Geology 100
Introduction to Geology
Transcript –Metamorphism THROUGHOUT HISTORY, MOUNTAINS HAVE BEEN DEEPLY EMBEDDED IN THE HUMAN EXPERIENCE. WE'VE WORSHIPPED THEM, CREATED NATIONS USING THEM AS BOUNDARIES, STRIPPED THEM OF VALUABLE RESOURCES, AND RETURNED TO THEM FOR INSPIRATION AND RECREATION. IF YOU ARE AT ALL CURIOUS ABOUT THE EARTH, YOU'VE PROBABLY WONDERED WHY MOUNTAINS EXIST. THIS QUESTION HAS INTRIGUED EARTH SCIENTISTS EVER SINCE THE EMERGENCE OF GEOLOGY AS A SCIENCE IN THE LATE 18th CENTURY. THE MORE WE LEARN ABOUT MOUNTAINS AND WHAT THEY'RE MADE OF, THE MORE FASCINATING THIS QUESTION BECOMES. MOST MOUNTAINS ARE FORMING TODAY IN TECTONICALLY ACTIVE REGIONS WHERE THE MOVEMENTS OF PLATES DEFORM THE ROCKS OF THE EARTH'S LITHOSPHERE. THEIR TREMENDOUS ENERGY THAT'S EXPENDED IN THE MOUNTAIN-BUILDING PROCESS OFTEN HAS A PROFOUND EFFECT ON THESE ROCKS. THE GEOLOGIC EVENTS THAT ACCOMPANY MOUNTAIN-BUILDING, SUCH AS THE COLLISIONS BETWEEN PLATES, DEEP SUBSIDENCE OF PORTIONS OF THE EARTH'S CRUST, MOVING MASSES OF MAGMA, AND THE DISPLACEMENT OF ROCK BODIES ALONG FAULT ZONES FOCUS HEAT AND PRESSURE ON THE ROCKS. AS A RESULT, THESE ROCKS ARE CHANGED DRAMATICALLY. THIS PROCESS OF CHANGE BY HEAT AND PRESSURE IS CALLED METAMORPHISM-- A TERM DERIVED FROM THE GREEK WORDS META, WHICH MEANS CHANGE, AND MORPH, MEANING FORM. METAMORPHISM CHANGES THE APPEARANCE OF ROCKS, THEIR MINERAL COMPOSITION, AND EVEN THEIR AGE AS MEASURED BY RADIOMETRIC DATING. DURING METAMORPHISM, ATOMS WITHIN THE ROCK CAN DISLODGE THEMSELVES FROM MINERAL LATTICES AND MOVE ABOUT FREELY. THIS ATOMIC RESHUFFLING CAUSES EXISTING MINERALS TO RECRYSTALLIZE AND NEW MINERALS TO FORM. THIS PROCESS ALSO RESETS THE RADIOACTIVE CLOCK WITHIN THE ROCK TO THE TIME OF METAMORPHISM. METAMORPHISM CAN RESULT IN COMPLEX STRUCTURES AND RARE MINERALS THAT MAKE THESE SOME OF THE MOST BIZARRE-LOOKING AND STRIKINGLY BEAUTIFUL OF ALL CRUSTAL ROCKS. BUT TO A GEOLOGIST, THE REAL BEAUTY OF METAMORPHIC ROCKS IS THE...