Theory of Plate Tectonics

What are Plate Tectonics Earth is broken into large plates that change in their size and position Float on the molten interior layer of Earth Continents ride on the plates Continents move at a rate of 1cm/year Atlantic Ocean getting wider; Pacific Ocean getting narrower Cause of earthquakes and volcanoes and forms mountains

Shape and Structure of Earth Earth has 3 layers: Core Mantle Crust Each layer has unique chemical and physical characteristics Earth is shaped as an “oblate spheroid” Flattened poles; bulging equator

Shape and Structure of Earth Core: divided into an inner core and outer core Outer core is a liquid (molten) layer Inner core is at the center of Earth; is a solid Made of iron and nickel; 5000-6000 °C Mantle: layer below the crust Divided into sublayers: upper mantle, asthenosphere (magma), lower mantle Crust: outermost layer of the Earth Made of solid rock Lithosphere: made up of continental and oceanic plates; includes crust and upper mantle

Asthenosphere and convection Currents Asthenosphere is the hotter upper mantle below lithosphere Flows like silly putty but it’s not a liquid layer Large temperature difference between upper mantle (1400 °C) and lower mantle (2600 °C)

Asthenosphere and Convection Currents Difference in temperature creates convection currents Convection current – transfer of heat in a liquid or gas that causes magma to rise Rises up through the mantle and into the crust Causes molten rock to move Formation of oceanic ridges (seafloor spreading) and mid-ocean islands

Major Plates Geologists have divided tectonic plates into three arbitrary categories: Major plates: Pacific Plate, North American Plate, Eurasian Plate, African Plate, Antarctic Plate, Indo-Australian Plate, South American Plate Minor/secondary plates: Somali Plate, Nazca Plate, Philippine Sea Plate, Arabian Plate, Caribbean Plate, Cocos Plate, Scotia Plate Microplates

Major Plates

Plate Boundaries Plates interact with each other at three types of boundaries: Convergent Divergent Transform Interactions between these plates results in geological features and activity

Convergent Boundary Convergent boundary: two plates come together and push against one another i.e. Boundary between South American plate and the Nacza plate One plate rides up over the lithosphere of another plate, forming a subduction zone

Convergent Boundary Results in the formation of mountain ranges and volcanoes (volcanic arcs) Continental – Continental boundary: creation of large mountain ranges; both plates too light to subduct Continental – Oceanic boundary: creation of volcanic arcs Oceanic – Oceanic boundary: creation of island arcs and formation of deep trenches

Divergent Boundary Divergent boundary: two plates move away from each other Creates a gap of magma to form new crust between the two i.e. Mid-Atlantic ridge; separation between South American and African plate

Divergent Boundary Oceanic Plates Rising convection currents lift the lithosphere Creates a fissure in the plate Magma flows into the fissure, solidifies, and then repeats itself. Continental Plates Pulling apart of plates produces a rift As rifts grow deeper dropping below sea level, water will enter i.e. Red Sea

Transform Boundary Transform boundary: two plates slide past one another Results in strong earthquakes but no loss or gain of sea floor i.e. Boundary between the Pacific plate and the North American plate