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SF State GEOL 426 - Igneous - field relationships

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Chapter 4: Igneous Structures and Field RelationshipsStructures and Field RelationshipsPowerPoint PresentationSlide 4Slide 5Slide 6Slide 7Slide 8Slide 9Magma mixing & minglingSlide 11Enclaves or xenolithsSlide 13Slide 14Slide 15Slide 16Slide 17Slide 18Chapter 4: Igneous Structures Chapter 4: Igneous Structures and Field Relationshipsand Field RelationshipsFigure 4-1. a.Figure 4-1. a. Calculated viscosities of anhydrous silicate liquids at one atmosphere pressure, calculated by the Calculated viscosities of anhydrous silicate liquids at one atmosphere pressure, calculated by the method of Bottinga and Weill (1972) by Hess (1989), method of Bottinga and Weill (1972) by Hess (1989), Origin of Igneous Rocks. Harvard University Press. Origin of Igneous Rocks. Harvard University Press. b.b. Variation in the viscosity of basalt as it crystallizes (after Murase and McBirney, 1973), Variation in the viscosity of basalt as it crystallizes (after Murase and McBirney, 1973), Geol. Soc. Amer. Bull., Geol. Soc. Amer. Bull., 8484, , 3563-3592.3563-3592. c.c. Variation in the viscosity of rhyolite at 1000 Variation in the viscosity of rhyolite at 1000ooC with increasing HC with increasing H22O content (after Shaw, 1965, O content (after Shaw, 1965, Amer. J. Sci., Amer. J. Sci., 263263, 120-153, 120-153))..Figure 4-20Figure 4-20. . Schematic block diagram of some intrusive bodies. Schematic block diagram of some intrusive bodies. Structures and Field RelationshipsStructures and Field RelationshipsFigure 4-21. Kangâmiut dike swarm in the Søndre Strømfjord region of SE Greenland. From Escher et al. (1976), Geology of Greenland, © The Geological Survey of Denmark and Greenland. 77-95.Figure 4-22. a. Radial dike swarm around Spanish Peaks, Colorado. After Knopf (1936), Geol. Soc. Amer. Bull., 47, 1727-1784. b. Eroded remnant of a volcanic neck with radial dikes. Ship Rock, New Mexico. From John Shelton © (1966) Geology Illustrated. W. H. Freeman. San Francisco.Figure 4-23. The formation of ring dikes and cone sheets. a. Cross section of a rising pluton causing fracture and stoping of roof blocks. b. Cylindrical blocks drop into less dense magma below, resulting in ring dikes. c. Hypothetical map view of a ring dike with N-S striking country rock strata as might result from erosion to a level approximating X-Y in (b). d. Upward pressure of a pluton lifts the roof as conical blocks in this cross section. Magma follows the fractures, producing cone sheets. Original horizontal bedding plane shows offsets in the conical blocks. (a), (b), and (d) after Billings (1972), Structural Geology. Prentice-Hall, Inc. (c) after Compton (1985), Geology in the Field. © Wiley. New York.Figure 4-24. a. Map of ring dikes, Island of Mull, Scotland. After Bailey et al. (1924), Tertiary and post-tertiary geology of Mull, Loch Aline and Oban. Geol. Surv. Scot. Mull Memoir. Copyright British Geological Survey.Figure 4-25. Types of tabular igneous bodies in bedded strata based on method of emplacement. a. Simple dilation (arrows) associated with injection. b. No dilation associated with replacement or stoping. © John Winter and Prentice Hall.© John Winter and Prentice Hall.Structures and Field RelationshipsStructures and Field RelationshipsMay also see chilled margins along dike walls or May also see chilled margins along dike walls or when any plutonic body intrudes “cold” country rockwhen any plutonic body intrudes “cold” country rock..Figure 4-26. Shapes of two concordant plutons. a. Laccolith with flat floor and arched roof. b. Lopolith intruded into a structural basin. The scale is not the same for these two plutons, a lopolith is generally much larger. © John Winter and © John Winter and Prentice Hall.Prentice Hall.Structures and Field RelationshipsStructures and Field RelationshipsFrom the AGI Glossary of Geology —Cactolith: a quasi-horzontal chonolith composed of anastomosing ductoliths whose distal ends curl like a harpolith, thin like a sphenolith, or bulge discordantly like an akmolith or ethmolith.Figure 4-27Figure 4-27.. Gradational border zones between homogeneous igneous rock (light) and country rock (dark). After Gradational border zones between homogeneous igneous rock (light) and country rock (dark). After Compton (1962), Compton (1962), Manual of Field GeologyManual of Field Geology. © R. Compton. . © R. Compton. Structures and Field RelationshipsStructures and Field RelationshipsMagma mixing & minglingMagma mixing & minglingFigure 4-28Figure 4-28.. Marginal foliations developed within a pluton as a result of differential motion across the contact. From Marginal foliations developed within a pluton as a result of differential motion across the contact. From Lahee (1961), Lahee (1961), Field Geology. © Field Geology. © McGraw Hill. New York. McGraw Hill. New York. Structures and Field RelationshipsStructures and Field RelationshipsPhoto showsPhoto showsweak magmatic weak magmatic foliation. Note foliation. Note K-feldsparsK-feldsparsaligned with aligned with pencil.pencil.Enclaves or xenolithsEnclaves or xenolithsFigure 4-29Figure 4-29. . Continuity of foliation across an igneous contact for a pre- or syn-tectonic Continuity of foliation across an igneous contact for a pre- or syn-tectonic pluton. From Compton (1962), pluton. From Compton (1962), Manual of Field GeologyManual of Field Geology. © R. Compton. . © R. Compton. Structures and Field RelationshipsStructures and Field RelationshipsSyn- and post-tectonic intrusions Post-tectonic intrusionFigure 4-30Figure 4-30.. Block diagram several kilometers across, illustrating some relationships with the country rock near the top Block diagram several kilometers across, illustrating some relationships with the country rock near the top of a barely exposed pluton in the epizone. The original upper contact above the surface is approximated by the dashed of a barely exposed pluton in the epizone. The original upper contact above the surface is approximated by the dashed line on the front plane. From Lahee (1961), line on the front plane. From Lahee (1961), Field Geology. © Field Geology. © McGraw Hill. New York. McGraw Hill. New York. Structures and Field RelationshipsStructures and Field RelationshipsFigure 4-31Figure 4-31.. a.a. General characteristics of plutons in the epizone, mesozone, and General characteristics of plutons in the epizone, mesozone, and catazone.catazone. From Buddington (1959), From Buddington (1959),


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