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Download met lab 1: introduction to metamorphic rocks
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GEOLOGY 13.53: Igneous and Metamorphic Petrology MET LAB 1: INTRODUCTION TO METAMORPHIC ROCKS Learning Objectives: • Students will be able to differentiate microtextures that characterize metamorphic rocks from those of their sedimentary and igneous protoliths • Students will be able to describe general trends in microtexture development with increasing grade in metamorphic rocks Key Minerals: Biotite, Calcite, Chlorite, Dolomite, Garnet, Hornblende, Muscovite, Plagioclase, Quartz 1. Thin-section 7345 is Berea sandstone (AKA Ohio Sandstone, a common building stone) and thin-section 7376 is quartzite (Baraboo Formation, WI). Examine each of these thin-sections and find areas where several quartz grains are in contact. Sketch these grain-contact textures below. 1 What are the most distinct textural differences between sandstone and quartzite? ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ What textural terms describe grain-boundaries in the quartzite? ________________________________________________________________ ________________________________________________________________ How does the extinction of quartz compare in sandstone and quartzite? What does this indicate about conditions associated with metamorphism? ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ 2 2. Thin-section 7359 is dolostone (Lockport Formation, NY) and thin-section 7372 is Tate Marble (a common building stone from Georgia). Examine each of these. Sketch examples of typical grain shapes and grain-contact textures below. What are the most distinct textural differences between dolostone and marble? ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ How does the distribution of grain size of carbonate minerals vary between the dolostone and marble samples? ________________________________________________________________ ________________________________________________________________ 3 How does the abundance of twins in carbonate minerals vary between the dolostone and marble samples? How might conditions of metamorphism account for this difference? ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ 3. Thin-section 7377 is slate (Martinsburg Formation, PA), thin-section 7378 is phyllite (Orfordville Formation, VT), and thin-section 7499 is a schist from Vermont. Examine each of these. Sketch examples of typical grain shapes and grain-contact textures below. What are the most distinct textural differences that develop with increasing metamorphic grade from slate to schist? ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ 4 How do contacts between quartz crystals in the schist compare with those in quartzite, or with carbonates in marble? ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ In terms of chemical composition, how do minerals that are unique to high-grade rocks (e.g., garnet) compare with minerals that are common in low-grade rocks (e.g., chlorite and muscovite)? ________________________________________________________________ ________________________________________________________________ 4. Thin-section W204 is gabbro, and thin-section Z3A is amphibolite. Examine each of these. Sketch examples of typical grain shapes and grain-contact textures below. What are the most distinct textural differences between gabbro and amphibolite? ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ 5 How do grain contacts between plagioclase in the amphibolite compare with those of quartz in quartzite, and with carbonates in marble? ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ How does the shape and orientation of plagioclase and hornblende crystals differ between gabbro and amphibolite? ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ 6
