Earth Science And the Ocean Part I

Structure of the Earth Plate Boundaries Driving Mechanisms of Plate Tectonics Plate Tectonics

The Earth can be considered as being made up of a series of concentric spheres, each made up of materials that differ in composition. We will Focus on 4 Layers Structure of the Earth

Crust and Lithosphere Crust : the outermost layer of the earth, a hard outer shell. Crust beneath the oceans and the continents is different: Oceanic crust : relatively thin, varying from 5 to 8 km (but thinner at Oceanic ridges) yet denser. Has the average composition of basaltic rock (Basalt) that is rich in silica and magnesium.

Continental Crust : thicker than oceanic crust but it is less dense Thickness ranges from 20 km to about 75 km (beneath mountain ranges). Has the average composition of granitic rock (Granite).

Lithosphere : The topmost layer of the upper mantle. The Lithosphere is more viscous (fluid) than any other part of the mantle. This is what the crustal plates are sitting on. Due to its elasticity and convection we have plate movement

USGS The crust and lithosphere are broken up into 25 Lithospheric Plates

Oceanic Vs Continental Made of BasaltMade of Granite ThinnerThicker More DenseLess Dense YoungerOlder

Continental Crust is _____ Oceanic Crust 1.Older than 2.Younger than 3.The same as 4.None of the above

Continental Crust is made of 1.Granite 2.Feldspar 3.Basalt 4.Quartz

Oceanic Crust is ______ Continental Crust 1.Thinner than 2.Thicker than 3.The same as

Oceanic Crust is made of 1.Granite 2.Feldspar 3.Basalt 4.Quartz

The Mantle includes the Lithosphere. Upper Mantle or Lithosphere: near its melting point so that it behaves like a plastic (Similar to Silly Putty ); the upper mantle material is more fluid Lower Mantle: solid material, rather than plastic. Upper mantle material MOVES by convection; transfers heat from within the Earth towards the surface.

The Core: the metallic portion of the Earth; Iron mixed with small amounts of Nickel. It is at the center Outer Core: probably liquid (based on studies of shock wave passage through the Earth). Inner Core: solid, made up of cooled liquid core material.

In a Nutshell……. The Earths interior is composed of 4 main layers. The Crust the outermost layer. Oceanic Crust Thinner, Denser, Younger and made of Basalt. Continental Crust Thicker, Older, Less Dense and made of Granite. The Mantle which includes the Lithosphere which is just under the crust. Largest of the layers It is composed of molten rock which has the consistency of Silly Putty. The Core Fe Ni inner core (solid) and a liquid outer core also made of nickel and iron.

The Outermost layer of the Geosphere is the 1.Inner Core 2.Outer Core 3.Mantle 4.Crust

There are ____ Crustal Plates

The Crustal plates sit or “Float” on top of the 1.Inner Core 2.Lithosphere 3.Crust 4.Outer Core

The Lithosphere is part of the 1.Crust 2.Inner Core 3.Outer Core 4.Mantle

Plate Boundaries The types of boundary movement between plates are distinguished by the type of relative plate motion along the boundary: Oceanic Ridge – Divergence Transform Margins – Horizontal slip Oceanic Trench – Convergence

Oceanic Ridge

More-or-less continuous volcanic mountain chain throughout the world's oceans. 65,000 km long. Average width approx. 1,000 km. Average depth approx. 2.3 km below sea level. Rise up to 3 km above the surrounding sea floor. A kilometre deep valley runs along much of the length of the ridge.

The ridge is a Divergent Plate Margin and divergence takes place by Sea Floor Spreading. From New crust is added from upwelling magma (molten rock) from the upper mantle. Older crust is pushed laterally away from the ridge axis – so that the sea floor spreads away from the ridge axis.

Oceanic crust becomes older with distance from the oceanic ridge. Spreading rates (distance per year that two points on either side of a ridge move apart) vary: N. Atlantic Ridge3cm/yr S. Atlantic 5cm/yr N. Pacific12.5cm/yr E. Pacific17.5 cm/yr

Divergent Boundaries Summary Crustal Plates are moving Away from each other at this boundary. Most well known is the “Mid Atlantic Ridge” Largest Geological structure on Earth Area of sea floor spreading – The Atlantic Ocean is getting bigger. Can be found on land in the country of Iceland Definitive Proof of Crustal Plate Movement - through Paleo Magnetism of rock.

The mid Atlantic Ridge is a ____________ plate boundary 1.Divergent 2.Convergent 3.Transform 4.Integral

The largest geological structure on Earth is 1.The Grand Canyon 2.Mid Atlantic Ridge 3.Challenger Deep 4.Mount Everest

The Atlantic Ocean is getting 1.Smaller 2.Bigger 3.Deeper 4.Shallower

The only place on Land you can see the Mid Atlantic Ridge is 1.Ireland 2.Greenland 3.Iceland 4.Norway

At divergent plate boundaries the plates are moving 1.Toward each other 2.Away from each other 3.Sliding past each other 4.down

Oceanic- Continental Oceanic – Oceanic Island Arcs (talk more about this later) Trenches

Magma material rises from descending slab and builds volcanoes in the rising mountains. Coastal mountain chains develop due to compressive forces and volcanics (e.g., the Andes of South America). Oceanic Crust – Continental Crust Basaltic oceanic crust descends beneath lighter continental crust.

Crust melts as it descends, beginning at 100 to 200 km depth and has melted completely by 700 km depth. The zone over which melting takes place is termed the Benioff Zone. Crust descends at angles from 35 to 90 degrees.

Melting crust rises and penetrates overlying crust to form volcanoes. Material (sediment and basaltic rock) is scraped off the subducting crust and accreted to the over-riding crust – termed the subduction complex.

Oceanic Trenches

Thousands of kilometers long, 50 to 100 km wide and several kilometers deep (below sea level). Longest trench: Peru-Chile trench at 5,900 km. Deepest trench: Mariana trench (western Pacific) at 11 km deep (almost 7 MILES deep)

Trenches are termed Convergent Plate Margins because they are locations where plates converge on, or push against, each other. Where oceanic crust is subducted back into the upper mantle.

Island Arcs parallel many oceanic trenches: arc- shaped chains of volcanic islands (e.g., Japan) due to the rising magma from melting subducted crust.

When one plate moves under another plate. This is called 1.Induction 2.Deduction 3.Subduction 4.Abduction

Older Oceanic Crust will move __________ Younger Crust 1.Over 2.Under 3.Sideways to 4.Into

Island Arcs form Parallel to Oceanic Trenches 1.True 2.False

The deepest trench is the 1.Marianas Trench 2.Tonga Trench 3.Japan Trench 4.Peru –Chile Trench

The longest trench is the 1.Tonga Trench 2.Peru- Chile Trench 3.Marianas Trench 4.Kermadec Trench

Continental Crust will subduct under Oceanic Crust. 1.True 2.False

The Area where the Oceanic crust is “melted” back into the Magma is called the 1.Benihoff Zone 2.Melt Zone 3.Magma Deep 4.Trench Zone

Continental Crust-Continental Crust Compressive forces driving plates fold and thrust the continental margins forming an extensive mountain belt (e.g., the Himalayan Mountains). Neither plate subducts (both too light).

Convergent Boundaries Summary These are areas where plates are moving toward each other. This is an area of Subduction The Oceanic plate will move under the continental plate. The Older Oceanic Crust will move under the Younger Crust This is where Trenches are formed The Oceanic plates get “recycled” back into the upper mantle Volcanic Island arcs are formed parallel to the trenches

The Deepest Trench is the Marianas Trench which is 11 KM deep The Longest Trench is the Peru- Chile Trench Benihoff Zone is the Area of the Mantle where the Oceanic crust is “Recycled” back into the Magma.

Plate margins along which the plates slip by each other. Termed: Transform Faults On either side of a transform fault plate motions are in opposite directions. Sudden Shifts will result in Earthquakes Transform Plate Margins

Transform faults displace the oceanic ridge.

The San Andreas Fault is a transform fault. The land east of the fault is on the North American Plate; the land west of the fault is on the Pacific Plate. The eastern side of the fault moves southeast and the western side moves to the northwest. Total movement along the fault has been 564 km over the past 30 million years (1.9 cm per year).

The San Andreas Fault is a __________ plate Margin 1.Divergent 2.Transform 3.Convergent 4.Invergent

Sudden Movement at a Transform Margin will result in a 1.Volcano 2.Trench 3.Ridge 4.Earthquake

But what drives plate tectonics? Two main hypotheses: 1. Convection Cells within the upper mantle (first postulated by Arthur Holmes a year before Wegener died). and 2. Ridge push and slab pull.

Giant convection cells within the upper mantle drag the plates along laterally. Where convection rises sea floor spreading takes place. Where the convection cells descend they drag crust down, causing subduction Mantle Convection

Where new, young crust forms its weight pushes down slope to drive the plates laterally. Once the crust has cooled, having been pushed away form the ridge, it sinks into the upper mantle and helps to pull adjacent crust along. This pushing and pulling provides the forces that drive plate tectonics. Ridge push and slab pull

Convection is caused by 1.Movement 2.Heat 3.Plates 4.Margins

Slab pull would occur at 1.Ridges 2.Trenches 3.Transform Margins 4.None of the Above

Slab pull would occur at 1.The Ridge 2.The Trenches 3.Transform Margins 4.Volcanoes

Convection can only occur when you heat gases like air 1.True 2.False