Geology 209 Final Chapter 12

Why does continental drift happen?

Sea floor spreading

How do we map the morphology of the oceanic floor?

Sonar

Abyssal plane

Occupies most of the oceanic floor, almost planar or with low rate of depth increase

Mid-oceanic ridge

A mountain chain developed towards the central part of the oceans and exist in all oceans

Oceanic trenches

Deepest portions of oceans, elongate form and occupy a much smaller area

Seamounts

Small sized structures, altitude of several thousands of metres and can rise above the ocean level to form an island

Flat topped mountains

The result of erosion and associated with volcanism

Island arcs

Elongate chains of generally small-sized islands that occur away from the continents, they are parallel to a nearby oceanic trench, volcanic and earthquake activity is frequent

Deep Sea Drilling Project

The investigation of sediments and sedimentary rocks in the deepest pats of the planetary ocean

What are the two patterns that important in recognizing oceanic basin evolution?

Sediment and oceanic crust ages & rock distribution function of their basic magnetic properties

Sediment and oceanic crust ages

Indicates youngest sediments occur in the proximity of the mid-oceanic ridge and the age increases towards the ocean’s margins

Magnetic zone distribution

Minerals behave as dipoles during crystallization in the case of igneous rocks and deposition in sedimentary rocks

Case of normal polarity

When the north magnetic pole is in the same hemisphere with the north geographic pole

Case of reversed polarity

When the north magnetic pole is situated at the Southern Hemisphere and southern magnetic pole is situated at the northern hemisphere

Magnetic reversal

Produced by the molten iron movement at the core/mantle boundary

Volcanoes

Frequent at the plate boundaries or in the continental areas

Earthquakes

Concentrated along the plate boundaries and in certain continental regions

Where do oceans start?

Continental zones

What happens when an ocean closes?

A mountain chain forms

Tectonic plates

Huge masses of lithosphere that present distinct movement, behaviour, and geological history

Divergent settings

Occur where the lithosphere plates move away from each other

Continental rift initiation

Produced by the ascending currents in the asthenosphere beneath the continental crust, creates divergent regime that stretches the crust and creates formation of faults

Continental rift formation

Occurs as the continental first stretching and thinning continues, formation of an elongate depression zone, molten matter reaches the surface

Early oceanic basin formation

Occurs when the continental first is split into two distinct parts that move away from each other due to the sea floor spreading

Mature oceanic basin formation

Happens with the continuation of the seafloor spreading, new oceanic crust, two continental areas that are being forced apart

Aborted oceans

When rifting stage is not followed by the seafloor spreading stages, known as aborted oceans

Convergent settings

Occur when two plates move against each other

Ocean-ocean convergent settings

Occur in the collision zone between two fragments of oceanic crust, one oceanic crust slab is sunken under the other along an inclined plane

Benioff plane

Also known as subduction plane, when one plane is under another

Accretionary prism

Consists of strongly folded rocks

Ocean-continent convergent settings

Occur at the collision between a slab of continental crust and one of oceanic crust, oceanic crust subduction under continental crust

Continent-continent convergent settings

Occurs where two slabs of continental crust collide, process involves the subduction and consumption of the slab of oceanic crust that initially separated the two

Wilson cycle

Represents the the cycle of birth, evolution and close-up of an oceanic basin