Geo - Week 4 notes

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Toronto Metropolitan University *

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Geology

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Oct 30, 2023

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GEO - Week 4 Rocks Pluton: the general term for any intrusive igneous body, regardless of size or shape Batholith: an irregular-shaped mass with an exposed surface greater than 100km. They form the mass of many large mountain ranges (Coast Range batholith of British Columbia and Washington, the Sierra Nevada batholith in California and the Patagonian batholith in South America) Sills: parallel to layers of sedimentary rocks Dikes: cross layers of the rock they invade. Sills and dikes are magma conduits that may solidify in cylindrical forms that stand starkly above the landscape when finally exposed by weathering and erosion. Lithification: occurs as loose sediment is hardened into solid rock. Alfred Wegener: hypothesized that the coal deposits found today in the midlati- tudes exist because these regions were once closer to the equator and were cov- ered in lush vegetation that later became lithified organic material that forms coal. He later concluded that all landmasses migrate, and that the formed one supercon- tinent that he named Pangaea. Laurasia (Europe Asia) and Gondwanaland (South America Australia) broke into two. He concluded this by looking at plant and animal fossils. Plate tectonics: is the theory that the lithosphere is divided into a number of plates that float independently over the mantle and along whose boundaries occur the formation of new crust, the building of mountains, and the seismic activity that causes earthquakes. Plate tectonics theory describes the motion of earths litho- sphere. Plate boundaries fall into three categories - Zones where two plates diverge - Zones where two plates converge - Zones where plates slide pass one another Type of plate Convergence - Convergence of oceanic crust within continental crust - Convergence of two plates carrying oceanic crusts - Convergence of two plates carrying continents crusts Subduction Zone: when one portion of the lithosphere descends beneath another and dives downward into the mantle. “Ring of fire” - Asia, North Pole to BC all the way down western side is where plate boundaries are located and where earthquakes are more likely to occur. Convergent Boundaries: crust is compressed and lost in a destruction process as it moves downwards into the mantle. Divergent Boundaries: occur in areas of seafloor spreading, where upwelling ma- terial from the mantle forms new seafloor and lithospheric plates spread apart. Transform Boundaries: occur where plates slide past one another, usually at right angles to a seafloor spreading centre. As plates move past each other horizon-

tally, they form a type of fault, or fracture, in Earths crust which is a transform Fault Earthquakes are results of continuous stress accumulation and strain release along faults. Fore shocks - Micro or small tremors of vibrations often signalling an impending earthquake of the plate boundaries (brittle and fracture) Folding: occurs when rocks are deformed as a result of compressional stress and shortening. Anticline : an upward slope where the rock slopes downwards Syncline : a downward fold where the strata slopes upward Faulting: occurs when rocks on either side of the fracture shift relative to the other side. Fault zones : are areas where fractures in the rick demonstrate crustal movement. Types of Faults Normal Faults (tensional): When forces pull rocks apart so rock on one side moves vertically along an inclined fault plane. Reverse Faults (Compression): When forces push rocks together, such as when plates converge, the compression causes rocks to move upward along the fault plane. Strike - Slip (Lateral - Shearing): When lateral shear causes horizontal move- ment along a fault plane, such as that produced along a transform boundary and the associated transform faults. Horst: applies to upward-faulted blocks Graben: refers to downward-faulted blocks Orogenesis: the term used for mountain building. An orogeny is a mountain-building episode, occurring over millions of years, usually caused by large-scale deformation and uplift of the crust.

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