Solid Earth

Minerals definition – naturally occurring, inorganic solid, unique chemical structure made of elements, some just one, most more than one rocks = aggregate of minerals atomic structure – protons, neutrons, electrons ion = atom which has gained or lost one or more electrons atoms bond to form compounds ionic bonding (some atoms lose electrons, others gain them; opposite charges attract) covalent bonding (atoms share electrons) - eg. in water to bond H and O atoms metallic bonding bonded chemical groups often found in minerals, e.g. carbonate, sulfate, hydroxyl, silicate mineral properties crystalline structure luster color streak fracture specific gravity (density) hardness (Mohs scale) cleavage 4000 named minerals, 8 elements make up bulk of these minerals and represent over 98% of the continental crust: O (46.6%), Si (27.7%), Al (8.0 %), Fe (5%), Ca, Na, K, Mg Si + O make up silicates = most common mineral group (75% of earth’s crust) – silica tetrahedron, chains 2 groups of silicates: ferromagnesian (contain Fe and Mg) – dark in color non-ferromagnesian feldspars are most plentiful – over 50% of earth’s crust quartz = 2nd most abundant silicates form from molten rock as it cools, and crystallize at different temperatures ¼ of the earth’s crust are nonsilicate minerals: carbonates = eg. calcite (major constituent of limestone and marble) gypsum halite (salt) gemstones (many have names different from their mineral names) diamond sapphire = corundum = aluminum oxide + impurities with titanium + iron (blue sapphire) with chromium (red ruby) Rocks The Rock Cycle Igneous Rocks form as magma cools and crystallizes sometimes ejected in volcanic eruptions (extrusive or volcanic), contain vesicles sometimes crystallizes at depth in the earth (intrusive or plutonic) if magma cools slowly – large crystals, quick cooling – small crystals, instant quenching – no crystals (glassy) Bowen’s series for crystallization temperature Classification of igneous rocks – by amount of silica present rich = felsic (eg granite, rhyolite) intermediate (eg diorite, andesite) poor = mafic (eg. basalt, gabbro) low in silica = low viscosity = flows easily high in silica = high viscosity kinds of feldspars present, other minerals Sedimentary Rocks weathering moves particles and deposits them as a sediment compaction and cementation majority of rocks exposed at earth’s surface are sedimentary important for determining earth’s history (put down in layers, contain fossils) lithification (= transformation of sediments into sedimentary rock) 2 sources of particles (solid – from weathered rock = detritus) (soluble material = chemical sedimentary) detrital – dominated by clay minerals and quartz classified by particles size (eg. conglomerate, sandstone, shale) particle size related to distance from source and transport mechanism chemical sedimentary rocks material carried in solution to lakes and seas physical precipitation biochemical (water ingested by water-dwelling creatures and solid material is precipitated out to make hard parts - eg sea shells) most abundant = limestone (calcite), 90% is biochemical halite (rock salt), gypsum, chert Metamorphic Rocks can form from igneous, sedimentary or other metamorphic rocks changed by heat, pressure, chemically-active fluids metamorphic changes take place a few km below earth’s surface metamorphism can align grains in rocks contact metamorphism – rocks are heated by adjacent mass of hot rock limestone -> marble sandstone -> quartzite basalt -> amphibolite Plate Tectonics evidence for movement of plates: continental fit glacial (including pattern of striations) fossil mountain ranges (Appalachians extend into Greenland) magnetic evidence (trace the apparent direction of the Earth’s N. magnetic pole) theory: discovery of Mid-Atlantic Ridge evidence of sea-floor spreading types of crust: continental, oceanic – density difference – oceanic is thinner and denser, continental is lighter and thicker. When 2 plates come together the oceanic plate is the one that subducts plate boundaries: divergent vs convergent – know structure of these (eg. subduction cross-section) divergent: oceanic: Mid-ocean ridges with rift valley continental: eg. East African rift valley convergent: oceanic-oceanic: volcanic island arc, offshore oceanic trench, eg. Aleutian islands oceanic-continental: volcanic mountain belt, orogenic mtns, eg. Andes continental-continental: (collisional) mountain belt (only minor volcanism) eg. Himalayas transform: fault valley, eg. San Andreas fault right lateral vs. left lateral driving force = convection in the mantle, push-pull force in slab hotspots: fixed point sources of heat (rising magma) moving plate causes chain of islands to form Earthquakes focus (= location of rupture within the earth) shallow, intermediate, deep epicenter = point on earth’s surface above focus determining the position of the epicenter location of earthquakes (on plate boundaries) seismic waves body waves (P and S waves) P waves = primary = compression waves = fastest S waves = secondary = perpendicular to direction of propagation, do not travel through liquids, slower (do not travel through outer core, produce shadow zone) surface waves (produce rolling or swaying motion) determining earthquake location from 3 seismographs intensity and geology (build your house on rock) magnitude (Richter scale) intensity (Mercalli scale) Internal Structure of Earth inner core – solid (iron with nickel) outer core – liquid (iron + nickel) mantle = silicates lower mantle = rigid upper mantle = asthenosphere (plastic) + lithosphere (solid – includes oceanic (basaltic) and continental crust(granitic)) Mountain Building deformation of rocks and metamorphism of rocks are results of mountain building response of rock to stress depends on temperature, pressure, strain rate and rock type stress = pressure = force/area compressional (usually in mtn building) tensional (eg. Rift valley) shear (eg. faults) strike-slip faults vs dip-slip faults normal fault, reverse fault, thrust fault hanging wall and footwall horst = uplifted block with faults on either side graben = block that has dropped down materials which break under stress = brittle materials which deform permanently = ductile folds = ductile deformation folds which arch upwards = anticlines folds that bend down = synclines plane along middle of fold = axial plane dip = angle layer makes with the horizontal Volcanoes molten rock below surface = magma molten rock on surface = lava types of igneous rock relationship between amount of silcate in rock, viscosity of rock, type of volcanic explosion, type of volcano, ie.: 1. basalt, low in silica, dark in color, runny, flows easily, can flow through cracks (fissures), comes from mantle and molten oceanic crust, forms non-explosive volcanoes, shield volcanoes (broad domes) 2. rhyolite, high in silica, light-colored, thick and viscous, comes from molten continental crust, explosive, steep-sided volcanoes, stratovolcanoes (steep sides) 3. andesite, intermediate rock (named from Andes mtns) when melted oceanic crust or magma from deep in mantle mixes with molten continental crust, eg. under oceanic-continental convergent plate boundary 3 places where volcanoes occur: Rifts (oceanic or continental ) Hot spots Subduction zones Geologic Time • relative dating – use geological record to order events sequentially • principle of superposition – oldest layers under newer layers • sediment settles in horizontal layers • principle of cross-cutting: fracture must be younger than the rock it cuts; feature that cuts across a rock must be younger than the rock it cuts • principle of inclusions – fragments of rock contained within another rock are older than the rock layer containing the inclusions