KEY Upper Penn. Lower Penn. Upper Miss. A Lower Miss. Devonia...

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KEY Upper Penn. Lower Penn. Upper Miss. A Lower Miss. Devonian Silurian Ordovician WIS. LAKE MICHIGAN Milwaukee Detroit MICHIGAN Chicago LAKE B ILL. ERIE INDIANA OHIO The major geologic structure traversed by the line A-B is best described as: TO T F D P G B J S Z M A o X S K E C V For the geologic cross section shown above, list, in order from earliest to latest, the sequence of 21 events indicated by the letters above: Note that items C, D, K and T, refer to faults, as indicated by the arrows. 1. 12. 2. 13. 3. 14. 4. 15. 5. 16. 6. 17. 7. 18. 8. 19. 9. 20. 10. 21. 11. For the four igneous rocks illustrated on the preceding pages, consult the diagram on p. 36 of the lab manual: 1. Composition 80% olivine, 12% pyroxene, 8% plagioclase; crystals visible naked eye. 2. Composition 28% amphibole, 60% plagioclase, 3% K-feldspar, 9% quartz; some amphibole and plagioclase crystals visible, in a matrix of crystals too small to be seen individually. 3. Composition 8% olivine, 57% pyroxene, 35% plagioclase; some plagioclase crystals visible, in a matrix of crystals too small to be seen individually. 4. Composition 2% amphibole, 4% biotite mica, 6% plagioclase, 50% K- feldspar, 32% quartz, 6% muscovite mica; no crystals visible. Classifications: 1 2 3 4 IGNEOUS ROCKS CLASSIFICATION 1. Mafic Color Index (MCI) Felsic Estimate the rock's Intermediate Mafic percent of mafic Ultramafic (green, dark gray, and black) mineral crystals. You can also use visual estimators in GeoTools 15 45 Felsic 85 1 and 2. (0 to 15% mafic crystals) Intermediate Mafic 100% 100% (16 to 45% mafic crystals) (46 to 85% mafic crystals) Ultramafic Muscovite 85% mafic crystals) Quartz 80 I Plagioclase 2. Minerals Feldspar Identify minerals in the rock, if possible, and 60 the percent of each one. You can use visual Potassium estimators in Feldspar GeoTools 1 and 2. (K-Spar) Skip this step if the Olivine rock is glassy or 40 aphanitic. Pyroxene 20 (augite) FELSIC Biotite Amphibole (hornblende) 3. Texture(s) Identify the rock's 4. Rock Name: Select name below, based on data from steps 1-3. texture(s). Pegmatitic: PEGMATITIC PEGMATITIC very PEGMATITIC PEGMATITIC GRANITE coarse-grained DIORITE GABBRO PERIDOTITE Phaneritic: coarse-grained GRANITE DIORITE GABBRO PERIDOTITE (SYENITE, if no quartz) Phenocrysts┬╣ PORPHYRITIC PORPHYRITIC PORPHYRITIC in a phaneritic PORPHYRITIC GRANITE DIORITE GABBRO groundmass PERIDOTITE Phenocrysts┬╣ PORPHYRITIC PORPHYRITIC PORPHYRITIC in an aphanitic RHYOLITE ANDESITE BASALT groundmass Aphanitic: RHYOLITE ANDESITE BASALT fine-grained Glassy OBSIDIAN KOMATITE (resembles basalt but has 1-10 cm long SCORIA criss-crossing needles PUMICE (resembles a sponge) of olivine or pyroxene) Vesicular (abundant tiny vesicles-like meringue; very lightweight; white or gray; floats in water) VESICULAR BASALT (has few scattered vesicles) Pyroclastic or VOLCANIC TUFF (fragments < 2 mm) Fragmental VOLCANIC BRECCIA (fragments > 2 mm) 1Phenocrysts are crystals conspicuously larger than the finer grained groundmass (main mass, matrix) of the rock. chart Ohtain shout in Stone 12 then uso that data data the rock to select the name

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The major geologic structure traversed by line A-B is best described as a basin. The youngest rocks are exposed in the center in a circular pattern...

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