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Tectonics and The Provinces of the Oceans. I. Theory of Plate Tectonics. A. The theory states that the earth’s crust is broken into 7 rigid pieces called PLATES . B. The plates are moving in different directions and at different speeds.
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I. Theory of Plate Tectonics A. The theory states that the earth’s crust is broken into 7 rigid pieces called PLATES. B. The plates are moving in different directions and at different speeds. C. The movement of the plates results in a geological FAULT
Fault – A fracture in the continuity of a rock formation. • Plate movement results not only fault formations. (Sea-floor spreading resulted in the formation of theMid-Oceanic Ridge)
II. Plate Tectonics Proof A. Radiometric Dating • steadily increasing age of the sedimentary rocks which rest on the crust with increasing distance from the ridges (radiometric dating) • most rocks have small amounts of radioactive elements (uranium, thorium, potassium) which decay into atoms of other elements
B. PaleomagnetizationPatterns 1) In the basaltic rocks magnetic patterns are retained (like a tape recording) on either side of the ridge. 2) These magnetic patterns can be dated to the time-scale of geomagnetic reversals, which occur at irregular intervals of every 300,000 to 500,000 years
C. Polar Wandering • Def - Migration of the magnetic poles of the Earth through geologic time. • Magnetic studies of rocks from many places and from each major division of geologic time reveal a change in pole locations relative to the continent. • The change in position formed a pole path, particular to that continent. The pole paths for adjacent continents could be made to coincide when the continents are brought back together. Thus the continents moved rather than the poles.
D. Formation of Mid-Oceanic Ridge 1. The existence of the ever-changing mid-oceanic ridge proves that tectonic plates move. 2. When the sea-floor spreads apart the magma from beneath rises up through the gap in the crust. 3. The result is the formation of an underwater volcanic mountain.
III. Provinces of the Ocean A. Sea-floor divided into 2 categories: 1. Deep-Sea Floor 2. Continental Margins B. Continental Margins - 1. Boundary between continental and oceanic crusts.
2. Parts of Continental Margin 1. Shelf – slightly slopping surface • 2. Submarine Canyon – Steep sided valley cut into the continental slope. 3. Shelf break – edge of the shelf separating the shelf from the slope. 4. Continental slope – steep descent from continent to the ocean bottom. 5. Continental rise – transitional region that gently slopes onto the ocean floor.
4. Types of Margins Passive Margin Active Margin
a. Passive Margins - inactive margin having flat coastal plains, wide shelves, and gradual continental slopes.
b. Active Margin - • Highly active with volcanoes and earthquakes. • Have little to no shelf and a steep slope ending in a trench, no rise.
Comprehension Check • The three main divisions of the Earth’s interior are __, __, and __. • A long chain of submarine volcanic mountains that runs throughout the world ocean is called the ___ system. • A single super continent called __ began to break up onto the present-day continents about __ years ago. • The continental margins consists of __, __, __, ___ and __. • The average depth of the ocean is __m.