GEO 101 1st Edition Lecture 10 Outline of Last Lecture 1 Clastic Sedimentary Rocks 2 Biochemical and Organic Rocks 3 Chemical Sedimentary Rocks 4 Sedimentary Structures 5 Bedforms 6 Bed Surface Markings 7 Depositional Environments Outline of Current Lecture 1 Sedimentary Basins 2 Diagenesis 3 Metamorphic rocks a Metamorphism b Agents of Metamorphism c Metamorphic Textures d Metamorphic Rocks e 3 Types of Metamorphic Environments f Metamorphism and Plate Tectonics Current Lecture Sedimentary Basins Sediments vary in thickness across Earth s surface o Thin to zero edge where non sedimentary rocks outcrop o Thicken to 10 to 20 km in sedimentary basins Subsidence Sinking of the land during sedimentations o Due to crustal flexure and faulting o Compounded by the weight of added sediments Basins are important locations for natural resources o Coal o Petroleum o Natural Gas o Uranium Basins form where tectonic activity creates space o Rift Basins Divergent pull apart plate boundaries These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Crust thins by stretching and rotational normal faulting Thinned crust subsides Sediment fills the down dropped basin o Passive Margin Basins Non plate boundary continental edge Underlain by crust thinned by pervious rifting Thinned curst subsides as it cools o Intercontinental Basins Interiors far from margins Results from differential thermal subsidence May be linked to failed crustal rifts o Foreland Basins Craton side of collisional mountain belt Flexure of the crust from loading creates a downwarp Fills with debris eroded off of the mountains Sea level changes o Sedimentary deposition is strongly linked to sea level o Changes in sea level are commonplace geologically Depositional belts shift landward or seaward in response Layers of strata record deepening or shallowing upward o Transgression Flooding due to sea level rise Sediment belts shift landward strata deepen upward o Regression Exposure due to sea level fall Depositional belts shift seaward strata shallow upward Regression tied to erosion less likely to be preserved o Sea level rise and fall creates a predictable pattern Diagenesis Physical chemical and biological changes to sediment o Bioturbation o Lithification o Dissolution o Mineral precipitation Temps between burial and metamorphism 300 C Integrates changes across the entire sediment history Metamorphic Rocks Metamorphism Formed by increase in temperatures and or pressures from o Igneous rocks o Sedimentary rocks o Other metamorphic rocks Low to high grade Rocks remain solid Agents of Metamorphism 1 Heat o Recrystallization results in new stable minerals o 2 sources Heat from magma Geothermal gradient 2 Pressure and Stress o Increase with depth o Forces applied in all directions 3 Fluids o Water and other volatiles o Enhance migration of ions o Recrystallization of existing minerals o Where does the water come from Pore spaces of sedimentary rocks Fractures in igneous rocks Hydrated minerals 4 Parent Rock o Minerals determines degree to which change occurs Metamorphic Textures Texture Size shape and arrangement of mineral grains Foliation Planar arrangement of mineral grains o Parallel alignment of platy and or elongated minerals o Compositional banding Foliation forms by o Rotation of platy and or elongated minerals o Recrystallization of minerals o Changing shape of grains into elongated shapes Types of foliated textures o Slaty Cleavage Planar surfaces along which rocks split Dullest o Schistosity Platy minerals exhibit layered structure Shiny o Gneissic Minerals segregate distinctively banded All of the dark crystals line up with each other and light crystals line up with each other and you see distinct bands Other metamorphic textures o Nonfoliated Minimal deformation Equidimensional crystals o Porphyroblasitc textures Large grains surrounded by fine grained matrix Metamorphic Rocks Foliated Rocks o Slate Fine grained Slaty cleavage Low grade metamorphism of shale o Phyllite Minerals not large enough to be identified Glossy sheen and wavy surfaces o Schist Medium to coarse grained Micas predominate Schistosity texture o Gneiss Medium to coarse grained Banded appearance High grade metamorphic Nonfoliated Rocks o Marble Coarse crystalline Calcite or dolomite o Quartzite Metamorphism of quartz rich sandstone Quartz grains interlocking 3 Types of Metamorphic Environments 1 Contact or thermal Metamorphism o Increase temperature from intruding magma o Zone of alteration aureole forms in rock surrounding magma 2 Hydrothermal Metamorphism o Chemical alteration caused when hot ion rich fluids circulate through cracks o Widespread along Mid Ocean Ridges 3 Regional or dynamothermal Metamorphism o Associated with mountain building Metamorphism and Plate Tectonics Continent Continent Collisions o Edges of plate deforms o Major mountains Alps Himalayas and Appalachians are metamorphic Subduction Zones o Linear belts of metamorphic rocks High pressure low temperature zones nearest to the trench High temperature low pressure zones further inland