“I CAN” Statements Theory of Plate Tectonics 2010_011ES092Seafloor Spreading 12/4/2018 “I CAN” Statements Theory of Plate Tectonics Explain each type of plates interactions, and give example of the end result(s) i.e. geological features [L2]

A scientific revolution begins 2010_011ES092Seafloor Spreading 12/4/2018 A scientific revolution begins PALEOMAGNETISM (evidence of past magnetism preserved in the rocks) was the most convincing evidence set forth to support the concepts of continental drift [polar wandering] and seafloor spreading [magnetic reversals].

Basalt is rich in iron-bearing materials, like magnetite. As the basalt lava cools, the Fe-bearing minerals become oriented parallel to the Earth’s magnetic field.

2010_011ES092Seafloor Spreading 12/4/2018 As the lava hardens, the magnetic orientation is preserved and provides a record of the current Earth’s magnetic field. Curie Point: temperature above which it is impossible for the atoms to magnetize. For magnetite it is 580C

Theory of Plate Tectonics From the hypotheses of Continental Drift and Seafloor Spreading was formulated the Theory of Plate Tectonics TECTONICS is the study of the features of the Earth’s crust [tektonikos = construction]

Theory of Plate Tectonics  The Earth’s crust and rigid upper mantle [LITHOSPHERE] are broken into huge slabs or plates.  Those plates are riding/floating onto the asthenosphere [like wood blocks on water], at different rates and different directions.

Directions and rates of plate motions Subduction Spreading

The oceans and the continents are carried as passengers onto the moving plates.

The constant movement of those plates is responsible for the changes to the Earth’s surface by the way of:

EARTHQUAKES

ERUPTIONS VOLCANIC

MOUNTAIN RANGES

8 major plates: North American South American Eurasian African Pacific [largest] Indian/ Australian Antarctica Nazca The minor ones: Juan de Fuca, Cocos, Caribbean, Scotia, Arabian, Philippine

BOUNDARIES Tectonic plates interact at places called BOUNDARIES. The continents / oceans do not necessarily resemble the outline of the plate boundaries. There are three types of boundaries Divergent Convergent Transform

Divergent Boundaries Two plates moving AWAY from each other and forming a gap or RIFT. Mostly associated with OCEANIC crust [seafloor spreading = Mid-Atlantic Ridge] as molten rock [MAGMA] from the asthenosphere rises the plates move apart, and fills the space between the plates. as it cools, it hardens onto the edges of the plates and creates new crust.

DIVERGENT PLATES

Divergent Boundaries Some involve the CONTINENTAL crust when it begins to separate, the stretched crust forms a long, narrow, depression called a RIFT VALLEY it is currently happening between the African and Arabian plates  Red Sea is therefore widening

The African and Arabian plates continue to rift apart, with the result that the Red Sea is ever widening RIFT VALLEYS

Mediterranean Sea Rhine Valley in Northern Europe is another example.

Divergent Boundaries Some involve the CONTINENTAL crust the crust can also stretch to the point of forming FISSURE VOLCANOES

Convergent Boundaries Two plates moving TOWARDS each other. Direct COLLISION of one plate with another one. There are three POSSIBILITIES: CONTINENTAL – OCEANIC OCEANIC – OCEANIC CONTINENTAL – CONTINENTAL

CONTINENTAL - OCEANIC As the plates are colliding, the denser plate will be forced downwards Since oceanic crust is denser than the continental crust [3.0 vs. 2.7g/cm3], the ocean plate is pushed under continental plate. [crust destruction] The area is called a SUBDUCTION ZONE, and forms a deep-ocean trench As the plate sinks into the asthenosphere, it melts and becomes magma. The magma rises through the continental plate [WHY?] and forms a volcanic chain

OCEANIC   CONTINENTAL

Cascades range was originally a volcanic arc that later uplifted… Cascades range was originally a volcanic arc that later uplifted…. [partial explanation] http://www.clas.ufl.edu/users/pciesiel/gly3150/cascade_mt.html

Mount St. Helens, Washington Cascades range

Volcanic mountains of the Andes, (Nazca and South American Plates)

TRENCH

Mariana trench and the Mariana Islands in the west Pacific ocean OCEANIC – OCEANIC The more dense of the 2 will go under and form a subduction zone / OCEAN TRENCH The new mantle material produced from the melting of the subducted plate will eventually resurface to produce chain of volcanic islands on the ocean floor called ISLAND ARCS As magma accumulates over time, the volcanoes may rise above sea level to form volcanic islands: Mariana trench and the Mariana Islands in the west Pacific ocean

OCEANIC- OCEANIC CONVERGENCE “DESTRUCTIVE”

CONVERGENT PLATES

CONTINENTAL - CONTINENTAL As the 2 continental plates are colliding, neither plate is subducted i.e. neither plate goes beneath the other  WHY? because the Continental crust is too buoyant to sink into the asthenosphere [2.7 vs. 3.3 to 5.5g/cm3] The colliding edges buckle [crumple] and are pushed upward [uplift] to form mountain ranges. Indian/Australian plate collide with the Eurasian plate to form the HIMALAYAS. Alps and Appalachians are other examples

CONTINENTAL CONVERGENCE – CONTINENTAL CONVERGENCE

The collision of India and Asia produced the Himalayas (before)

The collision of India and Asia produced the Himalayas (after)

Mountain Building