form of igneous rock is formed at mid-ocean ridges and volcanic hotspots. This recycling accounts for the recycling of 60 percent ofEarth’s surface every 200 million years, making the oldest recorded oceanic crust rock roughly the same age. Because of this recycling, the age of the oceanic crust varies depending on location. Areas where new crust is being formed at mid-ocean ridges are much younger than zones further away (Fig. 7.58). By contrast, continental crust is rarely recycled and is typically much older. The oldest recorded rocks on Earth are all located on continental crust in northern Canada and western Australia and date to approximately 3.8 to4.4 billion years old.
Background image
Metamorphism from a mudstoneMudstoneand shale (sedimentary rocks made from clay minerals) turn into a harder rock called hornfels when they are baked during thermalmetamorphism.Mud, when lithified, becomes mudstone or shale.o*lithification: to make into rockSlate: The finest-grained foliated metamorphic rock, slate, forms by metamorphism of shale or mudstone (rocks com- posed dominantly of clay) under relatively low pressures and temperatures. Slate contains a type of foliation called slaty cleavage. Slate splits into thin sheets, along slaty cleavage planes, and these sheets make excellent roof- ing shingles (Fig. 7.4a). Slaty cleavage develops when pres- sure solution removes portions of clay flakes that are not perpendicular to the compression direction, while clay flakes that are perpendicular to the compression direction grow. During the process, some flakes may passively rotate to be parallel with the plane of cleavage, pushed into the new orientation by compression. Horizontal compression of a sequence of shale beds produces vertical slaty cleavage, as well as folds (Fig. 7.4b).MarbleMetamorphic processesoRecrystallization—minerals change size and shape.Mineral identity doesn’t change.Example: Limestone Marble.Marble is a metamorphic rock consisting predominantly of calcite or dolomite. It is a metamorphosed carbonate rock (limestoneordolomite rock).GeologicLimestoneandMarble. Geologists are careful to distinguishlimestone fromdolomite rock, classifying both of thesecarbonate rocksassedimentary rocks.
Background image
Image of page 4

You've reached the end of your free preview.

Want to read all 16 pages?

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes