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Sedimentary_Lecture5_posting

Sedimentary_Lecture5_posting - Chapter7:SedimentaryRocks...

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Intrusive igneous rocks Dikes and sills Intrusives: granite, gabbro Weathering Mechanical versus chemical weathering Weathering of granite Sedimentary Rocks Origin Clastic versus chemical sediment Common clastic sedimentary rocks Chapter 7: Sedimentary Rocks Next lecture: Finish chapter 7, then chapter 9
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Intrusive Igneous Rocks:  Types of Intrusions (AGI) Rising magma cuts across layers in  dikes, and sometimes pools between  layers in sills.  A laccolith is a large  between-layer magma body that causes  the overlying rocks to dome upwards.
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 Dike or Sill? Both examples here are dikes.   The light brown rock above,  from the Isle of Mull, intruded  horizontally, but because it  cuts across the layering, which  is vertical here, it’s called a  dike (dyke, in British English).
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We rarely get to see an  actual magma chamber,  because they are so  deep.  However, drillers  looking for geothermal  energy recently struck  one in Hawaii, at a  depth of 2.5 km.  The  magma was 1050 ° C!  It  is now running a 30 MW  power plant.
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Intrusive igneous rocks Dikes and sills Intrusives: granite, gabbro Weathering Mechanical versus chemical weathering Weathering of granite Sedimentary Rocks Origin Clastic versus chemical sediment Common clastic sedimentary rocks Chapter 7: Sedimentary Rocks Next lecture: Finish chapter 7, then chapter 9
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Igneous Rock Classification (simplified) felsic mafic TEXTURE GABBRO BASALT GRANITE large crystals (intrusive) RHYOLITE small crystals (extrusive) MINERAL COMPOSITION
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In this photograph of a polished surface of granite we see large  pink crystals of K (potassium) feldspar, light gray crystals of Na  (sodium) plagioclase feldspar, and black crystals of biotite mica, a  mafic mineral.  Although quartz appears to be dark-colored, it is  actually transparent and we are seeing through the quartz crystal  deeper into the rock.
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A simplified geologic map of  Texas.  Each grouped set of  colors refers to a geologic  “province” or region where the  surface geology reflects a  unified history of geologic  development.
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This image emphasizes three major  geologic provinces in Texas:  the  Llano Uplift (black), Edwards  Plateau (green), and Gulf Coastal  Plain (brown to yellow).  Note that  Austin lies on the boundary between  two of these provinces.
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The Llano Uplift (black blob in the preceding image) is shown amplified  here, with further elaboration of the geology.  Yellow, green, and blue  refer to varieties of metamorphic rock.  Red refers to very large masses  of granite, called batholiths.  Everything not colored refers to  sedimentary rock of a great variety of different ages.
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GEO 303 field trip, Saturday, October 9.
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