Class Notes 9&10.docx

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Northeastern University
Earth & Environmental Sciences
ENVR 1200
Michael Penzo

D YNAMIC E ARTH C HAPTER 9 – M OUNTAIN BUILDING Mountains = evidence of tectonic activity Orogenesis = the process of mountain building G EOLOGIC PROCESSES - Uplift o Convergent plate boundaries  Subduction o Continental collisions  o Rifting  - Deformation - Metamorphism - Igneous activity - Sedimentation - Erosion M OUNTAIN LIFES PAN Young Mountains High, steep and still growing upward Middle-aged Lowered by erosion Mountains Old Mountains Deeply eroded remnants D EFORMATION Undeformed (unstrained) Deformed (strained) Horizontal beds Tilted beds (angled sedimentation) Spherical sand grains Metamorphic alteration No folds or faults Folding and faulting A craton is crust that hasn’t been deformed in 1 Ga - Shields = Precambrian metamorphic and igneous rocks - Platforms = shields covered by layers of Phanerozoic strata Three types of deformation : 1) Displacement – location 2)Rotation – orientation 3)Distortion – shape Strain = a change in shape due to deformation Brittle Deformation Ductile Deformation Rocks break by fracturing Rocks deformed by flowing and folding Occurs in the shallow crust Occurs at higher pressure and temp in the deeper crust Stress  Strain  Deformation T YPES OF STRESS Compression – pushed together Tension – pulled apart Shear – sliding past one another Pressure – same stress from all sides The 3D orientation of a plane is described by strike and dip - Strike = horizontal intersection with a tilted surface - Dip = the angle of the surface down from the horizontal J OINTS AND V EINS - Groundwater often flows through joints (cracks in a rock). - Dissolved minerals in groundwater precipitate in joints. - Joints filled with minerals are called veins. F AULTS Faults are planar fractures showing displacement. - They are abundant in the crust and occur at all scales. - Sudden movements along faults cause earthquakes. - Faults can be active or inactive. Fault Classification: - Dip slip – blocks move parallel to the dip of the fault - Strike slip – blocks move parallel to the fault plane strike - Oblique slip – components of both dip and strike slip Dip slip – blocks move parallel to the dip of the fault Strike slip – blocks move parallel to the fault plane strike Oblique slip – components of both dip and strike slip F OLD G EOMETRY Reverse faults – dip Anticline  opens downwards Syncline  opens upwards Monocline  dip in landscape° Thrust faults – dip is less than 35° Fig. 9.11b Fig. 9.11c Horizontal compression causes rocks to buckle: Shear causes rocks to fold over on themselves: C HAPTER 10 – A GE OF THE E ARTH JAMES H UTTON (1726-97) - “the father of modern geology” - First to articulate the principle of uniformitarianism o Geologic change is slow; large changes require
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