Low Grade  High grade UNG- GEOL 3010K Spring 2019 Study Guide Final Weathering of sedimentary rocks and examples for each Physical breakdown (disintegration) Frost wedging: alternate freezing and thawing of water in fractures and cracks promotes the disintegration of rocks Thermal expansion: alternate expansion and contraction due to heating and cooling Unloading - expansion and breaking of igneous and metamorphic rocks at the Earth’s surface due to a reduction in confining pressure (when the overlying rock is eroded away) Chemical alteration (decomposition) of rock at or near Earth’s surface Dissolution Oxidation - A reaction whereby a metal loses electrons Hydrolysis - Water breaks cation bonds in silicate minerals. Yields: Cations and Alteration residues Classifications of Sedimentary rocks and sedimentary textures- be able to label the diagrams used to classify sedimentary rocks Clastic - Discrete fragments and particles that are cemented and compacted together All detrital rocks have a clastic texture Nonclastic - Pattern of interlocking crystals. (May resemble an igneous rock) Chemical - sediment that was once in solution; inorganic evaporates and by products of chemical activity (chemical rocks) Organic water dwelling organisms and plant debris (organic rocks) bio chemical contain shells of organisms. Sorting and maturity and related diagrams Grain shapes; sphericity vs. rounding and related diagrams Stability of minerals against weathering Bowens Series backward. First minerals to form, are first to decompose Resistate vs. hydrolysate hydrolysate – dissolved materials resistate – solids (includes clays and quartz) Factors that affect the survival of resistates during decomposition Rock composition and structure, along with regional factors such as precipitation and humidity Digenesis, lithification, recrystallization (also stylolite and authigenic minerals) Diagenesis - refers to all of the chemical, physical, textural, and biological changes that take place after sediments are deposited – Heating, Pressure, Reaction w/ ground water Lithification - Transforms loose sediment into solid rock. Through burial (more sediments being added), compaction (reduction of pore space), and cementation (carbonate, silicate or authigenic minerals). Stylolites - grain deformation and dissolution of minerals into the pore fluid over time Agents of metamorphism Temperature, Heat sources: Magma Groundwater Radioactive decay Pressure, Types of stress: Lithostatic(applied equally) Normal stress(tension or compression) Shear(parallel or sliding) Metamorphic grades, zones, facies Zones: Distinct regions in which an index mineral appear/disappear and we can map out In an original mudrock: Chlorite zone Biotite zone Garnet zone Staurolite zone Kyanite zone Sillimanite zone Facies : Zeolite, Prehnite-pumpellvite, Amphibolite, Blueschist, Eclogite, Granulite, Hornfels Index minerals These are good indicators of the pressure and temperature that surrounding rocks were exposed to chlorite characterizes the lowest regional metamorphic grade biotite replaces chlorite at the next metamorphic grade, which could be considered medium-low grade garnet appears at the next metamorphic grade, medium grade staurolite marks the next metamorphic grade, which is medium-high grade sillimanite is a characteristic mineral of high grade metamorphic rocks Paragenesis- a set of minerals that form together Metamorphic settings and examples of rocks found in each environment Regional metamorphism produces most metamorphic rocks (Slate, Schist) Subduction- low temp high pressure (eclogite) Thermal (contact)- occur where there is a pluton along a convergent boundary (hornfels) Burial- also called static, temp and pressure vary with depth (quartzite) Dynamic metamorphism- occurs at depth and high temp, deformation cause by ductile flow (mylonite) Impact- meteorite impacts, extremely high pressure (Coesite) Hydrothermal Alteration (Deuteric reaction vs. metasomatism) Deuteric (Hydrothermal Alteration): o “Stewed in their own juices” because fluid comes from within the rock o Happens to igneous rocks o Includes rocks like albite · Metasomatism (Hydrothermal Alteration): o Changes occur in solid state o Source of water is outside the rock(ocean, lakes) o Leaching and precipitation from solution Classification of metamorphic rocks, textures and protoliths Low-grade, Intermediate grade, high grade Foliated, and non-foliated, porphyroblastic, Grain size Large grains, called porphyroblasts, surrounded by a fine-grained matrix of other minerals Protoliths: Pelites (pelitic)- Aluminized rocks such as shale, mudstone, graywacke and altered tuff Pelitic protoliths – Mud – Shale – Slate – Phyllite – Mica Schist - Paragneiss - Hornfels Quartz Feldspathic(Psammitic)- intermediate to felsic igneous rocks (no change in mineralogy) quartz, Kspar, plag, biotite, hornblende -> opx, garnet Granite – Quartzite, quartzofeldspathic gneiss, migmatitie Granitic Granodiorite – Rhyolite - Orthogneiss, granulite High Pressure- Blue schists, eclogite Basic Protolith Basalt – greenstone – greenschsit- blueschist- amphibolite – serpentinite- mafic orthogneiss Ultrabasic rock Metamorphosed Peridotite - Serpentinite – amphibolite – soapstone – Eclogite Calcareous Metamorphosed Limestone – Dolostone – Marble - Skarn · Neocrystallization- new minerals form that are stable under new conditions after a change Metamorphic diagrams and reactions Phase diagram and Gibbs free energy G rxn = G f(prod) - G f(react)