Tectonics

• The plate tectonic theory explains that the Earth’s lithosphere is broken up into huge pieces called tectonic plates and that the plate movements result in formation of landforms like mountain ranges/ oceanic trenches and phenomena like earthquakes/ tsunamis
• Oceanic crust are in found deep oceans while Continental crust are found beneath continental land masses and under the shallow seas near continental coastlines
• Oceanic crust has a density of 3.0 grams per cubic meter while Continental crust has a density of 2.6 grams per cubic meter
• Oceanic crust are rich in iron and magnesium but poor in silicon and aluminum while Continental crust are rich in silicon and aluminum but poor in iron and magnesium
• Lithosphere is the crust and upper most solid part of the mantle
• Divergent plate boundaries are where plates move away from each other
• Convergent plate boundaries where plate plates move towards each other
• Transform plate boundaries are where plates slide past each other
• Subduction is the process of an oceanic plate colliding and sinking beneath another less dense tectonic plate
• Asthenosphere is the semi-solid upper mantle that lies below the lithosphere
• Slab-pull force is the gravitational force that causes denser oceanic plate to sink further into the mantle under its own weight
• Convection currents and slab-pull force are the 2 forces responsible for plate movements
• Heat from the Earth’s core causes the mantle material to become less dense -> mantle material rises towards the surface -> rising convection currents then spread beneath the plates and drag them apart, causing divergent plate movement -> mantle material loses heat and sinks toward the core -> convergent plate movement occurs where the convection currents collide -> process repeats again -> rising and sinking of mantle material forms convection currents
• When 2 plates converge, the denser oceanic crust is pulled down by gravity as it subducts beneath the less dense crust -> denser oceanic crust sinks deeper into the mantle under its own weight, pulling the rest of the plate with it, contributing to further convergence
• When two plates move away from each other at divergent plate boundaries sea floor spreading occurs
• Magma from deep within the earth rises through the mid-oceanic ridge thus, new oceanic crust is formed
• Rocks further away from the mid-oceanic ridge are progressively older
• New oceanic crust is created at divergent boundaries and then moves laterally on both sides of the mid-oceanic ridge as seafloor spreading continues
• 1) North American

  2) Pacific

  3) Nazca

  4) South American

  5) Cocos

  6) Caribbean

  7) African

  8) Eurasian

  9) Arabian

  10) Indian

  11) Australian

  12)Phillipine

  13) Antartic

  
• In magnetic stripping, the magnetic North and magnetic South can shift, and they have reversed multiple times over geological time
• Normal polarity is when the Earth’s magnetic North points towards geographic North and magnetic South points towards geographic South
• Reverse polarity is when the Earth’s magnetic North points towards geographic South and magnetic South points towards geographic North
• Oceanic crusts are usually younger than continental crusts
• Magnetic stripping is the zebra-like pattern where there are strips of normal polarity rocks alternating alongside strips of reverse polarity rocks on the seafloor
• Magnetic striping occurs as basaltic rocks from oceanic crust are volcanic rocks formed from iron-rich lava
• The zebra-like pattern is symmetrical on either side of mid-oceanic ridges, showing that that this was not a random or isolated occurrence supporting the plate tectonic theory
• Sea floor spreading is the process by which new sea floor forms at divergent boundaries
• As magma cools it solidifies into basaltic rock
• The core is in the innermost position of the Earth with a temperature of 4400 - 6000 degrees Celsius and a thickness of 3300km
• The mantle is in the in between position with a temperature of 1000 - 3700 degree celsius and a thickness of 2900km
• The crust is in the outermost position with the lowest temperature and thickness of 6 - 70 km
• Transform plate boundaries are caused by shearing
• Divergent plate boundaries are caused by tensional forces
• Convergent plate boundaries are caused by compressional forces
• Deep trenches are features often formed where tectonic plates are being subducted beneath another plate
• Some oceanic features are oceanic trenches and fold mountains
• Some tectonic phenomenons are volcanic activity and earthquakes
• Shearing refers to the sliding motion