Office Hours Tuesday Thursday 11 00am 12 00pm or by appointment GEOL 1001 3 Instructor Dr Tiffany Roberts Room Howe Russell 130 Office E209 Howe Russell Office Phone 225 578 2801 Email tiffanyroberts lsu edu TA Abah Omale Email aomale1 lsu edu Office location 205 Howe Russell Office Hours M W 1 00 2 00pm Exam 3 Chapters 8 11 Date 14 Location Himes Testing Center 3 11 14 Chapter 8 Metamorphism and Metamorphic Rocks What is metamorphism Transformation of one rock parent rock to another rock type Important concepts Formation Agents Classification cid 127 Grade Texture Environments Sedimentary Igneous cid 127 Metamorphic Change form Temperature pressure Differential stress chemically active fluids Solid state changes mineralogy and texture Texture intergrown and interlocking grains cid 127 Mineralogy some that are only metamorphic cid 127 Metamorphic grade cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 Mineral grains change size and shape not necessarily mineralogical change Metamorphic agents Recrystallization Heat Increasing temperature Confining pressure Phase change polymorphs Crystal structure altered not chemical composition Differential stress Aligns perpendicular to the direction of maximum stress Direct unequal pressure Compressional stress Ductile plastic deformation Brittle Chemically active fluids cid 127 Metamorphic enhancement facilitate recrystalization Can all work together or autonomously Metamorphic textures Size shape arrangement of mineral grains Foliation preferred orientation of mineral constituents Rearrangement of atoms to develop parallel or near parallel alignments Realignment perpendicular to maximum directional stress Splits easily across bedding planes Rotation Solid state flow Pressure solution Foliated textures Rock or slaty cleavage Schistosity cid 127 Gneissic banding Conspicuous planar or layer structures Nonfoliated textures cid 127 Minimal to absent deformation Limestone marble cid 127 Quarts quartzite Porphyroblastic texture Developed minerals in smaller matrix Ion migration resulting in segregation of minerals light and dark cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 Sequence of shale parent rock illustrates the changes from low grade to high grade metamorphism Metamorphic classification Foliated Slate Phyllite Schist cid 127 Gneiss Nonfoliated cid 127 Marble cid 127 Quartzite Hornfels Metamorphic environments Contact thermal metamorphism Low high temperature low pressure Aureoles bakes zones Hydrothermal metamorphism Low high temperature low pressure 1 Cold seawater percolates into the hot newly formed crust 2 Hot mineral rich water rises to the seafloor Burial Low T and P Subduction zone Low T high P Regional Low high T and P Fault zone Impact cid 127 Great T and P High T and P great deaths Textural variations Relationship between grade and texture Shale is the parent rock for most metamorphic rocks 3 13 14 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 Chapter 9 Geologic Time Important concepts Relative dating Principles Application Numerical dating Fossils Stratigraphic correlation Relative Numerical Uniformitarianism Earth history and the magnitude of geologic time is recorded in the rocks Physical processes we observe today also operated in the past The present is key to the past Relative Dating Principles Sedimentary rocks Principle of Superposition Youngest on the top oldest on the bottom Principle of Original Horizontality cid 127 Originally horizontal are bent deformed Principle of Lateral Continuity eg grand canyon Center of sediment bed eroded away cid 127 Matching layers on opposite sides Principle of Cross Cutting Fault Dike Principle of Inclusion thus are younger Allows us to infer that the layers were originally continuous across the canyon Unconformities Conformable strata Horizontal deposition beds Unconformity Angular unconformity Deposition Uplift Erosion Deposition Disconformity cid 127 Gap in rock record represents a period of non deposition and erosion Younger horizontal sedimentary rocks on top Inclusions of igneous rock contained in the adjacent sedimentary layer indicate the sediments were deposited atop the weathered igneous mass and Xenoliths are inclusions in an igneous intrusion that form when pieces of surrounding rock are incorporated into magma cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 Older horizontal sedimentary rocks on the bottom Nonconformity Period of uplift and erosion that exposed the deep rocks at the surface Younger sedimentary layers deposited atop erosion surface cid 127 Older igneous and or metamorphic rocks that formed deep within the crust Remains or traces of prehistoric life Important inclusions in sediment sedimentary rocks 3 18 14 Fossils cid 127 What is a fossil Types of fossils Pre mineralization cid 127 Molds and casts Carbonization Impression Amber Trace fossil Tracks Trails Burrows Correlation Principle of faunal fossil succession Fossil organisms succeed one another in a definite and determinable order Therefore any time period can be recognized by its fossil content Index fossils cid 127 Geographically widespread Fossil assemblages But appeared and disappeared quickly loved a short span of geologic time Numerical dating Based on radioactive decay of atoms in minerals Isotopes Stable Radioactive Radioactive decay Parent isotope radioactive Daughter isotope stable Half life always 50 percent of atoms number of atoms decrease with each half life Numerical dating Various isotopes half lives cid 127 Minerals analyzed Igneous material cid 127 Metamorphic Sedimentary Radiocarbon dating Radioactive carbon isotope organic material Closure temperature when isotopes are no longer free to move cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127