GEOLOGY FOR MINING ENGINEERS. Prof.Dr.Kadir DİRİK Lecture Notes 2015

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1 GEOLOGY FOR MINING ENGINEERS Prof.Dr.Kadir DİRİK Lecture Notes 2015

2 THE SCIENCE OF GEOLOGY GEOLOGY is the study of the Earth, including the materials that it is made of, the physical and chemical changes that occur on its surface and in its interior, and the history of the planet and its life forms. Most of the Earth is solid rock, surrounded by the hydrosphere, the biosphere, and the atmosphere. Prof.Dr.Kadir Dirik Lecture Notes

3 The hydrosphere includes water in streams, wetlands, lakes, and oceans; in the atmosphere; and frozen in glaciers. It also includes ground water present in soil and rock to a depth of at least 2 kilometers. The atmosphere is a mixture of gases, mostly nitrogen and oxygen. It is held to the Earth by gravity and thins rapidly with altitude. Ninety nine percent is concentrated within 30 kilometers of the Earth s surface, but a few traces remain even 10,000 kilometers above the surface. The biosphere is the thin zone near the Earth s surface that is inhabited by life. Itincludestheuppermost solid Earth, thehydrosphere, and the lower parts of the atmosphere. Land plants grow on the Earth s surface, with roots penetrating at most a few meters into soil. Animals live on the surface, fly a kilometer or two above it, or burrow a few meters underground. Sea life also concentrates near the ocean surface, where sunlight is available. Some aquatic communities live on the deep sea floor, bacteria live in rock to depths of a few kilometers, and a few windblown micro organisms are found at heights of 10 kilometers or more. But even at these extremes, the biosphere is a very thin layer at the Earth s surface.

4 Most of the Earth is composed of rocks. Rocks, in turn, are composed of minerals

5 Most of the Earth is solid rock, surrounded by the hydrosphere, the biosphere, and the atmosphere. Although more than 3500 different minerals exist, fewer than a dozen are common. We study the origins, properties, and compositions of both rocks and minerals. There are two processes acting on the earth namely internal and external processes INTERNAL PROCESSES Processes that originate deep in the Earth s interior are called internal processes. These are the driving forces that raise mountains, cause earthquakes, and produce volcanic eruptions. SURFACE PROCESSES Surface processes are all of those processes that sculpt the Earth s surface. Most surface processes are driven by water, although wind, ice, and gravity are also significant.

6 UNIFORMITARIANISM AND CATASTROPHISM James Hutton was a gentleman farmer who lived in Scotland in the late 1700s. Although trained as a physician, he never practiced medicine and, instead, turned to geology. Hutton observed that a certain type of rock, called sandstone, is composed of sand grains cemented together. He also noted that rocks slowly decompose into sand, and that streams carry sand into the lowlands. He inferred that sandstone is composed of sand grains that originated by the erosion of ancient cliffs and mountains. Hutton s conclusions led him to formulate a principle now known as uniformitarianism. The principle states that geologic change occurs over long periods of time, by a sequence of almost imperceptible events. Hutton surmised that geologic processes operating today also operated in the past. Thus, scientists can explain events that occurred in the past by observing changes occurring today. Sometimes this idea is summarized in the statement The present is the key to the past.

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8 William Whewell, another early geologist, agreed that the Earth is very old, but he argued that geologic change was sometimes rapid. He wrote that the geologic past may have consisted of epochs of paroxysmal and catastrophic action, interposed between periods of comparative tranquility. Whewell was unable to give examples of such catastrophes. He argued that they happen so infrequently that none had occurred within human history. Today, we know that both Hutton s uniformitarianism and Whewell s catastrophism are correct. Thus, over the great expanses of geologic time, slow, uniform processes are significant, but improbable, catastrophic events radically modify the path of slow change. Gradual Change in Earth History Within the past few decades, geologists have learned that continents creep across the Earth s surface at a rate of a few centimeters every year. Catastrophic Change in Earth History Chances are small that the river flowing through your city will flood this spring, but if you lived to be 100 years old, you would probably see a catastrophic flood. When we study the 4.6 billion years of Earth history, they find abundant evidence of catastrophic events that are highly improbable in a human lifetime or even in human history. For example, giant meteorites have smashed into our planet, vaporizing enormous volumes of rock and spreading dense dust clouds over the sky. Similarly, huge volcanic eruptions have changed conditions for life across the globe. Geologists have suggested that these catastrophic events have driven millions of species into extinction.

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10 THE GEOLOGIC TIME SCALE Geologists have divided Earth history into units displayed in the geologic time scale. The units are called eons, eras, periods, and epochs and are identified primarily by the types of life that existed at the various times.

11 The Origin of the Solar System and the Differentiation of the Early Earth The currently accepted theory for the origin of our solar system involves: (a) a huge nebula condensing under its own gravitational attraction, then (b) contracting, rotating, and (c) flattening into a disk, with the Sun forming in the center and eddies gathering up material to form planets. As the sun contracted and began to visibly shine, (d) intense solar radiation blew away unaccreted gas and dust until finally, (e) the Sun began burning hydrogen and the planets completed their formation.

12 Heat from the Sun boiled most of the hydrogen, helium, and other light elements away from the inner Solar System. As a result, the four planets closest to the Sun Mercury, Venus, Earth, and Mars are now mainly rocky with metallic centers. These four are called the terrestrial planets because they are Earthlike. In contrast, the four outer planets Jupiter, Saturn, Uranus, and Neptune are called the Jovian planets and are composed primarily of liquids and gases with small rocky and metallic cores. (a) Mercury is a small planet close to the Sun. Consequently, most of the lighter elements have long since been boiled off into space, and today the surface is solid and rocky. (b) Jupiter, on the other hand, is composed mainly of gases and liquids, with a small solid core.

13 (a) The early Earth was probably of uniform Composition and density throughout, (b) Heating of the early Earth reached the melting point of iron and nickel, which, being denser than silicate minerals, settled to the Earh s center. At the same time, the lighter silicates flowed upward to form the mantle and the crust. (c) In this way, a differentiated Earth formed, consisting of a dense iron nickel core, an ironrich silicate mantle, and a silicate crust with continents and oceanbasin

14 A schematic view of the interior of the Earth Jumps in density between Earth s major layers caused by changes in their chemical composition

15 Continents float high because they are made of rocks with lower densities than rocks of the mantle or oceanic crust

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17 Axial ridge Givergent boundary Transform Subduction zone Convergent boundary Extensional zone in the continents Uncertainplate boundary

18 Convection carries heat upward by the motion of matter Continental lithosphere Trench Mid oceanic ridge Ocean Subduction Oceanic lithosphere Prof.Dr.Kadir Dirik Lecture Notes (Monroe&Wicander, 2005) 18

19 Mid oceanic ridge Transform plate boundary Divergent plate boundary Continental Continental convergent plate boundary Continental Oceanic convergent plate boundary Trench Divergent plate boundary Oceanic Oceanic convergent plate boundary Upwelling Asthenosphere Lithosphere An idealized cross section illustrating the relationship between lithosphere and underlying asthenosphere and the three principal types of boundaries convergent (yaklaşan), divergent (uzaklaşan) and transform (transform). Prof.Dr.Kadir Dirik Lecture Notes Upwelling (Monroe&Wicander, 2005) 19

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