Dynamic Earth Study Guide Chapter 8 10 12 16 17 19 23 Chapter 8 Review Questions 1 How are metamorphic rocks different from igneous and sedimentary rocks a A metamorphic rock is one that forms when a preexisting rock Protolith undergoes a solid state change Metamorphism It does NOT form by solidification Igneous rock is formed through the cooling and solidification of magma or lava Sedimentary rocks are types of rock that are formed by the deposition of material at the Earth s surface and within bodies of water Sedimentation is the collective name for processes that cause mineral and or organic particles detritus to settle and accumulate or minerals to precipitate from a solution 2 What two features characterize most metamorphic rocks a First it can possess metamorphic minerals Second metamorphic rocks can have a metamorphic texture 3 What phenomena cause metamorphism response to squeezing shear and shock 4 What is metamorphic foliation and how does it form a Change in temperature and or pressure as hydrothermal fluids pass through rock or in a Metamorphic foliation is the parallel alignment of platy material and or the presence of alternating light colored and dark layers Foliated metamorphic rocks are formed from a multi mineral mica rich rock that is subjected to progressively greater heat and direct pressure 5 How is a slate different from a phyllite How does a phyllite differ from schist How does schist differ from gneiss a A slate is formed from the metamorphism of mudstone or shale Contains slaty cleavage foliation by recrystallization look like roofing shingles Finest grained b A phyllite is caused by a foliation of fine grained mica by neocrystallization Fine grained c A schist possesses a type of foliation called schistosity defined by the preferred orientation of large mica flakes Medium grained d Gneiss is composed of alternating dark colored and light colored layers of metamorphic rock predominantly felsic minerals for the light layers and mafic materials for the dark layers 6 How does prograde metamorphism differ from retrograde metamorphism a Prograde metamorphism is when a rock gets buried progressively deeper and the temperature and pressure increases Retrograde is when the rock moves back towards the Earth s surface 7 Describe the geologic settings where thermal and dynamic metamorphism takes place a Thermal metamorphism develops where there is heat without a change in pressure and without differential stress Dynamic metamorphism takes place anywhere that faulting occurs at the depth in the crust 8 Why does metamorphism happen at the site of meteor impacts and along mid ocean ridges a Hot magma rises beneath the axis of mid ocean ridges so when the cold water sinks through the cracks down into the oceanic crust along ridges it heats up and transforms into hydrothermal fluid causing hydrothermal metamorphism When meteorites slam into the Earth a vast amount of kinetic energy instantly transforms into heat This heat may be enough to melt and transform rock causing shock metamorphism 9 How does plate tectonics explain the peculiar combination of low temperature but high pressure minerals found in a blue schist a Shearing along plate boundaries causes dynamic metamorphism and igneous plutons in rifts cause thermal metamorphism Unusual metamorphic rocks called blueschists form at the base of accretionary prisms 10 Where would you go if you wanted to find exposed metamorphic rocks How did such rocks return to the surface of the Earth after being at depth in the crust a You would go to an outcrop which is caused by exhumation When two continents push against each other cause the rock to be squeezed upward then the mountain range grows making the rock softer and finally erosion weathering landslides and river flows take place at the surface Key Terms o Burial Metamorphism drilling when the bottom of the hole reaches depths at which burial metamorphism has begun Causes the organic molecules of oil to break up for this reason oil drillers stop o Contact Metamorphism See Thermal Metamorphism o Differential Stress pull in one direction differs in magnitude from the push or pull in another direction Two kinds When a material is squeezed or stressed unequally from different sides The push or Normal Stress Pushes or pull perpendicular to the surface We can the push compression and the pull tension Compression flattens a material and tension stretches a material Shear Stress or shear moves one part of a material sideways relative to another For example you place a deck of cards on a table then set your hand on top of the deck and move your hand parallel to the table you shear the deck o Dynamic Metamorphism the rock recrystallize This occurs as a consequence of shearing alone under metamorphic conditions without requiring a change in foliation that roughly parallels the fault At greater depths rock is so warm that is behaves like soft plastic as shear in o Dynamothermal Metamorphism no change in temperature or pressure Metamorphism that occurs as a consequence of shearing alone with o Exhumation The process that returns deeply buried rocks to the surface o Foliation Refers to an assemblage of parallel planar surfaces and or layers in a metamorphic rock It gies metamorphic rocks a striped or streaked appearance in an outcrop and or gives them the ability to splits into thin sheets o Gneiss Is a compositionally layered metamorphic rock Typically composed of alternating dark colored and light colored layers that range in thickness from millimeters to meters This is formed at high temperatures however does not contain mica because at high temperatures mica react to form other minerals Gneissic banding can also form when the protolith undergoes an extreme amount of shearing under conditions in which the rock can flow like soft plastic o Hornfels This is a fine grained nonfoliated rock that contains a variety of metamorphic minerals The specific minerals assemblage in a hornfels depends on the composition of the protolith and on the temperature and pressure of metamorphism o Index Mineral of the rock The line on a map along which this mineral first appears is called an isograd The presence of certain minerals in a rock indicates the approximate metamorphic grade o Marble This is created from the metamorphism of limestone During the formation calcite composing the protolith recrystallizes so fossil shells pore space and the distinction between grains and cement disappear Typically
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