GEOL 108Lg 1st Edition Lecture 10Outline of Last LectureI. The Rock Cycle: Igneous, Sedimentary and Metamorphic II. The Wilson Cycle: Opening and Closing of Ocean Basins III. Intro to MineralsOutline of Current Lecture- Metamorphic rocks- Steno's rules- Mineral deposits- Carbon cycle and oil - Snowball Earth IntroCurrent LectureRo c k s IIMETAMORPHIC ROCKS have changed (meta) their form (morphic). Under the influence of heat, pressure and fluids, pre-existing rocks are modified to produce new rocks. This is done within the solid state, i.e. without melting.In metamorphic rocks, such as the one pictured below, the materials that are lighter are enriched in FLASIC materials. The darker ones are enriched in MAFIC materials.How close you are to the temperature anomaly - bring it up (vertical motion) - changestemperature and pressure - limestone shale sedimentary - granite intrusion - the close youare to a heat source, the more increase you have the metamorphic grade - if you find-Metamorphism of Shale - shale sedimentary rock - goes into slate - very-Foliation are planes of line crystal - the reorganization of crystals.Crystalline Structure ReviewChanging crystalline structure by heating it up and it makes the internal more mobile - change concentration - grain growth/shrinkage - processes are understood, say something about how the original cryst. structure has evolved since its original deformation-Regional metamorphism changes the rock texture - recrystallization - changing the microstrocture of the rock by heating it up and deforming it.View from a microscope. The size distribution of these grains tells you about how it wasdeformed - the stresses that were active during deformation - how strong the lithosphere is -how rocks behave in the first place - microstructure can tease out other processesThe subduction zone is cold, as it gathers material that just came from surface - colder - The other image might be somewhere in betweenSteno’s Law or the Law of SuperpositionSteno's Law of Original Horizontality states that most sediments, when originally formed, were laid down h or i z o n t all y . However, many layered rocks are no longer horizontal. Because of the Law of Original Horizontality, we can tell that sedimentary rocks that are not horizontal either were formed in special ways or, more often, were moved from their horizontal position by later events (fault movement, etc).-Principle of Superposition: Further down MUST be older: youngest rocks are at the top, oldest rocks are at the bottom-Principle of Lateral Continuity (cross cutting relationship) if you have a process modifying this such as deforming it by folding-Connectivity can go over huge scales - associate fossils in different layers with each other - photoexampleExample of Steno’s Law: A certain Rock structure at its top which might have certain fossils at the top while another structure parallel to it has the same sort of fossils in a different level. From this we can infer that the structure might have shifted around.Initially the two structures were connected-Deformed by folding, faulting-Dike injection-Faulting – a way to accommodate deformation, by earthquakes - narrow zone where the accommodation happens - brittleUnconformitiesParticular example -sitting on a sea floor - depositing sediments - move the beds above sea level - exposed to erosionCROSS CUTTING RELATIONSHIP IS USED TO ESTABLISH A RELATIVE CHRONOLOGYReview Important TermsThree Fundamental Rock Laws• Three fundamental laws in understanding therelationships of rocks and the earth history– The law of cross-cutting relationships: Rocks are younger than the ones that it cuts– The law of original horizontality: Sedimentary rock layers nearly horizontal under normal condition– The law of superposition: Rocks become progressively younger towards the top in an undisturbed and undeformed rock sequenceMining Minerals:Plate Tectonics and Minerals• Plate tectonic boundaries related to the origins of many ore deposits, Fe, Au, Cu, and Hg, etc.• Plate tectonic processes (high temp, high pressure, and partial melting) promoting release and enrichmentof metals along plate boundaries• Ore deposits at divergent boundaries is related to the migration (movement) of ocean water• Ore deposits at convergent boundaries: Related to partial melting of seawater-saturated rocks of the oceanic lithosphere in a subduction zone• Danger in oversimplification, not all directly related to plate boundariesKimberlite Pipe-Kimberlite pipes are created as magma flows through deep fractures in the Earth. The magma inside the kimberlite pipes acts like an elevator, pushing the diamonds and other rocks and minerals through the mantle and crust in just a few hours. These eruptions were short, but many times more powerful than volcanic eruptions that happen today.NOTE: Mercury deposits sit near subduction zones - Old subduction zonesPlate tectonics and minerals RELATE - Evolution of societies - access to resources – mineralsPlate Tectonics and Minerals• Plate tectonic boundaries related to the origins ofmany ore deposits, Fe, Au, Cu, and Hg, etc.• Plate tectonic processes (high temp, high pressure, and partial melting) promoting release and enrichment of metals along plate boundaries• Ore deposits at divergent boundaries is related to themigration (movement) of ocean water• Ore deposits at convergent boundaries: Related to partial melting of seawater-saturated rocks of the oceanic lithosphere in a subduction zone• Danger in oversimplification, not all directly related toplate boundariesMinerals use is the backbone of many modern societies – the availability of mineral resources used as a measure of the wealth of a society - important in people’s daily life as well as in the success of the overall economy - processed materials from minerals accounting for 5 percent of the U.S. GDP• Mineral resources: Usable economic commodity (profitable) extracted from naturally formed material (elements, compounds, minerals, or rocks)• Reserve: Portion of a resource that is identified and currently available to be extracted legally• Defning factors: Geologic, technological,economic, and legal factorsReserve: portion of a resource that is currently available to be extracted legallyDefining factors: geologic, technological, economic, etcMineral Resources and ReservesThe differentiation depends