Earth Science Q2

• Metamorphism


  Geologic processes in which rocks change in form, composition, and structure due to intense heat and pressure and sometimes with the introduction of chemically active fluids
• Factors Involved in Metamorphism

  • Temperature
  • Pressure
  • Hydrothermal fluids
• Temperature


  • Affects the rock's chemical composition, mineralogy, and texture
  • During burial metamorphism, at a depth of about 8 to 15 kilometers, metamorphic reactions begin
  • Rocks adjust to the new temperature causing their atoms and ions to recrystallize and form new arrangements, creating new mineral assemblages
  • During recrystallization, new crystals grow larger than the crystals in the original rock
• Example of temperature effect

  • Sedimentary rock (mudrock) - shale becomes buried deeper and deeper, the clay minerals in the rock will begin to recrystallize and form new minerals, such as micas in slate - a metamorphic rock from shale
  • With additional burial, at greater depth where the temperature is higher, mineral micas begin to transform into a new mineral garnet in schist - another metamorphic rock with a higher grade
• Geothermal gradient


  The rate at which temperature increases with depth in the Earth's crust, which varies on plate tectonic settings
• Pressure


  • Changes the composition, mineralogy, and texture of rocks
  • Two types of pressures: Vertical stress/Confining pressure and Directed/Differential pressure
  • Directed pressure guides the shape and orientation of the new crystals formed as minerals recrystallize under the influence of both heat and pressure
  • Pressure causes rocks to form folds in a particular direction and contributes to the formation of foliation

  
• Example of pressure effect

  • Minerals in shale, a sedimentary rock with beddings
  • Minerals in slate, a low-grade metamorphic rock from shale, with mica crystals orientated perpendicular to the direction of the pressure
  • Minerals in higher-grade metamorphic rock schist, with very evident foliation and larger bandings of minerals caused by even greater pressure
• Hydrothermal fluids


  Dissolved minerals in the fluids react with rocks causing changes in chemical and mineral compositions and sometimes completely replacing one mineral with another without changing the textures of the rocks
• Example of hydrothermal fluid effect

  • Alteration of feldspars to clays, and deposition of quartz, calcite, and other minerals in fractures or cracks and other open spaces forming veins
  • Serpentinization - formation of serpentines through oxidation and hydration chemical reaction of peridotites (olivine-rich rocks) at the base of the oceanic crust
• Types of Metamorphism


  • Regional Metamorphism
  • Contact Metamorphism
  • Shock Metamorphism
  • Burial Metamorphism
• Regional Metamorphism


  • Forms foliated metamorphic rocks such as Gneiss and Schist due to high temperature and pressure imposed on large parts of the crust
  • Mostly occurs within the continental crust
  • Confining and directing pressures by tectonic forces cause new alignment of minerals (foliation) during recrystallization

  
• Contact Metamorphism


  • Prominent in areas where surrounding rocks are exposed to heat coming from magma intrusion within the layers of the rocks
  • Forms marble, quartzite, and other granoblastic rocks with large visible crystals of minerals
• Examples of contact metamorphism

  • Quartz-rich sedimentary rock recrystallizes to form an interlocking mosaic of crystals, resulting in metaquartzite
  • Limestone transforms into marble with an interlocking mosaic of crystals
• Shock Metamorphism


  • Takes place when the heat and shock waves from meteor or asteroid impact transform rocks immediately around the impact site
• Examples of shock metamorphism


  • Transformation of mineral graphite into ultra-high-pressure polymorph diamond
  • Conversion of quartz minerals into coesite under high shock pressures
• Burial Metamorphism


  • Occurs at lower temperature and pressure, transforming sedimentary rocks that had undergone diagenesis into low-grade metamorphic rocks
  • Partial alteration of the mineralogy and texture may occur while other sedimentary structures are usually preserved
• In subduction zones, between two converging plates, high-pressure metamorphism occurs
• Metamorphic rocks created through high-pressure metamorphism are rarely found on the Earth's surface as they were formed in such great depth
• Example of high-pressure metamorphic rock

  • Eclogite, which has transformed with pressure greater than 28 kbar at a depth of approximately above 80 km
• Endogenic Process


  A geological process that was formed, originated, and located below the surface of the earth
• Endogenic Process


  • Involves geologic activities such as tectonic movements, metamorphism, seismic activities and magmatism
• Magma


  Formed under certain circumstances in special location deep in the crust or in the upper mantle

  
• How magma is formed

  1. Partial melting of mantle rocks

  2. Rocks undergo partial melting because the minerals that compose them melt at different temperatures

  3. Partial melting takes place because rocks are not pure materials

  4. As temperature rises, some minerals melt and others remain solid

  5. If the same conditions are maintained at any given temperature, the same mixture of solid and melted rock is maintained

  
• Pressure


  • Increases with depth as a result of the increased weight of overlying rock
  • Higher pressure leads to higher melting points
• Mechanisms of rock melting

  • Decompression melting
  • Flux melting
• Decompression melting


  1. Takes place within Earth when a body of rock is held at approximately the same temperature but the pressure is reduced

  2. Happens because the rock is being moved toward the surface, either at a mantle plume or in the upwelling part of a mantle convection cell

  3. If a rock that is hot enough which is close to its melting point is moved toward the surface, the pressure is reduced, and the rock can pass to the liquid side of its melting curve

  4. At this point, partial melting starts to take place

  
• Flux melting


  1. Happens if a rock is close to its melting point and some water or carbon dioxide is added to the rock

  2. The melting temperature is reduced and partial melting starts
• As magma moves toward the surface

  It interacts with the surrounding rock, typically leading to partial melting of the surrounding rock because most such magmas are hotter than the melting temperature of a crustal rock

  
• At very high temperatures (over 1300°C), most magmas are entirely liquid because there is too much energy for the atoms to bond together
• As temperature drops, usually because the magma is slowly moving upward


  1. Silicon and oxygen combine to form silica tetrahedra

  2. The tetrahedra start to link together to make chains (polymerize)

  3. These silica chains have the important effect of making the magma more viscous (less runny)

  4. Magma viscosity has significant implications for more explosive volcanic eruptions

  
• Intrusion


  Magma that moves up into a volcano without erupting

  
• Plutonism


  All sorts of igneous geological activities taking place below the Earth's surface

  
• Magma differentiation


  1. Gives birth to ideal conditions for metallogenesis

  2. This is the exact process that gives birth to magma, when the presence of various oxides, fluorine, sulfur, and chlorine compounds that are necessary for the creation of magma is guaranteed

  
• Plutonites


  Igneous rock formations created when the process of crystallization and solidification of magma takes places below the Earth's surface and particularly in the crust

  
• Extrusion


  An eruption of magmatic materials that causes land formation on the surface of the Earth

  
• Magma extrusion


  Causes the formation of volcanoes when the gas pressure is strong enough and there are cracks in the earth's crust

  
• Lava


  Magma that came out to the surface of the earth

  
• Magma moves up


  1. Because of a high pressure exerted by magma and gases

  2. Magma occupies a bag which is called magma chamber

  3. The depth of the magma chamber causes the differences in the strength of volcanic eruptions

  4. In general, the deeper the magma chamber, the stronger the explosion

  
• Volcanism


  Used to describe all geological phenomena that occurs on the natural terrestrial surface, such as the creation of volcanoes and hot springs

  
• Volcanism


  1. Refers to all sorts of geological activities correlated with the flow and transportation of igneous material from the planet's interior towards the natural terrestrial surface

  2. This motion takes place inside the cracks that are known among geologists as natural pipes that infiltrate the upper mantle

  3. The mantle allows massive quantities of liquids and gases to reach the upper layers of the planet and in various cases, even the natural terrestrial surface