Environmental Geology Chapter 3: The Solid Earth - Rocks, Minerals, and Plate Tectonics PDF

Notes on Wednesday, 2/12/2025 Will now start moving more into the geology of the Earth. Chapter 3 is a really short intro into the eld of geology Chapter...

Notes on Wednesday, 2/12/2025 Will now start moving more into the geology of the Earth. Chapter 3 is a really short intro into the eld of geology Chapter 3 The Solid Earth Pipkin Trent Hazlett Berman  Naturally occurring Inorganic Minerals Crystalline, with orderly our most very basic building-blocks atomic structure Narrow chemical composition aka a de ned chemical composition Characteristic physical properties associated with individual minerals  MOST COMMON IN EARTH’S CRUST Most common O Si Al Fe Ca Na K Mg *use this acronym elements: Oxygen, Silicon, Aluminum, Iron, Calcium, Sodium, Potassium, Magnesium Graph of relative abundance, by percent volume-- oxygen is almost half by volume O Si Al Fe Ca Na K Mg Na K Mg Ca Fe Al O Si Oxygen and silicon are the two major elements in Earth's crust  Some minerals come in many colors, Ex: quartz can be rose, clear, smoky gray Color: Elementary property. Generally unreliable. Streak is basically the powdered residue of that mineral Streak: Color observed by scratching the mineral on a porcelain plate. Mineral Mohs hardness scale: 1 (softest) – 10 (hardest) developed during a time of intense mining (easy to test Identification this while mining) Cleavage: characteristic way minerals split geometry as it breaks Fracture: patterns distinctive for many have no zones of weakness, minerals that don’t cleave therefore no cleavage Luster: how a mineral reflects light Ex: metallic, non-metallic, oily, earthy, dull  a) Feldspar In this class, our professor won't ask us about speci c b) Quartz mineral names- but might ask about mineral groupings (ex: c) Muscovite silicates) d) Horn blend Figure 3-4 p52 very soft hardest substance Table 3-3 p53 3 major types of rocks on earth: igneous, sedimentary, metamorphic Igneous rocks: crystallized from molten or partially molten material, namely magma Sedimentary rocks: - Lithified fragments of preexisting rocks OR - Rocks formed by chemical or biological action broken down pieces of other rocks, that have been lithi ed into new rocks can also form through chemical or biological action ex: oozing together jelly beans, then cooled and solidi ed Metamorphic rocks: rocks altered by heat, fluids, or pressure in a solid state new rock, formed from intense heat/pressure change, (but not the point of melting) Three Types of Rocks Igneous rocks- rocks that cool and crystalized from a melt ◦ Intrusive igneous rocks- when the magma has not made it all the way to the surface, but has moved away from the source, and cooled over time. EXAMPLE: granite, which tends to have large crystals, and also tends to be silica-rich (aka "felsic", a silica-rich rock) ◦ Extruded- Igneous rocks when the magma has erupted on the surface of the earth (volcanic eruption), and cooled more quickly due to its exposure to air ‣ Magma is thinner and runnier, and able to make it to the surface of the earth. Cools faster at the surface of the earth, and doesn't have the time to form large crystals ‣ Either have small crystals or micro-cystalline ‣ Example: Basalt, which is micro-crystalline, and poor in silica content (aka "ma c", a silica-poor extrusive rock) Sedimentary rocks- have been lithi ed, or transformed by either increased pressure, or chemical processes that form cementation ◦ Clastic sedimentary rocks- made of pieces or fragments of other rocks, that through burial, increased pressure, or cementation, are lithi ed into solid rock. Classify according to their grain-size. ‣ "Shale"- If the grains are smaller than sand-sized ‣ "Sandstone"- If equal to sand-sized particles ‣ "conglomerate"- larger than sand-sized particles ‣ Form through exposed rock, exposed to outside weathering processes > grains then begin to break down > through gravity/water/wind, eroded grains will be transported down to lower points, and collected there through alternating time periods. As the grains get buried together, they start to cement together > layered rock of clasts that have been lithi ed ‣ Formation process: 1) Weathering 2) Erosion 3) Transport 4) Deposition 5) Lithi cation into rock ‣ Clastic are predominantly SILICA RICH ◦ Chemical sedimentary rocks - include rocks that have been precipitated direction from a solution, these are generally precipitates also evaporites. Examples: chemical limestone (aka micrite), halite (aka rock-salt, where salts form as evaporites) ◦ Biogenic sedimentary rocks- form from biological activity, Example: coal that forms from lithi ed plant debris, also fossiliferous limestone (MADE FROM CALCIUM CARBONATE) which forms in marine basins, from calcium carbonate shells that settle at the sea oor, and then lithify into rock Metamorphic rocks- been altered by increased temperature and increased pressure, such as tectonic forces, burial, mountain building processes, but the not altered to the point of melting. A solid state form of change ◦ Start with a parent rock material, a "protolith"- and then after increased temperature and pressure, will create a metamorphic rock ◦ Ex: start with sedimentary shale, with increased temperature and pressure, forms slate, then as it continues to undergo increased temperature and pressure, forms shist, and then as it continues the solid-state mineralization will form bands and we get Nice ‣ Shale (not metamorphic) > Slate > Shist > Nice ◦ Ex: Sandstone (has silica) > quartzite ◦ Ex: limestone (has calcuim carbonate) > marble OVERALL ROCK CYCLE: *Know what's on arrows in-between types of rocks Rock Cycle NOT the hydrologic cycle, completely di erent Pretend everything in the sky is along a mountain range with exposed surfaces Rock Cycle  Di erent minerals settle out and crystalize out of magma in di erent orders. Ma c ones with Mg crystalize rst, leaving behind a melt with more felsic minerals Silica content determined by fractionation history of parent magma Mafic minerals rich in magnesium and iron Igneous Rock crystallize first Composition Felsic minerals richer in silica crystallize after and Texture Intrusive (slow cooling-phaneritic) and extrusive rocks (fast cooling-aphanetic) can have same composition but different textures. Glassy (cools very fast) extrusive rocks have micro-crystalline  Lithified: sediments turned to stone by pressure and/or cementation Clastic sedimentary rocks: clasts from Sedimentary preexisting rocks "clasts" aka fragments Rocks Chemical sedimentary rocks: chemically precipitated Biogenic sedimentary rocks: from biological activity More gradations of sedementary rocks that just the ones we focused on Sedimentary  don't go to complete melt Changed in solid state from preexisting rocks by: ◦ Heat ◦ Pressure ◦ Chemical processes Metamorphic New structures, textures, minerals Rocks Foliation: flattening and layering of minerals by non-uniform stresses Recrystallization: heat or uniform stresses create larger, more perfect grains Table 3-5 p60  Solid inner core, and liquid outer core Core: metallic iron and nickel, very dense Earth’s Mantle: magnesium-silicate, thickest layer mantle convects in convection cycles and convection cells Layers: Crust: thin “skin” Composition ◦ Oceanic crust of mostly basaltic rocks dense, ma c ◦ Continental crust is mostly silica-rich igneous and sedimentary rocks less dense, felsic Imagine the ratio of the skin of an apple to the inside of an apple- same for Earth with crust:everything else Hot chocolate analogy, where the continental crust is the marshmallows on top  lithosphere: From the asthenosphere down, is moving in convection cells and is in motion Earth Layers Earth Layers  Mantle convection: Hot chocolate/soup analogy Figure 3-22 p61  Tectonic plates- imagine chunks of hot chocolate or marshmallows breaking up Along the plate boundaries, you have sea- oor spreading, and new material emerging > can push or pull the tectonic plate a certain way > plate movement Paci c Plate- where Santa Barbara is, but is almost entirely oceanic Figure 3-23 p62  Example: Cascades, Ex: volcanic island arc Mt Shasta Example: Himalayas Ex: Mariana Trench Also subducts, forming Subducting slab a deep oceanic trench Hotspots- not part of the normal convection cell or cycle, just sort of a point of heat that makes its way all the way up, creating volcanism at the surface. Example: Hawaii Figure 3-24 p62 Looking at convection cells: (At yellow part), the continental crust will start to thin over time as the cell moves away, rifts, breakage, can even break into two pieces of continental crust > new oceanic crust > new ocean oor > "CONTINENTAL RIFT" AT A DIVERGENT PLATE BOUNDARY. EXAMPLE: MID-OCEAN RIDGES What if two pieces of continental crust collide? Moving towards one another, as they push (same density) > mountain building in a "CONTINENTAL INTERACTION" AT A CONVERGENT PLATE BOUNDARY. EXAMPLE: HIMALAYAS What if continental crust moves towards oceanic crust? Di erence in density at a convergent plate boundary> more dense oceanic crust dives below > melt > becomes less dense, more buoyant > volcanism > OCEANIC-CONTINENTAL, PLATE SUBDUCTION RESULTING IN VOLCANISM. EXAMPLE: CASCADE RANGE LIKE IN MT SHASTA OR MT ST HELENS IN WASHINGTON OCEANIC/OCEANIC INTERACTION also exists- as it comes to the surface, cools, and pushes apart continuously > new sea oor>  Plate boundaries will be either divergent or convergent Then, depending on either continental or oceanic... Tension pulls plates apart will eventually become two separate continents Continental crust: East African Rift valley Plate Boundaries: Oceanic crust: Mid-Ocean Ridge ◦ Seafloor spreading: plates move away from Divergent each other Volcanic eruptions at divergent boundaries  Compression drives plates together Oceanic-Continental: Subduction of oceanic crust under continental crust, Major earthquakes, Volcanic eruptions Plate Boundaries: Convergent Continental-Continental: Mountain-building  Evidence in Himalayas of Continent-Continent collision p82 Collision of the Indian and Asian plates, creating the Himalayan mountains  Accretion Sometimes part of subducting slab will be carrying more continental rock on top of it. The continental rock gets moved Accretions that came from somewhere else add onto the size of the continent; exotic terrain Lots of potential energy stored around Santa Barbara, whole piece is shearing o ; lots of earthquakes Plate Boundaries: Transform Shear forces cause plates to slide horizontally past each other Long linear faults ◦ San Andreas fault in California ◦ Major earthquakes Paci c plate is moving to the NW, while the North American plate is moving to the SE. A little sliver of crust is being sheared o of North America, including SB/SF HAWAII All the other islands to the left of the big island Hawaii are no longer active, hot spot has passed them Kauai is much older As a plate moves over a hot spot, whatever is currently over that hotspot is where the current volcanic activity will be, and as it moves, Hawaii will move o the hotspot, and the Loihi will start to grow in continental land mass Plate Motion over Hot Spot Will be a separate topic-- end of Ch3 lecture Geologic Time Study of the dating and relationships of geologic events Relative-age dating determines sequences of events Absolute-age dating provides actual ages for rocks Geologic Time Scale  Structural relations of rocks Law of Superposition: In undeformed sedimentary rocks, the top layer is youngest Relative-Age Law of Cross-Cutting Relationships: A fault is Dating younger than the youngest rocks it cuts Principle of Original Horizontality: Material was originally deposited horizontally  Discontinuity: Breaks in geological sequence (examples: angular, nonconformity, disconformity,) Relative-Age Inclusions: older than the rocks they are found in Dating (continued) Intrusions: younger than the rock formations that were intruded upon Absolute-Age Dating Law of Fossil Succession: indicator fossils Radiometric dating: ◦ Radioactive element decays and releases particles; can stay same element or become a new element ◦ Alpha decay: release helium atoms ◦ Beta decay: release electrons Absolute-Age Dating (continued) ◦ Half-life: time required for ½ of atoms to decay ◦ Different compounds have different half-lives and can be used for different age ranges