5_Sedimentary Rocks - Intrusive igneous rocks Dikes and...

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Unformatted text preview: 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 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. 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, its called a dike (dyke, in British English). 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. 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 Igneous Rock Classification (simplified) felsic mafic TEXTURE GABBRO BASALT GRANITE large crystals (intrusive) RHYOLITE small crystals (extrusive) MINERAL COMPOSITION 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. 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. 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. 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. GEO 303 field trip, Saturday, October 9....
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5_Sedimentary Rocks - Intrusive igneous rocks Dikes and...

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