Chapter 3 Earth Materials and Plate Tectonics BASIC GEOLOGY Chapter 3 Earth Materials and Plate Tectonics
Chapter Overview Rocks and Minerals of the Earth’s Crust Major Relief Features of the Earth’s Surface Plate Tectonics Continents of the Past Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust The Earth’s Interior Core: spherical central mass of the Earth composed largely of iron; consists of an outer liquid zone and an inner solid zone Mantle: rock layer of the Earth beneath the crust and surrounding the core, composed of ultramafic igneous rock of silicate minerals Crust: outermost solid layer of the Earth, composed largely of silicate minerals Oceanic crust: mafic rocks Continental crust: lower zone mafic rock, upper zone felsic Continental crust thicker than oceanic Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust The Earth’s Interior Most abundant elements in crust: Oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium Minerals: naturally occurring inorganic crystalline chemical compounds Rocks: Usually composed of 2 or more minerals Rock classes: igneous, sedimentary, metamorphic Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust Igneous Rocks Igneous rock: rock formed from the cooling of magma Intrusive Igneous rock: rock formed from magma that solidifies below the Earth’s surface Visible mineral crystals Extrusive igneous rock: rock formed from magma that cooled rapidly at the surface or under the ocean Mineral crystals microscopic Magma: mobile, high-temperature molten state of rock Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust Igneous Rocks Most composed of silicate minerals: contain silicon and oxygen Felsic rock: Felsic minerals Light-colored Less dense Mafic rock: Mafic minerals Dark-colored More dense Ultramafic rock: Heavy mafic minerals Very dense Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust Sediments and Sedimentary Rocks Sedimentary Rock: rock formed from the accumulation of sediment Clastic—formed from rock and mineral fragments Chemically precipitated: formed by chemical precipitation from seawater or salty inland lakes Organic: formed from organic material Insert figure 8.6 here Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust Sediments and Sedimentary Rocks Sandstone, deposited in layers Conglomerate Shale Chalk, a form of limestone Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust Sediments and Sedimentary Rocks Coal, a fossil fuel, is an organic sedimentary rock Fossil Fuels: naturally occurring hydrocarbon compounds produced from remains of organic matter enclosed in rock; examples are coal, petroleum (crude oil), and natural gas Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust Metamorphic Rocks Metamorphic Rock: rock altered in physical or chemical composition by heat, pressure, or other processes taking place at a substantial depth below the surface Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Rocks and Minerals of the Earth’s Crust The Cycle of Rock Change Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Major Relief Features of the Earth’s Surface The Geologic Timescale 4.5 billion years of Earth’s history Divided into Eons, Eras, Periods Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Major Relief Features of the Earth’s Surface The Lithosphere and Asthenosphere Lithosphere: rigid outer shell of Earth, includes crust and upper mantle Asthenosphere: plastic layer below the lithosphere Lithospheric Plate: segment of lithosphere moving as a unit, in contact with adjacent lithospheric plates along plate boundaries Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Major Relief Features of the Earth’s Surface Relief Features of the Continents Active mountain-making regions: Mountains result from volcanism or tectonic activity. Active mountain-making belts form alpine chains: narrow zones along the margins of lithospheric plates Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Major Relief Features of the Earth’s Surface Relief Features of the Continents Continental crust includes: Active mountain-making belts Regions of stable, older rock Continental shields: very old, low-lying igneous and metamorphic rocks Mountain roots: remains of older mountain belts, long, narrow ridges Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Major Relief Features of the Earth’s Surface Relief Features of the Ocean Basins Oceanic crust <60 million years old; continental crust >1 billion years old Ocean basins have: Midoceanic ridge Axial rift Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Major Relief Features of the Earth’s Surface Relief Features of the Ocean Basins Passive continental margins: no strong tectonic activity within 50 million years Active continental margins: deep offshore trenches, volcanic activity Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Plate Tectonics Motion of lithospheric plates drives formation of Earth’s mountains and other surface features. Extensional tectonic activity Spreading boundary Plates pulled apart Faults created Compressional tectonic activity Converging boundary Plates pushed together Creates folds and overthrust faults Plates move past each other Transform boundary Transform faults Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Plate Tectonics Plate Boundaries Spreading boundary Converging boundary Transform boundary Plate Tectonics: theory of tectonic activity dealing with lithospheric plates and their activity Subduction: descent of the edge of a lithospheric plate under an adjoining plate and into the asthenosphere Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Plate Tectonics Subduction Tectonics Plates undergoing subduction are associated with active continental margins Sediments accumulate in deep trench Deep ocean sediments Terrestrial sediments Deformed, scraped off subducting plate Wedge forms at the plate boundary Sediments transformed into metamorphic rock Subduction: descent of the edge of a lithospheric plate under an adjoining plate and into the asthenosphere Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Orogens and Collisions Plate Tectonics Orogens and Collisions Continental suture: Long, narrow zone of crustal deformation produced by a continental collision; examples: Himalayan Range, European Alps. Continental lithospheric plates converge: Both buoyantneither subducts Orogeny: major episode of tectonic activity resulting in strata being deformed by folding and faulting Nappe: overturned recumbent fold of strata, usually associated with thrust sheets in a collision orogen Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
The Lithospheric Plates and Their Motions Plate Tectonics The Global System of Lithospheric Plates The Lithospheric Plates and Their Motions Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Continental Rupture and New Ocean Basins Plate Tectonics Continental Rupture and New Ocean Basins Passive continental margins are created by continental rupture and spreading Crust uplifted and stretched Magma rises to form new rock Rift valley forms Rift widens and narrow ocean is formed Ocean basin widens Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
The Power Source for Plate Movements Plate Tectonics The Power Source for Plate Movements Radiogenic heat: heat generated by the decay of radioactive isotopes Heat generated by decay of isotopes of uranium, thorium, potassium Independent of surface conditions Heat keeps rock below crust close to melting point Radiogenic heat power source for plate motions Exact mechanism unknown Possibly convection currents in mantle Possibly gravity Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Continents of the Past Alfred Wegener proposed first full-scale scientific theory of the breakup of one supercontinent into multiple drifting continents Pangaea: supercontinent Intact about 300 million years ago Outlines of continents fit across ocean Tectonic structures match across continents Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Continents of the Past Wilson Cycle: the continents have united and broken up repeatedly through Earth’s history Movements of the continents from 200 million years ago to present Movements of the continents from 600 million years ago to 300 million years ago Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
Continents of the Past Satellite data show rates of plate movement from about 5 to 10 cm (2-4 inches) per year Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.