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Depositional Environments of Sedimentary Rocks Smaller….Rounder…..Better Sorted Clastic Sedimentary Rocks Nonclastic Sedimentary Rocks Basin Source Downstream Beach Offshore (Playa Lake) Halite, Gypsum, Chert (Evaporites) Coal Reef Swamp Coquina Limestone Read Solar Nebula Theory document Study Guide for exam 2 Study Area for lab has practice exam All missed labs must be made up before lab exam All missed homework must be made up before lecture exam 2 Study Area Felmley Hall 203 Lab Samples Practice Lab Exam Metamorphism and Metamorphic Rocks Rock Cycle Revisited And Sedimentary Rocks Metamorphic Rocks Erosion Heat and Pressure Magma Sediment Igneous Rocks Rock Textures Igneous Aphanitic -glassy -vesicular Phaneritic Sedimentary Nonclastic -biochemical (biogenic) -chemical Clastic Metamorphic Foliated -banded Nonfoliated Definitions Metamorphism – mineralogical, chemical, and physical changes that occur in solid rocks. Occurs at depths greater than that of lithification (Diagenesis). Solid state recrystallization – changes that occur without the rock melting (rocks that melt are igneous). Surface Sedimentary 15o C 5 km Metamorphic 30 km Magma 200o C 600o C Factors influencing Metamorphism •Temperature •Pressure •Pore Fluid •Time Temperature, Pressure and Rock Type Factors influencing Metamorphism Temperature • below about 200oC, most minerals are stable (little or no metamorphism) • above 200oC, reaction rate increases as temperature increases, new minerals begin to form • above 600oC, some minerals begin to melt (transition to igneous rocks) Factors influencing Metamorphism Pressure • as pressure increases, pore spaces reduced and density increases, pore fluids are expelled Differential stress • pressure is greater in one direction than in another Differential Stress Effects of Stress Uniform Differential Differential Stress Foliation – a metamorphic rock texture due to alignment of minerals as a result of differential stress Slaty cleavage – foliation that develops at low temperature and pressure (metamorphosed shale) Foliation In this schist, viewed between crossed polarisers, the parallel mica flakes show up in bright colors, and large rounded garnet crystals appear black. Field of view 6 mm, polarising filters. Burial Mountain Building Factors influencing Metamorphism Pore fluids (water and carbon dioxide) • as pressure increases, pore fluids are expelled Pore fluids increase the rate of metamorphic reactions by: • storing ions involved in reactions • moving ions from one place to another Pore Fluids Dissolution / Precipitation Factors influencing Metamorphism Time • solid state recrystallization is a slow process • in general, size of minerals increases with time Preferred Mineral Orientation (Foliation) •Ductile (plastic) Deformation •Pressure Solution •Grain Rotation •Growth in Preferred Orientation Ductile (plastic) Deformation Pressure Solution Grain Rotation Growth in Preferred Orientation Foliation Types of Metamorphism 1. Burial Metamorphism 2. Contact Metamorphism 3. Regional Metamorphism Types of Metamorphism Burial Metamorphism • most common type, occurs where crust is greater than 5 km thick Relatively low temperature and pressure (low grade metamorphism) Maximum stress vertical, foliation parallel to ground surface Burial Metamorphism Regional Metamorphism Types of Metamorphism Regional Metamorphism • associated with convergent plate margins • folding and faulting increase thickness of the crust • occurs over a range of temperatures and pressures • low grade to high grade metamorphism Grades of Regional Metamorphism Shale sedimentary rock Slate – aligned clay minerals Phyllite – muscovite mica Schist - Biotite mica/ garnet Gniess – quartz/ feldspar (banded) Metamorphic Grades Regional Metamorphism Contact Meta Contact Meta Types of Metamorphism Contact Metamorphism • occurs in rocks around a magma body • high temperature (heat from magma) • low pressure (occurs at shallow depths in the crust) Contact Metamorphism Metamorphic Grade Metamorphic Grade Low Grade Metamorphism Example: Slate • forms at low temperature and pressure • microscopic crystals • dull luster • clay and mica minerals • foliated Low Grade - Slate Metamorphic Grade Intermediate Grade Metamorphism Example: Phyllite • intermediate temperature and pressure • small crystals • shiny luster • mostly mica minerals • foliated Intermediate Grade – Phyllite Metamorphic Grade High Grade Metamorphism Example: Schist • high temperature and pressure • large crystals • mica-rich • foliated High Grade - Schist Top view Side view Metamorphic Grade High Grade Metamorphism Example: Gneiss • high temperature and pressure • large crystals • mica-poor • foliated High Grade - Gneiss Regional Revisited Slate Phyllite Schist, Gneiss Non-foliated Metamorphic Rocks • • • • granular texture interlocking grains composed primarily of one mineral uniform grain size Nonfoliated - Marble • metamorphosed limestone (CaCO3) • bedding and fossils obliterated Nonfoliated - Quartzite • metamorphosed quartz-rich sandstone • Pore spaces filled with SiO2