Plate Tectonics and Mantle Convection

• Plate tectonics is a powerful scientific concept that elegantly explains various phenomena.
• These phenomena are the distribution of igneous, sedimentary, and metamorphic rocks, the distribution of earthquakes and volcanoes, the origin of continents and ocean basins and the distribution of fossil plants, animals and the formation and destruction of mountain chains.
• Plate tectonics also explains the concept of ​​Continental drift.

What Makes the Plates Move?

• Mantle convection is created by differences in temperature and density in the mantle.
• Slab push and pull, and the gravitational force, which is the weight of the crustal plate which is solid.
• Convection cells are no longer considered the primary drivers of plate motion.
• Convection does occur, but plate motions are too complex to be solely driven by it.

Plate Driving Forces

• Ridge Push develops with the gravitational energy associated with the topographic elevation of the mid-ocean ridge.
• Slab Pull develops because older oceanic lithosphere is denser than the underlying asthenosphere, causing it to sink.

Plate Tectonics - Ways Plates Move

• Plates move away from each other at divergent boundaries.
• Plates move toward each other at convergent boundaries.
• Plates move sideways past each other at transform boundaries.

Divergent Boundaries

• The plates move apart due to ridge push, and magma wells up to fill the gap.
• The magma cools, adding material to each plate, ultimately leading to seafloor spreading and rift valleys.
• Continental rifting example is the East African Rift System.
• Rifting has progressed to sea-floor spreading in certain areas, such as the Red Sea and the Gulf of Aden.
• The East African Rift is an ongoing rift with thinned crust, an elongate trough, volcanoes, and earthquakes.

Mid-Ocean Ridge

• The Mid-Atlantic Ridge is a locus of spreading where the youngest crust is always at the ridge.
• "Smokers" are found at some mid-ocean ridges and there is abundant marine life.

Convergent Boundaries

• Subduction leads to earthquakes and volcanoes.
• Trenches are formed.
• Mountain building occurs.
• The Pacific "Ring of Fire" shows the volcanic and earthquake activity associated with convergence and destruction of lithospheric plates.
• Ocean-continent subduction zones feature continental arcs with active volcanoes that are often accompanied by compression of the upper crust.
• Examples of ocean-continent subduction zones include the Andes, Japan, and Indonesia, with specific volcanoes such as Mt. St. Helens, Krakatoa, and Thira.
• Continent-continent collision at continent-continent boundaries involves convergence and is accommodated by folding, strike-slip faulting, and underthrusting.
• The Himalayas and the Tibetan Plateau are examples of continent-continent collision consequences

Transform Boundaries

• Transform boundaries characterized by faulting, as plates slide past each other.
• Two plates slide past each other along wrench faults (transform), resulting earthquakes, but no volcanoes or mountain building.
• An example of a transform boundary is the San Andreas Fault.
• Transform faults on the ocean floor connect and offset ridge segments.
• Active faulting, indicated by earthquakes, occurs in the part of the fracture zone between ridge axes.

Tectonic Plate Boundaries

• Plate boundaries evolve from the opening of oceans to the closing of oceans.
• This results in mountain building events, supercontinent formation, followed by erosion, and rifting, which restarts the cycle.

Plate Tectonic Cycle

• The cycle encompasses the lifecycle of the lithosphere and rock-forming environments.
• The cycle steps are: stable continent, rift basin formation, seafloor generation & spreading, subduction, and collision = mountain building.
• The rock cycle explains interactions between the three main rock-forming environments: igneous, metamorphic, and sedimentary.

Igneous Activity Distribution

• Tracks tectonic plate boundaries.
• Divergent boundaries – mafic igneous activity.
• Convergent boundaries – felsic igneous activity.
• Hot spots – mafic volcanic activity.

Driving Forces of the Rock Cycle

• Earth's internal heat drives plate movements and creates mantle plumes.
• Gravity drives plate movements and affects surface processes like rock falls.
• The Sun affects wind, rain, ice, and other aspects of weathering and erosion.
• Life adds oxygen to the atmosphere, aids in weathering, and modifies sediments and rocks on the surface.

Our Earth is a Dynamic Planet

• Earth's surface changes continuously.
• These changes appear slow but geologically, they're rapid.
• Earth looked different in the past and will look different in the future due to plate tectonics.